@article{koenig_wang_zhu_gupta_tucker_thompson_2024, title={In situ characterization of thermomechanically loaded solution strengthened, nanocrystalline nickel alloys}, volume={263}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2023.119462}, abstractNote={Nanocrystalline (NC) Ni-40Cu and Ni-40Cu-0.6P (at.%) alloys were mechanically loaded in tension at ambient (23 °C) and elevated (150 °C) temperatures with the deformed nanostructure captured by in situ transmission electron microscopy coupled with digital image correlation for data mining high strain regions prior to catastrophic failure. The addition of the P provided grain boundary partitioning that stabilized the NC structure under both loading cases, which was not found to be the case for the binary alloy. While mechanical strength softening was observed in each of the alloys upon thermomechanical loading, the retention of strength was substantially higher in the ternary alloy than its binary counterpart. Digital image correlation was found to be a useful means for image mining to identify different regions where failure mechanisms were initiated. Intergranular failure was observed as the dominant failure mechanism in all specimens with the binary alloy revealing a coarser fracture profile as compared to a finer fracture profile in the ternary alloy. Atomistic simulations are used to understand P solute strengthening of the grain boundaries against this fracture failure mode.}, journal={ACTA MATERIALIA}, author={Koenig, Thomas R. and Wang, Hongyu and Zhu, Yong and Gupta, Ankit and Tucker, Garritt J. and Thompson, Gregory B.}, year={2024}, month={Jan} }
 @article{wu_zhao_zhu_paulino_2024, title={Modular multi- degree- of- freedom soft origami robots with reprogrammable electrothermal actuation}, volume={121}, ISSN={["1091-6490"]}, DOI={10.1073/pnas.2322625121}, abstractNote={Soft robots often draw inspiration from nature to navigate different environments. Although the inching motion and crawling motion of caterpillars have been widely studied in the design of soft robots, the steering motion with local bending control remains challenging. To address this challenge, we explore modular origami units which constitute building blocks for mimicking the segmented caterpillar body. Based on this concept, we report a modular soft Kresling origami crawling robot enabled by electrothermal actuation. A compact and lightweight Kresling structure is designed, fabricated, and characterized with integrated thermal bimorph actuators consisting of liquid crystal elastomer and polyimide layers. With the modular design and reprogrammable actuation, a multiunit caterpillar-inspired soft robot composed of both active units and passive units is developed for bidirectional locomotion and steering locomotion with precise curvature control. We demonstrate the modular design of the Kresling origami robot with an active robotic module picking up cargo and assembling with another robotic module to achieve a steering function. The concept of modular soft robots can provide insight into future soft robots that can grow, repair, and enhance functionality.}, number={20}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Wu, Shuang and Zhao, Tuo and Zhu, Yong and Paulino, Glaucio H.}, year={2024}, month={May} }
 @article{shukla_wang_awartani_dickey_zhu_2024, title={Surface Embedded Metal Nanowire-Liquid Metal-Elastomer Hybrid Composites for Stretchable Electronics}, volume={16}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.4c00318}, DOI={10.1021/acsami.4c00318}, abstractNote={Both liquid metal (LM) and metallic filler-based conductive composites are promising stretchable conductors. LM alloys exhibit intrinsically high deformability but present challenges for patterning on polymeric substrates due to high surface tension. On the other hand, conductive composites comprising metallic fillers undergo considerable decrease in electrical conductivity under mechanical deformation. To address the challenges, we present silver nanowire (AgNW)-LM-elastomer hybrid composite films, where AgNWs and LM are embedded below the surface of an elastomeric matrix, using two fabrication approaches, sequential and mixed. We investigate and understand the process-structure-property relationship of the AgNW-LM-elastomer hybrid composites fabricated using two approaches. Different weight ratios of AgNWs and LM particles provide tunable electrical conductivity. The hybrid composites show more stable electromechanical performance than the composites with AgNWs alone. In particular, 1:2.4 (AgNW:LMP w/w) sequential hybrid composite shows electromechanical stability similar to that of the LM-elastomer composite, with a resistance increase of 2.04% at 90% strain. The sequential approach is found to form AgIn2 intermetallic compounds which along with Ga-In bonds, imparts large deformability to the sequential hybrid composite as well as mechanical robustness against scratching, cutting, peeling, and wiping. To demonstrate the application of the hybrid composite for stretchable electronics, a laser patterned stretchable heater on textile and a stretchable circuit including a light-emitting diode are fabricated.}, number={11}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Shukla, Darpan and Wang, Hongyu and Awartani, Omar and Dickey, Michael D. and Zhu, Yong}, year={2024}, month={Mar}, pages={14183–14197} }
 @article{liu_ahmad_venditti_velev_zhu_2024, title={Sustainable Soft Electronics Combining Recyclable Metal Nanowire Circuits and Biodegradable Gel Film Substrates}, volume={1}, ISSN={["2199-160X"]}, DOI={10.1002/aelm.202300792}, abstractNote={Abstract}, journal={ADVANCED ELECTRONIC MATERIALS}, author={Liu, Yuxuan and Ahmad, Mesbah and Venditti, Richard A. and Velev, Orlin D. and Zhu, Yong}, year={2024}, month={Jan} }
 @article{liu_sui_harbinson_pudlo_perera_zhang_liu_ku_islam_liu_et al._2023, title={A scalable microstructure photonic coating fabricated by roll-to-roll “defects” for daytime sub-ambient passive radiative cooling}, volume={23}, ISSN={["1530-6992"]}, url={https://doi.org/10.1021/acs.nanolett.3c00111}, DOI={10.1021/acs.nanolett.3c00111}, abstractNote={The deep space's coldness (∼4 K) provides a ubiquitous and inexhaustible thermodynamic resource to suppress the cooling energy consumption. However, it is nontrivial to achieve subambient radiative cooling during daytime under strong direct sunlight, which requires rational and delicate photonic design for simultaneous high solar reflectivity (>94%) and thermal emissivity. A great challenge arises when trying to meet such strict photonic microstructure requirements while maintaining manufacturing scalability. Herein, we demonstrate a rapid, low-cost, template-free roll-to-roll method to fabricate spike microstructured photonic nanocomposite coatings with Al2O3 and TiO2 nanoparticles embedded that possess 96.0% of solar reflectivity and 97.0% of thermal emissivity. When facing direct sunlight in the spring of Chicago (average 699 W/m2 solar intensity), the coatings show a radiative cooling power of 39.1 W/m2. Combined with the coatings' superhydrophobic and contamination resistance merits, the potential 14.4% cooling energy-saving capability is numerically demonstrated across the United States.}, number={17}, journal={Nano Letters}, author={Liu, S. and Sui, C. and Harbinson, M. and Pudlo, M. and Perera, Himendra and Zhang, Zhenzhen and Liu, Ruguan and Ku, Zahyun and Islam, Md Didarul and Liu, Yuxuan and et al.}, editor={Ryu, JongEditor}, year={2023}, pages={7767–7774} }
 @article{lee_hossain_jamalzadegan_liu_wang_saville_shymanovich_paul_rotenberg_whitfield_et al._2023, title={Abaxial leaf surface-mounted multimodal wearable sensor for continuous plant physiology monitoring}, volume={9}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.ade2232}, abstractNote={Wearable plant sensors hold tremendous potential for smart agriculture. We report a lower leaf surface-attached multimodal wearable sensor for continuous monitoring of plant physiology by tracking both biochemical and biophysical signals of the plant and its microenvironment. Sensors for detecting volatile organic compounds (VOCs), temperature, and humidity are integrated into a single platform. The abaxial leaf attachment position is selected on the basis of the stomata density to improve the sensor signal strength. This versatile platform enables various stress monitoring applications, ranging from tracking plant water loss to early detection of plant pathogens. A machine learning model was also developed to analyze multichannel sensor data for quantitative detection of tomato spotted wilt virus as early as 4 days after inoculation. The model also evaluates different sensor combinations for early disease detection and predicts that minimally three sensors are required including the VOC sensors.}, number={15}, journal={SCIENCE ADVANCES}, author={Lee, Giwon and Hossain, Oindrila and Jamalzadegan, Sina and Liu, Yuxuan and Wang, Hongyu and Saville, Amanda C. and Shymanovich, Tatsiana and Paul, Rajesh and Rotenberg, Dorith and Whitfield, Anna E. and et al.}, year={2023}, month={Apr} }
 @article{ren_song_zhu_o'connor_dong_2023, title={All Electrohydrodynamic Printed Flexible Organic Thin Film Transistors}, volume={6}, ISSN={["2365-709X"]}, url={https://doi.org/10.1002/admt.202300410}, DOI={10.1002/admt.202300410}, abstractNote={Abstract}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Ren, Ping and Song, Runqiao and Zhu, Yong and O'Connor, Brendan and Dong, Jingyan}, year={2023}, month={Jun} }
 @article{wu_hong_zhao_yin_zhu_2023, title={Caterpillar-inspired soft crawling robot with distributed programmable thermal actuation}, volume={9}, ISSN={["2375-2548"]}, DOI={10.1126/sciadv.adf8014}, abstractNote={Many inspirations for soft robotics are from the natural world, such as octopuses, snakes, and caterpillars. Here, we report a caterpillar-inspired, energy-efficient crawling robot with multiple crawling modes, enabled by joule heating of a patterned soft heater consisting of silver nanowire networks in a liquid crystal elastomer (LCE)–based thermal bimorph actuator. With patterned and distributed heaters and programmable heating, different temperature and hence curvature distribution along the body of the robot are achieved, enabling bidirectional locomotion as a result of the friction competition between the front and rear end with the ground. The thermal bimorph behavior is studied to predict and optimize the local curvature of the robot under thermal stimuli. The bidirectional actuation modes with the crawling speeds are investigated. The capability of passing through obstacles with limited spacing are demonstrated. The strategy of distributed and programmable heating and actuation with thermal responsive materials offers unprecedented capabilities for smart and multifunctional soft robots.}, number={12}, journal={SCIENCE ADVANCES}, author={Wu, Shuang and Hong, Yaoye and Zhao, Yao and Yin, Jie and Zhu, Yong}, year={2023}, month={Mar} }
 @article{negi_kim_hua_timofeeva_zhang_zhu_peters_kumah_jiang_liu_2023, title={Ferroelectric Domain Wall Engineering Enables Thermal Modulation in PMN-PT Single Crystals}, volume={4}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202211286}, DOI={10.1002/adma.202211286}, abstractNote={Abstract}, journal={ADVANCED MATERIALS}, author={Negi, Ankit and Kim, Hwang Pill and Hua, Zilong and Timofeeva, Anastasia and Zhang, Xuanyi and Zhu, Yong and Peters, Kara and Kumah, Divine and Jiang, Xiaoning and Liu, Jun}, year={2023}, month={Apr} }
 @article{yang_li_zhou_li_zhu_ma_2023, title={High-dielectric porous CaCu3Ti4O12/reduced graphene oxide/ polydimethylsiloxane foam for wearable, breathable and low crosstalk capacitive pressure sensor}, volume={40}, ISSN={["2452-2627"]}, DOI={10.1016/j.flatc.2023.100522}, abstractNote={High-dielectric porous CaCu3Ti4O12 (CCTO)/reduced graphene oxide (rGO)/polydimethylsiloxane (PDMS) foam is prepared through a simple sacrificial salt-templating method. By introducing CCTO and rGO fillers into the porous PDMS scaffold, a three-dimensional porous CCTO/rGO/PDMS foam with large dielectric constant of 107.8 is obtained. The CCTO/rGO/PDMS foam also has a low Young's modulus of 0.007 MPa as well as a high water vapor transmission (WVT) rate of 14 mg/cm2·h (0.5 mm thickness). A wearable, breathable and low crosstalk capacitive pressure sensor based on CCTO/rGO/PDMS foam and porous Ag nanowires (NW)/thermoplastic polyurethane (TPU) electrodes has been fabricated. The sensor displays fast response speed (<48 ms), excellent sensitivity (3.5 kPa−1), superior cyclic repeatability and stability (11,000 cycles), as well as high gas permeability (WVT rate of 13 mg/cm2·h). The sensor can be attached to different body positions to monitor diverse physiological activities including breathing, vocal cord vibration and finger touch pressure. Moreover, the pressure sensor array integrated by multiple sensor units with low crosstalk is fabricated to detect spatial pressure distribution.}, journal={FLATCHEM}, author={Yang, Qiuyue and Li, Chen and Zhou, Weixin and Li, Yi and Zhu, Yong and Ma, Yanwen}, year={2023}, month={Jul} }
 @article{shao_qu_wang_cui_liu_zhu_2023, title={Interfacial shear stress transfer between elastoplastic fiber and elastic matrix}, volume={173}, ISSN={["1873-4782"]}, DOI={10.1016/j.jmps.2023.105218}, abstractNote={Interfacial mechanics between elastoplastic fiber and elastic substrate/matrix is of critical importance for a range of applications such as metal nanowires on polymer substrate for flexible and stretchable electronics and metal fibers in ceramic matrix for multifunctional composites. Here analytical models of an elastoplastic fiber (e.g., nanowire) on the as-prepared or chemically treated elastic substrate are derived by using the nonlinear and bilinear cohesive shear-lag models, respectively, for the fiber/substrate interface. For the first time, the effect of plastic mechanical behavior of the fiber on the interfacial shear stress transfer characteristics is studied. Different cases considering the length of the plastic zone relative to the bonded, sliding, damaged and debonded zones are investigated. The effect of the substrate strain, nanowire length and diameters is investigated to predict the mechanical behavior of the nanowire, which provides a guide to the experiment with metal nanowires on a polymer substrate. This work can be extended to other elastoplastic fibers including 2D nanomaterials, metal particles, and metal thin films on elastic substrates or matrices.}, journal={JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS}, author={Shao, Li-Hua and Qu, Xiaodong and Wang, Tianyu and Cui, Zheng and Liu, Yuxuan and Zhu, Yong}, year={2023}, month={Apr} }
 @article{song_ren_liu_zhu_dong_brendan t. o'connor_2023, title={Stretchable Organic Transistor Based Pressure Sensor Employing a Porous Elastomer Gate Dielectric}, volume={4}, ISSN={["2365-709X"]}, url={http://dx.doi.org/10.1002/admt.202202140}, DOI={10.1002/admt.202202140}, abstractNote={Abstract}, journal={ADVANCED MATERIALS TECHNOLOGIES}, publisher={Wiley}, author={Song, Runqiao and Ren, Ping and Liu, Yuxuan and Zhu, Yong and Dong, Jingyan and Brendan T. O'Connor}, year={2023}, month={Apr} }
 @article{he_cheng_zhu_park_2023, title={Surface Adatom Diffusion-Assisted Dislocation Nucleation in Metal Nanowires}, volume={23}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.3c01660}, abstractNote={We employ a hybrid diffusion- and nucleation-based kinetic Monte Carlo model to elucidate the significant impact of adatom diffusion on incipient surface dislocation nucleation in metal nanowires. We reveal a stress-regulated diffusion mechanism that promotes preferential accumulation of diffusing adatoms near nucleation sites, which explains the experimental observations of strong temperature but weak strain-rate dependence as well as temperature-dependent scatter of the nucleation strength. Furthermore, the model demonstrates that a decreasing rate of adatom diffusion with an increasing strain rate will lead to stress-controlled nucleation being the dominant nucleation mechanism at higher strain rates. Overall, our model offers new mechanistic insights into how surface adatom diffusion directly impacts the incipient defect nucleation process and resulting mechanical properties of metal nanowires.}, number={12}, journal={NANO LETTERS}, author={He, Lijie and Cheng, Guangming and Zhu, Yong and Park, Harold S.}, year={2023}, month={Jun}, pages={5779–5784} }
 @article{harbinson_pudlo_liu_chaudhry_liu_sui_zhu_hsu_ryu_2023, title={Template-free scalable roll-to-roll fabrication of textured transparent film for passive radiation cooling of photovoltaics}, volume={35}, ISSN={["2213-8463"]}, DOI={10.1016/j.mfglet.2023.08.006}, abstractNote={Solar panels contributed to over 115,000 GWh of energy being produced in the United States and solar panel energy consumption has increased by 27 % at the start of the 21st century. Given the decrease of photovoltaic efficiency at higher temperatures and the increasing demand for clean energy, the development of an economical technology for solar panel cooling is necessary. Passive cooling can be achieved by infrared radiating into space. Typical solar arrays require large functional areas in order to supply a significant amount of power as compared to other sources. As such, any method to help reduce the temperature of the solar panel surfaces needs to maintain manufacturing scalability for sustainable use. We demonstrate a rapid, low-cost, template-free roll coating method to fabricate photonic composite film with SiO2 nanoparticles which possess high emissivity in the atmospheric transparent window while passing visible and near infrared light to photovoltaics beneath. When facing direct sunlight at summer noon, the coatings show a 3.5°C temperature decrease without loss of photovoltaic efficiency while having hydrophobic and contamination-resistance merits.}, journal={MANUFACTURING LETTERS}, author={Harbinson, Myers and Pudlo, Michael and Liu, Sipan and Chaudhry, Taimur and Liu, Yuxuan and Sui, Chenxi and Zhu, Yong and Hsu, Po-Chun and Ryu, Jong E.}, year={2023}, month={Aug}, pages={166–173} }
 @article{karbalaeisadegh_yao_zhu_grimal_muller_2023, title={Ultrasound Characterization of Cortical Bone Using Shannon Entropy}, volume={49}, ISSN={["1879-291X"]}, DOI={10.1016/j.ultrasmedbio.2023.04.006}, abstractNote={Ultrasound backscattered signals encompass information on the microstructure of heterogeneous media such as cortical bone, in which pores act as scatterers and result in the scattering and multiple scattering of ultrasound waves. The objective of this study was to investigate whether Shannon entropy can be exploited to characterize cortical porosity.In the study described here, to demonstrate proof of concept, Shannon entropy was used as a quantitative ultrasound parameter to experimentally evaluate microstructural changes in samples with controlled scatterer concentrations made of a highly absorbing polydimethylsiloxane matrix (PDMS). Similar assessment was then performed using numerical simulations on cortical bone structures with varying average pore diameter (Ct.Po.Dm.), density (Ct.Po.Dn.) and porosity (Ct.Po.).The results suggest that an increase in pore diameter and porosity lead to an increase in entropy, indicating increased levels of randomness in the signals as a result of increased scattering. The entropy-versus-scatterer volume fraction in PDMS samples indicates an initial increasing trend that slows down as the scatterer concentration increases. High levels of attenuation cause the signal amplitudes and corresponding entropy values to decrease drastically. The same trend is observed when porosity of the bone samples is increased above 15%.Sensitivity of entropy to microstructural changes in highly scattering and absorbing media can potentially be exploited to diagnose and monitor osteoporosis.}, number={8}, journal={ULTRASOUND IN MEDICINE AND BIOLOGY}, author={Karbalaeisadegh, Yasamin and Yao, Shanshan and Zhu, Yong and Grimal, Quentin and Muller, Marie}, year={2023}, month={Aug}, pages={1824–1829} }
 @article{chen_poblete_bagal_zhu_chang_2022, title={Anelasticity in thin-shell nanolattices}, volume={119}, ISSN={["1091-6490"]}, DOI={10.1073/pnas.2201589119}, abstractNote={In this work, we investigate the anelastic deformation behavior of periodic three-dimensional (3D) nanolattices with extremely thin shell thicknesses using nanoindentation. The results show that the nanolattice continues to deform with time under a constant load. In the case of 30-nm-thick aluminum oxide nanolattices, the anelastic deformation accounts for up to 18.1% of the elastic deformation for a constant load of 500 μN. The nanolattices also exhibit up to 15.7% recovery after unloading. Finite element analysis (FEA) coupled with diffusion of point defects is conducted, which is in qualitative agreement with the experimental results. The anelastic behavior can be attributed to the diffusion of point defects in the presence of a stress gradient and is reversible when the deformation is removed. The FEA model quantifies the evolution of the stress gradient and defect concentration and demonstrates the important role of a wavy tube profile in the diffusion of point defects. The reported anelastic deformation behavior can shed light on time-dependent response of nanolattice materials with implication for energy dissipation applications.}, number={38}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Chen, I-Te and Poblete, Felipe Robles and Bagal, Abhijeet and Zhu, Yong and Chang, Chih-Hao}, year={2022}, month={Sep} }
 @article{hong_chi_wu_li_zhu_yin_2022, title={Boundary curvature guided programmable shape-morphing kirigami sheets}, volume={13}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-022-28187-x}, abstractNote={Abstract}, number={1}, journal={NATURE COMMUNICATIONS}, author={Hong, Yaoye and Chi, Yinding and Wu, Shuang and Li, Yanbin and Zhu, Yong and Yin, Jie}, year={2022}, month={Jan} }
 @article{liu_zheng_o'connor_dong_zhu_2022, title={Curvilinear soft electronics by micromolding of metal nanowires in capillaries}, volume={8}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.add6996}, DOI={10.1126/sciadv.add6996}, abstractNote={
            Soft electronics using metal nanowires have attracted notable attention attributed to their high electrical conductivity and mechanical flexibility. However, high-resolution complex patterning of metal nanowires on curvilinear substrates remains a challenge. Here, a micromolding-based method is reported for scalable printing of metal nanowires, which enables complex and highly conductive patterns on soft curvilinear and uneven substrates with high resolution and uniformity. Printing resolution of 20 μm and conductivity of the printed patterns of ~6.3 × 10
            6
            S/m are achieved. Printing of grid structures with uniform thickness for transparent conductive electrodes (TCEs) and direct printing of pressure sensors on curved surfaces such as glove and contact lens are also realized. The printed hybrid soft TCEs and smart contact lens show promising applications in optoelectronic devices and personal health monitoring, respectively. This printing method can be extended to other nanomaterials for large-scale printing of high-performance soft electronics.
          }, number={46}, journal={SCIENCE ADVANCES}, author={Liu, Yuxuan and Zheng, Michael and O'Connor, Brendan and Dong, Jingyan and Zhu, Yong}, year={2022}, month={Nov} }
 @article{poblete_mondal_ma_dickey_genzer_zhu_2022, title={Direct measurement of rate-dependent mode I and mode II traction-separation laws for cohesive zone modeling of laminated glass}, volume={279}, ISSN={["1879-1085"]}, DOI={10.1016/j.compstruct.2021.114759}, abstractNote={This paper reports a combined experimental-modeling study on the adhesion at glass/poly(vinyl butyral) (PVB) interfaces. PVB is a critical component in laminated glasses that provides impact resistance and prevents spallation in the event of glass breakage. We characterize the mode I (normal) and mode II (shear) interfacial fracture behaviors in glass/PVB/glass laminates and obtained independent cohesive (traction–separation) laws for the two modes. We observe a pronounced rate dependence of both traction-separation laws. Specifically, with increasing loading rate, the interfacial stiffness, the peak stress, and the fracture toughness increase while the critical opening or shear displacement decreases. These measured traction-separation laws are used as inputs in finite element analysis to predict the mechanical behavior of the peel test, which agrees reasonably well with the experimental results. Finite element analysis of a glass laminate subjected to impact loading demonstrates how the measured interfacial properties can be used to predict the mechanical behavior and failure of laminated glass.}, journal={COMPOSITE STRUCTURES}, author={Poblete, Felipe R. and Mondal, Kunal and Ma, Yinong and Dickey, Michael D. and Genzer, Jan and Zhu, Yong}, year={2022}, month={Jan} }
 @article{shukla_liu_zhu_2022, title={Eco-friendly screen printing of silver nanowires for flexible and stretchable electronics}, ISSN={["2040-3372"]}, DOI={10.1039/d2nr05840e}, abstractNote={This paper reports an eco-friendly method for screen printing of silver nanowires on a diverse range of substrates with high resolution and high electric conductivity. A low annealing temperature makes the method compatible with plastic substrates.}, journal={NANOSCALE}, author={Shukla, Darpan and Liu, Yuxuan and Zhu, Yong}, year={2022}, month={Dec} }
 @article{vargas_huang_zhu_hu_2022, title={Evoked Tactile Feedback and Control Scheme on Functional Utility of Prosthetic Hand}, volume={7}, ISSN={["2377-3766"]}, url={http://dx.doi.org/10.1109/lra.2021.3139147}, DOI={10.1109/LRA.2021.3139147}, abstractNote={Fine manual control relies on intricate action-perception coupling to effectively interact with objects. Here, we evaluated how electrically evoked artificial tactile sensation can be integrated into the functional utility of a prosthetic hand. Using different myoelectric-control strategies, participants performed a modified box-and-block task using a prosthetic hand. Transcutaneous nerve stimulation was employed to elicit somatotopic fingertip tactile feedback reflecting prosthetic fingertip forces. This feedback was evoked using an electrode grid placed along the participants’ upper arm targeting the median and ulnar nerve bundles. Myoelectric signals from the finger flexor and extensor controlled the prosthetic joint velocity or position. Participants lifted, held, and transported cubes of varying weights using their minimum grip forces. The results showed that participants exerted lower forces and presented lower number of failed trials (prematurely dropped objects) when feedback was provided with respect to without feedback. We also found that position control required more flexor muscle activation compared with velocity control when tactile feedback was provided. Our findings reveal that non-invasively evoked tactile feedback could be used to effectively enable human-in-the-loop control of a prosthetic hand. The outcomes can provide a platform to characterize the action-perception couplings during prosthetic control, in order to improve user experience and system functionality.}, number={2}, journal={IEEE ROBOTICS AND AUTOMATION LETTERS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2022}, month={Apr}, pages={1300–1307} }
 @article{wu_moody_kollipara_zhu_2022, title={Highly Sensitive, Stretchable, and Robust Strain Sensor Based on Crack Propagation and Opening}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.2c16741}, abstractNote={Soft and stretchable strain sensors have been attracting significant attention. However, the trade-off between the sensitivity (gauge factor) and the sensing range has been a major challenge. In this work, we report a soft stretchable resistive strain sensor with an unusual combination of high sensitivity, large sensing range, and high robustness. The sensor is made of a silver nanowire network embedded below the surface of an elastomeric matrix (e.g., poly(dimethylsiloxane)). Periodic mechanical cuts are applied to the top surface of the sensor, changing the current flow from uniformly across the sensor to along the conducting path defined by the open cracks. Both experiment and finite element analysis are conducted to study the effect of the slit depth, slit length, and pitch between the slits. The stretchable strain sensor can be integrated into wearable systems for monitoring physiological functions and body motions associated with different levels of strain, such as blood pressure and lower back health. Finally, a soft three-dimensional (3D) touch sensor that tracks both normal and shear stresses is developed for human-machine interfaces and tactile sensing for robotics.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Wu, Shuang and Moody, Katherine and Kollipara, Abhiroop and Zhu, Yong}, year={2022}, month={Dec} }
 @article{son_lee_wang_samson_wei_zhu_you_2022, title={Integrating charge mobility, stability and stretchability within conjugated polymer films for stretchable multifunctional sensors}, volume={13}, ISSN={["2041-1723"]}, url={https://doi.org/10.1038/s41467-022-30361-0}, DOI={10.1038/s41467-022-30361-0}, abstractNote={Abstract}, number={1}, journal={NATURE COMMUNICATIONS}, author={Son, Sung Yun and Lee, Giwon and Wang, Hongyu and Samson, Stephanie and Wei, Qingshan and Zhu, Yong and You, Wei}, year={2022}, month={May} }
 @article{kathavate_prasad_kiran_zhu_2022, title={Mechanical characterization of piezoelectric materials: A perspective on deformation behavior across different microstructural length scales}, volume={132}, ISSN={["1089-7550"]}, DOI={10.1063/5.0099161}, abstractNote={Piezoelectric materials (PEMs) find a wide spectrum of applications that include, but are not limited to, sensors, actuators, semiconductors, memory devices, and energy harvesting systems due to their outstanding electromechanical and polarization characteristics. Notably, these PEMs can be employed across several length scales (both intrinsic and extrinsic) ranging from mesoscale (bulk ceramics) to nanoscale (thin films) during their applications. Over the years, progress in probing individual electrical and mechanical properties of PEM has been notable. However, proportional review articles providing the mechanical characterization of PEM are relatively few. The present article aims to give a tutorial on the mechanical testing of PEMs, ranging from the conventional bulk deformation experiments to the most recent small-scale testing techniques from a materials science perspective. The advent of nanotechnology has led materials scientists to develop in situ testing techniques to probe the real-time electromechanical behavior of PEMs. Therefore, this article presents a systematic outlook on ex situ and in situ deformation experiments in mechanical and electromechanical environments, related mechanical behavior, and ferroelectric/elastic distortion during deformation. The first part provides significant insights into the multifunctionality of PEM and various contributing microstructural length scales, followed by a motivation to characterize the mechanical properties from the application's point of view. In the midst, the mechanical behavior of PEM and related mechanical characterization techniques (from mesoscale to nanoscale) are highlighted. The last part summarizes current challenges, future perspectives, and important observations.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Kathavate, V. S. and Prasad, K. Eswar and Kiran, Mangalampalli S. R. N. and Zhu, Yong}, year={2022}, month={Sep} }
 @article{vargas_huang_zhu_hu_2022, title={Object Recognition via Evoked Sensory Feedback during Control of a Prosthetic Hand}, volume={7}, ISSN={["2377-3766"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85118588970&partnerID=MN8TOARS}, DOI={10.1109/LRA.2021.3122897}, abstractNote={Haptic and proprioceptive feedback is critical for sensorimotor integration when we use our hand to perform daily tasks. Here, we evaluated how externally evoked haptic and proprioceptive feedback and myoelectric control strategies affected the recognition of object properties when participants controlled a prosthetic hand. Fingertip haptic sensation was elicited using a transcutaneous nerve stimulation grid to encode the prosthetic's fingertip forces. An array of tactors elicited patterned vibratory stimuli to encode tactile-proprioceptive kinematic information of the prosthetic finger joint. Myoelectric signals of the finger flexor and extensor were used to control the position or velocity of joint angles of the prosthesis. Participants were asked to perform object property (stiffness and size) recognition, by controlling the prosthetic hand with concurrent haptic and tactile-proprioceptive feedback. With the evoked feedback, intact and amputee participants recognized the object stiffness and size at success rates ranging from 50% to 100% in both position and velocity control with no significant difference across control schemes. Our findings show that evoked somatosensory feedback in a non-invasive manner can facilitate closed-loop control of the prosthetic hand and allowed for simultaneous recognition of different object properties. The outcomes can facilitate our understanding on the role of sensory feedback during bidirectional human-machine interactions, which can potentially promote user experience in object interactions using prosthetic hands.}, number={1}, journal={IEEE ROBOTICS AND AUTOMATION LETTERS}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2022}, month={Jan}, pages={207–214} }
 @article{vargas_huang_zhu_kamper_hu_2022, title={Resembled Tactile Feedback for Object Recognition Using a Prosthetic Hand}, volume={7}, ISSN={["2377-3766"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85136090957&partnerID=MN8TOARS}, DOI={10.1109/LRA.2022.3196958}, abstractNote={Tactile feedback in the hand is essential for interaction with objects. Here, we evaluated how artificial tactile sensation affected the recognition of object properties using a myoelectrically controlled prosthetic hand. Electromyogram signals from the flexor and extensor finger muscles were used to continuously control either prosthetic joint velocity or position. Participants grasped objects of varying shape or size using the prosthetic hand. Tactile feedback was evoked by transcutaneous nerve stimulation along the participant's upper arm and modulated based on the prosthetic-object contact force. Multi-channel electrical stimulation targeted the median and ulnar nerve bundles to produce resembled tactile sensations at distinct hand regions. The results showed that participants could gauge the onset timing of tactile feedback to discern object shape and size. We also found that the position-controller led to a greater recognition accuracy of object size compared with velocity-control, potentially due to supplemental joint position information from muscle activation level. Our findings demonstrate that non-invasive tactile feedback can enable effective object shape and size recognition during prosthetic control. The evaluation of tactile feedback across myoelectric controllers can help understand the interplay between sensory and motor pathways involved in the control of assistive devices.}, number={4}, journal={IEEE ROBOTICS AND AUTOMATION LETTERS}, author={Vargas, Luis and Huang, He and Zhu, Yong and Kamper, Derek and Hu, Xiaogang}, year={2022}, month={Oct}, pages={10977–10984} }
 @article{booth_schrickx_hanby_liu_qin_ade_zhu_brendan t. o'connor_2022, title={Silver Nanowire Composite Electrode Enabling Highly Flexible, Robust Organic Photovoltaics}, volume={6}, ISSN={["2367-198X"]}, DOI={10.1002/solr.202200264}, abstractNote={Using Ag nanowires (NWs) is a promising approach to make flexible and transparent conducting electrodes for organic photovoltaics (OPVs). However, the roughness of the NWs can decrease device performance. Herein, a Ag NW electrode embedded in a UV‐curable epoxy that uses a simple mechanical lift‐off process resulting in highly planar electrodes is demonstrated. A bimodal blend of Ag NWs with varying aspect ratios is used to optimize the transparency and conductivity of the electrode. In addition, a ZnO layer is coated on the Ag NWs prior to the embedding process to ensure low contact resistance in the OPV cells. The resulting resin‐embedded ZnO‐encapsulated silver nanowire (REZEN) electrode is found to have excellent mechanical stability. REZEN electrode‐based OPV cells exhibit comparable performance with reference devices, achieving maximum power conversion efficiency (PCE) of 13.5% and 13.6% respectively. The REZEN‐based OPV cells are also mechanically robust, retaining 97% of their PCE after 5000 cycles at R = 1.2 mm and 94% PCE after 1000 cycles at R = 0.55 mm. This flexibility is among the highest reported for freestanding devices. Thus, the REZEN electrode is a promising and simple strategy to achieve mechanically robust ITO‐free flexible OPV cells.}, journal={SOLAR RRL}, author={Booth, Ronald E. and Schrickx, Harry M. and Hanby, Georgia and Liu, Yuxuan and Qin, Yunpeng and Ade, Harald and Zhu, Yong and Brendan T. O'Connor}, year={2022}, month={Jun} }
 @article{yao_cui_cui_zhu_2022, title={Soft electrothermal actuators using silver nanowire heaters (vol 9, pg 3797, 2017)}, volume={14}, ISSN={["2040-3372"]}, DOI={10.1039/d2nr90086f}, abstractNote={Correction for ‘Soft electrothermal actuators using silver nanowire heaters’ by Shanshan Yao et al., Nanoscale, 2017, 9, 3797–3805, https://doi.org/10.1039/C6NR09270E.}, number={17}, journal={NANOSCALE}, author={Yao, Shanshan and Cui, Jianxun and Cui, Zheng and Zhu, Yong}, year={2022}, month={May}, pages={6671–6671} }
 @misc{liu_shukla_newman_zhu_2022, title={Soft wearable sensors for monitoring symptoms of COVID-19 and other respiratory diseases: a review}, volume={4}, ISSN={["2516-1091"]}, DOI={10.1088/2516-1091/ac2eae}, abstractNote={The COVID-19 pandemic has put extraordinary stress on medical systems and global society more broadly. The condition of infected patients may deteriorate rapidly due to overburdened hospital systems. This raises an urgent need for real-time and remote monitoring of physiological parameters to address the challenges associated with the COVID-19 pandemic. This review will present recent progress on soft wearable sensors that can potentially be used for monitoring respiratory diseases such as COVID-19. First, emerging monitoring devices and systems that can monitor key physiological parameters as suggested by the Centers for Disease Control and Prevention (e.g. body temperature, respiration rate, heart rate, oxygen saturation and body movement) are reviewed. Then, multimodal sensor systems consisting of two or more correlative sensors are presented. This review will conclude with challenges and future directions for wearable sensors for the diagnosis and therapy of respiratory diseases. While this review focuses on COVID-19, the sensing technologies reviewed can be applicable to other respiratory diseases such as H1N1 influenza.}, number={1}, journal={PROGRESS IN BIOMEDICAL ENGINEERING}, author={Liu, Yuxuan and Shukla, Darpan and Newman, Holly and Zhu, Yong}, year={2022}, month={Jan} }
 @article{lee_zarei_wei_zhu_lee_2022, title={Surface Wrinkling for Flexible and Stretchable Sensors}, volume={9}, ISSN={["1613-6829"]}, url={https://doi.org/10.1002/smll.202203491}, DOI={10.1002/smll.202203491}, abstractNote={Abstract}, journal={SMALL}, author={Lee, Giwon and Zarei, Mohammad and Wei, Qingshan and Zhu, Yong and Lee, Seung Goo}, year={2022}, month={Sep} }
 @article{islam_perera_black_phillips_chen_hodges_jackman_liu_kim_zikry_et al._2022, title={Template‐Free Scalable Fabrication of Linearly Periodic Microstructures by Controlling Ribbing Defects Phenomenon in Forward Roll Coating for Multifunctional Applications}, volume={9}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/admi.202201237}, DOI={10.1002/admi.202201237}, abstractNote={Abstract}, number={27}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Islam, Md Didarul and Perera, Himendra and Black, Benjamin and Phillips, Matthew and Chen, Muh‐Jang and Hodges, Greyson and Jackman, Allyce and Liu, Yuxuan and Kim, Chang‐Jin and Zikry, Mohammed and et al.}, year={2022}, month={Aug}, pages={2201237} }
 @article{yao_zhou_hinson_dong_wu_ives_hu_huang_zhu_2022, title={Ultrasoft Porous 3D Conductive Dry Electrodes for Electrophysiological Sensing and Myoelectric Control}, volume={5}, ISSN={["2365-709X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85132598682&partnerID=MN8TOARS}, DOI={10.1002/admt.202101637}, abstractNote={Abstract}, number={10}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Yao, Shanshan and Zhou, Weixin and Hinson, Robert and Dong, Penghao and Wu, Shuang and Ives, Jasmine and Hu, Xiaogang and Huang, He and Zhu, Yong}, year={2022}, month={May} }
 @article{wu_cui_baker_mahendran_xie_zhu_2021, title={A Biaxially Stretchable and Self-Sensing Textile Heater Using Silver Nanowire Composite}, volume={13}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.1c17651}, abstractNote={Wearable heaters have garnered significant attention from academia and industry for their great potential in thermotherapy. Silver nanowire (AgNW) is a promising conductive material for flexible and stretchable electrodes. Here, a resistive, biaxially stretchable heater based on AgNW composite is reported for the first time, where a AgNW percolation network is encased in a thin polyimide (PI) film and integrated with a highly stretchable textile. AgNW/PI is patterned with a 2D Kirigami structure, which enables constant resistance under a large tensile strain (up to uniaxial 100% strain and 50% biaxial strain). The heater can achieve a high temperature of ∼140 °C with a low current of 0.125 A, fast heating and cooling rates of ∼16.5 and ∼14.1 °C s-1, respectively, and stable performance over 400 heating cycles. A feedback control system is developed to provide constant heating temperature under a temperature change of the surrounding environment. Demonstrated applications in applying thermotherapy at the curvilinear surface of the knee using the stretchable heater illustrate its promising potential for wearable applications.}, number={49}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Wu, Shuang and Cui, Zheng and Baker, G. Langston and Mahendran, Siddarth and Xie, Ziyang and Zhu, Yong}, year={2021}, month={Dec}, pages={59085–59091} }
 @article{ren_liu_song_o'connor_dong_zhu_2021, title={Achieving High-Resolution Electrohydrodynamic Printing of Nanowires on Elastomeric Substrates through Surface Modification}, volume={3}, ISSN={["2637-6113"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85099220488&partnerID=MN8TOARS}, DOI={10.1021/acsaelm.0c00747}, abstractNote={Stretchable electronics based on nanomaterials has received much interest recently. However, it is challenging to print 1D nanomaterials (e.g., nanowires) with high resolution on stretchable elasto...}, number={1}, journal={ACS APPLIED ELECTRONIC MATERIALS}, publisher={American Chemical Society (ACS)}, author={Ren, Ping and Liu, Yuxuan and Song, Runqiao and O'Connor, Brendan and Dong, Jingyan and Zhu, Yong}, year={2021}, month={Jan}, pages={192–202} }
 @article{vargas_huang_zhu_hu_2021, title={Closed-loop control of a prosthetic finger via evoked proprioceptive information}, volume={18}, ISSN={["1741-2552"]}, url={http://dx.doi.org/10.1088/1741-2552/ac3c9e}, DOI={10.1088/1741-2552/ac3c9e}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF NEURAL ENGINEERING}, publisher={IOP Publishing}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2021}, month={Dec} }
 @article{prasad_farella_paulin_yao_zhu_vuuren_2021, title={Effect of electrode characteristics on electromyographic activity of the masseter muscle}, volume={56}, ISSN={["1873-5711"]}, DOI={10.1016/j.jelekin.2020.102492}, abstractNote={The study investigated effects of electrode material, inter-electrode distance (IED), and conductive gel on electromyographic (EMG) activity recorded from the masseter muscle. EMG was recorded unilaterally, as ten volunteers performed standardized oral tasks. Ag/AgCl and Ag coated with Au were the gel-based; Ag alloy coated with graphene, pure Ag coated with graphene and silver nanowire embedded electrodes were the gel-free materials tested. Ag/AgCl electrodes were tested at three different IEDs (i.e. 15 mm, 20 mm, 25 mm). An electrode relative performance index (ERPI) was defined and calculated for each of the standardized oral tasks that the volunteers performed. ERPI values obtained for the different oral tasks with different electrode materials and IEDs were compared using two-way repeated-measures ANOVA. ERPI values were not significantly influenced by IED. However, for the electrode materials statistically significant differences were found in ERPI values for all oral tasks. Of the gel-free electrode materials tested, pure silver electrodes coated with graphene had the highest ERPI values followed by Ag alloy electrodes coated with graphene and silver nanowire embedded electrodes. Within the limitations of the study, IED between 15 and 25 mm has a negligible effect on masseter muscle EMG. Graphene coated and silver nanowire embedded electrodes show promise as gel-free alternatives.}, journal={JOURNAL OF ELECTROMYOGRAPHY AND KINESIOLOGY}, author={Prasad, Sabarinath and Farella, Mauro and Paulin, Michael and Yao, Shanshan and Zhu, Yong and Vuuren, Ludwig Jansen}, year={2021}, month={Feb} }
 @article{lee_wei_zhu_2021, title={Emerging Wearable Sensors for Plant Health Monitoring}, volume={10}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.202106475}, abstractNote={Abstract}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Lee, Giwon and Wei, Qingshan and Zhu, Yong}, year={2021}, month={Oct} }
 @article{wu_baker_yin_zhu_2021, title={Fast Thermal Actuators for Soft Robotics}, ISSN={["2169-5180"]}, DOI={10.1089/soro.2021.0080}, abstractNote={Thermal actuation is a common actuation method for soft robots. However, a major limitation is the relatively slow actuation speed. Here we report significant increase in the actuation speed of a bimorph thermal actuator by harnessing the snap-through instability. The actuator is made of silver nanowire/polydimethylsiloxane composite. The snap-through instability is enabled by simply applying an offset displacement to part of the actuator structure. The effects of thermal conductivity of the composite, offset displacement, and actuation frequency on the actuator speed are investigated using both experiments and finite element analysis. The actuator yields a bending speed as high as 28.7 cm-1/s, 10 times that without the snap-through instability. A fast crawling robot with locomotion speed of 1.04 body length per second and a biomimetic Venus flytrap were demonstrated to illustrate the promising potential of the fast bimorph thermal actuators for soft robotic applications.}, journal={SOFT ROBOTICS}, author={Wu, Shuang and Baker, Gregory Langston and Yin, Jie and Zhu, Yong}, year={2021}, month={Dec} }
 @article{peng_chen_sim_zhu_jiang_2021, title={Noninvasive and Nonocclusive Blood Pressure Monitoring via a Flexible Piezo-Composite Ultrasonic Sensor}, volume={21}, ISSN={["1558-1748"]}, DOI={10.1109/JSEN.2020.3021923}, abstractNote={Continuous blood pressure monitoring in everyday life is important and necessary to detect and control high blood pressure in advance. While the existing blood pressure monitoring techniques are well suited for applications in current clinical settings, they are inadequate for next-generation wearable long-term monitoring of blood pressure on a daily basis. In this study, a flexible piezo-composite ultrasonic sensor was reported, for the first time, for continuous blood pressure measurement through ultrasonic motion tracking of blood vessel wall. A flexible piezo-composite ultrasonic sensor was designed and fabricated with a layer of PZT-5A/ polydimethylsiloxane (PDMS) anisotropic 1–3 composite and silver nanowire based stretchable electrodes. The material properties and dimensions of the sensor were determined according to the volume fraction of PZT-5A and the material properties of PZT-5A and PDMS. The experimental results illustrated that the flexible sensor possessed adequate bandwidth and sensitivity for blood pressure monitoring. Continuous blood pressure measurement was successfully conducted with the ulnar artery on a volunteer’s right arm. Compared with the measurement results using a clinical ultrasound probe and a commercial upper arm blood monitor, the results obtained in this study demonstrated the capability of the proposed flexible sensor to continuously monitor blood pressure waveforms during cardiac cycles. The flexible sensor provides a promising solution for noninvasive, nonocclusive and calibration-free blood pressure monitoring. It has great potential to be integrated into a wearable ultrasonic healthcare sensing system for blood pressure and flow monitoring.}, number={3}, journal={IEEE SENSORS JOURNAL}, author={Peng, Chang and Chen, Mengyue and Sim, Hun Ki and Zhu, Yong and Jiang, Xiaoning}, year={2021}, month={Feb}, pages={2642–2650} }
 @article{huang_zhu_2021, title={Patterning of Metal Nanowire Networks: Methods and Applications}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.1c14816}, abstractNote={With the advance in flexible and stretchable electronics, one-dimensional nanomaterials such as metal nanowires have drawn much attention in the past 10 years or so. Metal nanowires, especially silver nanowires, have been recognized as promising candidate materials for flexible and stretchable electronics. Owing to their high electrical conductivity and high aspect ratio, metal nanowires can form electrical percolation networks, maintaining high electrical conductivity under deformation (e.g., bending and stretching). Apart from coating metal nanowires for making large-area transparent conductive films, many applications require patterned metal nanowires as electrodes and interconnects. Precise patterning of metal nanowire networks is crucial to achieve high device performances. Therefore, a high-resolution, designable, and scalable patterning of metal nanowire networks is important but remains a critical challenge for fabricating high-performance electronic devices. This review summarizes recent advances in patterning of metal nanowire networks, using subtractive methods, additive methods of nanowire dispersions, and printing methods. Representative device applications of the patterned metal nanowire networks are presented. Finally, challenges and important directions in the area of the patterning of metal nanowire networks for device applications are discussed.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Huang, Qijin and Zhu, Yong}, year={2021}, month={Dec} }
 @article{vargas_huang_zhu_hu_2021, title={Perception of Static Position and Kinesthesia of the Finger using Vibratory Stimulation}, volume={2021-May}, ISSN={["1948-3546"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85107464376&partnerID=MN8TOARS}, DOI={10.1109/NER49283.2021.9441255}, abstractNote={Proprioception provides information regarding the state of an individual's limb in terms of static position and kinesthesia (dynamic movement). When such feedback is lost or impaired, the performance of dexterous control of our biological limbs or assistive devices tends to deteriorate. In this study, we determined if external vibratory stimulation patterns could allow for the perception of a finger's static position and kinesthesia. Using four tactors and two stimulus levels, eight vibratory settings corresponded to eight discrete finger positions. The transition patterns between these eight settings corresponded to kinesthesia. Three experimental blocks assessed the perception of a finger's static position, speed, and movement (amplitude and direction). Our results demonstrated that both position and kinesthesia could be recognized with over 93% accuracy. The outcomes suggest that vibratory stimulus can inform subjects of static and dynamic aspects of finger proprioception. This sensory stimulation approach can be implemented to improve outcomes in clinical populations with sensory deficits, and to enhance user experience when users interact with assistive devices.}, journal={2021 10TH INTERNATIONAL IEEE/EMBS CONFERENCE ON NEURAL ENGINEERING (NER)}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2021}, pages={1087–1090} }
 @article{barthelat_zavattieri_zhu_2021, title={Preface-Horacio D. Espinosa}, volume={48}, ISSN={["2352-4316"]}, DOI={10.1016/j.eml.2021.101449}, journal={EXTREME MECHANICS LETTERS}, author={Barthelat, Francois and Zavattieri, Pablo and Zhu, Yong}, year={2021}, month={Oct} }
 @article{li_liu_bhuiyan_zhu_yao_2021, title={Printed Strain Sensors for On-Skin Electronics}, ISSN={["2688-4062"]}, DOI={10.1002/sstr.202100131}, abstractNote={On‐skin electronics have drawn extensive attention as they revolutionize many aspects of healthcare, motion tracking, rehabilitation, robotics, human–machine interaction, among others. Flexible and stretchable strain sensors represent one of the most explored devices for on‐skin electronics. Many printing techniques have recently emerged showing great promises for manufacturing strain sensors. Herein, it is aimed to provide a timely survey of recent advancements in printed strain sensors for on‐skin electronics. This review starts with an overview of sensing mechanisms for printed strain sensors, followed by a review of various printing techniques employed in fabricating these sensors. The materials, structures, and printing processes of representative strain sensors are discussed in detail for each printing method. Finally, potential applications of printed flexible and stretchable strain sensors are presented focusing on three areas: healthcare, sports performance monitoring, and human–machine interfaces. The review concludes with a discussion of challenges and opportunities for future research.}, journal={SMALL STRUCTURES}, author={Li, Yizong and Liu, Yuxuan and Bhuiyan, Shah Rifat Alam and Zhu, Yong and Yao, Shanshan}, year={2021}, month={Nov} }
 @article{li_liu_hossain_paul_yao_wu_ristaino_zhu_wei_2021, title={Real-time monitoring of plant stresses via chemiresistive profiling of leaf volatiles by a wearable sensor}, volume={4}, ISSN={["2590-2385"]}, DOI={10.1016/j.matt.2021.06.009}, abstractNote={Determination of plant stresses such as infections by plant pathogens is currently dependent on time-consuming and complicated analytical technologies. Here, we report a leaf-attachable chemiresistive sensor array for real-time fingerprinting of volatile organic compounds (VOCs) that permits noninvasive and early diagnosis of plant diseases, such as late blight caused by Phytophthora infestans. The imperceptible sensor patch integrates an array of graphene-based sensing materials and flexible silver nanowire electrodes on a kirigami-inspired stretchable substrate, which can minimize strain interference. The sensor patch has been mounted on live tomato plants to profile key plant volatiles at low-ppm concentrations with fast response (<20 s). The multiplexed sensor array allows for accurate detection and classification of 13 individual plant volatiles with >97% classification accuracy. The wearable sensor patch was used to diagnose tomato late blight as early as 4 days post inoculation and abiotic stresses such as mechanical damage within 1 h.}, number={7}, journal={MATTER}, author={Li, Zheng and Liu, Yuxuan and Hossain, Oindrila and Paul, Rajesh and Yao, Shanshan and Wu, Shuang and Ristaino, Jean B. and Zhu, Yong and Wei, Qingshan}, year={2021}, month={Jul}, pages={2553–2570} }
 @article{liu_wang_zhu_2021, title={Recycling of Nanowire Percolation Network for Sustainable Soft Electronics}, ISSN={["2199-160X"]}, DOI={10.1002/aelm.202100588}, abstractNote={Abstract}, journal={ADVANCED ELECTRONIC MATERIALS}, author={Liu, Yuxuan and Wang, Hongyu and Zhu, Yong}, year={2021}, month={Jul} }
 @article{vargas_huang_zhu_hu_2021, title={Static and dynamic proprioceptive recognition through vibrotactile stimulation}, volume={18}, ISSN={["1741-2552"]}, url={http://dx.doi.org/10.1088/1741-2552/ac0d43}, DOI={10.1088/1741-2552/ac0d43}, abstractNote={Objective. Proprioceptive information provides individuals with a sense of our limb’s static position and dynamic movement. Impaired or a lack of such feedback can diminish our ability to perform dexterous motions with our biological limbs or assistive devices. Here we seek to determine whether both static and dynamic components of proprioception can be recognized using variation of the spatial and temporal components of vibrotactile feedback. Approach. An array of five vibrotactors was placed on the forearm of each subject. Each tactor was encoded to represent one of the five forearm postures. Vibratory stimulus was elicited to convey the static position and movement of the forearm. Four experimental blocks were performed to test each subject’s recognition of a forearm’s simulated static position, rotational amplitude, rotational amplitude and direction, and rotational speed. Main results. Our results showed that the subjects were able to perform proprioceptive recognition based on the delivered vibrotactile information. Specifically, rotational amplitude recognition resulted in the highest level of accuracy (99.0%), while the recognition accuracy of the static position and the rotational amplitude-direction was the lowest (91.7% and 90.8%, respectively). Nevertheless, all proprioceptive properties were perceived with >90% accuracy, indicating that the implemented vibrotactile encoding scheme could effectively provide proprioceptive information to the users. Significance. The outcomes suggest that information pertaining to static and dynamic aspects of proprioception can be accurately delivered using an array of vibrotactors. This feedback approach could be used to potentially evaluate the sensorimotor integration processes during human–machine interactions, and to improve sensory feedback in clinical populations with somatosensory impairments.}, number={4}, journal={JOURNAL OF NEURAL ENGINEERING}, publisher={IOP Publishing}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2021}, month={Aug} }
 @article{songkakul_wu_ahmmed_reynolds_zhu_bozkurt_2021, title={Wearable Bioimpedance Hydration Monitoring System using Conformable AgNW Electrodes}, ISSN={["1930-0395"]}, url={http://dx.doi.org/10.1109/sensors47087.2021.9639469}, DOI={10.1109/SENSORS47087.2021.9639469}, abstractNote={Monitoring hydration level could be vital for maintaining physiological and cognitive performance during physical exertion and thermal stress. We present a custom miniaturized wearable bioimpedance spectroscopy (BIS) system consisting of a Bluetooth-enabled system-on-a-chip and an analog front-end circuit integrated with conformable, flexible, and stretchable silver-nanowire electrodes. This system is capable of performing four-electrode BIS at a range of frequencies between 5 kHz and 195 kHz, transmitting the data wirelessly to a data aggregator, and configuring the front-end circuit parameters over-the-air when needed. A 150 mAh lithium polymer battery can power the system for 18 hours. In this study, proof-of-concept in-vitro validation of the system generated promising results.}, journal={2021 IEEE SENSORS}, publisher={IEEE}, author={Songkakul, Tanner and Wu, Shuang and Ahmmed, Parvez and Reynolds, William D., Jr. and Zhu, Yong and Bozkurt, Alper}, year={2021} }
 @article{wu_yao_liu_hu_huang_zhu_2020, title={Buckle-Delamination-Enabled Stretchable Silver Nanowire Conductors}, volume={12}, ISSN={["1944-8252"]}, url={http://dx.doi.org/10.1021/acsami.0c09775}, DOI={10.1021/acsami.0c09775}, abstractNote={Controlled buckling and delamination of thin films on a compliant substrate has attracted much attention for applications ranging from micro/nanofabrication to flexible and stretchable electronics to bioengineering. Here a highly conductive and stretchable conductor is fabricated by attaching a polymer composite film (with a thin layer of silver nanowires embedded below the surface of the polymer matrix) on top of a pre-stretched elastomer substrate followed with releasing the prestrain. A partially delaminated wavy geometry of the polymer film is created. During the evolution of the buckle delamination, the blisters pop up randomly but self-adjust into a uniform distribution, which effectively reduces the local strain in the silver nanowires. The resistance change of the conductor is less than 3% with the applied strain up to 100%. A theoretical model on the buckle-delamination structure is developed to predict the geometrical evolution, which agrees well with experimental observation. Finally, an integrated silver nanowire/elastomer sensing module and a stretchable thermochromic device are developed to demonstrate the utility of the stretchable conductor. This work highlights the important relevance of mechanics-based design in nanomaterial-enabled stretchable devices.}, number={37}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Wu, Shuang and Yao, Shanshan and Liu, Yuxuan and Hu, Xiaogang and Huang, He Helen and Zhu, Yong}, year={2020}, month={Sep}, pages={41696–41703} }
 @article{yin_cheng_zhu_gao_2020, title={Competition between shear localization and tensile detwinning in twinned nanowires}, volume={4}, ISSN={["2475-9953"]}, DOI={10.1103/PhysRevMaterials.4.023603}, abstractNote={Recently, a transition of deformation mechanism from localized dislocation slip to delocalized plasticity via an anomalous tensile detwinning mechanism has been discovered in bitwinned metallic nanowires (NWs) with a single twin boundary (TB) running parallel to the NW length. However, experiments showed that the anomalous tensile detwinning in most of bitwinned NWs does not propagate through the whole NW, which limits the NWs failure strain when compared to the twinning-induced superplasticity in single-crystalline NWs. An elusive but fundamentally important question is that what factors might affect the propagation of tensile detwinning in such bitwinned NWs. In addition, can this tensile detwinning mechanism be applied to other types of twinned NWs? Here, based on in situ transmission electron microscopy testing and molecular dynamics simulations, a competition between shear localization and tensile detwinning is identified. By dividing the tensile detwinning mechanism into two steps and investigating each step separately, it is found that the quality of a single-crystalline embryo formed during step one determines the succeeding detwinning propagation (step two) and the final plastic strain. Furthermore, this anomalous tensile detwinning mechanism is extended to other metallic NWs with multiple TBs running parallel to the length direction, such as asymmetric pentatwinned NWs and NWs with multiple parallel TBs. This work highlights the important role of detwinning in large plasticity in metallic NWs with different twin structures.}, number={2}, journal={PHYSICAL REVIEW MATERIALS}, author={Yin, Sheng and Cheng, Guangming and Zhu, Yong and Gao, Huajian}, year={2020}, month={Feb} }
 @article{song_yao_liu_wang_dong_zhu_brendan t. o'connor_2020, title={Facile Approach to Fabricating Stretchable Organic Transistors with Laser-Patterned Ag Nanowire Electrodes}, volume={12}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.0c15339}, DOI={10.1021/acsami.0c15339}, abstractNote={Stretchable electronics are poised to revolutionize personal healthcare and robotics, where they enable distributed and conformal sensors. Transistors are fundamental building blocks of electronics, and there is a need to produce stretchable transistors using low-cost and scalable fabrication techniques. Here, we introduce a facile fabrication approach using laser patterning and transfer printing to achieve high-performance, solution-processed intrinsically stretchable organic thin-film transistors (OTFTs). The device consists of Ag nanowire (NW) electrodes, where the source and drain electrodes are patterned using laser ablation. The Ag NWs are then partially embedded in a poly(dimethylsiloxane) (PDMS) matrix. The electrodes are combined with a PDMS dielectric and polymer semiconductor, where the layers are individually transfer printed to complete the OTFT. Two polymer semiconductors, DPP-DTT and DPP-4T, are considered and show stable operation under the cyclic strain of 20 and 40%, respectively. The OTFTs maintain electrical performance by adopting a buckled structure after the first stretch-release cycle. The conformability and stretchability of the OTFT is also demonstrated by operating the transistor while adhered to a finger being flexed. The ability to pattern highly conductive Ag NW networks using laser ablation to pattern electrodes as well as interconnects provides a simple strategy to produce complex stretchable OTFT-based circuits.}, number={45}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Song, Runqiao and Yao, Shanshan and Liu, Yuxuan and Wang, Hongyu and Dong, Jingyan and Zhu, Yong and Brendan T. O'Connor}, year={2020}, month={Nov}, pages={50675–50683} }
 @article{zhou_yao_wang_du_ma_zhu_2020, title={Gas-Permeable, Ultrathin, Stretchable Epidermal Electronics with Porous Electrodes}, volume={14}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.0c00906}, abstractNote={We present gas-permeable, ultrathin, and stretchable electrodes enabled by self-assembled porous substrates and conductive nanostructures. Efficient and scalable breath figure method is employed to introduce the porous skeleton and then silver nanowires (AgNWs) are dip-coated and heat-pressed to offer electric conductivity. The resulting film has a transmittance of 61%, sheet resistance of 7.3 Ω/sq, and water vapor permeability of 23 mg cm-2 h-1. With AgNWs embedded below the surface of the polymer, the electrode exhibits excellent stability with the presence of sweat and after long-term wear. We demonstrate the promising potential of the electrode for wearable electronics in two representative applications - skin-mountable biopotential sensing for healthcare and textile-integrated touch sensing for human-machine interfaces. The electrode can form conformal contact with human skin, leading to low skin-electrode impedance and high-quality biopotential signals. In addition, the textile electrode can be used in a self-capacitance wireless touch sensing system.}, number={5}, journal={ACS NANO}, author={Zhou, Weixin and Yao, Shanshan and Wang, Hongyu and Du, QIngchuan and Ma, Yanwen and Zhu, Yong}, year={2020}, month={May}, pages={5798–5805} }
 @article{cheng_yin_li_chang_richter_gao_zhu_2020, title={In-situ TEM study of dislocation interaction with twin boundary and retraction in twinned metallic nanowires}, volume={196}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2020.06.055}, abstractNote={Metallic nanowires (NWs) with twin boundaries (TBs) running parallel to the NW length direction exhibit unusual plastic strain recovery owing to the interaction of dislocations with TBs. Here, based on in-situ transmission electron microscopy nanomechanical testing and molecular dynamics simulations, we report observation and quantification of dislocation nucleation, interaction with TBs, and retraction in bi-twinned Ag NWs with a single TB along the NW length direction. Our results show that leading partial dislocations nucleated from the free surface can be hindered by the TB, and upon unloading all or part of the leading partials can retract due to the repulsive force from the TB, leading to full or partial plastic strain recovery (Bauschinger effect), respectively. The bi-twinned Ag NWs can undergo stress relaxation, even at a stress below the yield strength, where the plastic strain also recovers upon unloading. The relaxation and recovery behaviors are compared to those of penta-twinned Ag NWs. Our results illustrate that the internal TBs in NWs can interact with surface-nucleated dislocations, leading to time-dependent plastic strain recovery and Bauschinger effect.}, journal={ACTA MATERIALIA}, author={Cheng, Guangming and Yin, Sheng and Li, Chengjun and Chang, Tzu-Hsuan and Richter, Gunther and Gao, Huajian and Zhu, Yong}, year={2020}, month={Sep}, pages={304–312} }
 @article{li_cheng_wang_zhu_2020, title={Microelectromechanical Systems for Nanomechanical Testing: Displacement- and Force-Controlled Tensile Testing with Feedback Control}, volume={60}, ISSN={["1741-2765"]}, DOI={10.1007/s11340-020-00619-z}, number={7}, journal={EXPERIMENTAL MECHANICS}, author={Li, C. and Cheng, G. and Wang, H. and Zhu, Y.}, year={2020}, month={Sep}, pages={1005–1015} }
 @article{li_zhang_cheng_zhu_2020, title={Microelectromechanical Systems for Nanomechanical Testing: Electrostatic Actuation and Capacitive Sensing for High-Strain-Rate Testing}, volume={60}, ISSN={["1741-2765"]}, DOI={10.1007/s11340-019-00565-5}, number={3}, journal={EXPERIMENTAL MECHANICS}, author={Li, C. and Zhang, D. and Cheng, G. and Zhu, Y.}, year={2020}, month={Mar}, pages={329–343} }
 @article{vargas_huang_zhu_hu_2020, title={Object Shape and Surface Topology Recognition Using Tactile Feedback Evoked through Transcutaneous Nerve Stimulation}, volume={13}, ISSN={["2329-4051"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85078214377&partnerID=MN8TOARS}, DOI={10.1109/TOH.2020.2967366}, abstractNote={Tactile feedback is critical for distinguishing different object properties. In this article, we determined if tactile feedback evoked by transcutaneous nerve stimulation can be used to detect objects of different shape and surface topology. To evoke tactile sensation at different fingers, a 2x8 electrode grid was placed along the subject's upper arm, and two concurrent electrical stimulation trains targeted the median and ulnar nerve bundles, which evoked individually modulated sensations at different fingers. Fingertip forces of the prosthetic hand were transformed to stimulation current amplitude. Object shape was encoded based on finger-object contact timing. Surface topology represented by ridge height and spacing was encoded through current amplitude and stimulation time interval, respectively. The elicited sensation allowed subjects to determine object shape with success rates >84%. Surface topology recognition resulted in success rates >81%. Our findings suggest that tactile feedback evoked from transcutaneous nerve stimulation allows the recognition of object shape and surface topology. The ability to recognize these properties may help improve object manipulation and promote fine control of a prosthetic hand.}, number={1}, journal={IEEE TRANSACTIONS ON HAPTICS}, author={Vargas, Luis and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2020}, pages={152–158} }
 @article{poblete_cui_liu_zhu_2020, title={Stretching nanowires on a stretchable substrate: A method towards facile fracture testing and elastic strain engineering}, volume={41}, ISSN={["2352-4316"]}, DOI={10.1016/j.eml.2020.101035}, abstractNote={Nanomaterials are building blocks for a wide range of applications. They typically exhibit ultrahigh strength, which make them also promising candidates for elastic strain engineering. Here we demonstrate a potentially facile method to measure fracture strain and strain distribution of nanomaterials, with Ag nanowires as an example. Nanowires are placed on top of or embedded in a stretchable substrate (i.e., elastomer), either as-prepared (van der Waals interactions) or treated with UV ozone (chemical bonding), which is subjected to uniaxial tensile loading. Nonlinear and bilinear cohesive shear-lag models can well capture the interfacial shear stress transfer characteristics associated with the two types of interactions, respectively. For each type, interfacial parameters such as stiffness, shear strength, and/or fracture toughness are identified by fitting the measured average strains of the nanowires. The nanowires embedded in as-prepared and on top of treated substrate are found to fracture under large substrate strain. The fracture strain and strain distribution along the nanowires are predicted using the shear-lag models. This method can be readily applied to investigate fracture and elastic strain engineering of 1D nanomaterials (regardless of aligned or inclined with respect to the stretching direction) and 2D nanomaterials.}, journal={EXTREME MECHANICS LETTERS}, author={Poblete, Felipe R. and Cui, Zheng and Liu, Yuxuan and Zhu, Yong}, year={2020}, month={Nov} }
 @article{qin_li_yao_liu_huang_zhu_2019, title={Electrocardiogram of a Silver Nanowire Based Dry Electrode: Quantitative Comparison With the Standard Ag/AgCl Gel Electrode}, volume={7}, ISSN={["2169-3536"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85062896682&partnerID=MN8TOARS}, DOI={10.1109/ACCESS.2019.2897590}, abstractNote={Novel dry electrodes have promoted the development of wearable electrocardiogram (ECG) that is collected in daily life to monitor the ambulatory activity of heart status. To evaluate the performance of a dry electrode, it is necessary to compare it with the commercial disposable silver/silver chloride (Ag/AgCl) gel electrode. In this paper, a silver nanowire (AgNW)-based dry electrode was fabricated for noninvasive and wearable ECG sensing. Signals from the AgNW electrode and the Ag/AgCl electrode were simultaneously collected in two conditions: sitting and walking. Signal quality was evaluated in terms of ECG morphology, R-peak to R-peak interval, and heart rate variability analysis. Quantitative comparisons showed that the AgNW electrode could collect acceptable ECG waveforms as the Ag/AgCl electrode in both the sitting and walking conditions. However, the baseline drift and waveform distortions existed in the AgNW electrode, likely due to electrode motion. If the skin-electrode contact is improved, the dry electrode can be a promising substitute for the Ag/AgCl electrode.}, journal={IEEE ACCESS}, author={Qin, Qin and Li, Jianqing and Yao, Shanshan and Liu, Chengyu and Huang, He and Zhu, Yong}, year={2019}, pages={20789–20800} }
 @article{jiang_wang_ruan_zhu_2019, title={Equi-biaxial compressive strain in graphene: Gruneisen parameter and buckling ridges}, volume={6}, ISSN={["2053-1583"]}, DOI={10.1088/2053-1583/aaf20a}, abstractNote={Strain and defects in graphene have critical impact on morphology and properties of graphene. Here we report equi-biaxial compressive strain in monolayer graphene on SiO2 and Si3N4 substrates induced by thermal cycling in vacuum. The equi-biaxial strain is attributed to the mismatch in coefficient of thermal expansion between graphene and the substrate and sliding of graphene on the substrate. The sliding occurs during heating at the temperatures of 390 and 360 K for graphene on SiO2 and Si3N4 substrates, respectively. The biaxial Grüneisen parameter is determined to be 1.95 and 3.15 for G and 2D Raman bands of graphene, respectively. As the heating temperature exceeds a threshold temperature (1040 K for graphene/SiO2 and 640 K for graphene/Si3N4), buckling ridges are observed in graphene after the thermal cycle, from which the biaxial buckling strain of graphene on SiO2 and Si3N4 substrates are obtained as 0.21% and 0.22%, respectively. Importantly, the induced buckling ridges in graphene exhibit a pattern representing the symmetry of graphene crystal structure, which indicates that graphene relieves the compressive stress mainly along its lattice symmetry directions. These thermally induced graphene ridges are also found reminiscent of those in the synthesized graphene, suggesting the same origin of formation of the buckling ridges under biaxial compression.}, number={1}, journal={2D MATERIALS}, author={Jiang, Tao and Wang, Zuyuan and Ruan, Xiulin and Zhu, Yong}, year={2019}, month={Jan} }
 @article{vargas_whitehouse_huang_zhu_hu_2019, title={Evoked Haptic Sensation in the Hand With Concurrent Non-Invasive Nerve Stimulation}, volume={66}, ISSN={["1558-2531"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85077396250&partnerID=MN8TOARS}, DOI={10.1109/TBME.2019.2895575}, abstractNote={Objective: Haptic perception is critical for prosthetic users to control their prosthetic hand intuitively. In this study, we seek to evaluate the haptic perception evoked from concurrent stimulation trains through multiple channels using transcutaneous nerve stimulation. Methods: A 2 × 8 electrode grid was used to deliver current to the median and ulnar nerves in the upper arm. Different electrodes were first selected to activate the sensory axons, which can elicit sensations at different locations of the hand. Charge-balanced bipolar stimulation was then delivered to two sets of electrodes concurrently with a phase delay (dual stimulation) to determine whether the evoked sensation can be constructed from sensations of single stimulation delivered separately at different locations (single stimulation) along the electrode grid. The temporal delay between the two stimulation trains was altered to evaluate potential interference. The short-term stability of the haptic sensation within a testing session was also evaluated. Results: The evoked sensation during dual stimulation was largely a direct summation of the sensation from single stimulations. The delay between the two stimulation locations had minimal effect on the evoked sensations, which was also stable over repeated testing within a session. Conclusion: Our results indicated that the haptic sensations at different regions of the hand can be constructed by combining the response from multiple stimulation trains directly. The interference between stimulations were minimal. Significance: The outcomes will allow us to construct specific haptic sensation patterns when the prosthesis interacts with different objects, which may help improve user embodiment of the prosthesis.}, number={10}, journal={IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING}, author={Vargas, Luis and Whitehouse, Graham and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2019}, month={Oct}, pages={2761–2767} }
 @article{yin_cheng_chang_richter_zhu_gao_2019, title={Hydrogen embrittlement in metallic nanowires}, volume={10}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-019-10035-0}, abstractNote={Abstract}, journal={NATURE COMMUNICATIONS}, author={Yin, Sheng and Cheng, Guangming and Chang, Tzu-Hsuan and Richter, Gunther and Zhu, Yong and Gao, Huajian}, year={2019}, month={May} }
 @article{cheng_zhang_chang_liu_chen_lu_zhu_zhu_2019, title={In Situ Nano-thermomechanical Experiment Reveals Brittle to Ductile Transition in Silicon Nanowires}, volume={19}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.9b01789}, abstractNote={Silicon (Si) nanostructures are widely used in microelectronics and nanotechnology. Brittle to ductile transition in nanoscale Si is of great scientific and technological interest, but this phenomenon and its underlying mechanism remain elusive. By conducting in situ temperature-controlled nanomechanical testing inside a transmission electron microscope (TEM), here we show that the crystalline Si nanowires under tension are brittle at room temperature, but exhibit ductile behavior with dislocation-mediated plasticity at elevated temperatures. We find that reducing the nanowire diameter promotes the dislocation-mediated responses, as shown by 78 Si nanowires tested between room temperature and 600 K. In situ high resolution TEM imaging and atomistic reaction pathway modeling reveal that the unconventional ½〈110〉{001} dislocations become highly active with increasing temperature and thus play a critical role in the formation of deformation bands, leading to transition from brittle fracture to dislocation-mediated failure in Si nanowires at elevated temperatures. This study provides quantitative characterization and mechanistic insight for the brittle to ductile transition in Si nanostructures.}, number={8}, journal={NANO LETTERS}, author={Cheng, Guangming and Zhang, Yin and Chang, Tzu-Hsuan and Liu, Qunfeng and Chen, Lin and Lu, Wei D. and Zhu, Ting and Zhu, Yong}, year={2019}, month={Aug}, pages={5327–5334} }
 @article{poblete_zhu_2019, title={Interfacial shear stress transfer at nanowire-polymer interfaces with van der Waals interactions and chemical bonding}, volume={127}, ISSN={0022-5096}, url={http://dx.doi.org/10.1016/J.JMPS.2019.03.013}, DOI={10.1016/J.JMPS.2019.03.013}, abstractNote={Interfacial mechanics between nanostructures and matrix is of critical importance for a range of device applications of the nanostructures. However, it is challenging to characterize interfacial shear stress transfer at such nanoscale interfaces. In this work, we report a new method to study the interfacial shear stress transfer of single Si nanowires on top of a polymer substrate that is subjected to uniaxial tensile loading. In-situ atomic force microscopy (AFM) testing is used to measure the nanowire deformation, more specifically, average axial strain, as a function of the applied strain to the substrate. Two types of substrates, as-prepared and chemically treated, are selected to examine the effect of van der Waals interactions and chemical bonding. It is found that nonlinear and bilinear cohesive shear-lag models can well capture the interfacial shear stress transfer characteristics associated with the two types of interactions, respectively. For each type, the interface parameters such as interfacial stiffness, shear strength, and/or fracture toughness are identified by fitting the experimental results. This work provides valuable insights into fundamental mechanisms underlying the interfacial shear-lag models. In addition, a parametric study with different nanowire dimensions is carried out, which can provide a guide to experimental design of elastic strain engineering and fracture of Si nanowires.}, journal={Journal of the Mechanics and Physics of Solids}, publisher={Elsevier BV}, author={Poblete, Felipe Robles and Zhu, Yong}, year={2019}, month={Jun}, pages={191–207} }
 @article{wang_yang_wang_zhu_fang_2019, title={Maximum Spread of Droplet Impacting onto Solid Surfaces with Different Wettabilities: Adopting a Rim-Lamella Shape}, volume={35}, ISSN={["0743-7463"]}, url={https://doi.org/10.1021/acs.langmuir.8b03748}, DOI={10.1021/acs.langmuir.8b03748}, abstractNote={Experimental and theoretical investigations are presented for the maximum spread factor (βm) of an impacting droplet onto solid surfaces with contact angle hysteresis. Experiments were conducted with deionized water on six surfaces with different wettabilities. The examined Weber number ( We) falls between 10-1 and 103. A new energetic model adopting a rim-lamella shape is proposed to better represent the droplet shape at the maximum spread. The dynamic contact angle at the maximum spread (θβm) is introduced in the model to account for the curvature of the surrounding rim induced by surface wettabilities. A lamella-rim thickness ratio κ ≈ AWe- B ( A, B > 0) is utilized successfully to depict the droplet shape at different We in a unifying manner. Comprehensive evaluations of the model demonstrate that the theoretical prediction can well recover the features of the experimental observations. The L2-error analysis demonstrates the improvement of the proposed model in predicting βm for a wide range of We = 10-1 to 103: the calculated errors are smaller than 8% for all six surfaces. Moreover, the proposed model can also be applied to predict energy conversion/dissipation during the droplet spreading process and the effects of surface wettability on βm in a reasonable manner. The variation of the percentage of the surface energy and viscous dissipation is consistent with that in previous simulations. The weakness of the current model for predicting βm at extremely low Weber number ( We < 1) is also explained.}, number={8}, journal={LANGMUIR}, publisher={American Chemical Society (ACS)}, author={Wang, Fujun and Yang, Lei and Wang, Libing and Zhu, Yong and Fang, Tiegang}, year={2019}, month={Feb}, pages={3204–3214} }
 @article{yao_yang_poblete_hu_zhu_2019, title={Multifunctional Electronic Textiles Using Silver Nanowire Composites}, volume={11}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.9b07520}, abstractNote={Textiles represent an appealing platform for continuous wearable applications due to the exceptional combination of compliance, water vapor permeability, and comfortableness for long-term wear. We present mechanically and electrically robust integration of nanocomposites with textiles by laser scribing and heat press lamination. The simple and scalable integration technique enables multifunctional E-textiles without compromising the stretchability, wearability and washability of textiles. The textile-integrated patterns exhibit small linewidth (135 µm), low sheet resistance (0.2 Ω/sq), low Young's modulus, good washability, and good electromechanical performance up to 50% strain, which is desirable for wearable and user-friendly electronic textiles. To demonstrate the potential utility, we developed an integrated textile patch comprising four dry electrophysiological electrodes, a capacitive strain sensor, and a wireless heater for electrophysiological sensing, motion tracking, and thermotherapy, respectively. Beyond the applications demonstrated in this paper, the materials and methods presented here pave the way for various other wearable applications in healthcare, activity tracking, rehabilitation, and human-machine interactions.}, number={34}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Yao, Shanshan and Yang, Ji and Poblete, Felipe R. and Hu, Xiaogang and Zhu, Yong}, year={2019}, month={Aug}, pages={31028–31037} }
 @article{yao_ren_song_liu_huang_dong_o'connor_zhu_2019, title={Nanomaterial‐Enabled Flexible and Stretchable Sensing Systems: Processing, Integration, and Applications}, volume={32}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.201902343}, DOI={10.1002/adma.201902343}, abstractNote={Abstract}, number={15}, journal={Advanced Materials}, publisher={Wiley}, author={Yao, Shanshan and Ren, Ping and Song, Runqiao and Liu, Yuxuan and Huang, Qijin and Dong, Jingyan and O'Connor, Brendan T. and Zhu, Yong}, year={2019}, month={Aug}, pages={1902343} }
 @misc{huang_zhu_2019, title={Printing Conductive Nanomaterials for Flexible and Stretchable Electronics: A Review of Materials, Processes, and Applications}, volume={4}, ISSN={["2365-709X"]}, DOI={10.1002/admt.201800546}, abstractNote={Abstract}, number={5}, journal={ADVANCED MATERIALS TECHNOLOGIES}, author={Huang, Qijin and Zhu, Yong}, year={2019}, month={May} }
 @article{zhu_saif_delrio_2019, title={Recent Advances in Micro, Nano, and Cell Mechanics}, volume={59}, ISSN={["1741-2765"]}, DOI={10.1007/s11340-019-00497-0}, number={3}, journal={EXPERIMENTAL MECHANICS}, author={Zhu, Y. and Saif, T. and DelRio, F. W.}, year={2019}, month={Mar}, pages={277–278} }
 @article{cui_poblete_zhu_2019, title={Tailoring the Temperature Coefficient of Resistance of Silver Nanowire Nanocomposites and their Application as Stretchable Temperature Sensors}, volume={11}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.9b04045}, abstractNote={Body temperature is an important indicator of the health condition. It is of critical importance to develop a smart temperature sensor for wearable applications. Silver nanowire (AgNW) is a promising conductive material for developing flexible and stretchable electrodes. Here, a stretchable and breathable thermoresistive temperature sensor based on AgNW composites is developed, where a AgNW percolation network is encased in a thin polyimide film. The temperature coefficient of resistance of the AgNW network is tailored by modifying nanowire density and thermal annealing temperature. The temperature sensor is patterned with a Kirigami structure, which enables constant resistance under a large tensile strain (up to 100%). Demonstrated applications in monitoring the temperatures at biceps and knees using the stretchable temperature sensor illustrate the promising potential for wearable applications.}, number={19}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Cui, Zheng and Poblete, Felipe Robles and Zhu, Yong}, year={2019}, month={May}, pages={17836–17842} }
 @article{yin_cheng_richter_gao_zhu_2019, title={Transition of Deformation Mechanisms in Single-Crystalline Metallic Nanowires}, volume={13}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.9b03311}, abstractNote={Twinning and dislocation slip are two competitive deformation mechanisms in face-centered cubic (FCC) metals. For FCC metallic nanowires (NWs), the competition between these mechanisms was found to depend on loading direction and material properties. Here, using in situ transmission electron microscopy tensile tests and molecular dynamics simulations, we report an additional factor, cross-sectional shape, that can affect the competition between the deformation mechanisms in single crystalline FCC metallic NWs. For a truncated rhombic cross-section, the extent of truncation determines the competition. Specifically, a transition from twinning to localized dislocation slip occurs with increasing extent of truncation. Theoretical and simulation results indicate that the energy barriers for twinning and dislocation slip depend on the cross-sectional shape of the NW. The energy barrier for twinning is proportional to the change of surface energy associated with the twinning. Thus, the transition of deformation modes can be attributed to the change of surface energy as a function of the cross-sectional shape.}, number={8}, journal={ACS NANO}, author={Yin, Sheng and Cheng, Guangming and Richter, Gunther and Gao, Huajian and Zhu, Yong}, year={2019}, month={Aug}, pages={9082–9090} }
 @article{yao_vargas_hu_zhu_2018, title={A Novel Finger Kinematic Tracking Method Based on Skin-Like Wearable Strain Sensors}, volume={18}, ISSN={["1558-1748"]}, DOI={10.1109/jsen.2018.2802421}, abstractNote={Deficits in hand function are common in a majority of stroke survivors. Although hand performance can be routinely assessed during rehabilitation training, a lack of hand usage information during daily activities could prevent clinicians or therapists from making informative therapeutic decisions. In this paper, we demonstrated and validated the application of silver nanowire-based capacitive strain sensors for finger kinematic tracking. The fabricated strain sensors show high sensitivity (gauge factor close to one), low hysteresis, good linearity, large stretchability (150%), and skin-like mechanical property (Young’s modulus of 96 kPa). All these features allow the sensors to be conformally attached onto the skin to track finger joint movement with minimal interference to daily activities. Recordings of the skin deformation from the strain sensors and joint angles from reflective markers are highly correlated (>93%) for different joint oscillation speeds in a stroke survivor and a control subject, indicating the high accuracy of the strain sensors in joint motion tracking. With the wearable silver nanowire-based strain sensors, accurate hand utility information on the impaired hand of stroke survivors can be acquired in a continuous and unobtrusive manner.}, number={7}, journal={IEEE SENSORS JOURNAL}, author={Yao, Shanshan and Vargas, Luis and Hu, Xiaogang and Zhu, Yong}, year={2018}, month={Apr}, pages={3010–3015} }
 @article{cheng_zhu_2018, title={Anelastic Behavior in Crystalline Nanowires}, volume={24}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927618010024}, DOI={10.1017/S1431927618010024}, abstractNote={NWs exhibit a host of novel properties that are being exploited for many applications including energy harvesting and storage, flexible/stretchable electronics, sensing, and nanoelectromechanical systems. So far a vast majority of research on mechanical properties of NWs has been focused on size-dependent elastic modulus and strength, with very few studies on time-dependent responses [1]. This work reports an unexpected phenomenon of anelastic relaxation in crystalline NWs under bending [2]. Anelastic materials exhibit gradual full recovery of deformation once a load is removed, leading to efficient dissipation of internal mechanical energy. As a consequence, anelastic materials are being investigated for energy damping applications. At macroscopic scale, however, anelaticity is usually very small or negligible, especially in single-crystalline materials. Here we show that single-crystalline ZnO can exhibit anelastic behavior that is up to four orders of magnitude larger than the largest anelasticity observed in bulk materials, with a recovery time-scale in the order of minutes. In-situ scanning electron microscope (SEM) tests of individual NWs showed that, upon removal of the bending load and instantaneous recovery of the elastic strain, a substantial portion of the total strain gradually recovers with time (Fig. 1). We attribute the observed large anelasticity to stress-gradient-induced migration of point defects, as supported by quantitative electron energy loss spectroscopy (EELS) measurements [2] and also by the fact that no anelastic behavior could be observed under tension. The bending tests were performed at the room temperature using a microelectromechanical system (MEMS) based nanomechanical testing stage inside an SEM [3,4]. After the NW was held at a bent configuration for certain time (holding time), the MEMS actuator was retracted and the shape of the NW was monitored in real time (Fig. 1). It can be seen}, number={S1}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Cheng, Guangming and Zhu, Yong}, year={2018}, month={Aug}, pages={1908–1909} }
 @article{cheng_sheng_gao_zhu_2018, title={Anomalous Tensile Detwinning in Twinned Metallic Nanowires}, volume={24}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927618009601}, DOI={10.1017/S1431927618009601}, abstractNote={Nanowires (NWs) are among the most important building blocks for many applications ranging from nanosensors to energy harvesting/storage to flexible/stretchable electronics, to name a few. Operation and reliability of the NW-based devices call for a thorough understanding of their mechanical behaviors. Dislocation nucleation from free surfaces has been identified as a dominant deformation mechanism in NWs, in contrast to the forest dislocation dynamics in bulk materials. Extensive studies have been reported for defect-free, single crystalline metallic NWs where surface dislocation nucleation is dominant [1-3]. Such NWs exhibit ultrahigh yield strength, but typically with limited or no strain hardening and low tensile ductility due to the absence of effective obstacles within the NWs that could block the movement of dislocations. On the other hand, as-synthesized NWs typically possess different types of preexisting microstructures such as twin boundaries (TBs) [2-4], and there is still a general lack of understanding on how preexisting microstructures interact with the surface-nucleated dislocations and affect the mechanical behaviors of NWs. Here, based on a recently developed testing platform combining state-of-the-art microelectromechanical system (MEMS) technology and in situ TEM tensile tests, we conduct a systematic investigation of the deformation mechanisms in bi-twinned Ag NWs, each having a single TB running parallel to the NW length direction [5]. We performed in situ TEM tensile testing of individual NWs using a MEMS-based tensile testing stage that allows accurate measurements of both load and displacement simultaneously, as well as real-time imaging of microstructure evolution during deformation [2,4}, number={S1}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Cheng, Guangming and Sheng, Yin and Gao, Huajian and Zhu, Yong}, year={2018}, month={Aug}, pages={1824–1825} }
 @article{min_chen_chen_sun_lee_li_zhu_o'connor_parsons_chang_2018, title={Atomic Layer Deposition: Conformal Physical Vapor Deposition Assisted by Atomic Layer Deposition and Its Application for Stretchable Conductors (Adv. Mater. Interfaces 22/2018)}, volume={5}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/ADMI.201870109}, DOI={10.1002/ADMI.201870109}, abstractNote={Physical vapor deposition of thin films on nanostructure topography is typically limited by line-of-sight transfer. This study demonstrates that by introducing an oxide interlayer using atomic layer deposition, the film uniformity and electrical properties can be improved. Enabling conformal coating at low cost, this method can find applications in manufacturing of integrated circuit and stretchable electronics. More details can be found in article number 1801379 by Joong-Hee Min, Chih-Hao Chang, and co-workers.}, number={22}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Min, Joong‐Hee and Chen, Yi‐An and Chen, I‐Te and Sun, Tianlei and Lee, Dennis T. and Li, Chengjun and Zhu, Yong and O'Connor, Brendan T. and Parsons, Gregory N. and Chang, Chih‐Hao}, year={2018}, month={Nov}, pages={1870109} }
 @article{kong_wei_zhu_cohen_dong_2018, title={Characterization and Modeling of Catalyst-free Carbon-Assisted Synthesis of ZnO Nanowires}, volume={32}, ISSN={["1526-6125"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85044172611&partnerID=MN8TOARS}, DOI={10.1016/j.jmapro.2018.03.018}, abstractNote={ZnO nanowires have been widely studied due to their unique material properties and many potential applications in electronic and optoelectronic devices. Many growth processes have been developed to synthesize ZnO nanowires. It is critically important to develop predictive process models so as to maximize the output of the nanowire synthesis. Here we report a method to characterize, quantify, and model a catalyst-free carbon-assisted ZnO nanowire growth process. Two key factors were identified for the synthesis conditions, which are reaction temperature and flow rate. Based on a factorial design method, we conducted experiments with different combinations of the two factors to study their effects on the process output (i.e. density of the nanowires), which was evaluated by a scanning electron microscope (SEM). The experimental results were analyzed using ANOVA test, and then a semi-empirical model was built to correlate the ZnO nanowire output with synthesis conditions. This model was able to describe the ZnO nanowire density with respect to synthesis conditions, which can provide guideline for synthesis parameters selection and process optimization.}, journal={JOURNAL OF MANUFACTURING PROCESSES}, author={Kong, Xiangcheng and Wei, Chuang and Zhu, Yong and Cohen, Paul and Dong, Jingyan}, year={2018}, month={Apr}, pages={438–444} }
 @article{min_chen_chen_sun_lee_li_zhu_brendan t. o'connor_parsons_chang_2018, title={Conformal Physical Vapor Deposition Assisted by Atomic Layer Deposition and Its Application for Stretchable Conductors}, volume={5}, ISSN={["2196-7350"]}, DOI={10.1002/admi.201801379}, abstractNote={Abstract}, number={22}, journal={ADVANCED MATERIALS INTERFACES}, author={Min, Joong-Hee and Chen, Yi-An and Chen, I-Te and Sun, Tianlei and Lee, Dennis T. and Li, Chengjun and Zhu, Yong and Brendan T. O'Connor and Parsons, Gregory N. and Chang, Chih-Hao}, year={2018}, month={Nov} }
 @article{cui_adams_zhu_2018, title={Controlled bending and folding of a bilayer structure consisting of a thin stiff film and a heat shrinkable polymer sheet}, volume={27}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665x/aab9d9}, abstractNote={Bending pre-designed flat sheets into three-dimensional (3D) structures is attracting much interest, as it provides a simple approach to make 3D devices. Here we report controlled bending and folding of a bilayer structure consisting of a heat shrinkable polymer sheet and a thin stiff film (not thermally responsive). Upon heating, the prestrained polymer sheet shrinks, leading to bending or folding of the bilayer. We studied the effect of relative dimensions of the two layers on the bending behavior and demonstrated the transition from longitudinal bending to transverse bending of the bilayer strip. Transverse bending was utilized to fold origami structures, including several flat letters, a crane, and a corrugated metal sheet via Miura-ori folding. We developed a method to further control the bending orientation based on bio-inspired anisotropic bending stiffness. By bending the metal foil in different orientations, several structures were obtained, including cylindrical surfaces and left-handed/right-handed helical structures.}, number={5}, journal={SMART MATERIALS AND STRUCTURES}, author={Cui, Jianxun and Adams, John G. M. and Zhu, Yong}, year={2018}, month={May} }
 @article{cui_han_huang_dong_zhu_2018, title={Electrohydrodynamic printing of silver nanowires for flexible and stretchable electronics}, volume={10}, ISSN={["2040-3372"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85045850487&partnerID=MN8TOARS}, DOI={10.1039/c7nr09570h}, abstractNote={High-resolution, large-scale printing of highly conductive AgNWs for flexible and stretchable electronics using EHD printing is presented. The printed patterns show the smallest line width of 45 μm and electrical conductivity as high as ∼5.6 × 106S m−1. AgNW-based wearable heaters and ECG electrodes are fabricated.}, number={15}, journal={NANOSCALE}, author={Cui, Zheng and Han, Yiwei and Huang, Qijin and Dong, Jingyan and Zhu, Yong}, year={2018}, month={Apr}, pages={6806–6811} }
 @article{shin_watkins_huang_zhu_hu_2018, title={Evoked haptic sensations in the hand via non-invasive proximal nerve stimulation}, volume={15}, ISSN={["1741-2552"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85049836114&partnerID=MN8TOARS}, DOI={10.1088/1741-2552/aabd5d}, abstractNote={Objective. Haptic perception of a prosthetic limb or hand is a crucial, but often unmet, need which impacts the utility of the prostheses. In this study, we seek to evaluate the feasibility of a non-invasive transcutaneous nerve stimulation method in generating haptic feedback in a transradial amputee subject as well as intact able-bodied subjects. Approach. An electrode grid was placed on the skin along the medial side of the upper arm beneath the short head of the biceps brachii, in proximity to the median and ulnar nerves. Varying stimulation patterns were delivered to different electrode pairs, in order to emulate different types of sensations (Single Tap, Press-and-Hold, Double Tap) at different regions of the hand. Subjects then reported the magnitude of sensation by pressing on a force transducer to transform the qualitative haptic perception into a quantitative measurement. Main results. Altering current stimulations through electrode pairs on the grid resulted in repeatable alterations in the percept regions of the hand. Most subjects reported spatial coverage of individual fingers or phalanges, which can resemble the whole hand through different pairs of stimulation electrodes. The different stimulation patterns were also differentiable by all subjects. The amputee subject also reported haptic sensations similar to the able-bodied subjects. Significance. Our findings demonstrated the capabilities of our transcutaneous stimulation method. Subjects were able to perceive spatially distinct sensations with graded magnitudes that emulated tapping and holding sensation in their hands. The elicitation of haptic sensations in the phantom hand of an amputee is a significant step in the development of our stimulation method, and provides insight into the future adaptation and implementation of prostheses with non-invasive sensory feedback to the users.}, number={4}, journal={JOURNAL OF NEURAL ENGINEERING}, author={Shin, Henry and Watkins, Zach and Huang, He and Zhu, Yong and Hu, Xiaogang}, year={2018}, month={Aug} }
 @article{huang_zhu_2018, title={Gravure Printing of Water-based Silver Nanowire ink on Plastic Substrate for Flexible Electronics}, volume={8}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-018-33494-9}, abstractNote={Abstract}, journal={SCIENTIFIC REPORTS}, author={Huang, Qijin and Zhu, Yong}, year={2018}, month={Oct} }
 @article{kong_wei_zhu_cohen_dong_2018, title={Modeling of Catalyst-free Growth Process of ZnO Nanowires}, volume={26}, ISSN={2351-9789}, url={http://dx.doi.org/10.1016/J.PROMFG.2018.07.043}, DOI={10.1016/J.PROMFG.2018.07.043}, abstractNote={ZnO nanowires have been widely studied due to their unique material properties and many potential applications in electronic and optoelectronic devices. Many growth processes have been developed to synthesize ZnO nanowires. It is critically important to develop predictive process models so as to maximize the output of the nanowire synthesis. Here we report a method to characterize, quantify, and model a catalyst-free carbon-assisted ZnO nanowire growth process. Two key factors were identified for the synthesis conditions, which are reaction temperature and flow rate. Based on a factorial design method, we conducted experiments with different combinations of the two factors to study their effects on the process output (i.e. density of the nanowires), which was evaluated by a scanning electron microscope (SEM). The experimental results were analyzed using ANOVA test, and then a semi-empirical model was built to correlate the ZnO nanowire output with synthesis conditions. This model was able to describe the ZnO nanowire density with respect to synthesis conditions, which can provide a guideline for synthesis parameters selection and process optimization.}, journal={Procedia Manufacturing}, publisher={Elsevier BV}, author={Kong, Xiangcheng and Wei, Chuang and Zhu, Yong and Cohen, Paul and Dong, Jingyan}, year={2018}, pages={349–358} }
 @misc{yao_swetha_zhu_2018, title={Nanomaterial-Enabled Wearable Sensors for Healthcare}, volume={7}, ISSN={["2192-2659"]}, DOI={10.1002/adhm.201700889}, abstractNote={Abstract}, number={1}, journal={ADVANCED HEALTHCARE MATERIALS}, author={Yao, Shanshan and Swetha, Puchakayala and Zhu, Yong}, year={2018}, month={Jan} }
 @article{cui_poblete_zhu_2018, title={Origami/Kirigami-Guided Morphing of Composite Sheets}, volume={28}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201802768}, abstractNote={Abstract}, number={44}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Cui, Ianxun and Poblete, Felipe R. and Zhu, Yong}, year={2018}, month={Oct} }
 @article{cui_poblete_zhu_2018, title={Shape Morphing: Origami/Kirigami-Guided Morphing of Composite Sheets (Adv. Funct. Mater. 44/2018)}, volume={28}, ISSN={1616-301X}, url={http://dx.doi.org/10.1002/ADFM.201870314}, DOI={10.1002/ADFM.201870314}, abstractNote={In article number 1802768, Yong Zhu and co-workers report a novel approach to transform 2D sheets into 3D structures by embedding stiff kirigami patterns in heat shrinkable polymer sheets. This approach combines continuous shape morphing and origami-inspired self-folding, two previously separated approaches for 3D transformation. The cover shows that a flat checkerboard transforms into 3D. Cover design: Ye Tao, Zhejiang University.}, number={44}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Cui, Jianxun and Poblete, Felipe R. and Zhu, Yong}, year={2018}, month={Oct}, pages={1870314} }
 @article{yao_myers_malhotra_lin_bozkurt_muth_zhu_2017, title={A Wearable Hydration Sensor with Conformal Nanowire Electrodes}, volume={6}, ISSN={2192-2640}, url={http://dx.doi.org/10.1002/ADHM.201601159}, DOI={10.1002/ADHM.201601159}, abstractNote={A wearable skin hydration sensor in the form of a capacitor is demonstrated based on skin impedance measurement. The capacitor consists of two interdigitated or parallel electrodes that are made of silver nanowires (AgNWs) in a polydimethylsiloxane (PDMS) matrix. The flexible and stretchable nature of the AgNW/PDMS electrode allows conformal contact to the skin. The hydration sensor is insensitive to the external humidity change and is calibrated against a commercial skin hydration system on an artificial skin over a wide hydration range. The hydration sensor is packaged into a flexible wristband, together with a network analyzer chip, a button cell battery, and an ultralow power microprocessor with Bluetooth. In addition, a chest patch consisting of a strain sensor, three electrocardiography electrodes, and a skin hydration sensor is developed for multimodal sensing. The wearable wristband and chest patch may be used for low‐cost, wireless, and continuous monitoring of skin hydration and other health parameters.}, number={6}, journal={Advanced Healthcare Materials}, publisher={Wiley}, author={Yao, Shanshan and Myers, Amanda and Malhotra, Abhishek and Lin, Feiyan and Bozkurt, Alper and Muth, John F. and Zhu, Yong}, year={2017}, month={Jan}, pages={1601159} }
 @misc{akinwande_brennan_bunch_egberts_felts_gao_huang_kim_li_li_et al._2017, title={A review on mechanics and mechanical properties of 2D materials-Graphene and beyond}, volume={13}, ISSN={["2352-4316"]}, DOI={10.1016/j.eml.2017.01.008}, abstractNote={Since the first successful synthesis of graphene just over a decade ago, a variety of two-dimensional (2D) materials (e.g., transition metal-dichalcogenides, hexagonal boron-nitride, etc.) have been discovered. Among the many unique and attractive properties of 2D materials, mechanical properties play important roles in manufacturing, integration and performance for their potential applications. Mechanics is indispensable in the study of mechanical properties, both experimentally and theoretically. The coupling between the mechanical and other physical properties (thermal, electronic, optical) is also of great interest in exploring novel applications, where mechanics has to be combined with condensed matter physics to establish a scalable theoretical framework. Moreover, mechanical interactions between 2D materials and various substrate materials are essential for integrated device applications of 2D materials, for which the mechanics of interfaces (adhesion and friction) has to be developed for the 2D materials. Here we review recent theoretical and experimental works related to mechanics and mechanical properties of 2D materials. While graphene is the most studied 2D material to date, we expect continual growth of interest in the mechanics of other 2D materials beyond graphene.}, journal={EXTREME MECHANICS LETTERS}, author={Akinwande, Deji and Brennan, Christopher J. and Bunch, J. Scott and Egberts, Philip and Felts, Jonathan R. and Gao, Huajian and Huang, Rui and Kim, Joon-Seok and Li, Teng and Li, Yao and et al.}, year={2017}, month={May}, pages={42–77} }
 @article{cheng_yin_chang_richter_gao_zhu_2017, title={Anomalous Tensile Detwinning in Twinned Nanowires}, volume={19}, ISSN={["1079-7114"]}, DOI={10.1103/physrevlett.119.256101}, abstractNote={In spite of numerous studies on mechanical behaviors of nanowires (NWs) focusing on the surface effect, there is still a general lack of understanding on how the internal microstructure of NWs influences their deformation mechanisms. Here, using quantitative in situ transmission electron microscopy based nanomechanical testing and molecular dynamics simulations, we report a transition of the deformation mechanism from localized dislocation slip to delocalized plasticity via an anomalous tensile detwinning mechanism in bitwinned metallic NWs with a single twin boundary (TB) running parallel to the NW length. The anomalous tensile detwinning starts with the detwinning of a segment of the preexisting TB under no resolved shear stress, followed by the propagation of a pair of newly formed TB and grain boundary leading to a large plastic deformation. An energy-based criterion is proposed to describe this transition of the deformation mechanism, which depends on the volume ratio between the two twin variants and the cross-sectional aspect ratio.}, number={25}, journal={PHYSICAL REVIEW LETTERS}, author={Cheng, Guangming and Yin, Sheng and Chang, Tzu-Hsuan and Richter, Gunther and Gao, Huajian and Zhu, Yong}, year={2017}, month={Dec} }
 @article{jiang_cui_yue_zhu_werner_2017, title={Compact, Highly Efficient, and Fully Flexible Circularly Polarized Antenna Enabled by Silver Nanowires for Wireless Body-Area Networks}, volume={11}, ISSN={["1940-9990"]}, DOI={10.1109/tbcas.2017.2671841}, abstractNote={A compact and flexible circularly polarized (CP) wearable antenna is introduced for wireless body-area network systems at the 2.4 GHz industrial, scientific, and medical (ISM) band, which is implemented by employing a low-loss composite of polydimethylsiloxane (PDMS) and silver nanowires (AgNWs). The circularly polarized radiation is enabled by placing a planar linearly polarized loop monopole above a finite anisotropic artificial ground plane. By truncating the anisotropic artificial ground plane to contain only 2 by 2 unit cells, an integrated antenna with a compact form factor of 0.41λ0 × 0.41λ0 × 0.045λ0 is obtained, all while possessing an improved angular coverage of CP radiation. A flexible prototype was fabricated and characterized, experimentally achieving S 11 <− 15 dB, an axial ratio of less than 3 dB, a gain of around 5.2 dBi, and a wide CP angular coverage in the targeted ISM band. Furthermore, this antenna is compared to a conventional CP patch antenna of the same physical size, which is also comprised of the same PDMS and AgNW composite. The results of this comparison reveal that the proposed antenna has much more stable performance under bending and human body loading, as well as a lower specific absorption rate. In all, the demonstrated wearable antenna offers a compact, flexible, and robust solution which makes it a strong candidate for future integration into body-area networks that require efficient off-body communications.}, number={4}, journal={IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS}, author={Jiang, Zhi Hao and Cui, Zheng and Yue, Taiwei and Zhu, Yong and Werner, Douglas H.}, year={2017}, month={Aug}, pages={920–932} }
 @article{cui_yao_huang_adams_zhu_2017, title={Controlling the self-folding of a polymer sheet using a local heater: the effect of the polymer-heater interface}, volume={13}, ISSN={["1744-6848"]}, DOI={10.1039/c7sm00568g}, abstractNote={Self-folding of a pre-strained shape memory polymer (SMP) sheet was demonstrated using local joule heating. Folding is caused by shrinkage variation across the thickness of the SMP sheet. The folding direction can be controlled by the interfacial interaction between the heater and the SMP sheet. When the heater is placed on the SMP sheet with no constraint (weak interface), the SMP sheet folds toward the heater. Temperature gradient across the SMP thickness gives rise to the shrinkage variation. By contrast, when the heater is fixed to the SMP sheet (strong interface), the SMP sheet can fold away from the heater. In this case shrinkage variation is dictated by the constraining effect of the heater. In either mode, 180 degrees folding can be achieved. The folding angle can be controlled by varying the heater width and folding time. This method is simple and can be used to fold structures with sharp angles in a sequential manner. A variety of structures were folded as demonstrations, including digital numbers 0-9, a cube, a boat, and a crane.}, number={21}, journal={SOFT MATTER}, author={Cui, Jianxun and Yao, Shanshan and Huang, Qijin and Adams, John G. M. and Zhu, Yong}, year={2017}, month={Jun}, pages={3863–3870} }
 @article{yao_myers_malhotra_lin_bozkurt_muth_zhu_2017, title={Hydration Sensing: A Wearable Hydration Sensor with Conformal Nanowire Electrodes (Adv. Healthcare Mater. 6/2017)}, volume={6}, ISSN={2192-2640}, url={http://dx.doi.org/10.1002/ADHM.201770031}, DOI={10.1002/ADHM.201770031}, abstractNote={A wearable skin hydration sensor is developed by Y. Zhu, J. F. Muth, and co-workers in article number 1601159. The sensor is made of silver nanowires inlaid in a silicone substrate, which renders the sensor flexible and stretchable. Integrated systems with multimodal sensing capability (e.g., hydration, strain/motion and electrophysiological sensing) are demonstrated in two form factors — wristband and chest patch. Image design by Shanshan Yao.}, number={6}, journal={Advanced Healthcare Materials}, publisher={Wiley}, author={Yao, Shanshan and Myers, Amanda and Malhotra, Abhishek and Lin, Feiyan and Bozkurt, Alper and Muth, John F. and Zhu, Yong}, year={2017}, month={Mar} }
 @article{yu_qian_zhang_cui_zhu_shen_ligler_buse_gu_2017, title={Hypoxia and H2O2 Dual-Sensitive Vesicles for Enhanced Glucose-Responsive Insulin Delivery}, volume={17}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.6b03848}, abstractNote={A glucose-responsive closed-loop insulin delivery system mimicking pancreas activity without long-term side effect has the potential to improve diabetic patients' health and quality of life. Here, we developed a novel glucose-responsive insulin delivery device using a painless microneedle-array patch containing insulin-loaded vesicles. Formed by self-assembly of hypoxia and H2O2 dual-sensitive diblock copolymer, the glucose-responsive polymersome-based vesicles (d-GRPs) can disassociate and subsequently release insulin triggered by H2O2 and hypoxia generated during glucose oxidation catalyzed by glucose specific enzyme. Moreover, the d-GRPs were able to eliminate the excess H2O2, which may lead to free radical-induced damage to skin tissue during the long-term usage and reduce the activity of GOx. In vivo experiments indicated that this smart insulin patch could efficiently regulate the blood glucose in the chemically induced type 1 diabetic mice for 10 h.}, number={2}, journal={NANO LETTERS}, author={Yu, Jicheng and Qian, Chenggen and Zhang, Yuqi and Cui, Zheng and Zhu, Yong and Shen, Qundong and Ligler, Frances S. and Buse, John B. and Gu, Zhen}, year={2017}, month={Feb}, pages={733–739} }
 @article{bagal_zhang_shahrin_dandley_zhao_poblete_oldham_zhu_parsons_bobko_et al._2017, title={Large-Area Nanolattice Film with Enhanced Modulus, Hardness, and Energy Dissipation}, volume={7}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/S41598-017-09521-6}, DOI={10.1038/S41598-017-09521-6}, abstractNote={Abstract}, number={1}, journal={Scientific Reports}, publisher={Springer Science and Business Media LLC}, author={Bagal, Abhijeet and Zhang, Xu A. and Shahrin, Rahnuma and Dandley, Erinn C. and Zhao, Junjie and Poblete, Felipe R. and Oldham, Christopher J. and Zhu, Yong and Parsons, Gregory N. and Bobko, Christopher and et al.}, year={2017}, month={Aug} }
 @misc{zhu_2017, title={Mechanics of Crystalline Nanowires: An Experimental Perspective}, volume={69}, ISSN={["0003-6900"]}, DOI={10.1115/1.4035511}, abstractNote={A wide variety of crystalline nanowires (NWs) with outstanding mechanical properties have recently emerged. Measuring their mechanical properties and understanding their deformation mechanisms are of important relevance to many of their device applications. On the other hand, such crystalline NWs can provide an unprecedented platform for probing mechanics at the nanoscale. While challenging, the field of experimental mechanics of crystalline nanowires has emerged and seen exciting progress in the past decade. This review summarizes recent advances in this field, focusing on major experimental methods using atomic force microscope (AFM) and electron microscopes and key results on mechanics of crystalline nanowires learned from such experimental studies. Advances in several selected topics are discussed including elasticity, fracture, plasticity, and anelasticity. Finally, this review surveys some applications of crystalline nanowires such as flexible and stretchable electronics, nanocomposites, nanoelectromechanical systems (NEMS), energy harvesting and storage, and strain engineering, where mechanics plays a key role.}, number={1}, journal={APPLIED MECHANICS REVIEWS}, author={Zhu, Yong}, year={2017}, month={Jan} }
 @article{kim_saini_kim_gopalarathnam_zhu_palmieri_wohl_jiang_2017, title={Piezoelectric Floating Element Shear Stress Sensor for the Wind Tunnel Flow Measurement}, volume={64}, ISSN={["1557-9948"]}, DOI={10.1109/tie.2016.2630670}, abstractNote={A piezoelectric (PE) sensor with a floating element was developed for direct measurement of flow induced shear stress. The PE sensor was designed to detect the pure shear stress while suppressing the effect of normal stress generated from the vortex lift up by applying opposite poling vectors to the PE elements. During the calibration stage, the prototyped sensor showed a high sensitivity to shear stress (91.3 ± 2.1 pC/Pa) due to the high PE coefficients (<inline-formula><tex-math notation="LaTeX">$d_{{31}}=- $</tex-math></inline-formula>1330 pC/N) of the constituent 0.67Pb(Mg<inline-formula><tex-math notation="LaTeX">$_{1/3} $</tex-math></inline-formula>Nb<inline-formula> <tex-math notation="LaTeX">$_{2/3} $</tex-math></inline-formula>)O<sub>3</sub>–0.33PbTiO<sub>3</sub> (PMN–33%PT) single crystal. By contrast, the sensor showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the sensing structure. The usable frequency range of the sensor is up to 800 Hz. In subsonic wind tunnel tests, an analytical model was proposed based on cantilever beam theory with an end-tip-mass for verifying the resonance frequency shift in static stress measurements. For dynamic stress measurements, the signal-to-noise ratio (SNR) and ambient vibration-filtered pure shear stress sensitivity were obtained through signal processing. The developed PE shear stress sensor was found to have an SNR of 15.8 ± 2.2 dB and a sensitivity of 56.5 ± 4.6 pC/Pa in the turbulent flow.}, number={9}, journal={IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS}, author={Kim, Taeyang and Saini, Aditya and Kim, Jinwook and Gopalarathnam, Ashok and Zhu, Yong and Palmieri, Frank L. and Wohl, Christopher J. and Jiang, Xiaoning}, year={2017}, month={Sep}, pages={7304–7312} }
 @article{cui_adams_zhu_2017, title={Pop-up assembly of 3D structures actuated by heat shrinkable polymers}, volume={26}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665x/aa9552}, abstractNote={Folding 2D sheets into desired 3D structures is a promising fabrication technique that can find a wide range of applications. Compressive buckling provides an attractive strategy to actuate the folding and can be applied to a broad range of materials. Here a new and simple method is reported to achieve controlled compressive buckling, which is actuated by a heat shrinkable polymer sheet. The buckling deformation is localized at the pre-defined creases in the 2D sheet, resulting in sharp folding. Two approaches are developed to actuate the transformation, which follow similar geometric rules. In the first approach, the 2D precursor is pushed from outside, which leads to a 3D structure surrounded by the shrunk polymer sheet. Assembled 3D structures include prisms/pyramids with different base shapes, house roof, partial soccer ball, Miura-ori structure and insect wing. In the second approach, the 2D precursor is pulled from inside, which leads to a 3D structure enclosing the shrunk polymer sheet. Prisms/pyramids with different base shapes are assembled. The assembled structures are further tessellated to fabricate cellular structures that can be used as thermal insulator and crash energy absorber. They are also stacked vertically to fabricate complex multilayer structures.}, number={12}, journal={SMART MATERIALS AND STRUCTURES}, author={Cui, Jianxun and Adams, J. G. M. and Zhu, Yong}, year={2017}, month={Dec} }
 @article{yao_cui_cui_zhu_2017, title={Soft electrothermal actuators using silver nanowire heaters}, volume={9}, ISSN={["2040-3372"]}, DOI={10.1039/c6nr09270e}, abstractNote={Low-voltage and extremely flexible electrothermal bimorph actuators were fabricated in a simple, efficient and scalable process. The bimorph actuators were made of flexible silver nanowire (AgNW) based heaters, which exhibited a fast heating rate of 18 °C s-1 and stable heating performance with large bending. The actuators offered the largest bending angle (720°) or curvature (2.6 cm-1) at a very low actuation voltage (0.2 V sq-1 or 4.5 V) among all types of bimorph actuators that have been reported to date. The actuators can be designed and fabricated in different configurations that can achieve complex patterns and shapes upon actuation. Two applications of this type of soft actuators were demonstrated towards biomimetic robotics - a crawling robot that can walk spontaneously on ratchet surfaces and a soft gripper that is capable of manipulating lightweight and delicate objects.}, number={11}, journal={NANOSCALE}, author={Yao, Shanshan and Cui, Jianxun and Cui, Zheng and Zhu, Yong}, year={2017}, month={Mar}, pages={3797–3805} }
 @article{zhang_yu_wang_hanne_cui_qian_wang_xin_cole_gallippi_et al._2017, title={Thrombin-responsive transcutaneous patch for auto-anticoagulant regulation}, volume={29}, DOI={10.1002/adma.201770028}, abstractNote={A thrombin-responsive microneedle-based transcutaneous patch is developed by C. M. Gallippi, Y. Zhu, Z. Gu, and co-workers, as demonstrated in article 1604043. The anticoagulant drug heparin is loaded into the hyaluronic acid needles through a thrombin cleavable peptide linker. This heparin patch can sense the thrombin level in blood vessels and autoregulate blood coagulation in a long-term manner. Cover design credit: Yuqi Zhang.}, number={4}, journal={Advanced Materials}, author={Zhang, Y. Q. and Yu, J. C. and Wang, J. Q. and Hanne, N. J. and Cui, Z. and Qian, C. G. and Wang, C. and Xin, H. L. and Cole, Jacqueline and Gallippi, C. M. and et al.}, year={2017} }
 @article{di_yu_wang_yao_suo_ye_pless_zhu_jing_gu_2017, title={Ultrasound-triggered noninvasive regulation of blood glucose levels using microgels integrated with insulin nanocapsules}, volume={10}, ISSN={1998-0124 1998-0000}, url={http://dx.doi.org/10.1007/S12274-017-1500-Z}, DOI={10.1007/S12274-017-1500-Z}, number={4}, journal={Nano Research}, publisher={Springer Nature}, author={Di, Jin and Yu, Jicheng and Wang, Qun and Yao, Shanshan and Suo, Dingjie and Ye, Yanqi and Pless, Matthew and Zhu, Yong and Jing, Yun and Gu, Zhen}, year={2017}, month={Mar}, pages={1393–1402} }
 @article{kim_saini_kim_gopalarathnam_zhu_palmieri_wohl_jiang_2016, title={A piezoelectric shear stress sensor}, volume={9803}, ISSN={["1996-756X"]}, DOI={10.1117/12.2219185}, abstractNote={In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress, suppressing effects of normal stress components, by applying opposite poling vectors to the piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces where it demonstrated high sensitivity to shear stress (91.3 ± 2.1 pC/Pa) due to the high piezoelectric coefficients of 0.67Pb(Mg1∕3Nb2∕3)O3-0.33PbTiO3 (PMN-33%PT, d31=-1330 pC/N). The sensor also exhibited negligible sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is up to 800 Hz.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2016}, author={Kim, Taeyang and Saini, Aditya and Kim, Jinwook and Gopalarathnam, Ashok and Zhu, Yong and Palmieri, Frank L. and Wohl, Christopher J. and Jiang, Xiaoning}, year={2016} }
 @article{barsh_bergman_brown_singh_copenhaver_2016, title={Bringing PLOS Genetics Editors to Preprint Servers}, volume={12}, ISSN={["1553-7404"]}, DOI={10.1371/journal.pgen.1006448}, abstractNote={1 HudsonAlpha Institute for Biotechnology, Huntsville, Alabama, United States of America, 2 Department of Genetics, Stanford University School of Medicine, Stanford, California, United States of America, 3 Department of Genetics, University of Georgia, Athens, Georgia, United States of America, 4 Department of Genetics, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America, 5 Program in Genetics, Department of Biological Sciences, North Carolina State University, Raleigh, North Carolina, United States of America, 6 Department of Biology and the Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, United States of America}, number={12}, journal={PLOS GENETICS}, author={Barsh, Gregory S. and Bergman, Casey M. and Brown, Christopher D. and Singh, Nadia D. and Copenhaver, Gregory P.}, year={2016}, month={Dec} }
 @article{zhu_gianola_zhu_2016, title={Editorial for the focus issue on "Nanomechanics'' in Extreme Mechanics Letters}, volume={8}, ISSN={["2352-4316"]}, DOI={10.1016/j.eml.2016.07.008}, journal={EXTREME MECHANICS LETTERS}, author={Zhu, Yong and Gianola, Daniel and Zhu, Ting}, year={2016}, month={Sep}, pages={125–126} }
 @article{zhang_yu_zhu_gu_2016, title={Elastic drug delivery: could treatments be triggered by patient movement?}, volume={11}, ISSN={["1748-6963"]}, DOI={10.2217/nnm.15.197}, abstractNote={NanomedicineVol. 11, No. 4 EditorialFree AccessElastic drug delivery: could treatments be triggered by patient movement?Yuqi Zhang, Jicheng Yu, Yong Zhu & Zhen GuYuqi Zhang Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill & North Carolina State University, Raleigh, NC 27695, USASearch for more papers by this author, Jicheng Yu Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill & North Carolina State University, Raleigh, NC 27695, USASearch for more papers by this author, Yong Zhu Department of Mechanical & Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USASearch for more papers by this author & Zhen Gu*Author for correspondence: E-mail Address: zgu@email.unc.edu Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill & North Carolina State University, Raleigh, NC 27695, USASearch for more papers by this authorPublished Online:19 Jan 2016https://doi.org/10.2217/nnm.15.197AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinkedInReddit Keywords: drug deliverymechanical-responsivenanoparticlewearable devicesFirst draft submitted: 22 October 2015; Accepted for publication: 12 November 2015; Published online: 19 January 2016Nanoparticle-based drug delivery systems have drawn extensive attention for treating a broad range of diseases during the last few decades [1,2]. In order to enhance therapeutic efficacy, reduce side effects and prolong action time, vast efforts have been dedicated to the development of on-demand, precise drug release. In light of this, numerous stimuli-responsive designs have been exploited, including external triggers like mechanical force, temperature, light, ultrasound, electric current and magnetic field as well as internal factors like pH, redox, enzymes, ATP and hypoxia [3–8]. Compared with other stimuli-responsive designs, the macroscopic mechanical force-mediated approach, as one of the most promising strategies, possesses several advantages. It can be generated on-demand during the patients’ daily movement, such as tension in bone joints, tendons and muscles, or compression in cartilage and bones. Therefore, a self-administrated therapy can be readily achieved without requirement of additional instrumentations. In addition, in contrast to the inaccurate internal factors due to the complicated physiological environment, the degree of stretch or compression is more conveniently controlled by the patient themselves, leading to a precise dosage-, spatial- and temporal-controllable administration of drug release.Physical deformation of drug carriers supported on an elastomer substrate caused by stretch or compression is one of the most important strategies for mechanical force-triggered release. Mooney group designed a compression-responsive system for controlled release of growth factor [9]. Inspired by the natural extracellular matrices, they developed a hydrogel with reversible binding of drug as synthetic extracelluar matrices. The physical-loaded hydrogel could respond to repeated compression stimulus and as a result released free drug. Afterward, the matrices could be refilled by free drug during relaxation via dissociation of previously bound drug. Using VEGF as a model drug in in vivo studies, they demonstrated that the implanted hydrogels allowed an increase in VEGF concentration near implantation site as applying mechanical signals, subsequently leading to a local enhanced vascularization. In another case, Jeong group developed a strain-sensitive patch consisting of arrays of microcapsules onto a rubbery substrate for drug release [10]. When stretch was applied to the elastomer substrate, the volume of the stretchable microcapsules encapsulating cargoes decreased accordingly with the substrate, then pumping out the preloaded molecules. Under different degrees of mechanical stretching, the release rate and amount of cargoes could be adjusted. This patch has the potential to respond to body motions, even to the mechanical stretching of organs, muscles and tendons when it is implanted into body.We have recently developed a multipurpose wearable, tensile strain-triggered drug delivery device, which comprised of a stretchable elastomer and microgel depots containing drug-loaded nanoparticles [11]. The drugs can be continuously released from the nanoparticles and temporarily stored in the microgels. When applying a tensile strain, the drugs were released from micro-depots due to the enlarged surface area for diffusion and Poisson's ratio-induced compression toward the microgels. Therefore, a sustained drug release can be conveniently achieved by daily body motion, while a pulsatile release is able to be controlled through intentional administration. We demonstrated that this device could be simply attached to a finger joint, and stretched to trigger the drug release when the finger is flexed for multiple cycles, which allowed patients to control the dose and release timing of antibacterial drug on their own.Furthermore, we integrated this stretch-sensitive device with a microneedle array patch for on-demand transcutaneous insulin delivery [3], which allowed the blood glucose level of mice to decline quickly to a normoglycemic range within 0.5 h. Meanwhile, the obvious pulsatile and continuous reduction in blood glucose level were observed when applying a strain with an interval of 4 h. Based on this technology, the diabetic patients can easily maintain normoglycemia through simple joint movement instead of a traditional painful insulin injection. This skin-mountable device can be further extended for anti-inflammatory, anti-infective drug or painkiller delivery. More importantly, this facile strategy allows immediate medical treatment in emergency situation by patient's simple body movement.Besides the direct drug release via changing diffusion area or pumping out caused by physical deformation, tension or compression can also generate energy to change the physical properties of drug carriers. For example, Pioletti group exploited dissipation properties of hydrogel as an internal heat source to trigger the thermal-sensitive drug release instead of additional external heat source [12]. Self heating was quickly produced after 5 min cyclic mechanical loading. The increased temperature further caused the shrinkage of thermal-responsive nanoparticles entrapped in the hydrogel and subsequent drug release.In addition, mechanical stretch or compression is able to tune the molecular conformation and intermolecular interaction between host molecule and guest molecule, resulting in a force-triggered drug release [13,14]. Based on this phenomenon, Ariga group reported a mechanically controlled monolayer formed by a steroid cyclophane molecule with a cyclic core linked to four steroid moieties via the flexible L-lysine spacer [13]. The applied compression could lead to a cavity-forming conformation of the cyclophane. Therefore, the hydrophobic model drug was easily trapped in this hydrophobic cavity. In contrast, expansion of the monolayer could release the encapsulated drug through the molecular transformation from cavity to planarity. Similarly, they developed a mechanical stimulus-activated β-cyclodextrin (CyD)-crosslinked alginate gel [15]. As applying mild mechanical compression, the model drug ondansetron, the entrapped guest, could be released from the host CyD moieties, due to the change in inclusion ability of CyD. The host–guest interactions dominated by van der Waals interactions and hydrogen bonds in a gel matrix can be more easily broken than covalent bonds, which provide a convenient on-demand administration of medicines operated intentionally by the patient.The research and development of patients’ movement-controlled drug delivery systems hold promise in improving patients’ compliance by providing a self-directed and on-demand treatment. Nonetheless, there are still many remaining challenges for clinical development. For example, the current systems cannot precisely control the release dose of therapeutics. A fundamental study on the dynamic relationships between the phase transitions of materials and the relevant release profile should be closely investigated. Moreover, regarding the different movement extent and ability for different individuals, how to generate a personalized platform and consistently apply the mechanical trigger signal are difficult tasks ahead that need to be addressed. Integration of this device with other wearable modalities to monitor the real-time physiological signals (e.g., electrocardiograph, blood glucose levels or body temperature [16,17]) and motion signals [18,19] might be able to provide feedback to guide the precise, personalized drug delivery. Last but not least, good biocompatibility and biodegradability for materials is extremely important for further translation of the elastic drug delivery system. Tailoring materials mimicking the structures and composites of natural systems offer a promising strategy [5,20].Financial & competing interests disclosureThe authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.No writing assistance was utilized in the production of this manuscript.References1 Jiang T, Mo R, Bellotti A, Zhou J, Gu Z. Gel–liposome‐mediated co‐delivery of anticancer membrane‐associated proteins and small‐molecule drugs for enhanced therapeutic efficacy. Adv. Funct. Mater. 24(16), 2295–2304 (2014).Crossref, CAS, Google Scholar2 Sun W, Jiang T, Lu Y, Reiff M, Mo R, Gu Z. Cocoon-like self-degradable dna nanoclew for anticancer drug delivery. J. Am. Chem. Soc. 136(42), 14722–14725 (2014).Crossref, Medline, CAS, Google Scholar3 Yu J, Zhang Y, Ye Y et al. Microneedle-array patches loaded with hypoxia-sensitive vesicles provide fast glucose-responsive insulin delivery. Proc. Natl Acad. Sci. USA 112(27), 8260–8265 (2015).Crossref, Medline, CAS, Google Scholar4 Mo R, Jiang T, Disanto R, Tai W, Gu Z. ATP-triggered anticancer drug delivery. Nat. Commun. 5, 3364 (2014).Crossref, Medline, Google Scholar5 Lu Y, Sun W, Gu Z. Stimuli-responsive nanomaterials for therapeutic protein delivery. J. Control. Release 194, 1–19 (2014).Crossref, Medline, CAS, Google Scholar6 Wu Z, Wu Y, He W, Lin X, Sun J, He Q. Self‐propelled polymer‐based multilayer nanorockets for transportation and drug release. Angew. Chem. Int. Ed. Engl. 52(27), 7000–7003 (2013).Crossref, Medline, CAS, Google Scholar7 Choi SW, Zhang Y, Xia Y. A temperature‐sensitive drug release system based on phase‐change materials. Angew. Chem. Int. Ed. Engl. 49(43), 7904–7908 (2010).Crossref, Medline, CAS, Google Scholar8 Zhang Y, Yin Q, Yin L, Ma L, Tang L, Cheng J. Chain‐shattering polymeric therapeutics with on‐demand drug‐release capability. Angew. Chem. Int. Ed. Engl. 52(25), 6435–6439 (2013).Crossref, Medline, CAS, Google Scholar9 Lee KY, Peters MC, Anderson KW, Mooney DJ. Controlled growth factor release from synthetic extracellular matrices. Nature 408(6815), 998–1000 (2000).Crossref, Medline, CAS, Google Scholar10 Hyun DC, Moon GD, Park CJ, Kim BS, Xia Y, Jeong U. Strain‐controlled release of molecules from arrayed microcapsules supported on an elastomer substrate. Angew. Chem. Int. Ed. Engl. 50(3), 724–727 (2011).Crossref, Medline, CAS, Google Scholar11 Di J, Yao S, Ye Y et al. Stretch-triggered drug delivery from wearable elastomer films containing therapeutic depots. ACS Nano 9(9), 9407–9415 (2015).Crossref, Medline, CAS, Google Scholar12 Moghadam MN, Kolesov V, Vogel A, Klok H-A, Pioletti DP. Controlled release from a mechanically-stimulated thermosensitive self-heating composite hydrogel. Biomaterials 35(1), 450–455 (2014).Crossref, Medline, CAS, Google Scholar13 Ariga K, Terasaka Y, Sakai D, Tsuji H, Kikuchi J-I. Piezoluminescence based on molecular recognition by dynamic cavity array of steroid cyclophanes at the air-water interface. J. Am. Chem. Soc. 122(32), 7835–7836 (2000).Crossref, CAS, Google Scholar14 Michinobu T, Shinoda S, Nakanishi T et al. Mechanical control of enantioselectivity of amino acid recognition by cholesterol-armed cyclen monolayer at the air-water interface. J. Am. Chem. Soc. 128(45), 14478–14479 (2006).Crossref, Medline, CAS, Google Scholar15 Izawa H, Kawakami K, Sumita M, Tateyama Y, Hill JP, Ariga K. β-Cyclodextrin-crosslinked alginate gel for patient-controlled drug delivery systems: regulation of host–guest interactions with mechanical stimuli. J. Mater. Chem. B 1(16), 2155–2161 (2013).Crossref, CAS, Google Scholar16 Myers AC, Huang H, Zhu Y. Wearable silver nanowire dry electrodes for electrophysiological sensing. RSC Adv. 5(15), 11627–11632 (2015).Crossref, CAS, Google Scholar17 Kim D-H, Lu N, Ma R et al. Epidermal electronics. Science 333(6044), 838–843 (2011).Crossref, Medline, CAS, Google Scholar18 Yao S, Zhu Y. Wearable multifunctional sensors using printed stretchable conductors made of silver nanowires. Nanoscale 6(4), 2345–2352 (2014).Crossref, Medline, CAS, Google Scholar19 Yao S, Zhu Y. Nanomaterial‐enabled stretchable conductors: strategies, materials and devices. Adv. Mater. 27(9), 1480–1511 (2015).Crossref, Medline, CAS, Google Scholar20 Mitragotri S, Anderson DG, Chen X et al. Accelerating the translation of nanomaterials in biomedicine. ACS Nano 9(7), 6644–6654 (2015).Crossref, Medline, CAS, Google ScholarFiguresReferencesRelatedDetailsCited ByExternal stimuli-responsive drug delivery systemsMechanical on-off gates for regulation of drug release in cutaneous or musculoskeletal tissue repairsMaterials Science and Engineering: C, Vol. 115Biomechano-Interactive Materials and Interfaces7 June 2018 | Advanced Materials, Vol. 30, No. 31Nanomaterial‐Enabled Wearable Sensors for Healthcare30 November 2017 | Advanced Healthcare Materials, Vol. 7, No. 1 Vol. 11, No. 4 Follow us on social media for the latest updates Metrics History Published online 19 January 2016 Published in print February 2016 Information© Future Medicine LtdKeywordsdrug deliverymechanical-responsivenanoparticlewearable devicesFinancial & competing interests disclosureThe authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.No writing assistance was utilized in the production of this manuscript.PDF download}, number={4}, journal={NANOMEDICINE}, author={Zhang, Yuqi and Yu, Jicheng and Zhu, Yong and Gu, Zhen}, year={2016}, pages={323–325} }
 @article{cheng_yao_sang_hao_zhang_yap_zhu_2016, title={Evolution of Irradiation-Induced Vacancy Defects in Boron Nitride Nanotubes}, volume={12}, ISSN={["1613-6829"]}, DOI={10.1002/smll.201502440}, abstractNote={Irradiation‐induced vacancy defects in multiwalled (MW) boron nitride nanotubes (BNNTs) are investigated via in situ high‐resolution transmission electron microscope operated at 80 kV, with a homogeneous distribution of electron beam intensity. During the irradiation triangle‐shaped vacancy defects are gradually generated in MW BNNTs under a mediate electron current density (30 A cm−2), by knocking the B atoms out. The vacancy defects grow along a well‐defined direction within a wall at the early stage as a result of the curvature induced lattice strain, and then develop wall by wall. The orientation or the growth direction of the vacancy defects can be used to identify the chirality of an individual wall. With increasing electron current density, the shape of the irradiation‐induced vacancy defects changes from regular triangle to irregular polygon.}, number={6}, journal={SMALL}, author={Cheng, Guangming and Yao, Shanshan and Sang, Xiahan and Hao, Boyi and Zhang, Dongyan and Yap, Yoke Khin and Zhu, Yong}, year={2016}, month={Feb}, pages={818–824} }
 @article{chen_liu_yan_zhu_chen_2016, title={Helical coil buckling mechanism for a stiff nanowire on an elastomeric substrate}, volume={95}, ISSN={["1873-4782"]}, DOI={10.1016/j.jmps.2016.05.020}, abstractNote={When a stiff nanowire is deposited on a compliant soft substrate, it may buckle into a helical coil form when the system is compressed. Using theoretical and finite element method (FEM) analyses, the detailed three-dimensional coil buckling mechanism for a silicon nanowire (SiNW) on a polydimethylsiloxane (PDMS) substrate is studied. A continuum mechanics approach based on the minimization of the strain energy in the SiNW and elastomeric substrate is developed. Due to the helical buckling, the bending strain in SiNW is significantly reduced and the maximum local strain is almost uniformly distributed along SiNW. Based on the theoretical model, the energy landscape for different buckling modes of SiNW on PDMS substrate is given, which shows that both the in-plane and out-of-plane buckling modes have the local minimum potential energy, whereas the helical buckling model has the global minimum potential energy. Furthermore, the helical buckling spacing and amplitudes are deduced, taking into account the influences of the elastic properties and dimensions of SiNWs. These features are verified by systematic FEM simulations and parallel experiments. As the effective compressive strain in elastomeric substrate increases, the buckling profile evolves from a vertical ellipse to a lateral ellipse, and then approaches to a circle when the effective compressive strain is larger than 30%. The study may shed useful insights on the design and optimization of high-performance stretchable electronics and 3D complex nano-structures.}, journal={JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS}, author={Chen, Youlong and Liu, Yilun and Yan, Yuan and Zhu, Yong and Chen, Xi}, year={2016}, month={Oct}, pages={25–43} }
 @misc{zhu_2016, title={In Situ Nanomechanical Testing of Crystalline Nanowires in Electron Microscopes}, volume={68}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-015-1614-2}, number={1}, journal={JOM}, author={Zhu, Yong}, year={2016}, month={Jan}, pages={84–93} }
 @article{dieffenderfer_goodell_mills_mcknight_yao_lin_beppler_bent_lee_misra_et al._2016, title={Low-Power Wearable Systems for Continuous Monitoring of Environment and Health for Chronic Respiratory Disease}, volume={20}, ISSN={2168-2194 2168-2208}, url={http://dx.doi.org/10.1109/JBHI.2016.2573286}, DOI={10.1109/jbhi.2016.2573286}, abstractNote={We present our efforts toward enabling a wearable sensor system that allows for the correlation of individual environmental exposures with physiologic and subsequent adverse health responses. This system will permit a better understanding of the impact of increased ozone levels and other pollutants on chronic asthma conditions. We discuss the inefficiency of existing commercial off-the-shelf components to achieve continuous monitoring and our system-level and nano-enabled efforts toward improving the wearability and power consumption. Our system consists of a wristband, a chest patch, and a handheld spirometer. We describe our preliminary efforts to achieve a submilliwatt system ultimately powered by the energy harvested from thermal radiation and motion of the body with the primary contributions being an ultralow-power ozone sensor, an volatile organic compounds sensor, spirometer, and the integration of these and other sensors in a multimodal sensing platform. The measured environmental parameters include ambient ozone concentration, temperature, and relative humidity. Our array of sensors also assesses heart rate via photoplethysmography and electrocardiography, respiratory rate via photoplethysmography, skin impedance, three-axis acceleration, wheezing via a microphone, and expiratory airflow. The sensors on the wristband, chest patch, and spirometer consume 0.83, 0.96, and 0.01 mW, respectively. The data from each sensor are continually streamed to a peripheral data aggregation device and are subsequently transferred to a dedicated server for cloud storage. Future work includes reducing the power consumption of the system-on-chip including radio to reduce the entirety of each described system in the submilliwatt range.}, number={5}, journal={IEEE Journal of Biomedical and Health Informatics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Dieffenderfer, James and Goodell, Henry and Mills, Steven and McKnight, Michael and Yao, Shanshan and Lin, Feiyan and Beppler, Eric and Bent, Brinnae and Lee, Bongmook and Misra, Veena and et al.}, year={2016}, month={Sep}, pages={1251–1264} }
 @misc{zhang_yu_bomba_zhu_gu_2016, title={Mechanical Force-Triggered Drug Delivery}, volume={116}, ISSN={["1520-6890"]}, DOI={10.1021/acs.chemrev.6b00369}, abstractNote={Advanced drug delivery systems (DDS) enhance treatment efficacy of different therapeutics in a dosage, spatial, and/or temporal controlled manner. To date, numerous chemical- or physical-based stimuli-responsive formulations or devices for controlled drug release have been developed. Among them, the emerging mechanical force-based stimulus offers a convenient and robust controlled drug release platform and has attracted increasing attention. The relevant DDS can be activated to promote drug release by different types of mechanical stimuli, including compressive force, tensile force, and shear force as well as indirect formats, remotely triggered by ultrasound and magnetic field. In this review, we provide an overview of recent advances in mechanically activated DDS. The opportunities and challenges regarding clinical translations are also discussed.}, number={19}, journal={CHEMICAL REVIEWS}, author={Zhang, Yuqi and Yu, Jicheng and Bomba, Hunter N. and Zhu, Yong and Gu, Zhen}, year={2016}, month={Oct}, pages={12536–12563} }
 @article{chen_zhu_chen_liu_2016, title={Mechanism of the Transition From In-Plane Buckling to Helical Buckling for a Stiff Nanowire on an Elastomeric Substrate}, volume={83}, ISSN={["1528-9036"]}, DOI={10.1115/1.4032573}, abstractNote={In this work, the compressive buckling of a nanowire partially bonded to an elastomeric substrate is studied via finite-element method (FEM) simulations and experiments. The buckling profile of the nanowire can be divided into three regimes, i.e., the in-plane buckling, the disordered buckling in the out-of-plane direction, and the helical buckling, depending on the constraint density between the nanowire and the substrate. The selection of the buckling mode depends on the ratio d/h, where d is the distance between adjacent constraint points and h is the helical buckling spacing of a perfectly bonded nanowire. For d/h > 0.5, buckling is in-plane with wavelength λ = 2d. For 0.27 < d/h < 0.5, buckling is disordered with irregular out-of-plane displacement. While, for d/h < 0.27, buckling is helical and the buckling spacing gradually approaches to the theoretical value of a perfectly bonded nanowire. Generally, the in-plane buckling induces smaller strain in the nanowire, but consumes the largest space. Whereas the helical mode induces moderate strain in the nanowire, but takes the smallest space. The study may shed useful insights on the design and optimization of high-performance stretchable electronics and three-dimensional complex nanostructures.}, number={4}, journal={JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME}, author={Chen, Youlong and Zhu, Yong and Chen, Xi and Liu, Yilun}, year={2016}, month={Apr} }
 @misc{yao_zhu_2016, title={Nanomaterial-Enabled Dry Electrodes for Electrophysiological Sensing: A Review}, volume={68}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-016-1818-0}, number={4}, journal={JOM}, author={Yao, Shanshan and Zhu, Yong}, year={2016}, month={Apr}, pages={1145–1155} }
 @article{chang_cheng_li_zhu_2016, title={On the size-dependent elasticity of penta-twinned silver nanowires}, volume={8}, ISSN={["2352-4316"]}, DOI={10.1016/j.eml.2016.03.007}, abstractNote={Penta-twinned metallic NWs have recently received much attention due to their excellent mechanical properties. However, their elasticity size effect remains not well understood due to the large discrepancy in the reported experimental and simulation results. This paper reports an experimental effort to address the discrepancy about the size-dependent Young’s modulus of penta-twinned Ag NWs. Two independent experiments on the same NW, in-situ resonance test and tensile test in a scanning electron microscope, were used to measure the Young’s moduli. The cross-sectional shape of the Ag NWs was found to transit from pentagon to circle with decreasing NW diameter, which can modify the Young’s modulus as much as 8% (for resonance test) and 19% (for tensile test) for the tested diameter range. This work confirmed that the Young’s modulus of penta-twinned Ag NWs increases with decreasing NW diameter.}, journal={EXTREME MECHANICS LETTERS}, author={Chang, Tzu-Hsuan and Cheng, Guangming and Li, Chengjun and Zhu, Yong}, year={2016}, month={Sep}, pages={177–183} }
 @inproceedings{lin_yao_mcknight_zhu_bozkurt_2016, title={Silver nanowire based wearable sensors for multimodal sensing}, DOI={10.1109/biowireless.2016.7445561}, abstractNote={We present multifunctional sensors based on highly stretchable silver nanowire conductors, which can be conformally attached to human skin for multimodal sensing. The wearable sensors were integrated with an interface circuit with wireless capability in the form of a chest patch. The capabilities of electrocardiography, strain/motion sensing and skin impedance sensing were demonstrated. Additionally, the impedance sensor with the interface circuit was packaged into a wrist watch for skin impedance monitoring.}, booktitle={Ieee topical conference on biomedical wireless technologies networks and}, author={Lin, F. Y. and Yao, S. S. and McKnight, M. and Zhu, Y. and Bozkurt, A.}, year={2016}, pages={55–58} }
 @article{jagannadham_cui_zhu_2016, title={Substrate Effects on Growth of MoS2 Film by Laser Physical Vapor Deposition on Sapphire, Si and Graphene (on Cu)}, volume={46}, ISSN={0361-5235 1543-186X}, url={http://dx.doi.org/10.1007/S11664-016-5060-X}, DOI={10.1007/S11664-016-5060-X}, number={2}, journal={Journal of Electronic Materials}, publisher={Springer Science and Business Media LLC}, author={Jagannadham, K. and Cui, J. and Zhu, Y.}, year={2016}, month={Oct}, pages={1010–1021} }
 @article{zhang_yu_wang_hanne_cui_qian_wang_xin_cole_gallippi_et al._2016, title={Thrombin-Responsive Transcutaneous Patch for Auto-Anticoagulant Regulation}, volume={29}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201604043}, DOI={10.1002/ADMA.201604043}, abstractNote={A thrombin-responsive closed-loop patch is developed for prolonged heparin delivery in a feedback-controlled manner. This microneedle-based patch can sense activated thrombin and subsequently releases heparin to prevent coagulation in the blood flow. This "smart" heparin patch can be transcutaneously inserted into skin without drug leakage and can sustainably regulate blood coagulation in response to thrombin.}, number={4}, journal={Advanced Materials}, publisher={Wiley}, author={Zhang, Yuqi and Yu, Jicheng and Wang, Jinqiang and Hanne, Nicholas J. and Cui, Zheng and Qian, Chenggen and Wang, Chao and Xin, Hongliang and Cole, Jacqueline H. and Gallippi, Caterina M. and et al.}, year={2016}, month={Nov}, pages={1604043} }
 @misc{zhu_chang_2015, title={A review of microelectromechanical systems for nanoscale mechanical characterization}, volume={25}, ISSN={["1361-6439"]}, DOI={10.1088/0960-1317/25/9/093001}, abstractNote={A plethora of nanostructures with outstanding properties have emerged over the past decades. Measuring their mechanical properties and understanding their deformation mechanisms is of paramount importance for many of their device applications. To address this need innovative experimental techniques have been developed, among which a promising one is based upon microelectromechanical systems (MEMS). This article reviews the recent advances in MEMS platforms for the mechanical characterization of one-dimensional (1D) nanostructures over the past decade. A large number of MEMS platforms and related nanomechanics studies are presented to demonstrate the unprecedented capabilities of MEMS for nanoscale mechanical characterization. Focusing on key design considerations, this article aims to provide useful guidelines for developing MEMS platforms. Finally, some of the challenges and future directions in the area of MEMS-enabled nanomechanical characterization are discussed.}, number={9}, journal={JOURNAL OF MICROMECHANICS AND MICROENGINEERING}, author={Zhu, Yong and Chang, Tzu-Hsuan}, year={2015}, month={Sep} }
 @article{guo_zhu_2015, title={Cohesive-Shear-Lag Modeling of Interfacial Stress Transfer Between a Monolayer Graphene and a Polymer Substrate}, volume={82}, ISSN={["1528-9036"]}, DOI={10.1115/1.4029635}, abstractNote={Interfacial shear stress transfer of a monolayer graphene on top of a polymer substrate subjected to uniaxial tension was investigated by a cohesive zone model integrated with a shear-lag model. Strain distribution in the graphene flake was found to behave in three stages in general, bonded, damaged, and debonded, as a result of the interfacial stress transfer. By fitting the cohesive-shear-lag model to our experimental results, the interface properties were identified including interface stiffness (74 Tpa/m), shear strength (0.50 Mpa), and mode II fracture toughness (0.08 N/m). Parametric studies showed that larger interface stiffness and/or shear strength can lead to better stress transfer efficiency, and high fracture toughness can delay debonding from occurring. 3D finite element simulations were performed to capture the interfacial stress transfer in graphene flakes with realistic geometries. The present study can provide valuable insight and design guidelines for enhancing interfacial shear stress transfer in nanocomposites, stretchable electronics and other applications based on graphene and other 2D nanomaterials.}, number={3}, journal={JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME}, author={Guo, Guodong and Zhu, Yong}, year={2015}, month={Mar} }
 @article{cui_poblete_cheng_yao_jiang_zhu_2015, title={Design and operation of silver nanowire based flexible and stretchable touch sensors}, volume={30}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2014.347}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Cui, Zheng and Poblete, Felipe R. and Cheng, Guangming and Yao, Shanshan and Jiang, Xiaoning and Zhu, Yong}, year={2015}, month={Jan}, pages={79–85} }
 @article{misra_bozkurt_calhoun_jackson_jur_lach_lee_muth_oralkan_oeztuerk_et al._2015, title={Flexible Technologies for Self-Powered Wearable Health and Environmental Sensing}, volume={103}, ISSN={["1558-2256"]}, DOI={10.1109/jproc.2015.2412493}, abstractNote={This article provides the latest advances from the NSF Advanced Self-powered Systems of Integrated sensors and Technologies (ASSIST) center. The work in the center addresses the key challenges in wearable health and environmental systems by exploring technologies that enable ultra-long battery lifetime, user comfort and wearability, robust medically validated sensor data with value added from multimodal sensing, and access to open architecture data streams. The vison of the ASSIST center is to use nanotechnology to build miniature, self-powered, wearable, and wireless sensing devices that can enable monitoring of personal health and personal environmental exposure and enable correlation of multimodal sensors. These devices can empower patients and doctors to transition from managing illness to managing wellness and create a paradigm shift in improving healthcare outcomes. This article presents the latest advances in high-efficiency nanostructured energy harvesters and storage capacitors, new sensing modalities that consume less power, low power computation, and communication strategies, and novel flexible materials that provide form, function, and comfort. These technologies span a spatial scale ranging from underlying materials at the nanoscale to body worn structures, and the challenge is to integrate them into a unified device designed to revolutionize wearable health applications.}, number={4}, journal={PROCEEDINGS OF THE IEEE}, author={Misra, Veena and Bozkurt, Alper and Calhoun, Benton and Jackson, Thomas N. and Jur, Jesse S. and Lach, John and Lee, Bongmook and Muth, John and Oralkan, Oemer and Oeztuerk, Mehmet and et al.}, year={2015}, month={Apr}, pages={665–681} }
 @article{cheng_miao_qin_li_xu_haftbaradaran_dickey_gao_zhu_2015, title={Large anelasticity and associated energy dissipation in single-crystalline nanowires}, volume={10}, ISSN={1748-3387 1748-3395}, url={http://dx.doi.org/10.1038/NNANO.2015.135}, DOI={10.1038/nnano.2015.135}, abstractNote={Anelastic materials exhibit gradual full recovery of deformation once a load is removed, leading to dissipation of internal mechanical energy. As a consequence, anelastic materials are being investigated for mechanical damping applications. At the macroscopic scale, however, anelasticity is usually very small or negligible, especially in single-crystalline materials. Here, we show that single-crystalline ZnO and p-doped Si nanowires can exhibit anelastic behaviour that is up to four orders of magnitude larger than the largest anelasticity observed in bulk materials, with a timescale on the order of minutes. In situ scanning electron microscope tests of individual nanowires showed that, on removal of the bending load and instantaneous recovery of the elastic strain, a substantial portion of the total strain gradually recovers with time. We attribute this large anelasticity to stress-gradient-induced migration of point defects, as supported by electron energy loss spectroscopy measurements and also by the fact that no anelastic behaviour could be observed under tension. We model this behaviour through a theoretical framework by point defect diffusion under a high strain gradient and short diffusion distance, expanding the classic Gorsky theory. Finally, we show that ZnO single-crystalline nanowires exhibit a high damping merit index, suggesting that crystalline nanowires with point defects are promising materials for energy damping applications.}, number={8}, journal={Nature Nanotechnology}, publisher={Springer Science and Business Media LLC}, author={Cheng, Guangming and Miao, Chunyang and Qin, Qingquan and Li, Jing and Xu, Feng and Haftbaradaran, Hamed and Dickey, Elizabeth C. and Gao, Huajian and Zhu, Yong}, year={2015}, month={Jul}, pages={687–691} }
 @article{jiang_zhu_2015, title={Measuring graphene adhesion using atomic force microscopy with a microsphere tip}, volume={7}, ISSN={["2040-3372"]}, DOI={10.1039/c5nr02480c}, abstractNote={This work reports a general method to measure adhesion energies between graphene and different materials using atomic force microscopy with microsphere tips.}, number={24}, journal={NANOSCALE}, author={Jiang, Tao and Zhu, Yong}, year={2015}, pages={10760–10766} }
 @misc{yao_zhu_2015, title={Nanomaterial-Enabled Stretchable Conductors: Strategies, Materials and Devices}, volume={27}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201404446}, abstractNote={Stretchable electronics are attracting intensive attention due to their promising applications in many areas where electronic devices undergo large deformation and/or form intimate contact with curvilinear surfaces. On the other hand, a plethora of nanomaterials with outstanding properties have emerged over the past decades. The understanding of nanoscale phenomena, materials, and devices has progressed to a point where substantial strides in nanomaterial‐enabled applications become realistic. This review summarizes recent advances in one such application, nanomaterial‐enabled stretchable conductors (one of the most important components for stretchable electronics) and related stretchable devices (e.g., capacitive sensors, supercapacitors and electroactive polymer actuators), over the past five years. Focusing on bottom‐up synthesized carbon nanomaterials (e.g., carbon nanotubes and graphene) and metal nanomaterials (e.g., metal nanowires and nanoparticles), this review provides fundamental insights into the strategies for developing nanomaterial‐enabled highly conductive and stretchable conductors. Finally, some of the challenges and important directions in the area of nanomaterial‐enabled stretchable conductors and devices are discussed.}, number={9}, journal={ADVANCED MATERIALS}, author={Yao, Shanshan and Zhu, Yong}, year={2015}, month={Mar}, pages={1480–1511} }
 @article{qin_yin_cheng_li_chang_richter_zhu_gao_2015, title={Recoverable plasticity in penta-twinned metallic nanowires governed by dislocation nucleation and retraction}, volume={6}, ISSN={["2041-1723"]}, DOI={10.1038/ncomms6983}, abstractNote={Abstract}, journal={NATURE COMMUNICATIONS}, author={Qin, Qingquan and Yin, Sheng and Cheng, Guangming and Li, Xiaoyan and Chang, Tzu-Hsuan and Richter, Gunther and Zhu, Yong and Gao, Huajian}, year={2015}, month={Jan} }
 @inproceedings{yao_lee_james_miller_narasimhan_dickerson_zhu_zhu_2015, title={Silver nanowire strain sensors for wearable body motion tracking}, DOI={10.1109/icsens.2015.7370650}, abstractNote={This paper demonstrates a wearable body motion tracking technology in the form of data glove to measure the instantaneous bending positions of individual finger knuckles. Attached to the glove is a highly stretchable and flexible silver nanowire (AgNW) based capacitive strain sensor which can adapt to curvilinear surfaces. The sensor shows a linear response to large tensile strain up to 60% with less than 5 msec response time. Such kind of merits enable many applications, e.g. Virtue Reality, gaming, and robot control, which desire natural human-machine interactions associated with typical human motions such as finger movements, walking, running and jumping, etc.}, booktitle={2015 ieee sensors}, author={Yao, S. S. and Lee, J. S. and James, K. and Miller, J. and Narasimhan, V. and Dickerson, A. J. and Zhu, X. and Zhu, Y.}, year={2015}, pages={1823–1826} }
 @article{narayanan_cheng_zeng_zhu_zhu_2015, title={Strain Hardening and Size Effect in Five-fold Twinned Ag Nanowires}, volume={15}, ISSN={["1530-6992"]}, DOI={10.1021/acs.nanolett.5b01015}, abstractNote={Metallic nanowires usually exhibit ultrahigh strength but low tensile ductility owing to their limited strain hardening capability. Here we study the unique strain hardening behavior of the five-fold twinned Ag nanowires by nanomechanical testing and atomistic modeling. In situ tensile tests within a scanning electron microscope revealed strong strain hardening behavior of the five-fold twinned Ag nanowires. Molecular dynamics simulations showed that such strain hardening was critically controlled by twin boundaries and pre-existing defects. Strain hardening was size dependent; thinner nanowires achieved more hardening and higher ductility. The size-dependent strain hardening was found to be caused by the obstruction of surface-nucleated dislocations by twin boundaries. Our work provides mechanistic insights into enhancing the tensile ductility of metallic nanostructures by engineering the internal interfaces and defects.}, number={6}, journal={NANO LETTERS}, author={Narayanan, Sankar and Cheng, Guangming and Zeng, Zhi and Zhu, Yong and Zhu, Ting}, year={2015}, month={Jun}, pages={4037–4044} }
 @article{di_yao_ye_cui_yu_ghosh_zhu_gu_2015, title={Stretch-Triggered Drug Delivery from Wearable Elastomer Films Containing Therapeutic Depots}, volume={9}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.5b03975}, abstractNote={Mechanical force-based stimulus provides a simple and easily accessible manner for spatiotemporally controlled drug delivery. Here we describe a wearable, tensile strain-triggered drug delivery device consisting of a stretchable elastomer and microgel depots containing drug loaded nanoparticles. By applying a tensile strain to the elastomer film, the release of drug from the microdepot is promoted due to the enlarged surface area for diffusion and Poisson's ratio-induced compression on the microdepot. Correspondingly, both sustained drug release by daily body motions and pulsatile release by intentional administration can be conveniently achieved. Our work demonstrated that the tensile strain, applied to the stretchable device, facilitated release of therapeutics from microdepots for anticancer and antibacterial treatments. Moreover, polymeric microneedles were further integrated with the stretch-responsive device for transcutaneous delivery of insulin and regulation of blood glucose levels of chemically induced type 1 diabetic mice.}, number={9}, journal={ACS NANO}, author={Di, Jin and Yao, Shanshan and Ye, Yanqi and Cui, Zheng and Yu, Jicheng and Ghosh, Tushar K. and Zhu, Yong and Gu, Zhen}, year={2015}, month={Sep}, pages={9407–9415} }
 @article{yao_zhu_2015, title={Stretchable Conductors: Nanomaterial-Enabled Stretchable Conductors: Strategies, Materials and Devices (Adv. Mater. 9/2015)}, volume={27}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/ADMA.201570061}, DOI={10.1002/ADMA.201570061}, abstractNote={On page 1480, Y. Zhu and S. Yao review the recent progress in stretchable conductors and related devices based on bottom-up assembled nanomaterials. Highly conductive and stretchable silver nanowire conductors can serve as the compliant electrodes for wearable sensors. Such wearable sensors can be used to monitor human motion and electrophysiological signals, as well as the surrounding environment, holding promise for prosthetics, robotics, and wearable healthcare applications.}, number={9}, journal={Advanced Materials}, publisher={Wiley}, author={Yao, Shanshan and Zhu, Yong}, year={2015}, month={Mar}, pages={1479–1479} }
 @article{peng_ke_liu_zhu_2015, title={Testing, Measurement, and Characterization of Nanomaterials}, volume={2015}, ISSN={["1687-4129"]}, DOI={10.1155/2015/751698}, abstractNote={1School of Mechatronics Engineering, University of Electronic Science and Technology of China, Chengdu, Sichuan 611731, China 2Department of Mechanical Engineering, Binghamton University, State University of New York (SUNY), Binghamton, NY 13902-6000, USA 3Department of Mechanical Engineering and Mechanics, Lehigh University, PA 18015, USA 4Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695-7910, USA}, journal={JOURNAL OF NANOMATERIALS}, author={Peng, Bei and Ke, Changhong and Liu, Yaling and Zhu, Yong}, year={2015} }
 @article{myers_huang_zhu_2015, title={Wearable silver nanowire dry electrodes for electrophysiological sensing}, volume={5}, ISSN={2046-2069}, url={http://dx.doi.org/10.1039/c4ra15101a}, DOI={10.1039/c4ra15101a}, abstractNote={We present wearable dry electrodes made of silver nanowires for long-term electrophysiological sensing such as electrocardiography and electromyography.}, number={15}, journal={RSC Advances}, publisher={Royal Society of Chemistry (RSC)}, author={Myers, Amanda C. and Huang, He and Zhu, Yong}, year={2015}, pages={11627–11632} }
 @article{jiang_huang_zhu_2014, title={Interfacial sliding and buckling of monolayer graphene on a stretchable substrate}, volume={24}, DOI={10.1002/adfm.201301999}, abstractNote={The nonlinear mechanical response of monolayer graphene on polyethylene terephthalate (PET) is characterised using in‐situ Raman spectroscopy and atomic force microscopy. While interfacial stress transfer leads to tension in graphene as the PET substrate is stretched, retraction of the substrate during unloading imposes compression in the graphene. Two interfacial failure mechanisms, shear sliding under tension and buckling under compression, are identified. Using a nonlinear shear‐lag model, the interfacial shear strength is found to range between 0.46 and 0.69 MPa. The critical strain for onset of interfacial sliding is ∼0.3%, while the maximum strain that can be transferred to graphene ranges from 1.2% to 1.6% depending on the interfacial shear strength and graphene size. Beyond a critical compressive strain of around −0.7%, buckling ridges are observed after unloading. The results from this work provide valuable insight and design guidelines for a broad spectrum of applications of graphene and other 2D nanomaterials, such as flexible and stretchable electronics, strain sensing, and nanocomposites.}, number={3}, journal={Advanced Functional Materials}, author={Jiang, T. and Huang, R. and Zhu, Y.}, year={2014}, pages={396–402} }
 @article{cheng_chang_qin_huang_zhu_2014, title={Mechanical Properties of Silicon Carbide Nanowires: Effect of Size-Dependent Defect Density}, volume={14}, ISSN={["1530-6992"]}, DOI={10.1021/nl404058r}, abstractNote={This paper reports quantitative mechanical characterization of silicon carbide (SiC) nanowires (NWs) via in situ tensile tests inside scanning electron microscopy using a microelectromechanical system. The NWs are synthesized using the vapor-liquid-solid process with growth direction of ⟨111⟩. They consist of three types of structures, pure face-centered cubic (3C) structure, 3C structure with an inclined stacking fault (SF), and highly defective structure, in a periodic fashion along the NW length. The SiC NWs are found to deform linear elastically until brittle fracture. Their fracture origin is identified in the 3C structures with inclined SFs, rather than the highly defective structures. The fracture strength increases as the NW diameter decreases from 45 to 17 nm, approaching the theoretical strength of 3C SiC. The size effect on fracture strength of SiC NWs is attributed to the size-dependent defect density rather than the surface effect that is dominant for single crystalline NWs.}, number={2}, journal={NANO LETTERS}, author={Cheng, Guangming and Chang, Tzu-Hsuan and Qin, Qingquan and Huang, Hanchen and Zhu, Yong}, year={2014}, month={Feb}, pages={754–758} }
 @inproceedings{myers_du_huang_zhu_2014, title={Novel wearable EMG sensors based on nanowire technology}, ISBN={9781424479290}, url={http://dx.doi.org/10.1109/embc.2014.6943928}, DOI={10.1109/embc.2014.6943928}, abstractNote={Wearable electrodes made of silver nanowires (AgNWs) have demonstrated great potential for sensing a variety of physical and physiological signals. This paper aimed to study the feasibility of AgNWs electrodes for measuring surface electromyographic (sEMG) signals. One human subject was recruited and instructed to perform wrist extension repetitively or to produce no movement in the experiment. sEMG signals were collected from the right extensor digitorum communis of the human subject by an AgNWs electrode and a commercially available Ag/AgCl wet sEMG electrode, separately. The quality of recorded sEMG in time and frequency domains was compared between the two types of electrodes. The results showed that the sEMG signals recorded by the AgNW electrode were comparable with that by the Ag/AgCl electrode. Since the dry AgNWs electrodes are flexible, wearable, and potentially robust for daily use, novel AgNW-based EMG electrodes are promising for many biomedical applications, such as myoelectric control of artificial limbs.}, booktitle={2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society}, publisher={IEEE}, author={Myers, Amanda and Du, Lin and Huang, He and Zhu, Yong}, year={2014}, month={Aug}, pages={1674–1677} }
 @article{song_myers_adams_zhu_2014, title={Stretchable and Reversibly Deformable Radio Frequency Antennas Based on Silver Nanowires}, volume={6}, ISSN={["1944-8252"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84896995952&partnerID=MN8TOARS}, DOI={10.1021/am405972e}, abstractNote={We demonstrate a class of microstrip patch antennas that are stretchable, mechanically tunable, and reversibly deformable. The radiating element of the antenna consists of highly conductive and stretchable material with screen-printed silver nanowires embedded in the surface layer of an elastomeric substrate. A 3-GHz microstrip patch antenna and a 6-GHz 2-element patch array are fabricated. Radiating properties of the antennas are characterized under tensile strain and agree well with the simulation results. The antenna is reconfigurable because the resonant frequency is a function of the applied tensile strain. The antenna is thus well suited for applications like wireless strain sensing. The material and fabrication technique reported here could be extended to achieve other types of stretchable antennas with more complex patterns and multilayer structures.}, number={6}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Song, Lingnan and Myers, Amanda C. and Adams, Jacob J. and Zhu, Yong}, year={2014}, month={Mar}, pages={4248–4253} }
 @article{gurarslan_yu_su_yu_suarez_yao_zhu_ozturk_zhang_cao_2014, title={Surface-Energy-Assisted Perfect Transfer of Centimeter-Scale Mono layer and Few-Layer MoS2 Films onto Arbitrary Substrates}, volume={8}, ISSN={["1936-086X"]}, DOI={10.1021/nn5057673}, abstractNote={The transfer of synthesized 2D MoS2 films is important for fundamental and applied research. However, it is problematic to translate the well-established transfer processes for graphene to MoS2 due to different growth mechanisms and surface properties. Here we demonstrate a surface-energy-assisted process that can perfectly transfer centimeter-scale monolayer and few-layer MoS2 films from original growth substrates onto arbitrary substrates with no observable wrinkles, cracks, and polymer residues. The unique strategies used in this process include leveraging the penetration of water between hydrophobic MoS2 films and hydrophilic growth substrates to lift off the films and dry transferring the film after the lift off. This is in stark contrast with the previous transfer process for synthesized MoS2 films, which explores the etching of the growth substrate by hot base solutions to lift off the films. Our transfer process can effectively eliminate the mechanical force caused by bubble generations, the attacks from chemical etchants, and the capillary force induced when transferring the film outside solutions as in the previous transfer process, which consists of the major causes for the previous unsatisfactory transfer. Our transfer process also benefits from using polystyrene (PS), instead of poly(methyl methacrylate) (PMMA) that was widely used previously, as the carrier polymer. PS can form more intimate interaction with MoS2 films than PMMA and is important for maintaining the integrity of the film during the transfer process. This surface-energy-assisted approach can be generally applied to the transfer of other 2D materials, such as WS2.}, number={11}, journal={ACS NANO}, author={Gurarslan, Alper and Yu, Yifei and Su, Liqin and Yu, Yiling and Suarez, Francisco and Yao, Shanshan and Zhu, Yong and Ozturk, Mehmet and Zhang, Yong and Cao, Linyou}, year={2014}, month={Nov}, pages={11522–11528} }
 @article{yao_zhu_2014, title={Wearable multifunctional sensors using printed stretchable conductors made of silver nanowires}, volume={6}, ISSN={["2040-3372"]}, DOI={10.1039/c3nr05496a}, abstractNote={Considerable efforts have been made to achieve highly sensitive and wearable sensors that can simultaneously detect multiple stimuli such as stretch, pressure, temperature or touch. Here we develop highly stretchable multifunctional sensors that can detect strain (up to 50%), pressure (up to ∼1.2 MPa) and finger touch with high sensitivity, fast response time (∼40 ms) and good pressure mapping function. The reported sensors utilize the capacitive sensing mechanism, where silver nanowires are used as electrodes (conductors) and Ecoflex is used as a dielectric. The silver nanowire electrodes are screen printed. Our sensors have been demonstrated for several wearable applications including monitoring thumb movement, sensing the strain of the knee joint in patellar reflex (knee-jerk) and other human motions such as walking, running and jumping from squatting, illustrating the potential utilities of such sensors in robotic systems, prosthetics, healthcare and flexible touch panels.}, number={4}, journal={NANOSCALE}, author={Yao, Shanshan and Zhu, Yong}, year={2014}, pages={2345–2352} }
 @article{chang_zhu_2013, title={A microelectromechanical system for thermomechanical testing of nanostructures}, volume={103}, ISSN={["1077-3118"]}, DOI={10.1063/1.4858962}, abstractNote={We report an integrated microelectromechanical system (MEMS) with an on-chip heater for in-situ mechanical testing of nanostructures from room to elevated temperatures. Multiphysics simulation is used to predict the temperature distribution in air and vacuum conditions. The temperature simulation in air agrees well with the measurement based on Raman spectroscopy. Mechanical testing of single crystalline silicon nanowires is carried out to investigate the brittle-to-ductile transition, demonstrating the efficacy of the MEMS stage. The stage reported here could be applied to investigate the temperature effect on mechanical properties at the nanoscale.}, number={26}, journal={APPLIED PHYSICS LETTERS}, author={Chang, Tzu-Hsuan and Zhu, Yong}, year={2013}, month={Dec} }
 @article{durham_zhu_2013, title={Fabrication of Functional Nanowire Devices on Unconventional Substrates Using Strain-Release Assembly}, volume={5}, ISSN={["1944-8244"]}, DOI={10.1021/am302384z}, abstractNote={We report three representative nanowire (NW) devices for applications in stretchable electronics, strain sensing, and optical sensing. Fabrication of such devices is based on a recently developed strain-release assembly method. NWs are first aligned transversely on an elastomeric substrate using the strain-release assembly. Constant resistance is achieved in silicon (Si) NW devices stretched up to ~40% of axial strain, highlighting a new concept of transverse buckling. Combining the NW assembly with transfer printing extends suitable device substrates beyond elastomers to other unconventional materials (e.g., flexible and transparent materials). Following this combined process, flexible SiNW strain sensors are fabricated on plastics capable of sensing up to 1.6% bending strain and gauge factors >1000; flexible zinc oxide NW ultraviolet sensors are demonstrated with quick recovery (~2 s) and excellent repeatability on plastics. Our results show promise for the strain-release assembly as a simple and cost-effective process to fabricate NW devices on unconventional substrates.}, number={2}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Durham, John W., III and Zhu, Yong}, year={2013}, month={Jan}, pages={256–261} }
 @article{zu_li_zhu_zhu_wang_byun_chou_2013, title={Stress relaxation in carbon nanotube-based fibers for load-bearing applications}, volume={52}, ISSN={["0008-6223"]}, DOI={10.1016/j.carbon.2012.09.036}, abstractNote={Carbon nanotube (CNT) based continuous fiber, a CNT assembly that could retain the superb properties of individual CNTs on a macroscopic scale, has emerged as a promising candidate for reinforcement in multifunctional composites. While existing research has extensively examined their short-term mechanical properties based upon quasi-static measurements, the long-term durability of CNT fibers has been largely neglected. Here we report time-dependent behavior of CNT fibers, with a particular focus on tensile stress relaxation. Both the pure CNT fiber and the CNT/epoxy composite fiber exhibited significant stress decay during the relaxation process, and this time-dependent behavior became more significant at a higher initial strain level, a lower strain rate and a greater gauge length. The present approach signifies a fundamental difference in the load-bearing characteristics between CNT fibers and traditional advanced fibers, which has major implications for the long-term durability of CNT fibers in load-bearing multifunctional applications.}, journal={CARBON}, author={Zu, Mei and Li, Qingwen and Zhu, Yuntian and Zhu, Yong and Wang, Guojian and Byun, Joon-Hyung and Chou, Tsu-Wei}, year={2013}, month={Feb}, pages={347–355} }
 @article{qin_zhu_2013, title={Temperature control in thermal microactuators with applications to in-situ nanomechanical testing}, volume={102}, ISSN={["1077-3118"]}, DOI={10.1063/1.4773359}, abstractNote={Thermal microactuators are used in many micro/nano-technologies. To circumvent undesired heating of the end effector, heat sink beams are co-fabricated with the thermal actuator and connected to the substrate. This paper reports a combined experimental and modeling study on the effect of such heat sink beams. Temperature distribution is measured and simulated using Raman scattering and multiphysics finite element method, respectively. Our results show that heat sink beams are effective in controlling the temperature of the thermal actuator. Insights on how to achieve both low temperature and large actuator displacement for in-situ mechanical testing of nanoscale specimens are provided.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Qin, Qingquan and Zhu, Yong}, year={2013}, month={Jan} }
 @article{ouyang_mcdonald_zhu_2013, title={Temperature-dependent material properties of Z-shaped MEMS thermal actuators made of single crystalline silicon}, volume={23}, ISSN={["1361-6439"]}, DOI={10.1088/0960-1317/23/12/125036}, abstractNote={MEMS thermal actuators have been employed in a broad range of applications, often operating in different environments (e.g. vacuum, air or liquid). Since the involved heat dissipation mechanisms are different in different operating environments, the device performances are expected to be different. In this paper, we report experimental measurement and multiphysics modeling of device performance metrics of a recently introduced thermal actuator, the Z-shaped thermal actuator, including temperature distribution, electric resistance and displacement in both air and vacuum environments. The temperature measurement was based on Raman scattering in air. Fully 3D multiphysics (coupled thermo-electro-mechanical) simulations were performed to treat both air and vacuum environments. Heat conduction through air to neighboring devices is important, while heat convection to air is negligible. The experimental and modeling results agreed well, which demonstrated the accuracy of the temperature-dependent material properties used in the modeling. Fully 3D multiphysics modeling combined with valid material property parameters will enable the exploration of the design space and the optimization of performances of the MEMS thermal actuators for different operating environments.}, number={12}, journal={JOURNAL OF MICROMECHANICS AND MICROENGINEERING}, author={Ouyang, Jing and McDonald, Margaret and Zhu, Yong}, year={2013}, month={Dec} }
 @inbook{kieffer_zhu_2013, title={Thermal Output Observations from Fe-Ni-Cr Metal Foil Strain Gages}, ISBN={9783319007670 9783319007687}, ISSN={2191-5644 2191-5652}, url={http://dx.doi.org/10.1007/978-3-319-00768-7_48}, DOI={10.1007/978-3-319-00768-7_48}, booktitle={Advancement of Optical Methods in Experimental Mechanics, Volume 3}, publisher={Springer International Publishing}, author={Kieffer, T. P. and Zhu, Y.}, year={2013}, month={Aug}, pages={379–387} }
 @inproceedings{zhu_2012, title={A new electrothermal microactuator with Z-shaped beams: Design and operation}, DOI={10.1115/imece2010-38611}, abstractNote={A new class of thermal microactuators, Z-shaped thermal actuator, is introduced in comparison with the well-established V-shaped thermal actuator. Though they share many features in common, Z-shaped thermal actuator offers several advantages: compatibility with anisotropic etching, smaller feature size, larger displacement, and larger variety of stiffness and output force. While the Z-shaped thermal actuator was modeled analytically and verified by multiphysics finite element analysis (FEA), the beam width and length of the central beam were identified as the major design parameters in tuning the device displacement, stiffness, stability and output force. Experimental measurements were taken on three arrays of Z-shaped thermal actuator with variable parameters. Results agreed well with the finite element analysis. The development of Z-shaped thermal actuator is applicable in simultaneous sensing and actuating applications. During the quasi-static test of individual Z-shaped thermal actuator, the average temperature in the device structure was estimated based on electric resistivity at each actuation voltage.}, booktitle={Proceedings of the ASME International Mechanical Engineering Congress and Exposition 2010, vol 12}, author={Zhu, Y.}, year={2012}, pages={77–81} }
 @article{zhu_xu_2012, title={Buckling of Aligned Carbon Nanotubes as Stretchable Conductors: A New Manufacturing Strategy}, volume={24}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201103382}, DOI={10.1002/adma.201103382}, abstractNote={A new manufacturing strategy for buckling of aligned carbon nanotubes is developed, which does not involve prestretching the substrate but relies on the interface interaction between the nanotubes and the substrate. More specifically, upon stretching the substrate the nanotubes slide on the substrate, but upon releasing the nanotubes buckle. Following this manufacturing strategy, stretchable conductors based on aligned carbon nanotubes are demonstrated.}, number={8}, journal={Advanced Materials}, publisher={Wiley}, author={Zhu, Yong and Xu, Feng}, year={2012}, month={Jan}, pages={1073–1077} }
 @article{xu_zhu_2012, title={Highly Conductive and Stretchable Silver Nanowire Conductors}, volume={24}, ISSN={["0935-9648"]}, DOI={10.1002/adma.201201886}, abstractNote={IO N Materials that are both conductive and stretchable could enable a spectrum of applications such as stretchable displays, [ 1 ] stretchable radiofrequency antennas, [ 2 ] artifi cial muscles [ 3 ] and conformal skin sensors. [ 4–7 ] A variety of such materials have been recently developed, such as wavy thin metals, [ 8 , 9 ] metal-coated net-shaped plastic fi lm, [ 10 ] graphene fi lms [ 11 ] and carbon nanotube (CNT)-based composites. [ 12–19 ] But several limitations typically exist in these materials including low conductivity, [ 13 , 15 , 16 , 19 ]}, number={37}, journal={ADVANCED MATERIALS}, author={Xu, Feng and Zhu, Yong}, year={2012}, month={Sep}, pages={5117–5122} }
 @article{qin_xu_cao_ro_zhu_2012, title={Measuring True Young's Modulus of a Cantilevered Nanowire: Effect of Clamping on Resonance Frequency}, volume={8}, ISSN={1613-6810}, url={http://dx.doi.org/10.1002/smll.201200314}, DOI={10.1002/smll.201200314}, abstractNote={Abstract}, number={16}, journal={Small}, publisher={Wiley}, author={Qin, Qingquan and Xu, Feng and Cao, Yongqing and Ro, Paul I. and Zhu, Yong}, year={2012}, month={May}, pages={2571–2576} }
 @article{zhu_qin_xu_fan_ding_zhang_wiley_wang_2012, title={Size effects on elasticity, yielding, and fracture of silver nanowires: In situ experiments}, volume={85}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.85.045443}, abstractNote={Thispaperreportsthequantitativemeasurementofafullspectrumofmechanicalpropertiesoffivefoldtwinned silver (Ag) nanowires (NWs), including Young’s modulus, yield strength, and ultimate tensile strength. In-situ tensile testing of Ag NWs with diameters between 34 and 130 nm was carried out inside a scanning electron microscope (SEM). Young’s modulus, yield strength, and ultimate tensile strength all increased as the NW diameter decreased. The maximum yield strength in our tests was found to be 2.64 GPa, which is about 50 times the bulk value and close to the theoretical value of Ag in the � 110� orientation. The size effect in the yield strength is mainly due to the stiffening size effect in the Young’s modulus. Yield strain scales reasonably well with the NW surface area, which reveals that yielding of Ag NWs is due to dislocation nucleation from surface sources. Pronounced strain hardening was observed for most NWs in our study. The strain hardening, which has not previously been reported for NWs, is mainly attributed to the presence of internal twin boundaries.}, number={4}, journal={PHYSICAL REVIEW B}, author={Zhu, Yong and Qin, Qingquan and Xu, Feng and Fan, Fengru and Ding, Yong and Zhang, Tim and Wiley, Benjamin J. and Wang, Zhong Lin}, year={2012}, month={Jan} }
 @article{xu_wang_zhu_zhu_2012, title={Wavy Ribbons of Carbon Nanotubes for Stretchable Conductors}, volume={22}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201102032}, abstractNote={Abstract}, number={6}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Xu, Feng and Wang, Xin and Zhu, Yuntian and Zhu, Yong}, year={2012}, month={Mar}, pages={1279–1283} }
 @article{ouyang_zhu_2012, title={Z-Shaped MEMS Thermal Actuators: Piezoresistive Self-Sensing and Preliminary Results for Feedback Control}, volume={21}, ISSN={["1941-0158"]}, DOI={10.1109/jmems.2012.2189361}, abstractNote={Feedback control of microactuators holds potential to significantly improve their performance and reliability. A critical step to realize the feedback control of microactuators is feedback sensing. In this paper, we report the feasibility of using a Z-shaped thermal actuator (ZTA) as a simultaneous force or displacement sensor. An in situ scanning electron microscope nanomanipulation process is used to characterize the piezoresistive response of ZTAs, which shows that ZTAs can be used as piezoresistive sensors. The experimental results agree very well with multiphysics (electric-thermal-structural-piezoresistive) simulations. A new feedback scheme is further explored, where the ZTA is treated as a two-input (applied current and external force) and two-output (displacement and electric resistance) system. Based on the calibrated relationships between the inputs and the outputs, a feedback system is developed, which can simultaneously sense the external force and generate updated current to actuate the ZTA to the desired position. We demonstrate preliminary results of this feedback control by holding the ZTA at a constant position under various external forces. The device and method presented in this paper are valuable for a range of microelectromechanical systems applications, including on-chip nanoscale mechanical testing and nanopositioning.}, number={3}, journal={JOURNAL OF MICROELECTROMECHANICAL SYSTEMS}, author={Ouyang, Jing and Zhu, Yong}, year={2012}, month={Jun}, pages={596–604} }
 @article{xu_lu_zhu_2011, title={Controlled 3D Buckling of Silicon Nanowires for Stretchable Electronics}, volume={5}, ISSN={["1936-0851"]}, DOI={10.1021/nn103189z}, abstractNote={Silicon (Si) nanowire (NW) coils were fabricated on elastomeric substrates by a controlled buckling process. Si NWs were first transferred onto prestrained and ultraviolet/ozone (UVO)-treated poly(dimethylsiloxane) (PDMS) substrates and buckled upon release of the prestrain. Two buckling modes (the in-plane wavy mode and the three-dimensional coiled mode) were found; a transition between them was achieved by controlling the UVO treatment of PDMS. Structural characterization revealed that the NW coils were oval-shaped. The oval-shaped NW coils exhibited very large stretchability up to the failure strain of PDMS (∼104% in our study). Such a large stretchability relies on the effectiveness of the coil shape in mitigating the maximum local strain, with a mechanics that is similar to the motion of a coil spring. Single NW devices based on coiled NWs were demonstrated with a nearly constant electrical response in a large strain range. In addition to the wavy shape, the coil shape represents an effective architecture in accommodating large tension, compression, bending, and twist, which may find important applications for stretchable electronics and other stretchable technologies.}, number={1}, journal={ACS NANO}, author={Xu, Feng and Lu, Wei and Zhu, Yong}, year={2011}, month={Jan}, pages={672–678} }
 @article{qin_zhu_2011, title={Static Friction between Silicon Nanowires and Elastomeric Substrates}, volume={5}, ISSN={["1936-086X"]}, DOI={10.1021/nn202343w}, abstractNote={This paper reports the first direct measurements of static friction force and interfacial shear strength between silicon (Si) nanowires (NWs) and poly(dimethylsiloxane) (PDMS). A micromanipulator is used to manipulate and deform the NWs under a high-magnification optical microscope in real time. The static friction force is measured based on "the most-bent state" of the NWs. The static friction and interface shear strength are found to depend on the ultraviolet/ozone (UVO) treatment of PDMS. The shear strength starts at 0.30 MPa without UVO treatment, increases rapidly up to 10.57 MPa at 60 min of treatment and decreases for longer treatment. Water contact angle measurements suggest that the UVO-induced hydrophobic-to-hydrophilic conversion of PDMS surface is responsible for the increase in the static friction, while the hydrophobic recovery effect contributes to the decrease. The static friction between NWs and PDMS is of critical relevance to many device applications of NWs including NW-based flexible/stretchable electronics, NW assembly and nanocomposites (e.g., supercapacitors). Our results will enable quantitative interface design and control for such applications.}, number={9}, journal={ACS NANO}, author={Qin, Qingquan and Zhu, Yong}, year={2011}, month={Sep}, pages={7404–7410} }
 @article{xu_durham_wiley_zhu_2011, title={Strain-Release Assembly of Nanowires on Stretchable Substrates}, volume={5}, ISSN={["1936-086X"]}, DOI={10.1021/nn103183d}, abstractNote={A simple yet effective method for assembly of highly aligned nanowires (NWs) on stretchable substrates is reported. In this method, NWs were first transferred to a strained stretchable substrate. After the strain was released, the NWs aligned in the transverse direction and the area coverage of the NWs on the substrate increased. This method can be applied to any NWs deposited on a stretchable film and can be repeated multiple times to increase the alignment and density of the NWs. For silver (Ag) and silicon (Si) NWs on poly(dimethylsiloxane) (PDMS) substrates, the probability of NW alignment increased from 29% to 90% for Ag NWs, and from 25% to 88% for Si NWs after two assembly steps; the density increased by 60% and 75% for the Ag and Si NWs, respectively. The large-strain elasticity of the substrate and the static friction between the NWs and the substrate play key roles in this assembly method. We find that a model that takes into account the volume incompressibility of PDMS reliably predicts the degree of NW alignment and NW density. The utility of this assembly method was demonstrated by fabricating a strain sensor array composed of aligned Si NWs on a PDMS substrate, with a device yield of 95%.}, number={2}, journal={ACS NANO}, author={Xu, Feng and Durham, John W., III and Wiley, Benjamin J. and Zhu, Yong}, year={2011}, month={Feb}, pages={1556–1563} }
 @article{guan_zhu_2010, title={An electrothermal microactuator with Z-shaped beams}, volume={20}, ISSN={["0960-1317"]}, DOI={10.1088/0960-1317/20/8/085014}, abstractNote={This paper introduces a Z-shaped thermal microactuator for in-plane motion, which could be complementary to the well-established comb drives and V-shaped thermal actuators. The Z-shaped actuators share many features in common with the V-shaped ones, but offer certain advantages such as smaller feature size and larger displacement. They also offer a large range of stiffness and output force that is between those of the V-shaped actuators and comb drives. In particular, they can achieve smaller stiffness without buckling, which renders them as simultaneous load sensors. The Z-shaped actuator was modeled analytically and verified by multiphysics finite element analysis. Among all the design parameters, the beam width and the length of the central beam were identified as the major ones in tuning the device displacement, stiffness, stability and output force. Experimental measurements of three arrays of Z-shaped thermal actuators agreed well with the finite element analysis. In addition, the quasi-static and dynamic performances of individual Z-shaped thermal actuators were measured. The average temperature in the device structure was estimated from the electric resistivity at each actuation voltage. The bandwidth of the Z-shaped thermal actuators can be increased for devices with a substrate underneath.}, number={8}, journal={JOURNAL OF MICROMECHANICS AND MICROENGINEERING}, author={Guan, Changhong and Zhu, Yong}, year={2010}, month={Aug} }
 @article{zhu_qin_gu_wang_2010, title={Friction and Shear Strength at the Nanowire-Substrate Interfaces}, volume={5}, ISSN={["1931-7573"]}, DOI={10.1007/s11671-009-9478-4}, abstractNote={Abstract}, number={2}, journal={NANOSCALE RESEARCH LETTERS}, author={Zhu, Yong and Qin, Qingquan and Gu, Yi and Wang, Zhong Lin}, year={2010}, month={Feb}, pages={291–295} }
 @article{xu_qin_mishra_gu_zhu_2010, title={Mechanical Properties of ZnO Nanowires Under Different Loading Modes}, volume={3}, ISSN={["1998-0124"]}, DOI={10.1007/s12274-010-1030-4}, abstractNote={A systematic experimental and theoretical investigation of the elastic and failure properties of ZnO nanowires (NWs) under different loading modes has been carried out. In situ scanning electron microscopy (SEM) tension and buckling tests on single ZnO NWs along the polar direction [0001] were conducted. Both tensile modulus (from tension) and bending modulus (from buckling) were found to increase as the NW diameter decreased from 80 to 20 nm. The bending modulus increased more rapidly than the tensile modulus, which demonstrates that the elasticity size effects in ZnO NWs are mainly due to surface stiffening. Two models based on continuum mechanics were able to fit the experimental data very well. The tension experiments showed that fracture strain and strength of ZnO NWs increased as the NW diameter decreased. The excellent resilience of ZnO NWs is advantageous for their applications in nanoscale actuation, sensing, and energy conversion.}, number={4}, journal={NANO RESEARCH}, author={Xu, Feng and Qin, Qingqun and Mishra, Ashish and Gu, Yi and Zhu, Yong}, year={2010}, month={Apr}, pages={271–280} }
 @article{zhu_liechti_ravi-chandar_2009, title={Direct extraction of rate-dependent traction-separation laws for polyurea/steel interfaces}, volume={46}, ISSN={["1879-2146"]}, DOI={10.1016/j.ijsolstr.2008.08.019}, abstractNote={Polyurea coatings on steel form tough, flexible and chemically resistant surfaces, making them ideal for a variety of applications. An important issue for polyurea coatings in some cases is their adhesion to steel under various loading conditions in aggressive environments. In this paper, adhesion was examined using steel/polyurea/steel sandwich specimens and interfacial fracture mechanics. The mode 1 and mode 2 interfacial fracture behaviors were characterized by two independent traction–separation laws. The traction–separation laws were measured directly by recording the J-integral and the end-opening displacement in the directions normal and tangential to the steel/polyurea interface. In each case, the traction was initially nonzero, increased with increasing separation, reached its peak value and then decreased with further increasing opening. Strong rate-dependent effects were found for both modes of fracture and were attributed to the interfacial behavior. Porosity introduced during the processing of the polyurea affected the traction–separation laws and associated fracture mechanisms.}, number={1}, journal={INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES}, author={Zhu, Yong and Liechti, Kenneth M. and Ravi-Chandar, K.}, year={2009}, month={Jan}, pages={31–51} }
 @article{zhu_xu_qin_fung_lu_2009, title={Mechanical Properties of Vapor-Liquid-Solid Synthesized Silicon Nanowires}, volume={9}, ISSN={["1530-6984"]}, DOI={10.1021/nl902132w}, abstractNote={The Young's modulus and fracture strength of silicon nanowires with diameters between 15 and 60 nm and lengths between 1.5 and 4.3 mum were measured. The nanowires, grown by the vapor-liquid-solid process, were subjected to tensile tests in situ inside a scanning electron microscope. The Young's modulus decreased while the fracture strength increased up to 12.2 GPa, as the nanowire diameter decreased. The fracture strength also increased with the decrease of the side surface area; the increase rate for the chemically synthesized silicon nanowires was found to be much higher than that for the microfabricated silicon thin films. Repeated loading and unloading during tensile tests demonstrated that the nanowires are linear elastic until fracture without appreciable plasticity.}, number={11}, journal={NANO LETTERS}, author={Zhu, Yong and Xu, Feng and Qin, Qingquan and Fung, Wayne Y. and Lu, Wei}, year={2009}, month={Nov}, pages={3934–3939} }
 @article{locascio_peng_zapol_zhu_li_belytschko_espinosa_2009, title={Tailoring the Load Carrying Capacity of MWCNTs Through Inter-shell Atomic Bridging}, volume={49}, ISSN={0014-4851 1741-2765}, url={http://dx.doi.org/10.1007/S11340-008-9216-3}, DOI={10.1007/S11340-008-9216-3}, number={2}, journal={Experimental Mechanics}, publisher={Springer Science and Business Media LLC}, author={Locascio, M. and Peng, B. and Zapol, P. and Zhu, Y. and Li, S. and Belytschko, T. and Espinosa, H. D.}, year={2009}, month={Jan}, pages={169–182} }
 @article{zhu_ke_espinosa_2007, title={Experimental Techniques for the Mechanical Characterization of One-Dimensional Nanostructures}, volume={47}, ISSN={0014-4851 1741-2765}, url={http://dx.doi.org/10.1007/S11340-006-0406-6}, DOI={10.1007/S11340-006-0406-6}, number={1}, journal={Experimental Mechanics}, publisher={Springer Science and Business Media LLC}, author={Zhu, Y. and Ke, C. and Espinosa, H. D.}, year={2007}, month={Jan}, pages={7–24} }
 @article{zhu_corigliano_espinosa_2006, title={A thermal actuator for nanoscale in situ microscopy testing: design and characterization}, volume={16}, ISSN={0960-1317 1361-6439}, url={http://dx.doi.org/10.1088/0960-1317/16/2/008}, DOI={10.1088/0960-1317/16/2/008}, abstractNote={This paper addresses the design and optimization of thermal actuators employed in a novel MEMS-based material testing system. The testing system is designed to measure the mechanical properties of a variety of materials/structures from thin films to one-dimensional structures, e.g. carbon nanotubes (CNTs) and nanowires (NWs). It includes a thermal actuator and a capacitive load sensor with a specimen in-between. The thermal actuator consists of a number of V-shaped beams anchored at both ends. It is capable of generating tens of milli-Newton force and a few micrometers displacement depending on the beams' angle and their number. Analytical expressions of the actuator thermomechanical response are derived and discussed. From these expressions, a number of design criteria are drawn and used to optimize the device response. The analytical predictions are compared with both finite element multiphysics analysis (FEA) and experiments. To demonstrate the actuator performance, polysilicon freestanding specimens cofabricated with the testing system are tested.}, number={2}, journal={Journal of Micromechanics and Microengineering}, publisher={IOP Publishing}, author={Zhu, Yong and Corigliano, Alberto and Espinosa, Horacio D}, year={2006}, month={Feb}, pages={242–253} }
 @article{zhu_moldovan_espinosa_2005, title={A microelectromechanical load sensor for in situ electron and x-ray microscopy tensile testing of nanostructures}, volume={86}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1844594}, DOI={10.1063/1.1844594}, abstractNote={We report on the performance of a microelectromechanical system (MEMS) designed for the in situ electron and x-ray microscopy tensile testing of nanostructures, e.g., carbon nanotubes and nanowires. The device consists of an actuator and a load sensor with a gap in between, across which nanostructures can be placed, nanowelded, and mechanically tested. The load sensor is based on differential capacitance measurements, from which its displacement history is recorded. By determining the sensor stiffness, the load history during the testing is obtained. We calibrated the device and examined its resolution in the context of various applications of interest. The device is the first true MEMS in which the load is electronically measured. It is designed to be placed in scanning and transmission electron microscopes and on x-ray synchrotron stages.}, number={1}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Zhu, Yong and Moldovan, N. and Espinosa, Horacio D.}, year={2005}, month={Jan}, pages={013506} }
 @article{zhu_espinosa_2005, title={An electromechanical material testing system for in situ electron microscopy and applications}, volume={102}, ISSN={0027-8424 1091-6490}, url={http://dx.doi.org/10.1073/pnas.0506544102}, DOI={10.1073/pnas.0506544102}, abstractNote={We report the development of a material testing system forin situelectron microscopy (EM) mechanical testing of nanostructures. The testing system consists of an actuator and a load sensor fabricated by means of surface micromachining. This previously undescribed nanoscale material testing system makes possible continuous observation of the specimen deformation and failure with subnanometer resolution, while simultaneously measuring the applied load electronically with nanonewton resolution. This achievement was made possible by the integration of electromechanical and thermomechanical components based on microelectromechanical system technology. The system capabilities are demonstrated by thein situEM testing of free-standing polysilicon films, metallic nanowires, and carbon nanotubes. In particular, a previously undescribed real-time instrumentedin situtransmission EM observation of carbon nanotubes failure under tensile load is presented here.}, number={41}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Zhu, Y. and Espinosa, H. D.}, year={2005}, month={Sep}, pages={14503–14508} }
 @article{bažant_guo_espinosa_zhu_peng_2005, title={Epitaxially influenced boundary layer model for size effect in thin metallic films}, volume={97}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1861150}, DOI={10.1063/1.1861150}, abstractNote={It is shown that the size effect recently observed by Espinosa et al., [J. Mech. Phys. Solids51, 47 (2003)] in pure tension tests on free thin metallic films can be explained by the existence of a boundary layer of fixed thickness, located at the surface of the film that was attached onto the substrate during deposition. The boundary layer is influenced by the epitaxial effects of crystal growth on the dislocation density and texture (manifested by prevalent crystal plane orientations). This influence is assumed to cause significantly elevated yield strength. Furthermore, the observed gradual postpeak softening, along with its size independence, which is observed in short film strips subjected to pure tension, is explained by slip localization, originating at notch-like defects, and by damage, which can propagate in a stable manner when the film strip under pure tension is sufficiently thin and short. For general applications, the present epitaxially influenced boundary layer model may be combined with the classical strain-gradient plasticity proposed by Gao et al., [J. Mech. Phys. Solids 47, 1239 (1999)], and it is shown that this combination is necessary to fit the test data on both pure tension and bending of thin films by one and the same theory. To deal with films having different crystal grain sizes, the Hall–Petch relation for the yield strength dependence on the grain size needs to be incorporated into the combined theory. For very thin films, in which a flattened grain fills the whole film thickness, the Hall–Petch relation needs a cutoff, and the asymptotic increase of yield strength with diminishing film thickness is then described by the extension of Nix’s model of misfit dislocations by Zhang and Zhou [J. Adv. Mater. 38, 51 (2002)]. The final result is a proposal of a general theory for strength, size effect, hardening, and softening of thin metallic films.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bažant, Zdeněk P. and Guo, Zaoyang and Espinosa, Horacio D. and Zhu, Yong and Peng, Bei}, year={2005}, month={Apr}, pages={073506} }
 @article{zhu_espinosa_2004, title={Effect of temperature on capacitive RF MEMS switch performance—a coupled-field analysis}, volume={14}, ISSN={0960-1317 1361-6439}, url={http://dx.doi.org/10.1088/0960-1317/14/8/021}, DOI={10.1088/0960-1317/14/8/021}, abstractNote={Three-dimensional multiphysics finite element analysis (FEA) was performed to investigate the reliability of RF MEMS switches at various operational temperatures. The investigated MEMS capacitive switch consists of a freestanding metal membrane actuated by a bottom electrode coated by a dielectric film. Coupled-field simulations between thermal, structural and electrostatic domains were performed. The simulations show that temperature significantly changes both the membrane stress state and out-of-plane geometry. In particular, the membrane buckles when temperature increase, from room temperature, takes place. The buckling temperature, i.e. the upper bound to the operational temperature, is a function of manufacturing residual stress state, membrane initial out-of-plane profile and a mismatch in materials coefficient of thermal expansion. The analysis also shows that temperature reduction, from room temperature to −40 °C, causes an increase in pull-in voltage to values that could compromise the switch reliability as a result of charge build-up in the dielectric layer. Our analyses illustrate that by proper designing of the membrane out-of-plane profile, it is possible to keep the pull-in voltage, at all operational temperatures, within allowable values. This design feature of RF MEMS switches offers an effective way to achieve reliable pull-in voltages in applications where large temperature variations are expected such as in satellites and airplane condition monitoring based on wireless communication.}, number={8}, journal={Journal of Micromechanics and Microengineering}, publisher={IOP Publishing}, author={Zhu, Yong and Espinosa, Horacio D}, year={2004}, month={Jun}, pages={1270–1279} }
 @article{zhu_espinosa_2004, title={Reliability of capacitive RF MEMS switches at high and low temperatures}, volume={14}, ISSN={1096-4290 1099-047X}, url={http://dx.doi.org/10.1002/mmce.20015}, DOI={10.1002/mmce.20015}, abstractNote={Some applications of RF MEMS switches, such as aircraft condition monitoring and distributed satellite communication, present a unique challenge for device design and reliability. This article examines these switches when operational temperatures in the range −60°C to 100°C are envisioned. The basic operation of a capacitive MEMS switch is described and two tools for examining device reliability, modeling, and on‐chip experimentation, are discussed in the case of capacitive MEMS switches. 1D, 2D, and 3D models are presented with emphasis on 3D coupled‐field finite‐element analysis, including temperature effects. Results and findings from the 3D simulations are reported. In particular, the advantages of employing corrugated membranes in the design of RF MEMS switches are assessed. Their performance in terms of reliability as a function of temperature is quantified. The effects of corrugation on the geometric parameters are discussed in the context of device‐design optimization. In order to assess reliability experimentally, the M‐test and the membrane deflection experiment (MDE) are reviewed due to their on‐chip characteristic and simplicity. Ways in which these experimental/computational methodologies can be combined for identifying material properties and device performance is also highlighted. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 317–328, 2004.}, number={4}, journal={International Journal of RF and Microwave Computer-Aided Engineering}, publisher={Wiley}, author={Zhu, Yong and Espinosa, Horacio D.}, year={2004}, pages={317–328} }