@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{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{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{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{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{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{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{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} }