@article{sakorikar_mihaliak_krisnadi_ma_kim_kong_awartani_dickey_2024, title={A Guide to Printed Stretchable Conductors}, volume={1}, ISSN={["1520-6890"]}, url={https://doi.org/10.1021/acs.chemrev.3c00569}, DOI={10.1021/acs.chemrev.3c00569}, abstractNote={Printing of stretchable conductors enables the fabrication and rapid prototyping of stretchable electronic devices. For such applications, there are often specific process and material requirements such as print resolution, maximum strain, and electrical/ionic conductivity. This review highlights common printing methods and compatible inks that produce stretchable conductors. The review compares the capabilities, benefits, and limitations of each approach to help guide the selection of a suitable process and ink for an intended application. We also discuss methods to design and fabricate ink composites with the desired material properties (e.g., electrical conductance, viscosity, printability). This guide should help inform ongoing and future efforts to create soft, stretchable electronic devices for wearables, soft robots, e-skins, and sensors.}, journal={CHEMICAL REVIEWS}, author={Sakorikar, Tushar and Mihaliak, Nikolas and Krisnadi, Febby and Ma, Jinwoo and Kim, Tae-il and Kong, Minsik and Awartani, Omar and Dickey, Michael D.}, year={2024}, month={Jan} }
 @article{kanetkar_shah_krisnadi_uppal_gandhi_dickey_wang_rykaczewski_2024, title={Particle-assisted formation of oil-in-liquid metal emulsions}, url={https://doi.org/10.1088/1361-648X/ad6521}, DOI={10.1088/1361-648X/ad6521}, abstractNote={Abstract Gallium-based liquid metals (LM) have surface tension an order of magnitude higher than water and break up into micro-droplets when mixed with other liquids. In contrast, silicone oil readily mixes into LM foams to create oil-in-LM emulsions with oil inclusions. Previously, the LM was foamed through rapid mixing in air for an extended duration (over 2 hours). This process first results in the internalization of oxide flakes that form at the air-liquid interface. Once a critical fraction of these randomly shaped solid flakes is reached, air bubbles internalize into the LM to create foams that can internalize secondary liquids. Here, we introduce an alternative oil-in-LM emulsion fabrication method that relies on the prior addition of SiO2 micro-particles into the LM before mixing it with the silicone oil. This particle-assisted emulsion formation process provides a higher control over the composition of the LM-particle mixture before oil addition, which we employ to systematically study the impact of particle characteristics and content on the emulsions' composition and properties. We demonstrate that the solid particle size (0.8 µm to 5 µm) and volume fraction (1% to 10%) have a negligible impact on the internalization of the oil inclusions. The inclusions are mostly spherical with diameters of 20 to 100 µm diameter and are internalized by forming new, rather than filling old, geometrical features. We also study the impact of the particle characteristics on the two key properties related to the functional application of the LM emulsions in the thermal management of microelectronics. In particular, we measure the impact of particles and silicone oil on the emulsion's thermal conductivity and its ability to prevent deleterious gallium-induced corrosion and embrittlement of contacting metal substrates.
}, journal={Journal of Physics: Condensed Matter}, author={Kanetkar, Shreyas and Shah, Najam Ul H and Krisnadi, Febby and Uppal, Aastha and Gandhi, Rohit M and Dickey, Michael D and Wang, Robert Y and Rykaczewski, Konrad}, year={2024}, month={Jul} }
 @article{krisnadi_kim_im_chacko_vong_rykaczewski_park_dickey_2024, title={Printable Liquid Metal Foams That Grow When Watered}, volume={1}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202308862}, DOI={10.1002/adma.202308862}, abstractNote={Abstract}, journal={ADVANCED MATERIALS}, author={Krisnadi, Febby and Kim, Seoyeon and Im, Sooik and Chacko, Dennis and Vong, Man Hou and Rykaczewski, Konrad and Park, Sungjune and Dickey, Michael D.}, year={2024}, month={Jan} }
 @article{shen_jiang_wang_song_vong_jung_krisnadi_kan_zheng_fu_et al._2023, title={Liquid metal-based soft, hermetic, and wireless-communicable seals for stretchable systems}, volume={379}, ISSN={["1095-9203"]}, url={https://doi.org/10.1126/science.ade7341}, DOI={10.1126/science.ade7341}, abstractNote={Soft materials tend to be highly permeable to gases, making it difficult to create stretchable hermetic seals. With the integration of spacers, we demonstrate the use of liquid metals, which show both metallic and fluidic properties, as stretchable hermetic seals. Such soft seals are used in both a stretchable battery and a stretchable heat transfer system that involve volatile fluids, including water and organic fluids. The capacity retention of the battery was ~72.5% after 500 cycles, and the sealed heat transfer system showed an increased thermal conductivity of approximately 309 watts per meter-kelvin while strained and heated. Furthermore, with the incorporation of a signal transmission window, we demonstrated wireless communication through such seals. This work provides a route to create stretchable yet hermetic packaging design solutions for soft devices.}, number={6631}, journal={SCIENCE}, author={Shen, Qingchen and Jiang, Modi and Wang, Ruitong and Song, Kexian and Vong, Man Hou and Jung, Woojin and Krisnadi, Febby and Kan, Ruyu and Zheng, Feiyu and Fu, Benwei and et al.}, year={2023}, month={Feb}, pages={488–493} }
 @article{ma_krisnadi_vong_kong_awartani_dickey_2023, title={Shaping a Soft Future: Patterning Liquid Metals}, volume={3}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202205196}, DOI={10.1002/adma.202205196}, abstractNote={Abstract}, journal={ADVANCED MATERIALS}, author={Ma, Jinwoo and Krisnadi, Febby and Vong, Man Hou and Kong, Minsik and Awartani, Omar M. and Dickey, Michael D.}, year={2023}, month={Mar} }
 @article{ankit_krisnadi_pethe_lim_kulkarni_accoto_mathews_2021, title={MXene incorporated polymeric hybrids for stiffness modulation in printed adaptive surfaces}, url={https://doi.org/10.1016/j.nanoen.2021.106548}, DOI={10.1016/j.nanoen.2021.106548}, abstractNote={Polymeric materials systems developed for actuators and human-machine interfaces suffer from limitations associated with effective force output due to their low mechanical modulus. New material solutions which can provide intrinsic multi-modal responses are needed to reversibly modulate rigidity; to be flexible, stretchable and bendable one moment, and to be rigid, able to bear load and resist deformation at another moment. Thermally modulated phase transition materials are promising for modulation of mechanical properties; however, they have not been explored for electrically driven shape morphing and responsive surfaces which require favourable electrical properties too. Polymers like polyethylene glycol (PEG) allow for low melting point (56 ℃) and high dielectric constant (10), however they are limited by slow crystallization kinetics and large temperature window. We architect an MXene incorporated PEG-water hybrid which allows for both reduction in melting point and rapid heterogeneous nucleation, which in turn increases the crystallization point. Multimodal response is demonstrated via thermal and electrical input, resulting in modulation of 700 times in Young's modulus, 100 times in flexural modulus and 10 times in hardness as well as large actuation strains (~28%) at low electric fields (~0.7 V/µm). They can be printed to create hardness domains, allowing for local and programmable modulation. An all-printed haptic device with an array of 3 × 3 pixels has been demonstrated, capable of independently varying the hardness values for each pixel.}, journal={Nano Energy}, author={Ankit and Krisnadi, Febby and Pethe, Shreyas and Lim, Kwang Jen Ryan and Kulkarni, Mohit Rameshchandra and Accoto, Dino and Mathews, Nripan}, year={2021}, month={Dec} }
 @misc{kwon_truong_krisnadi_im_ma_mehrabian_kim_dickey_2021, title={Surface Modification of Gallium-Based Liquid Metals: Mechanisms and Applications in Biomedical Sensors and Soft Actuators}, volume={3}, ISSN={["2640-4567"]}, url={http://dx.doi.org/10.1002/aisy.202000159}, DOI={10.1002/aisy.202000159}, abstractNote={This review focuses on surface modifications to gallium‐based liquid metals (LMs), which are stretchable conductors with metallic conductivity and nearly unlimited extensibility due to their liquid nature. Despite the enormous surface tension of LM, it can be patterned into nonspherical shapes, such as wires, due to the presence of a native oxide shell. Incorporating inherently soft LM into elastomeric devices offers comfort, mechanical compliance, and stretchability. The thin oxide layer also enables the formation of stable liquid colloids and LM micro/nanosized droplets that do not coalesce easily. The oxide layer can also be exfoliated and chemically modified into semiconductor 2D materials to create and deposit atomically thin materials at room temperature. Thus, the interface and its manipulation are important. This review summarizes physical and chemical methods of modifying the surface of LM to tune its properties. The surface modification of LM provides unique applications, including use in soft biomedical sensors and actuators with mechanical properties similar to human tissue.}, number={3}, journal={ADVANCED INTELLIGENT SYSTEMS}, author={Kwon, Ki Yoon and Truong, Vi Khanh and Krisnadi, Febby and Im, Sooik and Ma, Jinwoo and Mehrabian, Nazgol and Kim, Tae-il and Dickey, Michael D.}, year={2021}, month={Mar} }
 @article{krisnadi_nguyen_ankit_ma_kulkarni_mathews_dickey_2020, title={Directed Assembly of Liquid Metal–Elastomer Conductors for Stretchable and Self‐Healing Electronics}, url={http://dx.doi.org/10.1002/adma.202001642}, DOI={10.1002/adma.202001642}, abstractNote={Abstract}, journal={Advanced Materials}, author={Krisnadi, Febby and Nguyen, Linh Lan and Ankit and Ma, Jinwoo and Kulkarni, Mohit Rameshchandra and Mathews, Nripan and Dickey, Michael}, year={2020}, month={Jul} }
 @article{ankit_tiwari_ho_krisnadi_kulkarni_nguyen_koh_mathews_2020, title={High-k, Ultrastretchable Self-Enclosed Ionic Liquid-Elastomer Composites for Soft Robotics and Flexible Electronics}, url={http://dx.doi.org/10.1021/acsami.0c08754}, DOI={10.1021/acsami.0c08754}, abstractNote={Soft robotics focuses on mimicking natural systems to produce dexterous motion. Dielectric elastomer actuators (DEAs) are an attractive option due to their large strains, high efficiencies, lightweight design, and integrability, but require high electric fields. Conventional approaches to improve DEA performance by incorporating solid fillers in the polymer matrices can increase the dielectric constant but to the detriment of mechanical properties. In the present work, we draw inspiration from soft and deformable human skin, enabled by its unique structure, which consists of a fluid-filled membrane, to create self-enclosed liquid filler (SELF)-polymer composites by mixing an ionic liquid into the elastomeric matrix. Unlike hydrogels and ionogels, the SELF-polymer composites are made from immiscible liquid fillers, selected based on interfacial interaction with the elastomer matrix, and exist as dispersed globular phases. This combination of structure and filler selection unlocks synergetic improvements in electromechanical properties-doubling of dielectric constant, 100 times decrease in Young's modulus, and ∼5 times increase in stretchability. These composites show superior thermal stability to volatile losses, combined with excellent transparency. These ultrasoft high-k composites enable a significant improvement in the actuation performance of DEAs-longitudinal strain (5 times) and areal strain (8 times)-at low applied nominal electric fields (4 V/μm). They also enable high-sensitivity capacitive pressure sensors without the need of miniaturization and microstructuring. This class of self-enclosed ionic liquid polymer composites could impact the areas of soft robotics, shape morphing, flexible electronics, and optoelectronics.}, journal={ACS Applied Materials & Interfaces}, author={Ankit and Tiwari, Naveen and Ho, Fanny and Krisnadi, Febby and Kulkarni, Mohit Rameshchandra and Nguyen, Linh Lan and Koh, Soo Jin Adrian and Mathews, Nripan}, year={2020}, month={Aug} }
 @inproceedings{ankit_chan_nguyen_krisnadi_mathews_2019, title={Large-area, flexible, integrable and transparent DEAs for haptics}, url={http://dx.doi.org/10.1117/12.2514267}, DOI={10.1117/12.2514267}, abstractNote={With the focus on providing a sense of touch in robots, enabling feedback in virtual reality (VR) and augmented reality (AR) environment, telerobotics, remote sensing and improving user experience with touch sensitive devices like display kiosks and smartphones, haptic interfaces have become critical as they can convey information quickly. A human hand can feel different physical parameters such as roughness, softness and vibration and discern them as textures of the surface. Most of the technologies being employed for haptic feedback currently rely on simulating the perception of texture change, however few of the technologies like microfluidics and electroactive polymers (EAPs) can create actual topographical changes on the surface. Additionally, most of these haptic devices are opaque and they often serve as mere touchpads whilst the visual component of the simulation is projected elsewhere, so the user appears to interact with the simulated object indirectly. Dielectric elastomer actuators (DEAs), an EAP, is of peculiar interest owing to their characteristics like large actuation strains, facile fabrication, low costs of manufacturing and low power consumption. Herein, we demonstrate a large area, transparent tactile feedback device with 4 individually controlled active regions, that can be integrated onto electronic displays to provide unobstructed topographic texture change. We fabricate the device in a unique architecture, with the elastomeric layer, compliant electrodes, and the soft passive layer as all transparent materials. These devices show high transparency of over 70% in the visible region of the spectrum, and surface deformation of ~165 μm.}, booktitle={Electroactive Polymer Actuators and Devices (EAPAD) XXI}, author={Ankit, Ankit and Chan, Jun Yu and Nguyen, Linh Lan and Krisnadi, Febby and Mathews, Nripan}, year={2019}, month={Mar} }