Stanford Advisors

All Publications

  • A low-power stretchable neuromorphic nerve with proprioceptive feedback. Nature biomedical engineering Lee, Y., Liu, Y., Seo, D., Oh, J. Y., Kim, Y., Li, J., Kang, J., Kim, J., Mun, J., Foudeh, A. M., Bao, Z., Lee, T. 2022


    By relaying neural signals from the motor cortex to muscles, devices for neurorehabilitation can enhance the movement of limbs in which nerves have been damaged as a consequence of injuries affecting the spinal cord or the lower motor neurons. However, conventional neuroprosthetic devices are rigid and power-hungry. Here we report a stretchable neuromorphic implant that restores coordinated and smooth motions in the legs of mice with neurological motor disorders, enabling the animals to kick a ball, walk or run. The neuromorphic implant acts as an artificial efferent nerve by generating electrophysiological signals from excitatory post-synaptic signals and by providing proprioceptive feedback. The device operates at low power (~1/150 that of a typical microprocessor system), and consists of hydrogel electrodes connected to a stretchable transistor incorporating an organic semiconducting nanowire (acting as an artificial synapse), connected via an ion gel to an artificial proprioceptor incorporating a carbon nanotube strain sensor (acting as an artificial muscle spindle). Stretchable electronics with proprioceptive feedback may inspire the further development of advanced neuromorphic devices for neurorehabilitation.

    View details for DOI 10.1038/s41551-022-00918-x

    View details for PubMedID 35970931

  • Organic Neuro-Electronics: From Neural Interface to Neuroprosthetics. Advanced materials (Deerfield Beach, Fla.) Go, G. T., Lee, Y., Seo, D. G., Lee, T. W. 2022: e2201864


    This review outlines requirements and recent advances in research on organic neuro-electronics. Neuro-electronics such as neural interfaces and neuroprosthetics provide a promising approach to diagnose and treat neurological diseases. However, the current neural interfaces are rigid and not biocompatible, so they induce an immune response and deterioration of neural signal transmission. Organic materials are promising candidates for neural interfaces, due to mechanical softness, excellent electrochemical properties and biocompatibility. Also, organic nervetronics, which mimics functional properties of biological nerves system, is being developed to overcome limitations of complex and energy-consuming conventional neuroprosthetics that limit long-term implantations and daily-life usage. We review examples of organic materials for neural interfaces and neural signal recordings, and highlight recent advances of organic nervetronics that use organic artificial synapses are highlighted, then discuss further requirements for neuroprosthetics. Finally, we discuss future challenges that must be overcome to achieve ideal organic neuro-electronics for next-generation neuroprosthetics. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/adma.202201864

    View details for PubMedID 35925610

  • Neuromorphic Skin Based on Emerging Artificial Synapses ADVANCED MATERIALS TECHNOLOGIES Lee, Y., Oh, J., Lee, T. 2022
  • Standalone real-time health monitoring patch based on a stretchable organic optoelectronic system. Science advances Lee, Y., Chung, J. W., Lee, G. H., Kang, H., Kim, J., Bae, C., Yoo, H., Jeong, S., Cho, H., Kang, S., Jung, J. Y., Lee, D., Gam, S., Hahm, S. G., Kuzumoto, Y., Kim, S. J., Bao, Z., Hong, Y., Yun, Y., Kim, S. 2021; 7 (23)


    Skin-like health care patches (SHPs) are next-generation health care gadgets that will enable seamless monitoring of biological signals in daily life. Skin-conformable sensors and a stretchable display are critical for the development of standalone SHPs that provide real-time information while alleviating privacy concerns related to wireless data transmission. However, the production of stretchable wearable displays with sufficient pixels to display this information remains challenging. Here, we report a standalone organic SHP that provides real-time heart rate information. The 15-mum-thick SHP comprises a stretchable organic light-emitting diode display and stretchable organic photoplethysmography (PPG) heart rate sensor on all-elastomer substrate and operates stably under 30% strain using a combination of stress relief layers and deformable micro-cracked interconnects that reduce the mechanical stress on the active optoelectronic components. This approach provides a rational strategy for high-resolution stretchable displays, enabling the production of ideal platforms for next-generation wearable health care electronics.

    View details for DOI 10.1126/sciadv.abg9180

    View details for PubMedID 34088675

  • Stretchable self-healable semiconducting polymer film for active-matrix strain-sensing array. Science advances Oh, J. Y., Son, D., Katsumata, T., Lee, Y., Kim, Y., Lopez, J., Wu, H., Kang, J., Park, J., Gu, X., Mun, J., Wang, N. G., Yin, Y., Cai, W., Yun, Y., Tok, J. B., Bao, Z. 2019; 5 (11): eaav3097


    Skin-like sensory devices should be stretchable and self-healable to meet the demands for future electronic skin applications. Despite recent notable advances in skin-inspired electronic materials, it remains challenging to confer these desired functionalities to an active semiconductor. Here, we report a strain-sensitive, stretchable, and autonomously self-healable semiconducting film achieved through blending of a polymer semiconductor and a self-healable elastomer, both of which are dynamically cross-linked by metal coordination. We observed that by controlling the percolation threshold of the polymer semiconductor, the blend film became strain sensitive, with a gauge factor of 5.75 * 105 at 100% strain in a stretchable transistor. The blend film is also highly stretchable (fracture strain, >1300%) and autonomously self-healable at room temperature. We proceed to demonstrate a fully integrated 5 * 5 stretchable active-matrix transistor sensor array capable of detecting strain distribution through surface deformation.

    View details for DOI 10.1126/sciadv.aav3097

    View details for PubMedID 31723597

  • Stretchable organic optoelectronic sensorimotor synapse. Science advances Lee, Y., Oh, J. Y., Xu, W., Kim, O., Kim, T. R., Kang, J., Kim, Y., Son, D., Tok, J. B., Park, M. J., Bao, Z., Lee, T. 2018; 4 (11): eaat7387


    Emulation of human sensory and motor functions becomes a core technology in bioinspired electronics for next-generation electronic prosthetics and neurologically inspired robotics. An electronic synapse functionalized with an artificial sensory receptor and an artificial motor unit can be a fundamental element of bioinspired soft electronics. Here, we report an organic optoelectronic sensorimotor synapse that uses an organic optoelectronic synapse and a neuromuscular system based on a stretchable organic nanowire synaptic transistor (s-ONWST). The voltage pulses of a self-powered photodetector triggered by optical signals drive the s-ONWST, and resultant informative synaptic outputs are used not only for optical wireless communication of human-machine interfaces but also for light-interactive actuation of an artificial muscle actuator in the same way that a biological muscle fiber contracts. Our organic optoelectronic sensorimotor synapse suggests a promising strategy toward developing bioinspired soft electronics, neurologically inspired robotics, and electronic prostheses.

    View details for PubMedID 30480091

  • Stretchable organic optoelectronic sensorimotor synapse SCIENCE ADVANCES Lee, Y., Oh, J., Xu, W., Kim, O., Kim, T., Kang, J., Kim, Y., Son, D., Tok, J., Park, M., Bao, Z., Lee, T. 2018; 4 (11)
  • An integrated self-healable electronic skin system fabricated via dynamic reconstruction of a nanostructured conducting network NATURE NANOTECHNOLOGY Son, D., Kang, J., Vardoulis, O., Kim, Y., Matsuhisa, N., Oh, J., To, J. F., Mun, J., Katsumata, T., Liu, Y., McGuire, A. F., Krason, M., Molina-Lopez, F., Ham, J., Kraft, U., Lee, Y., Yun, Y., Tok, J., Bao, Z. 2018; 13 (11): 1057-+
  • An integrated self-healable electronic skin system fabricated via dynamic reconstruction of a nanostructured conducting network. Nature nanotechnology Son, D., Kang, J., Vardoulis, O., Kim, Y., Matsuhisa, N., Oh, J. Y., To, J. W., Mun, J., Katsumata, T., Liu, Y., McGuire, A. F., Krason, M., Molina-Lopez, F., Ham, J., Kraft, U., Lee, Y., Yun, Y., Tok, J. B., Bao, Z. 2018


    Electronic skin devices capable of monitoring physiological signals and displaying feedback information through closed-loop communication between the user and electronics are being considered for next-generation wearables and the 'Internet of Things'. Such devices need to be ultrathin to achieve seamless and conformal contact with the human body, to accommodate strains from repeated movement and to be comfortable to wear. Recently, self-healing chemistry has driven important advances in deformable and reconfigurable electronics, particularly with self-healable electrodes as the key enabler. Unlike polymer substrates with self-healable dynamic nature, the disrupted conducting network is unable to recover its stretchability after damage. Here, we report the observation of self-reconstruction of conducting nanostructures when in contact with a dynamically crosslinked polymer network. This, combined with the self-bonding property of self-healing polymer, allowed subsequent heterogeneous multi-component device integration of interconnects, sensors and light-emitting devices into a single multi-functional system. This first autonomous self-healable and stretchable multi-component electronic skin paves the way for future robust electronics.

    View details for PubMedID 30127474

  • A bioinspired flexible organic artificial afferent nerve SCIENCE Kim, Y., Chortos, A., Xu, W., Liu, Y., Oh, J., Son, D., Kang, J., Foudeh, A. M., Zhu, C., Lee, Y., Niu, S., Liu, J., Pfattner, R., Bao, Z., Lee, T. 2018; 360 (6392): 998-+


    The distributed network of receptors, neurons, and synapses in the somatosensory system efficiently processes complex tactile information. We used flexible organic electronics to mimic the functions of a sensory nerve. Our artificial afferent nerve collects pressure information (1 to 80 kilopascals) from clusters of pressure sensors, converts the pressure information into action potentials (0 to 100 hertz) by using ring oscillators, and integrates the action potentials from multiple ring oscillators with a synaptic transistor. Biomimetic hierarchical structures can detect movement of an object, combine simultaneous pressure inputs, and distinguish braille characters. Furthermore, we connected our artificial afferent nerve to motor nerves to construct a hybrid bioelectronic reflex arc to actuate muscles. Our system has potential applications in neurorobotics and neuroprosthetics.

    View details for PubMedID 29853682

  • Tough and Water-Insensitive Self-Healing Elastomer for Robust Electronic Skin ADVANCED MATERIALS Kang, J., Son, D., Wang, G., Liu, Y., Lopez, J., Kim, Y., Oh, J., Katsumata, T., Mun, J., Lee, Y., Jin, L., Tok, J., Bao, Z. 2018; 30 (13): e1706846


    An electronic (e-) skin is expected to experience significant wear and tear over time. Therefore, self-healing stretchable materials that are simultaneously soft and with high fracture energy, that is high tolerance of damage or small cracks without propagating, are essential requirements for the realization of robust e-skin. However, previously reported elastomers and especially self-healing polymers are mostly viscoelastic and lack high mechanical toughness. Here, a new class of polymeric material crosslinked through rationally designed multistrength hydrogen bonding interactions is reported. The resultant supramolecular network in polymer film realizes exceptional mechanical properties such as notch-insensitive high stretchability (1200%), high toughness of 12 000 J m-2 , and autonomous self-healing even in artificial sweat. The tough self-healing materials enable the wafer-scale fabrication of robust and stretchable self-healing e-skin devices, which will provide new directions for future soft robotics and skin prosthetics.

    View details for PubMedID 29424026

  • Deformable Organic Nanowire Field-Effect Transistors ADVANCED MATERIALS Lee, Y., Oh, J., Kim, T., Gu, X., Kim, Y., Wang, G., Wu, H., Pfattner, R., To, J. F., Katsumata, T., Son, D., Kang, J., Matthews, J. R., Niu, W., He, M., Sinclair, R., Cui, Y., Tok, J., Lee, T., Bao, Z. 2018; 30 (7)
  • Deformable Organic Nanowire Field-Effect Transistors. Advanced materials (Deerfield Beach, Fla.) Lee, Y., Oh, J. Y., Kim, T. R., Gu, X., Kim, Y., Wang, G. N., Wu, H. C., Pfattner, R., To, J. W., Katsumata, T., Son, D., Kang, J., Matthews, J. R., Niu, W., He, M., Sinclair, R., Cui, Y., Tok, J. B., Lee, T. W., Bao, Z. 2018; 30 (7)


    Deformable electronic devices that are impervious to mechanical influence when mounted on surfaces of dynamically changing soft matters have great potential for next-generation implantable bioelectronic devices. Here, deformable field-effect transistors (FETs) composed of single organic nanowires (NWs) as the semiconductor are presented. The NWs are composed of fused thiophene diketopyrrolopyrrole based polymer semiconductor and high-molecular-weight polyethylene oxide as both the molecular binder and deformability enhancer. The obtained transistors show high field-effect mobility >8 cm2 V-1 s-1 with poly(vinylidenefluoride-co-trifluoroethylene) polymer dielectric and can easily be deformed by applied strains (both 100% tensile and compressive strains). The electrical reliability and mechanical durability of the NWs can be significantly enhanced by forming serpentine-like structures of the NWs. Remarkably, the fully deformable NW FETs withstand 3D volume changes (>1700% and reverting back to original state) of a rubber balloon with constant current output, on the surface of which it is attached. The deformable transistors can robustly operate without noticeable degradation on a mechanically dynamic soft matter surface, e.g., a pulsating balloon (pulse rate: 40 min-1 (0.67 Hz) and 40% volume expansion) that mimics a beating heart, which underscores its potential for future biomedical applications.

    View details for DOI 10.1002/adma.201704401

    View details for PubMedID 29315845