Research Publications
Peer-reviewed international scientific journal articlesSelected Publications
Tension-driven three-dimensional printing of free-standing Field’s metal structures
Shaohua Ling, Xi Tian, Qihang Zeng, Zhihang Qin, Selman A. Kurt, Yu Jun Tan, Jerry Y.H. Fuh, Zhuangjian Liu, Michael D.Dickey, John S.Ho*, Benjamin C.-K. Tee*
Nature Electronics, 2024
The direct writing of complex three-dimensional (3D) metallic structures is of use in the development of advanced electronics. However, conventional direct ink writing primarily uses composite inks that have low electrical conductivity and require support materials to create 3D architectures. Here we show that Field’s metal—a eutectic alloy with a relatively low melting point—can be 3D printed using a process in which tension between the molten metal in a nozzle and the leading edge of the printed part allows 3D structures to be directly written. The use of tension avoids using external pressure for extrusion (which can cause beading of the printed structure), allowing uniform and smooth microwire structures to be printed on various substrates with speeds of up to 100 mm•s^(-1). We use the approach to print various free-standing 3D structures—including vertical letters, a cubic framework and scalable helixes—without post-treatment, and the resulting Field’s metal structures can offer electrical conductivity of 2 × 10^4 S•cm^(-1), self-healing capability and recyclability. We also use the technique to print a 3D circuit for wearable battery-free temperature sensing, hemispherical helical antennas for wireless vital sign monitoring and 3D metamaterials for electromagnetic-wave manipulation.
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A novel technique to fabricate three-dimensional circuits for advanced electronics
Frictionless multiphasic interface for near-ideal aero-elastic pressure sensing
Wen Cheng, Xinyu Wang, Ze Xiong, Jun Liu, Zhuangjian Liu, Yunxia Jin, Haicheng Yao, Tak-Sing Wong, John S Ho, and Benjamin C.-K. Tee*
Nature Materials, 2023
Conventional pressure sensors rely on solid sensing elements. Instead, inspired by the air entrapment phenomenon on the surfaces of submerged lotus leaves, we designed a pressure sensor that uses the solid–liquid–liquid–gas multiphasic interfaces and the trapped elastic air layer to modulate capacitance changes with pressure at the interfaces. By creating an ultraslippery interface and structuring the electrodes at the nanoscale and microscale, we achieve near-friction-free contact line motion and thus near-ideal pressure-sensing performance. Using a closed-cell pillar array structure in synergy with the ultraslippery electrode surface, our sensor achieved outstanding linearity (R^2 = 0.99944±0.00015; nonlinearity, 1.49±0.17%) while simultaneously possessing ultralow hysteresis (1.34±0.20%) and very high sensitivity (79.1±4.3 pF kPa^(-1)). The sensor can operate under turbulent flow, in in vivo biological environments and during laparoscopic procedures. We anticipate that such a strategy will enable ultrasensitive and ultraprecise pressure monitoring in complex fluid environments with performance beyond the reach of the current state-of-the-art.
Highlight in Nature Materials research briefing
Designing air-entrapment interfaces for near-ideal pressure sensors
Battery-free and AI-enabled multiplexed sensor patches for wound monitoring
Xin Ting Zheng, Zijie Yang, Laura Sutarlie, Moogaambikai Thangaveloo, Yong Yu, Nur Asinah Binte Mohamed Salleh, Jiah Shin Chin, Ze Xiong, David Lawrence Becker, Xian Jun Loh, Benjamin C.-K. Tee* and Xiaodi Su
Science Advances, 2023
Wound healing is a dynamic process with multiple phases. Rapid profiling and quantitative characterization of inflammation and infection remain challenging. We report a paper-like battery-free in situ AI-enabled multiplexed (PETAL) sensor for holistic wound assessment by leveraging deep learning algorithms. This sensor consists of a wax-printed paper panel with five colorimetric sensors for temperature, pH, trimethylamine, uric acid, and moisture. Sensor images captured by a mobile phone were analyzed by neural network–based machine learning algorithms to determine healing status. For ex situ detection via exudates collected from rat perturbed wounds and burn wounds, the PETAL sensor can classify healing versus nonhealing status with an accuracy as high as 97%. With the sensor patches attached on rat burn wound models, in situ monitoring of wound progression or severity is demonstrated. This PETAL sensor allows early warning of adverse events, which could trigger immediate clinical intervention to facilitate wound care management.
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PETAL bandage gives live reports on wounds, so they can be left alone
Artificially innervated self-healing foams as synthetic piezo-impedance sensor skins
Hongchen Guo, Yu Jun Tan, Ge Chen, Zifeng Wang, Glenys Jocelin Susanto, Hian Hian See, Zijie Yang, Zi Wei Lim, Le Yang & Benjamin C.-K. Tee*
Nature Communications, 2020
Human skin is a self-healing mechanosensory system that detects various mechanical contact forces efficiently through three-dimensional innervations. Here, we propose a biomimetic artificially innervated foam by embedding three-dimensional electrodes within a new low-modulus self-healing foam material. The foam material is synthesized from a one-step self-foaming process. By tuning the concentration of conductive metal particles in the foam at near-percolation, we demonstrate that it can operate as a piezo-impedance sensor in both piezoresistive and piezocapacitive sensing modes without the need for an encapsulation layer. The sensor is sensitive to an object’s contact force directions as well as to human proximity. Moreover, the foam material self-heals autonomously with immediate function restoration despite mechanical damage. It further recovers from mechanical bifurcations with gentle heating (70?°C). We anticipate that this material will be useful as damage robust human-machine interfaces.
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A transparent, self-healing and high-k dielectric for low-field-emission stretchable optoelectronics
Yu Jun Tan, Hareesh Godaba, Ge Chen, Siew Ting Melissa Tan, Guanxiang Wan, Guojingxian Li, Pui Mun Lee, Yongqing Cai, Si Li, Robert F. Shepherd, John S. Ho and Benjamin C.-K. Tee*
Nature Materials, 2019
Stretchable optoelectronic materials are essential for applications in wearable electronics, human–machine interfaces and soft robots. However, intrinsically stretchable optoelectronic devices such as light-emitting capacitors usually require high driving alternating voltages and excitation frequencies to achieve sufficient luminance in ambient lighting conditions. Here, we present a healable, low-field illuminating optoelectronic stretchable (HELIOS) device by introducing a transparent, high permittivity polymeric dielectric material. The HELIOS device turns on at an alternating voltage of 23?V and a frequency below 1?kHz, safe operating conditions for human–machine interactions. We achieved a brightness of 1,460?cd?m?2 at 2.5?V?µm?1 with stable illumination demonstrated up to a maximum of 800% strain. The materials also self-healed mechanically and electronically from punctures or when severed. We further demonstrate various HELIOS light-emitting capacitor devices in environment sensing using optical feedback. Moreover, our devices can be powered wirelessly, potentially enabling applications for untethered damage-resilient soft robots.
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A neuro-inspired artificial peripheral nervous system for scalable electronic skins
Wang Wei Lee, Yu Jun Tan, Haicheng Yao, Si Li, Hian Hian See, Matthew Hon, Kian Ann Ng, Betty Xiong, John S. Ho and Benjamin C.-K. Tee*
Science Robotics, 2019 (Selected as Cover)
The human sense of touch is essential for dexterous tool usage, spatial awareness, and social communication. Equipping intelligent human-like androids and prosthetics with electronic skins—a large array of sensors spatially distributed and capable of rapid somatosensory perception—will enable them to work collaboratively and naturally with humans to manipulate objects in unstructured living environments. Previously reported tactile-sensitive electronic skins largely transmit the tactile information from sensors serially, resulting in readout latency bottlenecks and complex wiring as the number of sensors increases. Here, we introduce the Asynchronously Coded Electronic Skin (ACES)—a neuromimetic architecture that enables simultaneous transmission of thermotactile information while maintaining exceptionally low readout latencies, even with array sizes beyond 10,000 sensors. We anticipate that the ACES platform can be integrated with a wide range of skin-like sensors for artificial intelligence (AI)–enhanced autonomous robots, neuroprosthetics, and neuromorphic computing hardware for dexterous object manipulation and somatosensory perception.
Self-healing Electronic skins for Aquatic Environments
Yue Cao, Yu Jun Tan, Si Li, Wang Wei Lee, Hongchen Guo, Yongqing Cai, Chao Wang, Benjamin C.-K. Tee*
Nature Electronics, 2019 (Selected as Cover)
Here we report a bio-inspired skin-like material that is transparent, electrically conductive and can autonomously self-heal in both dry and wet conditions. The material, which is composed of a fluorocarbon elastomer and a fluorine-rich ionic liquid, has an ionic conductivity that can be tuned to as high as 10e-3 S/cm and can withstand strains as high as 2,000%. Owing to ion–dipole interactions, it offers fast and repeatable electro-mechanical self-healing in wet, acidic and alkali environments. To illustrate the potential applications of the approach, we used our electronic skins to create touch, pressure and strain sensors. We also show that the material can be printed into soft and pliable ionic circuit boards.
Highlighted in News and Views article:
Soft circuits that self-heal under water, C. Majidi
Self-Healing Electronic Materials for a Smart and Sustainable Future
Yu Jun Tan, Jiake Wu, Hanying Li, Benjamin C-K. Tee*
ACS Appl. Mater. & Interfaces, 2018
The survivability of living organisms relies critically on their ability to self-heal from damage in unpredictable situations and environmental variability. Such abilities are most important in external facing organs such as the mammalian skin. However, the properties of bulk elemental materials are typically unable to perform self-repair. Consequently, most conventional smart electronic devices today are not designed to repair themselves when damaged. Thus, inspired by the remarkable capability of self-healing in natural systems, smart self-healing materials are being intensively researched to mimic natural systems to have the ability to partially or completely self-repair damages inflicted on them. This exciting area of research could potentially power a sustainable and smart future.
A skin-inspired organic digital mechanoreceptor
Benjamin C-K Tee*, A Chortos*, A Berndt*, A K Nguyen, A Tom, A McGuire, Z C Lin, K Tien, W G Bae, H Wang, P Mei, H H Chou, B Cui, K Deisseroth, T N Ng, and Z Bao
Science, 350, 313–316, 2015 (*equal contribution)
Featured on
An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications
B. C-K. Tee*, Chao Wang*, R. Allen, and Z. Bao
Nature Nanotechnology 7, 1–8, 2012
Featured on:
- Stanford Engineering News
- Science NOW
- CNET
- Mashable
Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care
Lisa Y Chen*, Benjamin C-K. Tee*, A. Chortos, G. Schwartz, V. Tse, D. J Lipomi, H S P. Wong, M. V McConnell and Z. Bao
Nature Communications, 5 , 1–10, 2014 (*equal contribution)
Tunable Flexible Pressure Sensors using Microstructured Elastomer Geometries for Intuitive Electronics
B. C-K. Tee, A. Chortos, R. R Dunn, G. Schwartz, E. Eason and Z. Bao,
Adv. Funct. Mater. 24, 5427–5434, 2014
Shape-Controlled, Self-Wrapped Carbon Nanotube 3D Electronics
H. Wang, Y. Wang, Benjamin C-K. Tee, K. Kim, J. Lopez, W. Cai, and Z. Bao Shape-Controlled, Self-Wrapped Carbon Nanotube 3D Electronics.
Adv. Science. 2, 2015
25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress
M. Hammock, A. Chortos, B. C-K. Tee, J. B.-H. Tok, and Z. Bao,
Advanced Materials 25, 5997–6038, 2013
Flexible polymer transistors with high pressure sensitivity for application in electronic skin and health monitoring
G. Schwartz, B. C-K. Tee, J. Mei, A. L Appleton, D. H. Kim, H. Wang, and Z. Bao, Nature Communications 4, 1859–8, 2013
Solution coating of large-area organic semiconductor thin films with aligned single-crystalline domains
Y. Diao, B. CK Tee, G. Giri, Jie Xu, H. A Becerril, R. M. Stoltenberg, T. Lee, G. Xue, S. CB Mannsfeld and Z. Bao,
Nature Materials 12, 665, 2013
Featured on cover of Nature Materials
Skin-Like Sensors of Pressure and Strain Enabled by Transparent, Elastic Films of Carbon Nanotubes
D.J. Lipomi*, M. Vosgueritchian*, B. C-K. Tee*, et. al.,
Nature Nanotechnology 6, 788-792, 2011
Highly sensitive flexible pressure sensors with micro-structured rubber dielectric layers
S.C. B. Mannsfeld, B. C-K. Tee, R. M. Stoltenberg, C. V. H-H. Chen, S. Barman, B. V. O. Muir, A. N. Sokolov, C. Reese & Z. Bao,
Nature Materials 9, 859–864, 2010
