(7bu) Intrinsically Stretchable Skin Electronics for Wearable Biomedical Applications

The next generation of consumable electronics and biomedical devices feature more intimate integration with human bodies and tissues, which will be subject to the requirements of the same mechanical properties with epidermis including being soft and stretchable. Using skin-like intrinsically stretchable polymer materials to build up electronics can effectively blur the interface between human body and electronics, both chemically and mechanically. The development of this emerging generation of electronics is still at its premature stage, which requires both materials platforms and technology platforms. For the materials platform, stretchable semiconductors are indispensible, but existing ones typically sacrifice charge transport mobility to achieve stretchability. I, and my colleague, developed a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. This methodology has been shown to be broadly applicable to various polymer semiconductors. In the next major step, the technology platform needs to be developed for fabricating multiple devices and connecting them together to form skin-like signal processing module. I have developed the first fabrication platform for intrinsically stretchable transistor array, which has material universal applicability, ultrahigh yield and uniformity for performance. The fabricated transistor array has the mobility comparable to amorphous silicon. High stretchability of all the material components concurrently gives rise to supreme stretchability with stable performance up to 100% strain, robustness up to 1000 cycles, and an unprecedentedly high device density. Using this platform, I have further built up the major circuit foundations for intrinsically stretchable skin electronics. Bridging materials to electronic development, this technological platform takes an important step forward towards the realization and wide application of intrinsically stretchable skin electronics. My future research interest involves the development of intrinsically stretchable high-performance polymer electronic materials, intrinsically stretchable transistors, sensors, actuators and human-interactive integrated system with unprecedented functionality and skin-like nature.

The skin-attached biomedical devices are desired to operate independently and maintenance-free, which requires power sources scavenging energy from human body. Mechanical energy is one of the most universally-existing, diversely-presenting, but usually-wasted energies in the natural environment. The triboelectric effectis a universal phenomenon that can generate electrostatic charges from mechanical contact. During my PhD research, I developed a new type of technology—triboelectric nanogenerators (TENGs), which can efficiently convert mechanical energy into electricity based on the coupling of triboelectrification and electrostatic induction. My research achievements expand the establishment of three basic modes/mechanisms of TENGs that serve as the basis for most of the TENG structures, the optimization of materials and device structure for performance enhancement and different applications, and the development of self-charging power unit for electronic devices by hybridizing a TENG with a flexible Li-ion-battery. This technology has shown the potential to utilize (bio)mechanical energy to realized self-powered systems. My future research interest would involve the development of bio-compatible mechanical energy harvesting materials and technology and the stretchable self-powered bio-medical and wearable systems.

Teaching Interests:

After an extensive training in interdisciplinary fields including, materials science and engineering, chemical engineering, electrical engineering, nanotechnology and electrochemistry, I am more than ready to share my knowledge with new generations of students. I am interested in and capable of teaching most of the major courses in Chemical Engieering, including Thermodynamics, Kinetics, Crystal structures and defects, Materials Characterization, Electrochemistry, Microfabrications, Nanoscience and Nanotechnology, Organic electronics, Green Energy Technology, Semiconductor Physics, etc.

I have served as TA for multiple courses during my graduate study. Also, I have the experiences of guest lecturer both in Stanford University and in Georgia Tech.

Selected Publications:

J. Xu*, S. Wang*, G.-J. N. Wang, C. Zhu, S. Luo, L. Jin, X. Gu, S. Chen, V. R. Feig, J.W.F. To, S. Rondeau-Gagné, J. Park, B. C. Schroeder, C. Lu, J. Y. Oh, Y. Wang, Y.-H. Kim, H. Yan, R. Sinclair, D. Zhou, G. Xue, B. Murmann, C. Linder, W Cai, J. B.-H. Tok, J. W. Chung, Z. Bao “Highly stretchable polymer semiconductor films through the nanoconfinement effect” Science, 355 (2017) 59.

S. Wang, Y. Zi, Y.S. Zhou, S.M. Li, F.R. Fan, L. Lin, Z.L. Wang “Molecular surface functionalization to enhance power output of triboelectric nanogenerators” Journal of Materials Chemistry A, 4 (2016) 3728.

Y.L. Zi*, J. Wang*, S. Wang*, S.M. Li, Z. Wen, H.Y. Guo, Z.L. Wang “Effective energy storage from triboelectric nanogenerators” Nature Communications, 7 (2016) 10987.

S. Wang, Y.N. Xie, S.M. Niu, L. Lin, C. Liu, Y.S. Zhou, Z.L. Wang “Maximum surface charge density for triboelectric nanogenerators achieved by ionized-air injection: methodology and understanding” Advanced Materials, 26 (2014) 6720.

S. Wang, S.M. Niu, J. Yang, L. Lin, Z.L. Wang “Quantitative measurements of vibration amplitude using a contact-mode freestanding triboelectric nanogenerator” ACS Nano, 8 (2014) 12004.

S. Wang, Y.N. Xie, S.M. Niu, L. Lin, Z.L. Wang “Freestanding-triboelectric-layer based nanogenerators for harvesting energy from a moving object or human motion in contact and non-contact modes” Advanced Materials, 26 (2014) 2818-2824.

S. Wang, L. Lin, Z.L. Wang “Triboelectric nanogenerators as self-powered active sensors” Nano Energy, 11 (2014) 436.

Y.N. Xie*, S. Wang*, S.M. Niu*, L. Lin, Q.S. Jing, J. Yang, Z.Y. Wu, Z.L. Wang “Grating-Structured Freestanding Triboelectric-layer Nanogenerator for Harvesting Mechanical Energy at 85% Total Conversion Efficiency” Advanced Materials, 26 (2014) 6599.

S. Wang, L. Lin, Y.N. Xie, Q.S. Jing, S.M. Niu, Z.L. Wang “Sliding-triboelectric nanogenerator based on in-plane charge-separation mechanism” Nano Letters, 13 (2013) 2226.

S. Wang, Z.–H. Lin, S.M. Niu, L. Lin, Y.N. Xie, K.C. Pradel, Z.L. Wang “Motion charged battery as sustainable flexible-power-unit” ACS Nano, 7 (2013) 11263.

S.M. Niu*, S. Wang*, L. Lin, Y. Liu, Y.S. Zhou, Y.F. Hu, Z.L. Wang “Theoretical Study of the Contact-Mode Triboelectric Nanogenerators as Effective Power Source” Energy & Environmental Science, 6 (2013) 3576.

S. Wang, L. Lin, Z.L. Wang “Nanoscale-triboelectric-effect enabled energy conversion for sustainably powering of portable electronics” Nano Letters, 12 (2012) 6339.