(6gz) Designing Nanomaterials and Electronic Devices for Multi-Level Neural Interfacing

Recent developments in materials, electronics and genetics have enabled both deeper understanding of nervous system as well as enhanced therapeutic solutions in neural diseases. The goal of my research program will be developing novel nanomaterials and flexible electronic devices for improved modulation and recording of neural activity, from inside the neurons to outside of the skin. The initial research areas in my proposed program will include: 1) understanding and improving neuronal uptake and axonal transport of functional nanomaterials for non-genetic, projection-specific neuromodulation and imaging. 2) developing advanced flexible electronic skin patches for treatment of peripheral nerve disorders.

My postdoc work with Prof. Karl Deisseroth (Department of Bioengineering, Stanford University) has focused on developing a non-genetic method for projection-specific modulation of neural activity. The current optogenetics and virology technology have demonstrated that modulating the neural activity of specific projections in the brain is capable of rescuing behavioral deficits, including those relevant to depression, autism and anxiety. However, this approach requires genetic modification of neurons via viral transduction of transducers of visible light, and light penetration depth is limited by the scattering of visible light. In my approach, gold nanorods are used as near−infrared light absorbers and heat generators for neuron modulation. I found that suitably functionalized gold nanorods are rapidly internalized by neuron soma or axon terminals, are transported retrogradely/anterogradely through axons and are sufficient to modulate neural activity under near-infrared (NIR) light after axonal transport both in vitro and in vivo. This nanoparticle-based methodology demonstrates a promising approach to non-­genetic, projection-­specific modulation of neural activity in freely behaving mice.

My graduate work with Prof. Zhenan Bao (Department of Chemical Engineering, Stanford University) has focused on developing conjugated polymer sorted carbon nanotubes for flexible electronics applications and it consists 3 parts. In part I, I developed several approaches for selective dispersion of semiconducting carbon nanotubes by conjugated polymers: Specifically, I designed planar backbone polymers and polymers with longer side chains to increase the surface contact area and improve the dispersion yield of semiconducting carbon nanotubes. I also found that only non-polar solvents allow the dispersion of semiconducting carbon nanotubes and proposed a new mechanism to explain the selective dispersion of semiconducting nanotubes. In part II, I developed several methods to improve the characteristics of carbon nanotube transistor for flexible electronics, including: 1) using printed molecular dopants to control the threshold voltage of carbon nanotube transistors for flexible circuits with robust performances, 2) applying fluorinated polymers to remove hysteresis and improve devices’ stability of carbon nanotube transistors, 3) applying N-type polymers to sort semiconducting carbon nanotubes for ambipolar transistors and circuits. In Part III, I utilized shape memory polymers to fabricate shape-controlled 3D-carbon nanotube transistors and sensors, which can wrap around any irregular surfaces, like our eyeglasses and key rings.

Teaching Interests:

During my PhD and postdoc training at Stanford, I have mentored 7 students in total, including 3 graduate students and 4 undergraduate students. Most of the students I have supervised had co-authored papers with me. I have also been very actively involved in the Stanford American Society for Engineering Education (ASEE) during my entire time at Stanford, including serving as the Vice-president of the society during 2014~2015. With another committee from ASEE, I co-developed and taught "Engineering 313: Topics in Engineering Education – Feedback and Assessment" class at spring quarter 2015 and was well received by the students. I have also been giving guest lectures to a variety of audiences, including the graduate course "CHEMENG 240: Micro and Nanoscale Fabrication Engineering", “MATSCI 384: Materials Advances for Neurotechnology” and undergraduate course “CHEM 26N: The What, Why, How and Wow's of Nanotechnology” for several years. I would be interested and capable in teaching the majority of the Chemical Engineering courses at both undergraduate and graduate levels, such as thermodynamics, kinetics, surfaces and interfaces, materials science, nanotechnology and neurotechnology.

Selective Publications:

1. H. Wang, L. Fenno, Y. Chen, C. Kim, C. Ramakrishnan, M. Inoue, S.Gambhir, K.Deisseroth, Projection-Specific Modulation of Neural Activity with a Non-Genetic Method, In preparation

2. J. Rivnay, H. Wang, L. Fenno, K. Deisseroth, G. G. Malliaras, Next-generation probes, particles, and proteins for neural interfacing, Science Advances, 3, e1601649, (2017)

3. H. Wang, Y. Wang, B. C.-K. Tee, K.-P. Kim, J. Lopez, W. Cai, Z. Bao, Shape-Controlled, Self-Wrapped Carbon Nanotube Three-Dimensional Electronics, Advanced Science, 2, 1500103, (2015)

4. H. Wang, Y. Li, G. Jiménez-Osés, P. Liu, Y. Fang, J. Zhang, Y.-C. Lai, S. Park, L. Chen, K. N. Houk, Z. Bao, N-type conjugated polymer-enabled selective dispersion of semiconducting carbon nanotubes for flexible CMOS-like circuits. Advanced Functional Materials, 25, 1837-1844 (2015)

5. H. Wang, B. Hsieh, G. Jiménez-Osés, P. Liu, C.J. Tassone, Y. Diao, T. Lei, K.N. Houk, Z. Bao, Solvent effects on polymer sorting of carbon nanotubes with applications in printed electronics, Small, 11, 126-133 (2015)

6. H. Wang, B. Cobb, A. Breemen, G. Gelinck, Z.Bao, Highly Stable Carbon Nanotube Top-Gate Transistors with Tunable Threshold Voltage, Advanced Materials, 26, 4588-4593 (2014)

7. H. Wang, P. Wei, Y. Li, J. Han, H. R. Lee, B. D. Naab, N. Liu, C. Wang, E. Adijanto, B. C-K. Tee, S. Morishita, Q. Li, Y. Gao, Y. Cui, Z. Bao, Tuning the Threshold Voltage of Carbon Nanotube Transistors by n-type Molecular Doping for Robust and Flexible Complementary Circuits, Proceedings of the National Academy of Science, 111(13), 4776-4781 (2014)

8. H. Wang, G. I. Koleilat, P. Liu, G. Jiménez-Osés, Y. Lai, M. Vosgueritchian, Y. Fang, S. Park, K. N. Houk, and Z Bao, High-Yield Sorting of Small-Diameter Carbon Nanotubes for Solar Cells and Transistors, ACS Nano, 8, 2609-2617 (2014)

9. H. Wang, J. Mei, P. Liu, K. Schmidt, G.J.Oses, S. Osuna, L Fang, C.J. Tassone, A.P. Zoombelt, A.N.Sokolov, K.N.Houk, M.F.Toney, Z. Bao. Scalable and Selective Dispersion of Semiconducting Arc-Discharged Carbon Nanotubes by Dithiafulvalene/Thiophene Copolymers for Thin Film Transistors. ACS Nano, 7, 2659-2668 (2013)

10. H. Wang, J. Luo, A. Robertson, Y. Ito, W. Yan, V. Lang, M. Zaka, F. Schaffel, M. H. Rummeli, G. A. D. Briggs, J. H. Warner. High performance field effect transistors from solution processed carbon nanotubes. ACS Nano, 4, 6659-6664 (2010)