Jaehyeon Ryu PhD Dissertation Defense

Title: Materials Strategies for Scaling Soft Neuroelectrode Arrays

Location: Snell 012/Teams

Committee Members:
Prof. Hui Fang (Advisor)
Prof. Yongmin Liu
Prof. Ryan Koppes

Abstract:
The evolution of electronics to seamlessly interface with biological tissue hinges on addressing multifaceted material constraints spanning electrochemical, electrical, and mechanical domains. Conventional bioelectronic interfaces, while endowed with established electrochemical functionality, remain hampered by rigidity that contradicts the pliability of surrounding tissue. While conductive materials exhibiting tissue-like softness and stretchability have been realized, their potential for electrochemical probing of tissue is impeded by strain-induced performance degradation and an ill-suited integration with the irregular tissue interface. Nevertheless, a significant challenge in ultrasoft bioelectronics pertains to scalability for achieving cellular resolution, primarily due to mechanical disparities between conventional microelectronic materials and soft elastomer substrates. In this thesis, by using a novel approach involving a multifunctional nanomesh, composed of distinct purposefully designed layers including polymer for mechanical buffering, metal for electrical conduction, and low impedance coating for electrochemical interfacing in the same nanomeshed structure, the resultant microelectrodes, scalable down to 20μm at cellular resolution, exhibit comparable performance to rigid devices alongside a stretchablity of approximately 50%, with potential for future enhancement through in-plane structural optimizations. In addition, we introduce a high-density neuroelectronic array featuring 256 filamentary neuroelectrodes on a flexible substrate. These electrodes are integrated with a single-transistor multiplexing acquisition circuit, effectively reducing noise and footprint while potentially extending device lifetime. Remarkably, the array’s rollable contact pad design allows for minimally invasive delivery through a syringe. Experimental validation demonstrates the array’s capability to record neural signals with high tone decoding accuracy. Utilizing high-density arrays of these microelectrode arrays, this unique frame works holds significant promise for advancing the field of neural interfacing, enabling a wide range of application from fundamental neuroscience studies to various biomedical applications.