| Description |
A critical challenge for ensuring a long-term brain-electrode interface is the staggering mismatch between the mechanical properties of the silicon/metal microelectrode arrays and brain tissue. There has been significant research on the development of more flexible implantable microelectrodes than silicon or metal microwire arrays. However, flexible electrodes buckle during insertion and require either a rigid outer shuttle system or a thicker coating to penetrate cortical tissue, creating a larger lesion than is necessary with stiffer implants. The next generation of microelectrode arrays may need to be mechanically rigid during the insertion procedure, then adapt to a more flexible implant with mechanical properties. Gallium could be the ideal material for next-generation mechanically adaptable microelectrode arrays. Gallium has a unique melting point of 29.36 °C. This indicates Gallium is a rigid solid at room temperature and a liquid (no mechanical strength) at body temperature. This offers an ideal mechanical transition (rigid to soft) between 25°C to 37°C for implantable microelectrode arrays. However, there is limited knowledge on the biocompatibility, biostability, and electrochemical performance of Gallium under physiological conditions. This dissertation represents a comprehensive investigation of Gallium chemistry under physiological conditions, improving Gallium material property for neural interface applications, and in vivo evaluation of Gallium-based microelectrodes. iv A thermal responsive Gallium/PEBAX core/shell structure is first fabricated to demonstrate the temperature-dependent mechanical change of the Gallium-based microelectrodes. However, various spectroscopic studies demonstrated Gallium itself is unstable under physiological conditions due to oxidation, biodegradation in aqueous solution, and biofouling by the interaction between ionized Gallium surface and the plethora of biomolecules in physiologic fluids. Various encapsulation strategies were performed to improve the biostability and electrochemical performance of Gallium under physiological conditions. Optimal electrochemical deposition conditions were confirmed for Au, CNT, and PEDOT on Gallium surfaces. Finally, in vivo physiological signals were recorded from soft encapsulation (PEDOT:BF4) and a Gallium-based liquid metal platform. Single-unit action potential recording using the PEDOT functionalized liquid metal electrodes was performed from nonhuman primates and confirmed the long-term recording stability from an invertebrate model. The in vivo results show our strategies can open numerous design opportunities for next-generation Gallium-based bioelectronic devices. |
