Flexible multichannel neural probe for stimulation and sensing

Abstract

Miniaturization and minimization of mechanical mismatch in neural probes have been two well-proven directions in suppressing immune response and improving spatial resolution for neuronal stimulations and recordings. While the high impedance brought by the miniaturization of electrodes have been addressed by using conductive polymers coatings in multiple reports, the stiffness of such coatings remains orders of magnitude higher than that of the brain tissue. In this thesis, we aim to tackle the mechanical and electrical issues of the current neural probes in chronic in vivo testing by developing a neural probe that possess simultaneous recordings and stimulation capabilities at multiple sites while maintaining high biocompatibility. We have developed a flat neural probe based on highly flexible microelectrode array neural probe with electrodeposited hydrogel coatings poly(2-hydroxyethyl methacrylate) (pHEMA) and conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS), with a cross-section area at only 300 μm  2.5 μm. Detailed fabrication procedures are described in the thesis. The PEDOT/PSS coating provides a low interfacial impedance, and the pHEMA deposition bridged the mechanical mismatch between the probe and the brain tissues. The two layers of polymers modification enhances the signal-to-noise ratio and allows the microelectrodes array to be engineered for both recording and stimulation purposes. Besides, In vivo testing of microelectrode arrays implanted in rat hippocampus confirmed high signal-to-noise ratio in neural signal recording and excellent charge injection capacity which can effectively induce long term potentiation in neural activities in hippocampus. The chronic testing of the neural probe demonstrated the stability of the probe for long-term implantation. The integration of OECTs into the neural probes on one hand boost the electrical signal sensing capabilities, and also opens up the possibilities of integration of various OECT-based sensors for different sensing applications.