Amorphous Silicon Carbide-based Intraneural Ultramicroelectrode Array for Selective Interfacing to the Rat Cervical Vagus Nerve
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With the ever-increasing applications of neuroprosthetics, improving their effectiveness and reducing their side effects are essential. This requires developing more selective and less invasive interfaces. The aim of this dissertation was to improve the selectivity and reduce the invasiveness of current peripheral nerve interfaces by reducing the electrode dimensions and array shafts. To that end, a 16-channel intraneural electrode array incorporating small electrodes and small cross-sectional area shafts was developed. Sputtered iridium oxide (SIROF) electrodes as small as 20µm2 are feasible to be used for neural recording and evoking functional responses in neural stimulation based on their electrochemical properties in a model of interstitial fluid. The unusual behavior attributed to ultramicroelectrodes (UMEs) was observed for SIROF electrodes smaller than 200µm2 in ferrocene and PBS electrolytes. This behavior is due to hemispherical diffusion of electroactive species to the electrode. In order to evaluate the effect of large current densities in UMEs on electrode degradation, the SIROF UMEs were subjected to continuous current pulses. After exposing to 1.7 billion pulses the electrochemical properties of SIROF UMEs (50µm2 ) remained stable and no effect of degradation was observed. While having smaller cross-sectional area shafts decrease the invasiveness and increases the flexibility of neural probes, it complicates the insertion. To facilitate the implantation and improve the nerve stability during acute surgeries, a polymeric structure named Neurocase using thin film technology was developed. Device’s functional selectivity was demonstrated by performing acute recordings from rat cervical vagus nerve (cVN) which is a multifunctional nerve. Different electrodes on the array recorded distinct activity upon evoking neural activity in the cVN by manipulating blood pressure, inducing oxygen restriction, and electrical stimulation of the subdiaphragmatic vagus nerve. As complete control over the nerve functionality is only possible through both stimulation and blocking, an equation for determining the electrode polarization during kilohertz frequency alternating current (KHFAC) nerve conduction blocking was derived. The effect of DCfiltering, electrode material, and stimulation parameters on the electrode polarization was investigated. It was observed that the choice of electrode material (platinum, titanium nitride or SIROF) did not affect the electrode polarization at frequencies higher than 10 kHz and the DC filter had a significant impact on reducing the electrode polarization.