The active electrode materials currently used in retinal prostheses currently include platinum (Pt) or iridium oxide (IrO2). Producing a sufficient signal to evoke a visual percept, requires operating the electrode above some minimum charge density (Qmin 0.1 - 6 mC/cm2). Both Pt and IrO2 electrodes are unable to operate throughout this range without electrolyzing water or corroding; water electrolysis and corrosion are detrimental to neural tissues and the device itself. We believe that doped-diamond electrodes, grown by chemical vapor deposition, will operate at charge densities 6 mc/cm2 without electrolyzing water, and resist corrosion. Therefore, we propose to 1)fabricate diamond electrodes, 2)measure in vitro the charge density at which water elecrolysis occurs, and 3)evaluate the corrosion resistance of diamond electrodes. The small business, North Coast Crystals, and the research institution, the University of North Carolina-Chapel Hill, will fabricate the diamond electrodes. The retinal prosthesis group at Johns Hopkins has agreed to perform gratis the in vitro electrode evaluation. Phase II will include demonstrating in vivo the biocompatibility and superior performance of diamond-based electrodes. We expect Johns Hopkins to become a Phase II partner and perform the in vivo demonstrations.
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