Implantable nanostructured microelectrode array with biphasic current stimulator for retinal prostheses.

Abstract

In retinal prosthetic systems on multi-channel microelectrodes to effectively stimulate retinal neurons, the electrode-electrolyte interface impedance of a microelectrode should be minimized to drive sufficiently large current at a given supply voltage. This paper presents the fabrication of the nanostructured microelectrode array with simplified fabrication and its characteristic evaluation using biphasic current stimulator. The nanostructured microelectrodes with the base diameter of 25 μm, 50 μm, 75 μm are fabricated, and the maximum allowable current injection limits are measured to verify the estimated injection limit. Also, a biphasic stimulator has been fabricated using the 2-stage amplifier and 4 switches based on a stimulator cell. The adjustable load resistance is adopted to control between 5 kΩ to 20 kΩ, and the biphasic stimulator can drive the stimulation current between 50 uA and 200 uA. The proposed electrode-electrolyte interface impedance of the fabricated nanostructured microelectrode is 3178 Ω, 1218 Ω and 798.8 Ω for electrodes with diameter of 25 μm, 50 μm, 75 μm, respectively. This paper shows the advantages of the nanostructured microelectrode arrays for high resolution retinal prostheses, which could be a basic experiment for artificial retina research.