Performance of laser fabricated stimulating electrode arrays for a retinal prosthesis in saline

Microelectrode arrays for a stimulating retinal prosthesis were fabricated from laser etched platinum (Pt) foil encased in silicone. A total of 12 arrays were fabricated to test performance in saline. Hexagonal arrangements (N=6) with multiple (6) return electrodes, as well as paired electrodes (N=6) with single returns were constructed. Electron microscopy of the electrode's surfaces was performed. Cyclic voltammetry was performed on all electrodes to measure the real surface area. The electrodes were submerged in saline in an incubator and biphasic pulses of ±162 μA and ±280 μA for 400 μs were applied at a rate of 67.1 Hz for 12 weeks. Microscopy and cyclic voltammetry were repeated and changes to the electrode's surfaces were observed both by visual inspection of the micrographs and analysis of the cyclic voltammetry curves. Extensive corrosion to those electrodes subjected to the higher current suggests a charge injection limit of less than the original 350μC/cm ² estimate. Analysis of different corrosion levels between the hexagonal and paired arrangements show that a hexagonally arranged electrode array, with multiple return electrodes, allows a greater stimulation current to be used without reaching the charge injection limit of the electrodes.