Performance improvement of a micro-stimulus electrode for retinal prosthesis by introducing a high-performance material and a three-dimensional structure

High-performance electrodes intended for retinal prosthesis were fabricated and evaluated. Iridium oxide (IrO_x) was introduced as a high-performance material. A three-dimensional (3D) structure was also introduced to enlarge the electrode's surface area. We tried to improve the electrode performance by combining these approaches, even if the electrode was miniaturized. The effectiveness of IrO_x was demonstrated through electrochemical evaluation by comparing it with Pt. IrO_x showed 1.6-6 times higher performance for the injection of stimulus pulse current than Pt. The performance of the 3D electrode compared with a planar electrode was also evaluated. Accordingly, the 3D electrode showed 2-4 times higher performance than the planar electrode by surface area enlargement. An ex vivo validation of the stimulus performance was conducted to demonstrate its practical use. A fabricated electrode was implanted in an extracted pig eyeball and the electrochemical performance was evaluated. The fabricated electrode showed sufficient performance of the retinal stimulation, with a high margin of safety. The proposed approach was successfully demonstrated as a stimulus electrode candidate for use in next-generation retinal prosthesis.