Development of Flexible Stimulation Devices for Vision Prosthesis

Electrical stimulation of the remaining retinal neurons to restore useful vision has been recently proposed in patients with retinitis pigmentosa or macular degeneration. Using the potentials of microsystem technology, neural prostheses become feasible which are implanted in the eyes. The active microimplants demand a high degree of device miniaturization without compromising design flexibility and biocompatibility requirements. This paper outlines our approach of interfacing the retina with flexible multielectrode structures. In order to overcome the brittleness of silicon, two kinds of light-weight and highly flexible polyimide based devices are proposed. Results are given on the material selection for substrate materials and the design for flexible stimulation devices. By means of cytotoxin testing, in our first step of an evaluation procedure, the biocompatibility of different substrate and coating materials has been investigated. Different geometries and packages have been created. By simulation and experiments, we obtained two appropriate designs. One is the "silicon island" for subretinal implants. The other is the "electrode array" for epiretinal implants. We used polyimide as substrate and insulation layers, silicone and parylene-C as coating materials, and gold as electrode material