Development of flexible stimulation devices for a retina implant system

Different research groups are focusing their work on the development of a neural prostheses to aid patients suffering from blindness. In some diseases (retinitis pigmentosa or macula degeneration), degeneration of the photoreceptors often leaves the ganglion cell layer and the central vision system largely intact. This paper outlines the authors' approach of interfacing the retina with flexible multielectrode structures for ganglion cell stimulation. Results are given on the material selection for substrate materials and the design for flexible stimulation devices. By means of cytotoxicity testing, in a first step of an evaluation procedure, the biocompatibility of different substrate and coating materials has been investigated. The methods were sensitive to such a degree that even the influence of changes in process technology on the material was detected. Different geometric test structures have been created that led to the design of flexible, light-weighted stimulation devices with integrated cables. The devices were fabricated using micromachining technology. The authors used polyimide as substrate and insulation layers and platinum as electrode and interconnect metallization layers. The first structures were distributed to the partners for acute and chronic implantation in animal models.