Engineering Development of a Prototype Wireless Subretinal Prosthesis

Abstract

Abstract: : Purpose: Development of a chronically implantable prototype for a wireless ab externo prosthesis to restore vision to patients with retinal degeneration. The initial goal is successful chronic implantation of a functioning prosthesis in the eye of a Yucatan mini–pig followed by wireless stimulation with cortical signal monitoring. Methods: Data and power are transmitted by RF. The initial design has 15 electrodes. The communication, control and signal–processing chip has variable current pulse duration, amplitude, interpulse interval, and electrode bias. The design, testing, and some construction steps were carried out in–house, including fabrication of microelectrode arrays and an early version of the flexible substrate, test system development, design and testing of the chip, transmitter design and construction, paralyene encapsulation, and soak testing. Processes sourced out to vendors included coil winding, flip–chip and wire bonding to the substrate, fabrication of the chip and later versions of the polyimide flexible substrate, teflon encapsulation, and iridium oxide deposition on the electrodes. Due to initial assembly failures, the electrode array and flexible substrate were redesigned to allow three bonding options: flip chip, wire bond and gold beam bond. Two different flexible substrate designs allowed chip bonding by flip chip or wire bond methods. Sputtered iridium oxide enhanced the charge capacity of the electrodes. Vapor deposited paralyene and alternatively teflon were used to encasulate different versions of the implant. The substrate geometry was repeatedly modified to satisfy surgical constraints, and a surgical method was developed that completely avoids entry into the eye. Results: The prototype has the functionality, dimensions and mechanical properties required for a human ab externo retinal prosthesis. The final version is still in assembly at the time of submission of this abstract. Surgical methods to insert the electrode array have reached a 70% success level. Conclusions: This prototype for animal studies has several features that enhance biocompatibility, including the penetration of the sclera only by an ultrathin electrode array and a design that attaches all remaining components to the outside wall of the eye.

Keywords: age-related macular degeneration • retina