High-density High Electrode Count Retinal Stimulating Arrays

Abstract

Abstract: : Purpose: In the development and design of epiretinal microelectronic arrays, the distance between the electrodes and the target tissue is very important since it can influence the efficacy of electrical stimulation. The aim of this study is to investigate technology for high-density array that minimizes separation between the electrodes and the retina. Methods: First generation microelectrode arrays fabricated in poly(dimethylsiloxane) (PDMS), an inert elastomeric material, were provided by LLNL. To fabricate the microelectrode array on PDMS, LLNL developed unique processes for photolithographically patterning PDMS, depositing metal traces and selectively passivating the traces with a second layer of PDMS. The array had the dimensions of 3mmX40mmX50um. Testing of surgical applicability and contact with the curvature of the retina was performed. The integrity of the thin film traces onto the PDMS were electrically tested before and after the implantation. SNL provided an adjustable epiretinal array made of electrodes mounted on MEMS (micro electro mechanical systems) springs, which were manufactured by silicon surface micro-machining. Results: The LLNL array was implanted into the eye of one dog epiretinally, following pars plana vitrectomy with separation of the posterior hyaloid. As the array was compliant and stretchable, it could be placed on the retina smoothly, appearing to fit the curvature of the retina. Surgical manipulation of the array broke an outer trace. The second-generation array was designed and fabricated, such that it contained micromolded ribs around the perimeter to facilitate handling during surgery and reinforce the metal traces near the edge. Also in the second generation device, a retinal tack hole was incorporated for attachment of the array to the eye. The SNL device was designed as a rigid array surrounded by a polymer frame to provide a flexible attachment and a mechanical buffer between the retina and the MEMS device. Handling of the device and the tacking could be made through this frame. Spring-mounted electrode tips enabled the full contact of the electrodes to the retinal curvature. Conclusion: Advancements in microfabrication technology have the potential to enable the development of high-density electronic-retina interfaces. The present study provides information about 2 different designs of epiretinal prostheses.

Keywords: retina • vitreoretinal surgery • retina: proximal(bipolar, amacrine, and gangli