# Micro-Fabrication of Components for a High-Density Sub-Retinal Visual Prosthesis
###### Abstract
We also discuss the processing and assembly of supporting micro-fabricated components that facilitated the surgical placement of the device components around the exterior of the eye, including the \"secondary\" radio frequency coil that provides power bi-directional wireless data (e.g., digitized details of the visual scene) to and from the \"primary\" radio frequency coil that is embedded within a pair of glasses worn by the user. Our micro-fabrication and surgical methods have been proven in extensive pre-clinical tests in miniature pig animal models. We are cautiously hopeful that our penetrating electrodes, which will deliver stimulation to small clusters of nearby neurons, will improve the quality of vision over what can be obtained with planar surface electrodes. Early in the development of prior generations of our visual prosthesis, we elected to build a device that would introduce electrical stimuli at a sub-retinal location, that is, adjacent to the zone where photoreceptor cells are lost in the degenerative diseases that we were targeting. This was a fundamental strategic change from the decade long experience we had working on the epiretinal surface and even performing acute (i.e., short duration) proof-of-concept retinal stimulation tests on blind volunteers [1; 2]. In essence, we accepted the consequences of a \"trade-off\" in that the surgical approach to the sub-retinal space requires breaching the highly vascular choroid, and the technical requirements were more challenging compared to conventional vitro-retinal surgery. Nonetheless, we gradually became convinced that the engineering and biological advantages of a sub-retinal approach would more likely lead to improved clinical results, as has been the case in recent studies by others [15]. We believe that these results may improve further by introducing highly localized electrical stimuli atop and/or beside penetrating posts that support the electrode structures. Indeed, we have fabricated such high-density 3D penetrating electrode arrays for our own devices, as have other groups more recently [18; 19; 20; 21], and we report on their fabrication technology below. Micro-fabrication is one of several key technological drivers that together enable higher channel counts for implantable neuro-stimulators generally, and for vision prostheses in particular. Unlike cochlear implants for the deaf, which can produce meaningful auditory percepts using modest numbers of electrodes, visual prostheses can require hundreds of individually-controllable stimulation channels to induce reasonably high-density disphenes so that detailed images can be interpreted [8; 22]. There are several micro-fabrication challenges to creating high-density flexible electrode arrays suitable for the sub-retinal space, and they are summarized below in Table 1. The aim of this work was to address these challenges in an integrated, multi-disciplinary manner in consultation with our surgical team members, and to produce robust, multi-layered, flexible components for our visual prostheses that could survive the implantation procedure and last in the body for perhaps up to 10 years thereafter. In reporting our results here, we emphasize the fabrication-related challenges that we faced which were more universal in nature, as opposed to those related solely to any technical limitations of the micro-processing equipment that we had at our disposal.