Micro-Fabrication of Components for a High-Density Sub-Retinal Visual Prosthesis

Abstract

We present a retrospective of unique micro-fabrication problems and solutions that were encountered through over 10 years of retinal prosthesis product development, first for the Boston Retinal Implant Project initiated at the Massachusetts Institute of Technology and at Harvard Medical School’s teaching hospital, the Massachusetts Eye and Ear—and later at the startup company Bionic Eye Technologies, by some of the same personnel. These efforts culminated in the fabrication and assembly of 256+ channel visual prosthesis devices having flexible multi-electrode arrays that were successfully implanted sub-retinally in mini-pig animal models as part of our pre-clinical testing program. We report on the processing of the flexible multi-layered, planar and penetrating high-density electrode arrays, surgical tools for sub-retinal implantation, and other parts such as coil supports that facilitated the implantation of the peri-ocular device components. We begin with an overview of the implantable portion of our visual prosthesis system design, and describe in detail the micro-fabrication methods for creating the parts of our system that were assembled outside of our hermetically-sealed electronics package. We also note the unique surgical challenges that sub-retinal implantation of our micro-fabricated components presented, and how some of those issues were addressed through design, materials selection, and fabrication approaches.

Correlated Activity in the Degenerate Retina Inhibits Focal Response to Electrical Stimulation

“…Although retinal prostheses have shown some clinical success, a patient’s visual acuity restored with electronic retinal devices is at best less than 20/420 ( Stingl et al, 2013 ; Ayton et al, 2020 ). To improve visual acuity, many engineers have attempted to increase the spatial resolution of electrical devices by integrating a large number of smaller electrodes on an electronic chip ( Zeng et al, 2019 ; Shire et al, 2020 ; Chenais et al, 2021b ), optimizing electrode configurations ( Wilke et al, 2011 ; Celik, 2017 ; Flores et al, 2018 ) or stacking more electrodes in a three-dimensional structure ( Bendali et al, 2015 ; Davidsen et al, 2019 ; Seo et al, 2019 ). Physiologists have searched for optimal stimulation protocols, such as the minimum stimulation threshold required for local activation of target neurons to avoid axon bundle activation or non-specific activation of nearby RGCs ( Sekirnjak et al, 2008 ; Jepson et al, 2013 ; Grosberg et al, 2017 ; Chang et al, 2019 ; Tandon et al, 2021 ).…”

Editorial for the Special Issue on Micro/Nanofabrication for Retinal Implants

“…Recently, these planar electrodes have been challenged by three-dimensional (3D) electrodes in diverse shapes [6,8,9]. In this Special Issue as well, the two articles by Shire et al and Seo et al [10,11] reported 3D pillar electrode structures. Their 3D microelectrodes are expected to be more efficient in subretinal stimulation by delivering electric current closer to target retinal neurons.…”