Microfabricated Multi-Electrode Arrays for in vitro Studying Neural Coding in the Retina

Abstract

Purpose: : This work is related to the efforts of the Boston Retinal Implant Project to develop a sub-retinal prosthesis to restore vision to the blind. The specific purpose of this presentation is to describe our efforts to micro-fabricate two generations of custom multi-electrode arrays (MEA) to interface with the Multichannel Systems MEA60 for in vitro neural coding studies. The MEAs were designed to help understand population responses of retinal ganglion cells (RGC) to various sizes of photic stimuli and compare them to various amplitudes of electrical current stimuli.

Methods: : A polyimide-based micro-fabrication process was initially used to create a substantially transparent MEA within which indium tin oxide (ITO) conductors and electrodes were embedded. The polyimide device was fabricated on a standard Si substrate. After the final outline etch, the polyimide MEA was removed from the Si substrate, attached to a glass substrate with wax and ultimately cut to size with a dicing saw. A second polyimide-based micro-fabrication process was developed to create a second-generation MEA that utilized gold conductors and electrodes. This MEA was designed with through-array holes to facilitate connection to a vacuum port that was etched through the Si carrier substrate from the back side.

Results: : A set of micro-fabrication processes, including spin coating, microlithography, physical vapor deposition, wet and dry etching, and through-wafer Bosch etching, has been engineered to create two generations of 60-channel MEAs. The first MEA was substantially transparent, whereas the second MEA featured through-array vacuum holes (see Figure).

Conclusions: : Two generations of MEAs have been successfully designed and micro-fabricated in a form that readily interfaces with the Multichannel Systems MEA60. These MEAs have been successfully utilized to perform in vitro experiments toward understanding neural coding in the retina.

Keywords: retina • electrophysiology: non-clinical • ganglion cells