Fabrication and Characterization of a Carbon Nanotube Microelectrode Array for Retinal Prostheses

Abstract

Abstract: : Purpose:Current retinal prostheses use metal planar electrodes. Our goal has been the development of an electrode array that could penetrate through retinal layers to reach target neurons, using flexible carbon nanotube (CNT) technology. Methods:Using conventional silicon–based micro–fabrication processes, we have grown vertically self–assembled, conductive, multi–walled CNT towers on pre–patterned metal circuits by chemical vapor deposition. The electrical properties of the CNT microelectrode array were characterized by impedance measurement in saline. Biocompatibility was tested by X–ray analysis, cell culture, as well as whole retina culture. Results:The size and spacing of the CNT microelectrodes could be controlled within 1µm precision. The heights of CNT microelectrodes exceeded 100µm. A tower aspect ratio of 4 was easily achieved, forming a microelectrode array that can penetrate the retina. Impedance in saline was extremely low (<5kΩ at 1kHz for a 50µm×50µm microelectrode). This is expected given the large surface area of these nanotube electrodes. X–ray Photoelectron Spectroscopy (XPS) analysis showed the CNT surface to be chemically biocompatible, and free of potentially toxic particles (e.g. iron catalyst). Postnatal retinal ganglion cells that were cultured on CNT substrates showed good viability and neurite outgrowth through at least 9 days of culture. Neurites also showed a strong tendency to grow along the CNT towers. Conclusions:A penetrating microelectrode array based on carbon nanotubes can be readily fabricated, and appears to be biocompatible. CNT electrodes have significant potentials as stimulators, but could also act as recording units for fundamental neuroscience research.

Keywords: age–related macular degeneration • retina • photoreceptors