Carbon Nanotube Based Electrodes for Neuroprosthetic Applications
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Carbon Nanotube Based Electrodes for Neuroprosthetic Applications Thomas S. Phely-Bobin1, Thomas Tiano1, Brian Farrell1, Radek Fooksa1, Lois Robblee2, David J Edell3, and Richard Czerw4 1 Materials Technology Group, Foster-Miller Inc., 195 Bear Hill Road, Waltham, MA, 02541 2 LSR Consulting, Peabody, MA, 01960 3 InnerSea Technology, Bedford, MA, 01730 4 NanoTechLabs Inc., Yadkinville, NC, 27055 ABSTRACT Foster-Miller Inc., in conjunction with InnerSea Technology, NanoTechLabs Inc. and Dr. Lois Robblee, has demonstrated a simple, low cost, room temperature self-assembly process for the fabrication of high capacitance, and low impedance carbon nanotube felt electrodes. Advantages of the carbon nanotube electrodes over state of the art activated iridium oxide electrodes include a more favorable distribution of charge capacity over the cathodic potentials experienced by a stimulation electrode receiving cathodal current pulses. INTRODUCTION Implantable microelectrodes for electrical stimulation of neurons and recording neuronal responses are essential tools for neurophysiologists studying the behavior of neurons in the brain, spinal cord and peripheral nerve. Critical properties of an electrode interface include: low noise, low impedance, biocompatibility, electrical stability during chronic use, and high charge capacity.1 Iridium oxide has all of these properties and thus has been utilized for significant developments in the neural prostheses area.2 However, these electrodes have several shortcomings, including: high material cost, labor-intensive processing, deterioration of long term stability if used beyond their charge injection limits and a requirement for circuitry to apply an anodic bias during cathodal charge injection.3, 4 The present work is focused on demonstrating the feasibility of using carbon nanotubes (CNTs) as a high capacitance, low impedance material for neuro-stimulation electrodes. Carbon nanotubes have attracted considerable attention since their discovery in 1991. They combine remarkable properties such as high surface area, high electrical conductivity and mechanical strength.5-8 Single wall carbon nanotube (SWCNT) felts have been previously investigated for their high capacitance.9-12 In this paper, we characterize the electrochemical performance of surface modified CNT assemblies prepared by a layer-by-layer (LbL) assembly for neuroprosthetic applications. EXPERIMENTAL Carbon Nanotubes were purchased from Carbon Nanotechnologies Inc. The proprietary self-assembly process developed at Foster-Miller is based on the surface modification of CNTs and layer-by-layer assembly. This self-assembly of CNTs was demonstrated on silicon wafers and platinum (Pt) disc electrodes from Bioanalytical Systems (BAS) Lafayette, IN. The Pt electrodes were first cleaned by repetitive cycling of the electrode potential between –0.25 V and 1.25 V vs. SCE in 0.5 M H2SO4 until surface hydride and oxide reactions were clearly resolved
in the resulting cyclic voltammograms. We assembled CNT films (70-500 n
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