Nanocomposites for Neural Interfaces
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Nanocomposites for Neural Interfaces Tanja Kmecko1, Gareth Hughes1, Larry Cauller2, Jeong-Bong Lee3, and Mario Romero-Ortega4 1 Zyvex Corporation, Richardson, Tx, 75081 2 School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, Tx, 75083 3 Erik Jonsson School of Engineering and Computer Science, University of Texas at Dallas, Richardson, Texas, 75083 4 Division of Regenerative Neurobiology, Texas Scottish Rite Hospital for Children, Dallas, Tx, 75219 ABSTRACT We have fabricated micro-probes consisting of gold microelectrode sites (500 µm long and 12 µm wide) modified with conductive polymers and carbon nanotubes to achieve intimate contact with the nervous system. The fabrication process includes photolithography, electroplating and micromachining techniques. In order to obtain a high quality neural contact, we have investigated the preparation and characterization of neural interface materials. Electrochemical polymerization using potentiostatic and galvanostatic methods was used to optimize the surface of the metal electrode sites. Scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to study the surface morphology, electrochemical properties, and stability of electrodeposited polymers. Cytotoxicity tests using fibroblasts and Schwann cells were performed to evaluate the biocompatibility of the micro-probes and neural interface materials. Normal rat kidney (NRK) cells and dorsal root ganglia (DRG) in vitro preparation was used to evaluate neuronal cell adhesion to the electrode. Polypyrrole (PPy), poly(3,4-ethylendioxythiophene) (PEDOT) were deposited onto microelectrode sites from aqueous solution with various thicknesses, dopants and electrochemical growth through self-assembly strategy to improve adhesion of PPy and PEDOT films to the electrode. The phenomenon of autoadsorption of thiolates on gold was used to anchor either monomer or CNT functionalization/dispersive agent to the electrode surface. Our results demonstrate that we can control the morphology, size and electrical properties of PPy and PEDOT by changing the polymerization conditions and adding dopant structures, such as chloride and CNTs. It was observed that the addition of carbon nanotubes favors the formation of nodules and increases the surface roughness. Also, electrochemical impedance spectroscopy revealed that conductive polymer composites lower the impedance of gold microelectrodes by three orders of magnitude. INTRODUCTION The most common conductive polymers used as neural interface materials in micromachined neural prosthetic devices are polypyrrole (PPy) and polythiophene [1-3]. These polymers are particularly interesting because of the polymer charge density control, which plays a very important role in dictating cell interaction with electrode site on the neural probes. Polypyrrole and polythiophene are ideally suited for in vivo application because of their biocompatibility and stability under physiological conditions. Poly(3,4-
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