Electrochemical Polymerization of Conducting Polymer Coatings on Neural Prosthetic Devices: Nanomushrooms of Polypyrrole
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Electrochemical Polymerization of Conducting Polymer Coatings on Neural Prosthetic Devices: Nanomushrooms of Polypyrrole Using Block Copolymer Thin Films as Templates Junyan Yang1, Yinghong Xiao1, and David C. Martin1,2,3 Department of Materials Science and Engineering1, Macromolecular Science and Engineering Center2, Department of Biomedical Engineering3, University of Michigan, Ann Arbor, MI 48109 ABSTRACT We have demonstrated a method to rapidly and reliably fabricate arrays based on the selfassembled morphology of block copolymer ultra thin films. An ordered, nanoporous structure obtained from the block copolymer thin films is used a template for the subsequent electrodeposition of conducting polymer nanomushrooms of polypyrrole (PPy). The influence of current density, deposition charge and morphology of the templates and nanostructured conducting polymer coatings has been investigated. The electrical properties of the polymer coatings were studied. INTRODUCTION Micromachined neural prosthetic devices facilitate the functional stimulation of and recording from the central nervous system (CNS). These devices have been fabricated to consist of silicon shanks that have gold or iridium sites along their surface. Our goal is to improve the biocompatibility and long-term performance of the neural prosthetic probes when they are implanted chronically in the brain. In our most recent efforts we have established that electrochemical polymerization can be used to deposit conducting polymers, such as polypyrrole (PPy), poly (3.4-ethylenedioxythiophene) (PEDOT), and PEDOT derivatives directly onto the electrode probes [1-4]. We found that the effective surface area of the electrode coated with conducting polymers is critical in determining its electrical properties, in promoting interaction with cells, and in providing a gradient in mechanical properties. For neural prosthetic devices that are intended for long term implantation, there would therefore be interest in making a layer with increased surface roughness on the electrode sites. This would provide more intimate contact and promote efficient signal transport at the interface of microelectrode array and brain tissue for long-term implantation. Although the precise surface morphology depends on the specific polymerization conditions used, only granular or fibrillar morphologies are observed by conventional electrochemical polymerization. More recently nanostructured conducting polymers have been attracted attention [5, 6]. Significant breakthroughs in the synthesis and fabrication of nanostructured conducting polymer with nanometer-scale control over microstructure have been made this possible. A number of approaches have been successfully used to produce nanostructured conducting polymers in recent years [7]. Among these techniques, the “template synthesis” method proposed by Martin et al [8] has been extensively used to produce nanotubes or nanofibers of conducting polymers inside the pores of commercial micro- or nanoporous membranes, with a wide range of po
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