Bio-Functionalized and Biomimetic Conjugated Polymers for Interfacing Prosthetic Devices with Neural Tissue.

Abstract

Conjugated polymers, such as poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy), have been developed as effective materials for interfacing prosthetic device electrodes with neural tissue. These polymers, which are semi-conducting, provide an improved interface compared to metal electrodes because of their ionic conductivity, relatively soft modulus, low electrical impedance and ability to incorporate biological molecules. Recent focus has been on the development of conjugated polymers that have biological components in order to improve the biological response upon implantation of these electrodes. In this thesis, carboxylic acid-functionalized 3,4-ethylenedioxythiophene (EDOTacid) monomer was synthesized in order to covalently bind peptides to the surface of conjugated polymer films. EDOTacid was copolymerized with EDOT monomer to form stable, electrically conductive copolymer films referred to as PEDOT-PEDOTacid. The peptide GGGGRGDS was bound to PEDOT-PEDOTacid and was used to increase the adhesion of primary rat motor neurons between 3 to 9 times higher than controls, thus demonstrating that the peptide maintained its biological activity. PEDOT-PEDOTacid films have the potential to bind to a number of neural specific peptides that could control the behavior of neurons and vastly improve the performance of implanted electrodes. The research in this thesis also investigated the ability of four different monomers – L-3,4-dihydroxyphenylalanine (L-DOPA), 5,6-dimethoxyindole-2-carboxylic acid (DMICA), 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI) – to form electrochemically polymerized conjugated polymer films that mimic the structure of eumelanin, a type of naturally occurring melanin. One of these polymers, poly(5,6-dimethoxyindole-2-carboxylic acid) (PDMICA), was easy to polymerize and had especially interesting electrochromic and nano-structural features. In addition, PDMICA had a relatively high charge capacity (6.5 mC/cm2) and was not cytotoxic toward cells, making it the best candidate for bio-electrode coatings. Since these films are biomimetic in structure they may produce a less severe immune reaction compared to purely synthetic conjugated polymers. Both PDMICA and PEDOT-PEDOTacid are new materials that could be used in the future to coat prosthetic device electrodes and improve communication and interface between these devices and biological tissue.