The objective of this project is to develop conducting polymer microelectrodes for neural prostheses using polypyrrole and related electronically-conducting polymers. these new materials are capable of high charge injection densities and long service life, and offer promise of considerable improvement over the metal electrodes currently in use. The high charge injection density is the result of the reduction/oxidation of the electronically conducting polymer with simple ion (usually anion) transfer in and out of the polymer compensating the change in electronic charge. This avoids the introduction of any toxic electrochemical reaction products into the solution. A 10-Mum thick layer has a faradaic capacitance of the order of 100,000 MuF cm to the minus 2 in comparison with the usual 20-40 MuF cm to the minus 2 for the ionic double layer capacitance of a smooth metal electrode. In addition, the use of polymeric materials shold avoid many of the fatigue and corrosion problems associated with metals. In contrast to most electronically conducting polymers, the polypyrroles are stable in the presence of water and oxygen over a useful range of potentials. The polymers to be used as electrodes will be prepared by electrochemical polymerization of pyrrole and related monomers under various conditions. Relevant chemical and physical properties will be studied as a function of formation conditions.
The aim will be to produce polymers with optimum stability, conductivity, fatigue resistance and charge injection capacity. These materials will be fabricated into neuromuscular stimulation electrodes and tested in vivo (both as active and passive implants) to determine their likely service life and compatibility with muscle tissue. Insulator adhesion is a problem with metal electrodes for neural prostheses. It should be possible to apply polymeric insulating layers to the surface of the conducting polymer electrodes with a much better match of mechanical properties. Methods of bonding insulator layers to the surface of conducting polymers will be investigated.
