Soft, Fuzzy, and Bioactive Conducting Polymers for Improving the Chronic Performance of Neural Prosthetic Devices
ABSTRACT Microfabricated electrodes for stimulating and recording signals from individual neurons have facilitated direct electrical connections with living tissue. While these devices have worked reasonably well in acute applications, chronically implanted electrodes have had more limited success [1,2]. To improve the long-term integration of these devices, coatings have been developed to accommodate the differences in mechanical properties, bioactivity, and mechanisms of charge transport between the engineered electronic device and living cells [3–10]. Conducting polymers can be directly deposited onto electrode surfaces with precisely controlled morphologies. The coatings lower the impedance of the electrodes and provide a mechanical buffer between the hard device and the soft tissue. These coatings can be tailored to incorporate and deliver pharmacological agents such as anti-inflammatory drugs and neurotrophic factors. In vivo studies to date have shown that these coatings improve the long-term recording performance of cortical electrodes . In this review we first discuss the development of neural prosthetic devices, including the history of their development, issues associated with the electrode–tissue interface, inflammation and neural loss in the tissue near the electrode surface, the mechanical property differences between the probe and the tissue, the geometry of the probe, and materials used to modify the electrode surface. We then discuss the design of materials for the electrode–tissue interface to help these probes function more effectively over the long term. These materials are intended to improve device performance by creating a mechanically compliant (soft), high-surface-area (fuzzy), low-impedance electrode–tissue interface that can have controlled biological functionality. We conclude by describing the results of work to date that have focused on the design, synthesis, and characterization of electrode interface materials, with particular attention to the use of conducting polymers that have been shown to significantly improve the electrical properties at these interfaces.