Functional conducting polymer nanomaterials and bioactive polymer nanofibers for neural prosthetic - nervous system interfaces

Neural prosthetic devices are artificial extensions to the body that restore or supplement function of the nervous system lost due to disease or injury. The fundamental process that occurs at the electrode-tissue interface is the transduction of charge carriers from electrons in the metal electrode to ions in the tissue. Unfortunately only a minority of the recording electrodes on these devices continue to function for long periods of time. Cellular reactive responses including an acute inflammatory response and chronic foreign body reaction around the insertion site are thought to contribute to neuronal cell loss and device failure. Although several attempts have been made to modify the surfaces of neural electrodes in order to improve the electrical properties and reduce the immune response, the improvements in device performance over extended periods of time have been limited. This dissertation was focused on the use of poly (pyrrole) (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) conducting polymer nanomaterials and bioactive polymers for modification of electrode-tissue interface of the neural microelectrodes. We successfully showed that: (1) PEDOT and PPy nanotubes could significantly reduce the impedance of neural electrode sites and increase the charge capacity. (2) Anti-inflammatory drugs (dexamethasone) could be precisely released at desired points in time from conducting polymer nanotubes by using electrical stimulation as low as 0.5 V. (3) Cell culture experiments of dorsal root ganglion explants revealed the biocompatibility and neurite guidance of conducting polymer nanomaterials, as seen by the sustained growth of neurons and alignment of neurites parallel to the fiber direction. (4) Alginate hydrogel coatings on the neural probes provided a mechanical buffer layer between the hard silicon-based probe and the soft brain tissue, a scaffold for growing conducting polymer, and a diffusion barrier for controlling drug release. (5) PEDOT nanotubes increased the signal-to-noise ratio of recording sites in vivo. In the chronic response period (>2 weeks) the SNR values for the coated recording sites were 6.7 +/- 3.7 percent higher than the uncoated sites.; In summary, we report novel bioactive coating methods and drug delivery strategies for extending the long-term performance of neural microelectrodes.