Intracortical neuroprostheses offer the prospect of bi-directional communication interfaces for treatment and scientific understanding of physical and mental neurological disorders; however, their long-term functionality is limited by our inability to compensate for the dynamics of the neural interface. The neural interface refers to the electrode-tissue interface formed by placing an electrode into neural tissue. The brain's reactive tissue response electrically and mechanically isolates the device from healthy tissue, reducing recording quality as well as stimulation performance. Additionally, current intracortical microstimulation materials are either unable to safely deliver charge, or materials degrade during applied electrical stimulation.

The objectives of the presented research were to enhance the long-term reliability of the intracortical neural interface by 1) improving the reliability and performance of micro-neural interface materials for electrical stimulation, and 2) forming an integrated neural interface after device implantation beyond the region of tissue affected by the reactive tissue response. Here we report the achievement of these objectives through the use of the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The techniques presented here offer unique neural interfacing approaches to improve the long term functionality of intracortical neuroprostheses.

In the first study, we evaluated the in vitro stability and in vivo performance of PEDOT coatings for microstimulation. Microelectrodes coated with PEDOT exhibited electrochemical properties superior to iridium oxide and remained stable after short-term repetitive pulsing at current densities damaging to iridium oxide. Further, chronically implanted PEDOT coated microelectrodes subjected to daily microstimulation displayed a more reliable, low-impedance interface which corresponded to safer, lower-amplitude voltage excursions. However, both electrode materials were equally effective in regards to behavioral thresholds suggesting similar amounts of tissue damage likely occurred with all implanted devices.

In the second study, we evaluated in vivo PEDOT polymerization as a technique to grow the neural interface after implantation to interface with healthy tissue beyond the region influenced by the reactive tissue response and potentially improve the safety of stimulation levels. In vivo PEDOT polymerization in the rat cerebral cortex resulted in lower impedance and improved recording quality. Histological analysis by optical microscopy confirmed successful integration of a dense PEDOT network within the tissue extending approximately 100-200 µm adjacent to the electrode.