Understanding the Effects of Conductive Polymer Electrode Coating on Recorded Neural Signals

Conductive polymer coatings have been extensively explored as a means of improving the quality of neural signals recorded with chronically implanted electrodes. They offer enhanced biocompatibility along with reduced electrode impedance and are reported to improve signal-to-noise ratio and signal amplitude. The mechanisms by which poly(3,4ethylenedioxythiophene) (PEDOT) and its derivatives enhance the quality of neural signals recorded in vivo, however, remain unclear. Here, a computational model of PEDOT:PTS (polythiophenesulfonyl chloride) coated neural recording electrodes is used to understand how the different properties of conductive electrode coatings influence local field potentials recorded in vivo. Impedance, histology and electrophysiology data were obtained from coated and uncoated microelectrodes chronically implanted in the rat basal ganglia and incorporated in the model. Together the simulation and experimental results indicate that improvements in signal quality with PEDOT:PTS coated electrodes are driven by greater neural proximity to the electrode, facilitated by reduced peri-electrode gliosis. Reductions in thermal noise with decreasing electrode impedance further contributed to a higher signal-to-noise ratio for PEDOT:PTS coated electrodes. Finally, the results demonstrate that, provided amplifier input impedance requirements are satisfied, the enhanced recording capability of polymer coated electrodes compared to uncoated electrodes is due primarily to improved biocompatibility rather than reduced electrode impedance.