Conductive polymers, particularly poly(3,4-ethylenedioxythiophene) (PEDOT), have attracted a good amount of interest in the past two decades as an alternative to platinum-based materials at the neural interface for electrical stimulation and recording. In addition to the reported higher charge storage and charge injection capacities, PEDOT-based coatings offer the advantages of unique physicomechanical properties, e.g., lower stiffness and a combination of electronic and ionic conductivity that could potentially create a more biomechanically compatible electrode/tissue interface.

However, questions remain in terms of the long-term physical and chemical/electrochemical stability of PEDOT:PSS and whether this or related materials can be a viable alternative to platinum alloys for long-term electrical stimulation. In this bench study, the stability of PEDOT:PSS was evaluated by subjecting coated electrodes, prepared through electropolymerization in an electrolyte containing 0.01 M of EDOT and 0.1 M of NaPSS, to biphasic constant current stimulation in 0.9% saline at 37^oC. The electrode potential during stimulation was measured versus a saturated calomel reference electrode (SCE) via an integrated oscilloscope. Electrochemical impedance spectroscopy (EIS) was used as a non-destructive tool to track and assess the stability and structural integrity of the coating as a function of stimulation over time.

It was found that the anode potential and cathode potential of PEDOT:PSS coated electrodes continue to drift up in anodic and cathodic direction, respectively, under stimulation. More importantly, the Interpulse potential of the cathode can be driven into high anodic potential region that can cause irreversible physical and chemical changes to the coating that indicates a lack of stability with chronic use, which was confirmed by post stimulation visual observation and XPS surface analysis on the electrodes.