Stability of Thin Film Neuromodulation Electrodes under Accelerated Aging Conditions

Thin film electrodes are becoming increasingly common for interfacing with tissue. However, their long-term stability has yet to be proven in neuromodulation applications where electrical stimulation over months to years is desired. Here, the stability of pristine and PEDOT:PSS-coated Au, as well as pristine PEDOT:PSS microelectrodes are examined over a period of 3 months in an accelerated aging setup where they are exposed to current stimulation, hydrogen peroxide, mechanical agitation, and high temperature. Pristine PEDOT:PSS electrodes show the highest stability, while pristine Au electrodes show the lowest stability. Failure mode analysis reveals that delamination and Au corrosion are the key drivers of electrode degradation. The PEDOT:PSS coating slows down Au corrosion to a degree that depends on the overlap between the two films. The results demonstrate that pristine PEDOT:PSS electrodes represent a promising way forward toward thin film devices for long-term in vivo neuromodulation applications.