Electropolymerized PEDOT Coatings on Penetrating Neural Probes Improve Chronic In Vivo Electrochemical Stability

The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a promising material for improving the stimulation efficiency of neural microelectrodes due to its many advantageous characteristics, such as mechanical compliancy, electrochemical stability, and high conductivity. Studies on the long-term in vivo electrochemical stability of penetrating PEDOT-coated electrodes undergoing high-frequency stimulation are not extensively done and the immune response of the brain towards PEDOT-coated stimulating neural probes is not well investigated. In this study, electropolymerized PEDOT doped with tetrafluoroborate (PEDOT:BF4) is selectively deposited on the electrodes of platinum iridium (PtIr) neural probes and implanted for 2 weeks and 2 months to evaluate the effect of implantation on the electrical performance, along with the foreign body response to the probes. Histological analysis after 8 weeks of implantation shows no difference in the degree of inflammation around PtIr and PEDOT probes. Furthermore, PEDOT and PtIr probes are implanted for 60 days, and subject to daily high frequency stimulation while being monitored for changes in electrochemical properties. Impedance measurements confirm an overall lower impedance for PEDOT probes. This study shows that PEDOT:BF4 coatings can contribute to the electrochemical stability of neural interfacing devices for stimulation and recording.