Conducting polymers have been widely explored as coating materials for metal electrodes to improve neural signal recording and stimulation because of their mixed electronic–ionic conduction and biocompatibility. In particular, the conducting polymer poly­(3,4-ethylenedioxythiophene) (PEDOT) is one of the best candidates for biomedical applications due to its high conductivity and good electrochemical stability. Coating metal electrodes with PEDOT has shown to enhance the electrode’s performance by decreasing the impedance and increasing the charge storage capacity. However, PEDOT-coated metal electrodes often have issues with delamination and stability, resulting in decreased device performance and lifetime. In this work, we were able to electropolymerize PEDOT coatings on sharp platinum-iridium recording and stimulating neural electrodes and demonstrated its mechanical and electrochemical stability. Electropolymerization of PEDOT:tetrafluoroborate was carried out in three different solvents: propylene carbonate, acetonitrile, and water. The stability of the coatings was assessed via ultrasonication, phosphate buffer solution soaking test, autoclave sterilization, and electrical pulsing. Coatings prepared with propylene carbonate or acetonitrile possessed excellent electrochemical stability and survived autoclave sterilization, prolonged soaking, and electrical stimulation without major changes in electrochemical properties. Stimulating microelectrodes were implanted in rats and stimulated daily, for 7 and 15 days. The electrochemical properties monitored in vivo demonstrated that the stimulation procedure for both coated and uncoated electrodes decreased the impedance.

Conductive polymer coatings on metal electrodes are an efficient solution to improve neural signal recording and stimulation due to their mixed electronic-ionic conduction and biocompatibility.To date only a few studies have been reported on conductive polymer coatings on metallic wire electrodes for muscle signal recording. These studies mainly deal with testing of electrodes for acute recording during anaesthesia. Chronic muscle signal recording in free-walking animals offers more challenges for the electrode coatings, due to the muscle displacements which may cause coating delamination and device failure. The poor adhesion of conductive polymers to some inorganic substrates and the possible degradation of their electrochemical properties after harsh treatments, such as sterilization, or during implantation still limit their use for biomedical applications.In this work, we developed mechanically and electrochemically stable invasive electrodes for muscle signal recording in small animals based on stainless steel multi-stranded wires coated with the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The electrochemical and mechanical stability was achieved by tuning the electropolymerization conditions. PEDOT doped with ClO4anions was galvanostatically electropolymerized using three different solvents:propylene carbonate (organic), acetonitrile (organic) and water (inorganic). The coating's adhesion to the metallic substrate was tested through ultrasonication and the electrochemical stability was evaluated through accelerated ageing in phosphate buffer solution and autoclave sterilization.The solvent played a key role in the adhesion of the PEDOT coating, with organic solvents giving the best mechanical stability. Electrodes prepared with these solvents possessed excellent electrochemical stability, and survived sterilization and prolonged soaking without major changes in electrochemical properties.PEDOT-coated and bare electrodes were implanted in the acromiotrapezius muscle of five mice for muscle signal recording during a period of 6 weeks. The PEDOT coating improved the electrochemical properties of the stainless steel electrodes, lowering the impedance, which resulted in enhanced signal to noise ratio during in vivo muscle signal recording compared to bare electrodes. ix