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.

Implantable biomedical electrodes are widely used for biological signal recording and stimulation, with applications ranging from Parkinson disease treatment to brain machine interfaces. Due to the inherent difficulties associated with...

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

require low-impedance at the electrodetissue interface to maintain efficient charge injection during stimulation. [4] The impedance of the electrode sites of neural probes steadily increases with time during implantation due to the immune system's response to the insertion of the probes into tissue. [5] Conducting polymers have been widely explored as coatings for stimulating neural probes to reduce the impedance at the electrode-tissue interface. [6,7] Among conducting polymers, poly(3,4ethylenedioxythiophene) (PEDOT) has significantly contributed to improving the electrical stability of neural probes due to its high conductivity, electrochemical stability under chronic exposure to biological environments, and compliant mechanical properties which provide a softer interface between brain tissue and stiff probes. [8][9][10] The stability of PEDOT coatings on the electrode sites of neural probes is critical for ensuring the long-term functionality of the neural device. [11] One major mode of PEDOT coating failure is through coating delamination or cracking. [12][13][14][15] The coating must be able to survive mechanical stresses, swelling, and electrode corrosion in order to be considered for use in clinical applications. [16] Substantial improvements in PEDOT stability have been achieved through tuning the polymerization parameters, accurately selecting dopants and solvents used for polymerization, and incorporating additives into the PEDOT film. [10,[17][18][19][20] Chronic stability of PEDOT-based recording neural electrodes has been extensively studied and reviewed. [8,19,[21][22][23][24][25][26][27][28][29] Studies of PEDOT coating stability under stimulation have been recently reviewed. [7,16,17] In one study, electropolymerized PEDOT, containing carbon nanotubes, on Pt microelectrodes was monitored over 3 months of soaking in phosphate buffered saline (PBS) with and without stimulation, and were reported to have stable impedance. [30] An in vivo study stimulated the Au electrode sites of a neural probe coated with PEDOT and carbon nanotubes for 1 h a day for 10 days (20 mA, 200 Hz). PEDOT demonstrated similar impedance values to Au electrode sites at the end of the study. [31] On the other hand, PEDOT doped with tetrafluoroborate (PEDOT:BF 4 ) electropolymerized on platinum iridium (PtIr) neural probes was implanted for 15 days, stimulated daily for 90 min (20 mA, 130 Hz) while monitoring the impedance. At the end of the implantation period, Resulting from its many unique properties, such as mechanical compliancy, electrochemical stability, and high conductivity, the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is a promising material for improving the stimulation efficiency of neural microelectrodes. The long-term electrochemical stability of penetrating PEDOT-coated electrodes undergoing high-frequency stimulation is not extensively studied in vivo and the inflammatory response of the brain to PEDOT-coated stimulating neural probes is not well understood. In this work, electropolymerized PE...

Highly stretchable and flexible bioelectronics should form close contact with skin and tissues while being able to withstand the stresses and strains endured by the body in order to reliably monitor physiological signals over time. Here, we report highly stretchable poly 3,4-ethylenedioxythiophene: polystyrene sulfonate (PEDOT:PSS) films printed on thermally resistant polyurethane (TPU) substrates. We established the stability of the conductivity of the devices under high strains up to 600%. The printed PEDOT:PSS film enabled the fabrication of printed organic electrochemical transistors (OECTs) with an ON/OFF ratio of 450 on a flexible substrate. We also acquired physiological signals from measuring the skin conductance arising from changes in sweat volume by directly interfacing a printed PEDOT:PSS-based sensor on TPU with human skin. Stretchable printed PEDOT:PSS films on TPU provide a facile method of producing highly stable stretchable sensors for bioelectronic applications, enabled with simple and direct printing fabrication.