Poly(3,4-ethylenedioxythiophene) (PEDOT) Coatings for High-Quality Electromyography Recording

Abstract

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

Tailoring the Self‐Healing Properties of Conducting Polymer Films

“…Besides PSS, other dopants such as para-toluene sulfonate, trifluoromethanesulfonate, and inorganic anions are used in PEDOT-based conducting polymers for wearable electronics and bioelectronics ( Figure S6, Supporting Information). [33,49,52] We produced PEDOT:Tos and PEDOT:OTf films via chemical polymerization, which showed electrical conductivities of ≈1600 and ≈2200 S cm −1 , respectively. Inter-estingly, the healing experiments showed that these materials can also be healed repeatedly by water, similarly to PEDOT:PSS (Figure 5a).…”

“…− is adopted as the dopant for PEDOT in electropolymerization because to small dopants generally have better electrochemical properties with respect to larger ones (e.g., PSS). [52][53][54][55] In this case, upon one cut, the water droplet cannot restore the initial current of PEDOT:ClO 4 film, and only induces a transient ionic current flow similar to that observed in PEDOT:PSS films soaked in sulfuric acid for 3 days (Figure 5a). The difference between the water-enabled healing abilities of these various conducting polymers is probably based on their ability to swell in water.…”

“…Synthesis of PEDOT:ClO 4 : Electropolymerization of PEDOT:ClO 4 was carried out galvanostatically in an acetonitrile solution containing 30 × 10 −3 m EDOT monomer and 120 × 10 −3 m LiClO 4 in a three-electrode electrochemical cell, using a Bio-Logic VSP-300 potentiostat equipped with the EC-Lab software. [52] Silver/ silver chloride (Ag/AgCl) was used as the reference electrode, a Pt wire as the counter electrode, and a stainless-steel sheet with a size of ≈(6 × 1) cm as the working electrode. All working electrodes were rinsed in acetone, IPA, and deionized water and dried with nitrogen.…”

“…However, the different swelling behavior of the PEDOT films investigated in this work deserves further investigation, as differences might arise from several factors, such as the size and type of dopants, the film morphology and the PEDOT chain length. [49,52,59]…”

Biomimetic Synthesized Conductive Copolymer EDOT-Pyrrole Electrodes for Electrocardiogram Recording in Humans

“…Bihar et al reported on PEDOT:PSS electrodes inkjet-printed on paper for ECG recording [7]. Rossetie et al coated electrochemical stainless steel microwires with PEDOT:PSS for electromyogram recording in rats [8]. Zahed et al manufactured PEDOT:PSS loaded laser-induced graphene (LIG) electrodes for ECG recording [9].…”