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Objective. To systematically compare the in vitro electrochemical and mechanical properties of several electrode coatings that have been reported to increase the efficacy of medical bionics devices by increasing the amount of charge that can be delivered safely to the target neural tissue. Approach. Smooth platinum (Pt) ring and disc electrodes were coated with reduced graphene oxide, conductive hydrogel, or electrodeposited Pt–Ir. Electrodes with coatings were compared with uncoated smooth Pt electrodes before and after an in vitro accelerated aging protocol. The various coatings were compared mechanically using the adhesion-by-tape test. Electrodes were stimulated in saline for 24 hours/day 7 days/week for 21 d at 85 °C (1.6-year equivalence) at a constant charge density of 200 µC/cm2/phase. Electrodes were graded on surface corrosion and trace analysis of Pt in the electrolyte after aging. Electrochemical measurements performed before, during, and after aging included electrochemical impedance spectroscopy, cyclic voltammetry, and charge injection limit and impedance from voltage transient recordings. Main results. All three coatings adhered well to smooth Pt and exhibited electrochemical advantage over smooth Pt electrodes prior to aging. After aging, graphene coated electrodes displayed a stimulation-induced increase in impedance and reduction in the charge injection limit (p   <  0.001), alongside extensive corrosion and release of Pt into the electrolyte. In contrast, both conductive hydrogel and Pt–Ir coated electrodes had smaller impedances and larger charge injection limits than smooth Pt electrodes (p   <  0.001) following aging regardless of the stimulus level and with little evidence of corrosion or Pt dissolution. Significance. This study rigorously tested the mechanical and electrochemical performance of electrode coatings in vitro and provided suitable candidates for future in vivo testing.

Neural electrodes used for in vivo biomedical applications (e.g. prostheses, bionic implants) result in glial invasion leading to the formation of a non-excitable scar which increases the distance between neurons and electrode and increases the resistance to current flow. The result is progressive deterioration in the performance of stimulation or recording of neural activity and inevitable device failure. Also, electrodes with a 2-dimenstional (2D) surface have a limited proximity to neurons. In the present study, a macroporous and fibrous 3-dimensional (3D) neural electrode was developed using poly-L-lactic acid fibrous membranes imbued with electroactive properties via a coating of the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT), using vapor phase polymerization. The electrical properties of the PEDOT coated substrates were studied using sheet resistance and impedance. PEDOT electrode biocompatibility was assessed through in vitro assays using patch clamp electrophysiology and calcium imaging of isolated and cultured rat hippocampal neurons. PEDOT fibers supported robust normal functional development of neurons, including synaptic networking and communication. Stimulation and recording of activity in brain slices, and from the surface of the brain using 3D-PEDOT fibrous electrodes were indistinguishable from recordings using conventional glass or platinum electrodes. In vivo studies revealed minimal reactive gliosis in response to electrode implantation.