The impact of chemical functionalization of carbon nanotubes on the electrochemical performance of carbon fiber/pyrocarbon/carbon nanotube composites as potential materials for electrodes for nerve cell stimulation

In this work, we propose a new carbon–carbon (C–C) composites as a potential materials for electrodes for neural stimulation in neurodegenerative disorders. The C–C composites were made via chemical vapour deposition (CVD) synthesis of pyrocarbon on carbon fibers, with subsequent thermal spray deposition of carbon nanotubes (CNT). Different CNT types were tested to evaluate their impact on electrochemical and biological performance. Materials were analyzed for microstructure, surface chemistry, and electrochemical properties, then tested using SH-SY5Y neuroblastoma cells for biological assessment. The C–C composites coated with a hydroxy-terminated CNT demonstrated significantly enhanced electrochemical properties, in particular increased cathodal charge capacity up to 12.51 mC cm−2, a wide safe potential window of −1.53 to 1.26 V, and decreased impedance, and cut-off frequency (fcut-off = 0.16 kHz). No acute negative biological responses of the materials were detected after 48 h of exposition. Such properties significantly outperform the properties of platinum, which is the basic element of platinum electrodes, demonstrating the excellent performance of the obtained composites and showing it may constitute the basic element of carbon electrodes for nerve stimulation in the future. Our work presents the method for obtaining biologically inert carbon composite micro-electrodes which can potentially be adapted to neural stimulation.