Electroactive covalent linkers for enhancing conducting polymer adhesion, charge transfer, and biological integration of PEDOT-coated carbon microfibers

Abstract

Poly(3,4-ethylenedioxythiophene) (PEDOT)-coated carbon microfibers (PCMFs) are a key technology for developing advanced neuroprosthetic electrodes and electroactive tissue scaffolds. However, for their successful application in human therapeutics, PEDOT adhesion to the carbon substrate must be enhanced without compromising electric charge transfer. Here, electrically functional linkers are synthesized to modify the surface at the nanoscale, facilitating the covalent bonding of EDOT to carbon. The properties of the resulting microfibers are compared before and after PEDOT polymerization. PCMFs deterioration is studied by applying controlled mechanical stress in vitro or by implanting them in the rodent spinal cord in vivo. Amino phenyl-EDOT derivatives allow for efficient covalent carbon surface functionalization and PEDOT electropolymerization but substantially reduce charge transfer as assessed by chronopotentiometry, electrochemical impedance spectroscopy, and cyclic voltammetry. Nevertheless, the azido-EDOT (EDOT-Ph-N3) derivative is similarly effective for carbon surface modification, enabling PEDOT polymerization to develop a nanostructured CMF surface based on robust covalent bonds, and enhancing both electric charge transfer and PEDOT adhesion to the carbon substrate. This makes PCMFs more resistant to polymer delamination when assessed in vitro or when implanted into the neural tissue. Azido-EDOT modified PCMFs also show excellent biological integration within the spinal cord, causing negligible tissue damage and cell reactivity. Overall, azido-EDOT provides a superior electroconducting linker for anchoring PEDOT and optimizes the electrical, mechanical, and biological performance of PCMFs.