Guide to Leveraging Conducting Polymers and Hydrogels for Direct Current Stimulation

The tunable electrical properties of conducting polymers (CPs), their biocompatibility, fabrication versatility, and cost-efficiency make them an ideal coating material for stimulation electrodes in biomedical applications. Several biological processes like wound healing, neuronal regrowth, and cancer metastasis, which rely on constant electric fields, demand electrodes capable of delivering direct current stimulation (DCs) for long times without developing toxic electrochemical reactions. Recently, CPs such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) have demonstrated outstanding capability for delivering DCs without damaging cells in culture while not requiring intermediate buffers, contrary to the current research setups relying on noble-metals and buffering bridges. However, clear understanding of how electrode design and CP synthesis influence DCs properties of these materials has not been provided until now. This study demonstrates that various PEDOT-based CP coatings and hydrogels on rough electrodes can deliver DCs without substantial changes to the electrode and the noticeable development of chemical by-products depending on the electrode area and polymer thickness. A comprehensive analysis of the tested coatings is provided according to the desired application and available resources, alongside a proposed explanation for the observed electrochemical behavior. The CPs tested herein can pave the way toward the widespread implementation of DCs as a therapeutic stimulation paradigm.