electronics), [1][2][3][4] solar cell technology, [5][6][7][8][9] solar water purification, [10] batteries (e.g., supercapacitors), [11][12][13][14] and biomedical engineering (e.g., electrode coating for recording and stimulation, drug delivery, scaffolds for tissue engineering). [15][16][17][18][19][20][21] The inherent conductivity of these polymers originates from their chemical structure consisting of repeating alternating chains of single and double (π-π) carbon bonds, allowing electrons to move freely alongside the polymeric backbone. Furthermore, these materials can be doped through several processes (e.g., chemically, electrochemically, photonically), effectively increasing their electrical conductivity through the buildup of polarons. [22] In addition to their outstanding and tunable electrical performance, CPs are a cost-effective alternative to metals, can be biodegradable and biocompatible, can be synthesized through a wide range of processes, and can be coated on different types of substrates. Amongst the most studied CPs, we find polypyrrole (PPy), polyaniline (PANI), and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). All these CPs have been extensively used in biomedical applications for bioelectrical measurements, electrical stimulation, drug delivery, and as bioactuators and biosensors. [23][24][25][26][27] Particularly, the use of PEDOT as a coating for stimulation electrodes has been at the center stage of research in the last decade due to the high electrochemical stability and three-dimensional structure of this polymer, 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...
