Carbon dot-doped PDMS composites for flexible electrode applications

Noble metals are the main materials used for implantable electrodes due to their high conductivity and stability. However, metals' harshness to biological tissues restricts their use for implantation purposes. Hence, alternative flexible, conductive, and stable materials are being explored to replace metal electrodes. Polydimethylsiloxane (PDMS) is a polymer long considered suitable for implantation due to its biocompatibility and ability to withstand long implantation periods without deteriorating. However, PDMS lacks the electrical conductivity required of electrode materials. Therefore, PDMS has been doped with a range of conductive fillers to yield a conductive and elastic electrode composite. In this study, boronic acid-modified carbon dots (BA-CDs) are explored for the first time as conductive PDMS fillers to develop a conductive yet flexible PDMS-based electrode material. Electrodes composed of 25% BA-CDs, 16% glycerol (dispersant), and 59% PDMS were prepared and evaluated for their bulk impedance, conductivity, electrochemical stability, and charge storage capacity using electrochemical impedance spectroscopy and cyclic voltammetry, and elasticity, using Young's modulus obtained from uniaxial tensile testing. Results of this study revealed relatively high conductivity of the electrode (6.93×10- ⁴ S/cm) with low bulk impedance (185 Ω), which is comparable to that of some PDMS-based electrodes in the literature. The electrode was also electrochemically stable and capable of charge storage. Mechanically, the electrodes possessed a Young's modulus of 0.1691 MPa that is mechanically compatible with biological tissue. Results presented in this study show encouraging electrical and mechanical characteristics and provide a foundation for future studies to transition this composite for implantable electrode applications such as electrical stimulation of muscles suffering from peripheral nerve injuries.