Transparent Conductive Silk Film with a PEDOT-OH Nano Layer as an Electroactive Cell Interface

Bioelectronics based on biomaterial substrates are advancing toward biomedical applications. As excellent conductors, poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have been widely developed in this field. However, it is still a big challenge to obtain a functional layer with a good electroconductive property, transparency, and strong adhesion on the biosubstrate. In this work, poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-OH) was chemically polymerized and deposited on the surface of a regenerated silk fibroin (RSF) film in an aqueous system. Sodium dodecyl sulfate (SDS) was used as the surfactant to form micelles which are beneficial to the polymer structure. To overcome the trade-off between transparency and the electroconductive property of the PEDOT-OH coating, a composite oxidant recipe of FeCl₃ and ammonium persulfate (APS) was developed. Through electrostatic interaction of oppositely charged doping ions, a well-organized conductive nanoscale coating formed and a transparent conductive RSF/PEDOT-OH film was produced, which can hardly be achieved in a traditional single oxidant system. The produced film had a sheet resistance (R_s) of 5.12 × 10⁴ Ω/square corresponding to a conductivity of 8.9 × 10^-2 S/cm and a maximum transmittance above 73% in the visible range. In addition, strong adhesion between PEDOT-OH and RSF and favorable electrochemical stability of the film were demonstrated. Desirable transparency of the film allowed real-time observation of live cells. Furthermore, the PEDOT-OH layer provided an improved environment for adhesion and differentiation of PC12 cells compared to the RSF surface alone. Finally, the feasibility of using the RSF/PEDOT-OH film to electrically stimulate PC12 cells was demonstrated.