Development of smart conductive hydrogels based on a gold-poly(ethylene glycol) diacrylate-liquid epoxidized natural rubber matrix for functional neuromodulation applications.

This study presents the development of liquid epoxidized natural rubber, LENR-based conductive hydrogels (LH) for functional electrical stimulation (FES) applications. Four formulations were prepared by incorporating poly(ethylene glycol) diacrylate (PEGDA) and gold nanoparticles into LENR biopolymers. LH4 hydrogel, containing both additives, showed superior performance with a conductivity of 0.0037 S/cm, low resistivity (230 Ω·cm), high conductivity (0.0167 S) and excellent tensile strength, which was maintained at over 87 % after 14 days in phosphate-buffered saline (PBS) at 37 °C. Electrochemical impedance spectroscopy (EIS) showed that LH4 hydrogel has the lowest charge transfer resistance (Rct = 48 ± 18 Ω), indicating effective ion transport. Functionally, LH4 hydrogel provided stable current and frequency responses during muscle stimulation, comparable to commercial FES systems. These results highlight the synergistic effect of PEGDA and gold nanoparticles, positioning LH4 hydrogel as a durable material suitable for wearable neuromodulation devices.