Soft, Stretchable and Patterned Hydrogel Electrodes for Small-Nerve Interfacing and Compound Muscle Action Potential Recording

Implantable electronic devices have broad applications for various disease diagnoses and treatments. Existing commercial electronic implants rely on conductive materials with high Young’s Modulus, such as gold and platinum. Mechanical disparity across rigid electronics-tissue interfaces has been a major drawback affecting the biocompatibility of electronic implants. Soft materials with Young’s modulus matching that of biological tissues can significantly reduce adverse immune responses and are highly desired for next-generation bioelectronics. In this work, we report soft conductive hydrogels with electronic and ionic dual conductivity for high-performance electronic implants. We introduced a nontoxic additive to poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) aqueous solution to form conductive hydrogels. The conductive hydrogels exhibit swelling reversibility, low modulus, and excellent electrical conductivity. Compared to platinum and gold electrodes, hydrogel electrodes possess lower electrical impedance, higher charge storage, and injection capacity. We demonstrated electrical stimulation of the sciatic nerve in a live rat and measured simultaneous compound muscle action potential using our developed tissue-like soft patterned cuff electrode. In chronic biocompatibility investigations, the soft cuff electrode showed no sign of inflammation, but the platinum electrode exhibited inflammation that could be attributed to the modulus disparity between the electrode materials and the delicate nerve tissue.