Hydration-adaptive and omnidirectionally stretchable silk/Ag@Au nanowire epidermal electrodes for unobtrusive long-term electrophysiological monitoring

Achieving high-performance epidermal electrodes for long-term electrophysiological monitoring remains a significant challenge, as it necessitates a delicate balance between high electrical conductivity, optical transparency, mechanical compliance, and environmental stability within a single platform. Herein, we present a multifunctional epidermal bioelectrode (silk/Ag@Au BioE) fabricated by combining a silver-gold core-sheath nanowire (Ag@Au NW) network with a silk fibroin (SF) substrate via direct ink writing and solution-casting transfer techniques. The resulting electrode exhibits superior optical transmittance (up to 94.3%) and a low sheet resistance of 10.9 Ω/sq. A unique hydration-induced plasticization is employed to transform the initially rigid SF film into an ultra-soft, conformal skin interface. This process induces the spontaneous formation of micro-wrinkled architectures, which, in synergy with a meticulously designed second-order serpentine mesh, imparts exceptional omnidirectional stretchability and robust mechanical durability. The electrode also demonstrates high breathability (1591 g/(m²·day)), excellent resistance to sweat and oxidation, and sustainable reusability over multiple hydration-dehydration cycles. This integrated design enables high-fidelity, long-term monitoring of electrocardiogram (ECG), electromyogram (EMG), and electrooculogram (EOG) signals under dynamic and harsh conditions, substantially outperforming conventional Ag/AgCl electrodes. This work provides a versatile and robust material platform for next-generation wearable healthcare diagnostics.