Sweat-Enhanced Biocomposite Electrodes for Dynamic Skin Electrophysiology

Electrophysiological monitoring is essential in healthcare and life science research, yet conventional Ag/AgCl gel or dry electrodes face challenges such as interfacial instability and susceptibility to sweat and motion artifacts. Herein, we propose a sweat-enhanced electrode design with a double-network hydrogel, comprising Ca²⁺-modified silk fibroin (SF) and poly(acrylic acid) grafted with <i>N</i>-hydroxysuccinimide ester (PAA-NHS). The obtained biocomposite SF-PAA-NHS (BioSP) forms robust skin adhesion through strong covalent crosslinking by NHS esters, along with other intermolecular forces at the BioSP/skin interface, leading to an interfacial toughness of 411 J m⁻². In the presence of sweat, SF enhances adhesion by increasing molecular chain mobility and facilitating mechanical interlock with the skin microstructure, resulting in a nearly 23% increase in interfacial toughness. Additionally, sweat electrolytes enhance the ionic conductivity of BioSP by about 45%, further improving its suitability for electrophysiological monitoring. Moreover, BioSP can be combined with elastomers to create electrodes with excellent anti-drying capability. Finally, high-fidelity and long-duration electrophysiological measurements validate the superior performance of the sweat-enhanced electrode during daily activities, such as exercise and perspiration. This work represents a significant step forward in skin electrode technology, promising improved reliability, longevity, and durability in electrophysiological monitoring systems, even on dynamic and sweaty tissue.