Lignin-Based Surface Adhesion Engineering Enables Tough Hydrogel for Flexible Epidermal Array Sensing

Biocompatible adhesive hydrogels demonstrate a promising potential to increase the sensing stability of wearable electronics. However, their application performance has been severely limited by the trade-off between interfacial adhesion and cohesion so far. Here, inspired by the robust adhesion of mussel foot proteins and the double-layer structure of spider silk, we propose a catechol lignin-based surface adhesion engineering strategy that enables in situ fabrication of tough adhesive hydrogels for wearable epidermal electrodes. The modified lignin stably binds to the hydrogel surface through multiple hydrogen bonds and electrostatic interactions and effectively overcomes the mechanical deterioration existing in conventional lignin bulk-doping hydrogels. The fabricated hydrogel exhibits strong adhesion to both skin and elastomer, with interfacial toughness values of 778 and 290 J·m^-2, demonstrating 9.4- and 18.6-fold enhancements over unmodified hydrogels. Accordingly, a hydrogel-elastomer hybrid bioelectrode is developed for physiological signal monitoring, showing a higher electromyography (EMG) signal-to-noise ratio (SNR) than commercial electrodes. Furthermore, a 6 × 4 electrode array is constructed and can maintain stable electrode-tissue interaction and 100% signal retention during intense contraction of biceps. This strategy provides new insight into the design of biomimetic adhesive hydrogels and promotes their application in wearable electronics.