Engineering low-swelling hydrogel electrodes for robust underwater surface electromyography via a dual-locking densification strategy

Dual-Locking strategy (ionic + physical) decouples swelling-conductivity trade-off. • Hydrogel achieves ultralow swelling (2.1%) and robust wet adhesion (>9 kPa). • Prevents micro-delamination, eliminating impedance drift and motion artifacts. • Enables 97.59% gesture accuracy and precise underwater muscle fatigue assessment. • Provides a reliable engineering paradigm for aquatic biopotential acquisition. Reliable acquisition of underwater surface electromyography (sEMG) is the cornerstone of aquatic health monitoring, yet it faces a critical challenge: the inevitable swelling of hydrogel electrodes disrupts the skin-electrode interface, leading to severe signal degradation. To address this dilemma, we propose a “Dual-Locking” densification strategy synergizing internal ionic locking (electrostatic interaction) and solvent-regulated physical crystallization to construct a robust polyphenol-based hydrogel (PTDG). This strategy effectively suppresses the swelling ratio (<3% in water; <9% in seawater) while preserving high ionic conductivity (1.84 S·m −1 ) and strong wet adhesion (9.33 kPa), successfully decoupling the trade-off between stability and electrochemical performance. Consequently, the PTDG electrode maintains a stable contact interface with minimal impedance drift, enabling high-fidelity sEMG recording with a signal-to-noise ratio of 36.47 dB even after 60 min of underwater operation. Validated by a rigorous session-wise deep learning evaluation (achieving a gesture recognition accuracy of 97.59% and a Macro-F1 score of 97.09%) and precise muscle fatigue monitoring, this work presents a versatile solution for reliable underwater biopotential acquisition. Download: Download high-res image (534KB) Download: Download full-size image