Stable bioelectronic interfaces are essential for high-quality surface electromyography (sEMG) monitoring, especially under long-term wearing, sweating, and humid or aqueous conditions. Conventional Ag/AgCl gel electrodes can provide acceptable signal quality in short-term tests, but the drying of the conductive gel, unstable interfacial contact, and limited mechanical compliance often lead to impedance drift and motion artifacts during prolonged use. Conductive hydrogels have attracted increasing attention as soft electrode materials because of their tissue-like mechanical properties and intrinsic ionic conductivity. However, many hydrogel electrodes still suffer from excessive swelling in electrolyte-rich environments, which changes the electrode geometry and contact area and consequently deteriorates signal reproducibility. In this work, a polyelectrolyte-enhanced anti-swelling hydrogel electrode was developed for stable sEMG acquisition and muscle fatigue assessment. The hydrogel was constructed with polyvinyl alcohol (PVA) and gelatin as the physically crosslinked skeleton, while sodium polyacrylate (PAAS) and [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETMAC) were introduced to form an ionically conductive polyelectrolyte network. The charged polymer chains provided abundant mobile counterions and continuous ion-transport pathways, while the osmotic regulation associated with PAAS effectively restricted excessive water invasion in physiological saline and artificial sweat. Tannic acid (TA) and partially reduced graphene oxide (p-rGO) were further incorporated to improve interfacial adhesion, network energy dissipation, and electrical conduction. The resulting hydrogel exhibited a low equilibrium swelling ratio of 4.36% after long-term immersion in physiological saline and maintained a similarly low swelling ratio of approximately 4.56% in standard artificial sweat, demonstrating robust environmental stability under simulated sweating conditions. The optimized electrode also showed an ionic conductivity of 1.54 S/m and skin-relevant adhesion strength of 11.36 kPa on porcine skin, enabling conformal attachment to curved and deformable body surfaces. Mechanical tests indicated that the hydrogel possessed a skin-matched modulus and good cyclic deformation tolerance, which was favorable for reducing motion-induced interfacial fluctuation during dynamic monitoring. Based on the developed hydrogel electrode, a portable sEMG acquisition system was established. The system integrated differential amplification, anti-aliasing filtering, analog-to-digital conversion, and wireless data transmission, and the sampling rate was set at 450 Hz to cover the characteristic frequency range associated with muscle fatigue. Compared with commercial Ag/AgCl electrodes, the hydrogel electrode produced stable and clearly distinguishable sEMG waveforms during both hand and leg movements. The signal-to-noise ratios reached 35.66 dB for forearm signals and 36.46 dB for leg signals, indicating high-fidelity bioelectrical signal acquisition. During a 60 min stability test under aqueous conditions, no obvious signal attenuation was observed, suggesting that the anti-swelling polyelectrolyte network contributed to maintaining stable interfacial impedance. Finally, a 30 min isometric grip fatigue experiment was performed to evaluate the capability of the electrode for physiological monitoring. Time-domain and frequency-domain features were extracted through RMS analysis and Welch power spectral density estimation. As fatigue developed, the RMS value gradually increased, while the median frequency shifted from 64.2 Hz to 58.3 Hz, reflecting the typical spectral compression caused by reduced muscle fiber conduction velocity. These results demonstrate that the proposed polyelectrolyte hydrogel electrode can simultaneously achieve anti-swelling stability, wet adhesion, mechanical compliance, and high-quality sEMG acquisition. This work provides a feasible material and device strategy for wearable health monitoring, rehabilitation training, and human-machine interaction in humid or aqueous environments.
Key words
surface electromyography /
polyelectrolyte hydrogel /
interfacial adhesion /
anti-swelling /
double-network structure /
fatigue assessment
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Funding
Joint Funds for Innovation in the Science and Technology Field of Medicine and Health in Fujian Province (2025Y9591); Major Science and Technology Project of Fujian Province (2024HZ022013); National Natural Science Foundation of China (52575458, 52405424)
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