On-Demand Detachable Hydrogel Electrodes with Robust Adhesion for Epidermal Electrophysiological Monitoring

Abstract

With the rapid development of bio-flexible electronic devices, achieving long-term and comfortable health monitoring is of crucial importance. Currently, a key contradiction exists in epidermal electrodes based on adhesive hydrogels: namely, maintaining high-quality electrophysiological signal acquisition while achieving controllable and non-invasive interface separation. This limitation severely restricts their practical application in dynamic environments or among sensitive populations. To address this, we developed a temperature-responsive and reversibly adhesive hydrogel, P(AA-co-NIPAAM). By utilizing a self-catalytic redox system composed of tannic acid (TA) and ferric chloride hexahydrate (FeCl3·6H2O), ammonium persulfate (APS) is rapidly activated at ambient temperature to initiate the free radical copolymerization of acrylic acid (AA) and N-isopropylacrylamide (NIPAAM), achieving the formation of an electrode interface capable of in situ gelation on the skin surface. At physiological temperature (37 ℃), this hydrogel exhibits excellent adhesion performance with skin tissue (Interfacial toughness > 200 J m-2) and a low modulus (~ 1.86 kPa) matching skin tissue; however, after mild heating (46 ℃), its adhesion performance rapidly decreases (Interfacial toughness < 50 J m-2), enabling gentle and non-damaging removal within 30 s. In various practical scenarios such as running, showering, and daily activities, the P(AA-co-NIPAAM) hydrogel electrode demonstrates significantly superior signal-to-noise ratios (SNR) in acquired electrocardiographic (ECG) and electromyographic (EMG) signals compared to commercial Ag/AgCl electrodes. This study provides an innovative material design strategy to resolve the core contradiction between strong adhesion and easy removal at the bio-electronic interface, which is of great significance for promoting the development of next-generation wearable medical devices and long-term health monitoring systems.