An Adhesive Tough and Residue-Free Peeling Conductive Hydrogel Strain Sensor for Ultrasensitive Healthcare Monitoring

Conductive hydrogels have attracted considerable attention for use in flexible sensors, electronic skin, and biomedical applications because of their unique combination of mechanical flexibility and electrical conductivity. However, development of hydrogels with multifunctions, such as good mechanical robustness, high sensitivity, strong adhesion, and residue-free peeling capability, remains a challenge, which is crucial for practical wearable sensing applications. Here, we report a multifunctional organic hydrogel composed of polyacrylamide (PAM), carboxylated cellulose nanofibers (CCNF), carboxymethyl chitosan (CMCS), and polypyrrole (PPy). The hydrogel integrates abundant intermolecular interactions, including hydrogen bonds, metal–ligand coordination, and ionic bonds, which endow the hydrogel with strong interfacial adhesion to various substrates (up to 396.2 kPa on ceramic and 81 kPa on pork skin), while allowing for clean detachment without residual debris. The dual physical–chemical cross-linking architecture made the hydrogel have good mechanical properties and excellent tensile properties (353.13 kPa at 1370%). The hydrogel also exhibits high electrical conductivity (6.54 S/m), along with excellent freeze resistance (−80 °C) and good moisture-retention capability. As a strain sensor, the hydrogel shows high sensitivity (gauge factor = 7.56, strain range: 410–1200%) and a short response time (98 ms). When applied for monitoring electrocardiogram signals, the hydrogel enables highly sensitive and continuous monitoring, with significantly enhanced signal fidelity compared to standard commercial electrodes. This highly adhesive and residue-free peeling conductive hydrogel demonstrates significant potential for biomedical applications and shows broad application prospects in wearable devices, personal healthcare, and human–machine interfaces.