Ultrastretchable, Self-Adhesive, UV-Shielding Conductive Hydrogel as a Flexible Wearable Sensor for Human-Machine Interaction.

Conductive hydrogels are promising candidates for next-generation wearable electronics due to their flexibility, biocompatibility, and ion-conductive properties. However, achieving a balance among electrical conductivity, mechanical robustness, interfacial adhesion, and environmental stability remains a key challenge. Herein, we present a multifunctional hydrogel synthesized via a one-pot free radical polymerization of acrylic acid, methacryloxyethyltrimethylammonium chloride, tannic acid, and calcium ions. The designed hydrogel exhibits ultrastretchability (strain up to 2900%) and strong interfacial adhesion (160.92 kPa) owing to a synergistic cross-linked network formed by hydrogen bonding, ionic complexation, coordination, and covalent interactions. Adhesion capacity remains above 80% after ten peel cycles, indicating persistent interfacial coupling. It exhibits two linear sensitivity regimes, with gauge factors of 1.9 below 300% strain and 2.5 up to 1000%, and maintains stable electrical performance over 300 cycles. Its high ionic conductivity (30.24 mS/cm) supports low-impedance signal transmission, while its intrinsic UV-shielding property, derived from the catechol chemistry of tannic acid, enables reliable outdoor operation. The hydrogel also exhibits a rapid response time of 65 ms, allowing accurate detection of dynamic biomechanical signals. This conductive hydrogel holds great promise for real-time monitoring of human motion and microexpressions, as well as for secure communication applications such as Morse code encryption. This hydrogel design offers a promising route toward next-generation wearable electronics with potential applications in smart healthcare, human-machine interaction, and secure communication.