Conductive hydrogel interfaces for flexible bioelectronics: Design, coupling, and applications

Bioelectrical signal detection is evolving toward continuous, intelligent, and flexible monitoring. Compared with conventional Ag/AgCl wet electrodes, metal dry electrodes, and flexible thin-film electrodes, conductive hydrogels combine high water content, low modulus, good biocompatibility, and tunable electrical, adhesive, and mechanical properties, enabling stable conformal contact on skin or soft tissues, reduced interfacial impedance, and unique advantages in wet, underwater, and dynamic environments. This review systematically summarizes conductive hydrogel interfaces for bioelectrical signal detection. First, the three major conduction modes, including ionic conduction, electronic conduction, and ion–electron synergistic conduction, are introduced, together with design strategies such as multi-network construction, layered heterogeneous architectures, microstructure regulation, and fabrication methods. Then, the key factors governing device performance, including mechanical matching, interfacial adhesion, interfacial impedance, electrochemical stability, long-term stability, and biocompatibility, are discussed. Subsequently, recent advances in conductive hydrogels for epidermal wearable bioelectrical monitoring, implantable and tissue-integrated bioelectrical interfaces, and multifunctional intelligent integrated systems are reviewed. Finally, the remaining challenges and future directions are outlined, with emphasis on performance synergy, long-term reliability, system integration, and clinical translation.