Mussel inspired Cu-tannic autocatalytic strategy for rapid self-polymerization of conductive and adhesive hydrogel sensors with extreme environmental tolerance

Conductive hydrogels have broad application prospects in skin sensors and biomedical monitoring. However, the time-consuming and energy-consuming polymerization process and functional declination in harsh environments hinder its practical application. Herein, highly ionic conductive hydrogels with adhesiveness, flexibility, water-retention and anti-freezing properties are fabricated by a facile and rapid strategy through the combination of tannic acid coated cellulose nanofibers (TA@CNF), metal ion Cu2+, glycerol and polyacrylamide (PAM) chains. Interestingly, the reversible redox catalytic system constructed by TA and Cu2+ in an alkaline environment can significantly shorten the time required (<1 min) for hydrogel polymerization at room temperature. Meanwhile, hydrogen bonds between glycerol and water molecules elevate hydrogel environmental tolerance (-20 to 60 °C), endowing them with excellent flexibility and reproducible adhesion in a long-term usage environment. CNFs, as nano-reinforcements, construct a three-dimensional network structure with PAM for energy dissipation through multiple bonding and endowing the hydrogel with excellent mechanical strength (156.4 kPa) and stretchability (1624.8 %) while providing a tough and stable electron transport network for copper ions, which in turn exhibits excellent electrical conductivity (43.6 mS/m). Obviously, this strategy of preparing multifunctional hydrogels based on catechol metal ion rapid catalytic system will provide a new way for the design and development of advanced skin sensors.