Conductive cellulose nanofibrils-reinforced hydrogels with synergetic strength, toughness, self-adhesion, flexibility and adjustable strain responsiveness.

The development of biomass-based hydrogel conductive devices is a promising but challenging subject. Here, cellulose was used to develop a strong, tough, and self-adhesive conductive hydrogel by constructing a synergistic covalent cross-link network and multiple physical interactions. Tannic acid-coated cellulose nanofibrils (TA@CNFs), poly(acrylamide), and ferric ions (Fe3+) were introduced in a composite network by coordination and hydrogen bonds. The strategy of interpenetrating network endowed this hydrogel with high mechanical strength (storage modulus over 14 K Pa), and strong toughness and tensile strength (fracture stress up to 108 K Pa). Chelated Fe3+ by metal coordination as inorganic conductive phase leads to good electrical conductivity (conductivity up to 3.12 S m-1). The obtained hydrogel also exhibited fine flexibility, extensive self-adhesion, and adjustable strain responsiveness for monitoring human joint movements. This work provided a new approach to design conductive hydrogels, and also can expand the application of cellulose-reinforced materials in the sensor field.