Robust cellulose nanofiber/sodium alginate/poly(vinyl alcohol) hydrogels engineered by ionic coordination bonds for strain sensors

Poly(vinyl alcohol) (PVA)-based conductive hydrogels have exhibited significant application potential in flexible sensors because of their low cost, superior biocompatibility, and simple gelation process. However, the limited tensile performance of the PVA hydrogels restricts their applications in wearable devices and electronic skin. In this work, cellulose nanofiber/sodium alginate/PVA (CNF/SA/PVA) hydrogels with a triple-network interlocking structure have been successfully prepared without the need for repeated freezing-thawing cycles. The introduction of carboxylated cellulose nanofibers (CCNFs) provides a novel energy dissipation network via the synergistic effects of hydrogen bonds and ionic coordination bonds between the nanofiber reinforcement and the polymer matrix. The CCNF/SA/PVA hydrogels achieved a high tensile strength of ~4.7 MPa and a corresponding toughness of 4090 kJ m −3 . Polypyrrole (PPy) was deposited onto the CCNF/SA/PVA hydrogels to further improve the conductivity, resulting in the composite hydrogels with high sensitivity (GF = 3.38), excellent cyclic stability, rapid response performance (100 ms) and superior biocompatibility. In addition, the hydrogel sensors could monitor a wide range of human movements and physiological activities in real time.