Muscle-inspired double-network hydrogels with robust mechanical property, biocompatibility and ionic conductivity

•Double network hydrogels with hierarchically aligned structures were fabricated.•Strength and elongation-at-break of the hydrogels were 11 MPa and 480 % respectively.•Ionic conductivity of the hydrogels containing 1.5 % LiCl was up to 0.022 S/cm.•The hydrogels showed superior biocompatibility.•Hydrogels showed potential applications as bionic muscles and muscle-like sensors. Inspired by muscle architectures, double network hydrogels with hierarchically aligned structures were fabricated, where cross-linked cellulose nanofiber (CNF)/chitosan hydrogel threads obtained by interfacial polyelectrolyte complexation spinning were collected in alignment as the first network, while isotropic poly(acrylamide-co-acrylic acid) (PAM-AA) served as the second network. After further cross-linking using Fe3+, the hydrogel showed an outstanding mechanical performance, owing to effective energy dissipation of the oriented asymmetric double networks. The average strength and elongation-at-break of PAM-AA/CNF/Fe3+ hydrogel were 11 MPa and 480 % respectively, which the strength was comparative to that of biological tissues. The aligned CNFs in the hydrogels provided probable ion transport channels, contributing to the high ionic conductivity, which was up to 0.022 S/cm when the content of LiCl was 1.5 %. Together with superior biocompatibility, the well-ordered hydrogel showed a promising potential in biological applications, such as artificial soft tissue materials and muscle-like sensors for human motion monitoring.