Tough and stretchable cellulose hydrogels engineered via the synergy of entanglements and cross-links

Hydrogels are attractive for various applications, including engineering artificial tissue, flexible electronic devices, and structural biomaterials, due to their advantageous characteristics such as flexibility, hydrophilicity, and biocompatibility. However, the strengthening and toughening of sustainable crystalline polysaccharide hydrogels remain challenging due to their high water content and limited energy dissipation mechanisms. Here we present a strategy to produce a dual cross-linked cellulose hydrogel with remarkable toughness and stretchability via the synergy of entanglements and cross-links in a hierarchical structure. The cellulose hydrogels are consisted of cellulose chains that strongly interact with each other through physical interactions, while both cellulose chains and long-chain chemical cross-linkers are densely entangled in molecular-scale, which lead to an intertwined nanofibrillar architecture with high content of cellulose II crystalline hydrates in nano- and micro-scale. The resultant macroscale cellulose hydrogels have a water content ranging from 72% to 82%. The maximum values for tensile strength, tensile strain, and work of fracture were 9.5 ± 2 MPa, 267 ± 18%, and 11.7 ± 0.3 MJ/m³, respectively. The strategy suggested in this study has the potential to be extended to other biomacromolecules, thereby enhancing the applicability of structural hydrogels in scenarios that demand superior mechanical properties.