Strong and tough fibrous hydrogels reinforced by multiscale hierarchical structures with multimechanisms

Tough natural materials such as nacre, bone, and silk exhibit multiscale hierarchical structures where distinct toughening mechanisms occur at each level of the hierarchy, ranging from molecular uncoiling to microscale fibrillar sliding to macroscale crack deflection. An open question is whether and how the multiscale design motifs of natural materials can be translated to the development of next-generation biomimetic hydrogels. To address this challenge, we fabricate strong and tough hydrogel with architected multiscale hierarchical structures using a freeze-casting-assisted solution substitution strategy. The underlying multiscale multimechanisms are attributed to the gel's hierarchical structures, including microscale anisotropic honeycomb-structured fiber walls and matrix, with a modulus of 8.96 and 0.73 MPa, respectively; hydrogen bond-enhanced fibers with nanocrystalline domains; and cross-linked strong polyvinyl alcohol chains with chain-connecting ionic bonds. This study establishes a blueprint of structure-performance mechanisms in tough hierarchically structured hydrogels and can inspire advanced design strategies for other promising hierarchical materials.