Tough and tear resistant hydrogel with a sandwich mineralized structure induced by bidirectional ion migration

Despite the advantages of hydrogels, such as softness and biological affinity, their applications are often severely limited by the inadequate mechanical properties that result from their loose and homogeneous structure. Here, we propose an enhanced hydrogel structure prepared via a universal freeze-assisted bidirectional ion migration strategy, yielding energy dissipating structures from the millimeter scale to the nanometer scale. A dense‒porous‒dense sandwich structure surrounds a mineralized physical crosslinking center, which allows stress to pass between the multilayers of the interlayers and the mineralized center under force, resulting in hydrogels with a strength of 33.51 MPa, an fracture energy of 286.39 kJ·m-2, and similar mechanical properties in the perpendicular and parallel directions in the plane. This strategy for constructing tough, robust hydrogels is broadly applicable to different combinations of mineralized ions and facilitates recyclability. This simple approach provides a general strategy for overcoming the long-standing application problems of hydrogels in harsh mechanical loading applications. Hydrogels have some desirable properties, but applications can be limited if they are too fragile. Here, the authors report the development of a freeze-assisted bidirectional ion migration strategy for the fabrication of tough hydrogels.