Coordinatively Stiffen and Toughen Hydrogels with Adaptable Crystal-domain Cross-linking.

Conventional hydrogels usually suffer from the inherent conflict between stiffness and toughness, severely hampering their applications as load-bearing materials. Herein, we reported an adaptable crystal-domain cross-linking design to overcome this inherent trade-off for hydrogels by taking full advantage of both deformation-resisting and energy-dissipating capacities of cross-linking points. Through solvent exchange to homogenize the polymer network, followed by salting out to foster crystallization, a class of sal-exogels with high number densities of uniform crystalline domains embedded in homogeneous networks was constructed. During the deformation, those adaptive crystalline domains initially survive to arrest deformation, while later disentangle gradually to efficiently dissipate energy, crucial to the realization of the desirable compatibility between stiffness and toughness. The resultant sal-exogel achieved coordinatively enhanced stiffness (52.3 ± 2.7 MPa) and toughness (120.7 ± 11.7 kJ/m 2 ), reconciling the challenging trade-off between them. Our finding provides a practical and universal route to design stiff and tough hydrogels, and would have a profound impact on many applications requiring hydrogels with such combined mechanical properties. This article is protected by copyright. All rights reserved.