One-step soaking strategy toward mechanical double-network hydrogel

Double-network (DN) hydrogels, which comprise noncovalent interacting networks, are highly sought after due to their controlled compositions and environmental friendliness. However, the complex preparation methods hinder the application of these hydrogels. In this study, we present a simple and feasible approach for fabricating hybrid PAA-CS DN hydrogels by post-treating the PAA-CS composite hydrogels with CuSO4 solutions to induce the formation of physical networks through CS chain entanglement. The composite hydrogel, composed of chitosan (CS) and polyacrylic acid (PAA), readily transforms into a DN hydrogel after soaking in a CuSO4 solution, thanks to in situ formation of chain entanglements, hydrogen bonds, and ionic coordination. The resulting hybrid DN hydrogels exhibit porous networks, high tensile strength, and exceptional toughness. This facile but effective soaking method can be universally applied to fabricate mechanically robust hydrogels, modulate noncovalent interactions, and broaden their potential applications.