Strong and tough self-wrinkling polyelectrolyte hydrogels constructed via a diffusion-complexation strategy.

Self-wrinkling hydrogels enable various engineering and biomedical applications. The major challenge is to couple the self-wrinkling technologies and enhancement strategies, so as to get rid of the poor mechanical properties of existing self-wrinkling gels. Herein we present a facile diffusion-complexation strategy for constructing strong and ultratough self-wrinkling polyelectrolyte hydrogels with programmable wrinkled structures and customizable 3D configurations. Driven by the diffusion of low-molecular-weight chitosan polycations into the polyanion hydrogels, the high-modulus polyelectrolyte complexation shells can form directly on the hydrogel surface. Meanwhile, the polyanion hydrogels deswell/shrink due to the low osmotic pressure, which applies an isotropous surface compressive stress for inducing the formation of polygonal wrinkled structures. When the diffusion-complexation reaction occurs on a pre-stretched hydrogel sheet, the long-range ordered wrinkled structures can form during the springback/recovery of the hydrogel matrix. Moreover, through controlling the regions of diffusion-complexation reaction on the pre-stretched hydrogels, they can be spontaneously transformed into various 3D configurations with ordered wrinkled structures. Notably, because of the introduction of plenty of electrostatic binding ( i.e. , sacrificial bonds), the as-prepared self-wrinkling gels possess outstanding mechanical properties, far superior to the reported ones. This diffusion-complexation strategy paves the way for the on-demand design of high-performance self-wrinkling hydrogels.