Switchable adhesion between hydrogels by wrinkling

On-demand adhere to and detach from soft and wet surfaces are crucial for hydrogels for applications in tissue engineering, soft machines, and soft robotics. Whereas strong adhesion has been achieved between hydrogels, on-demand switching from strong adhesion to weak adhesion for benign detachment is still under explorations. Herein, we report an approach for switchable adhesion between hydrogels by invoking a mechanical process, wrinkling. The approach is demonstrated by bonding two hydrogel adherends with a wrinkled hydrogel adhesive, with the formation and characterizations of wrinkles tailored by regulating the prestretch of adherend and optimizing the ingredients of adhesive synergistically. On one hand, the formation of wrinkles enhances adhesion by creating a tortuous path for crack propagation and an extended energy dissipation zone. The resulting adhesion is robust to elicit bulk dissipation within the adherend and transform the once adhesive failure to cohesive failure. On the other hand, the suppression of wrinkles deactivates the adhesion enhancement mechanism to facilitate effortless debonding. As a proof-of-concept, a hydrogel patch that can strongly adhere to a damaged hydrogel device for repair and gently detach after repairing, based on the switchable hydrogel adhesion, is demonstrated. The proposed method expands the design space for hydrogel adhesion.