Hydrogel Adhesion by Wrinkling Films.

A novel adhesion control method for hydrogels utilizing swelling-induced wrinkling gel films is developed. Structures such as flat, crease, and wrinkle at the interface of adhered gels are controlled by swelling ratio of gel films. The role of microstructures at the gel-gel interface is investigated by adhesive strength measurement. Aligned wrinkles are fabricated with anisotropic swelling films. The adhesive strength of hydrogels with wrinkles parallel to tensile direction is larger than that with perpendicular wrinkles. Adhered gels detach without damage to their surfaces when the wrinkle structures are disrupted by peeling of the wrinkled film. Moreover, thermoresponsive film is used to control wrinkle structures at the adhered interface by temperature. The adhered interface is stable in cold water because of the existence of wrinkles; however, they detach in hot water due to wrinkle deformation. By using wrinkle structure at adhesive interfaces, both strong adhesion and easy detachment of hydrogels are achieved.