Kirigami-inspired adhesion with high directional asymmetry

Robust adhesion to and effortless removal from various substrates are of great importance to soft adhesives in myriad applications. However, controlled regulation between strong attachment and easy detachment in a same system remains challenging. Herein, we report a kirigami-inspired approach to control adhesion with high directional asymmetry. By inscribing a specially designed labyrinth pattern in an adhesive film, the adhesion is enhanced against peeling along a particular direction – the peak peel force builds up at a much smaller peeling angle, and the adhesion energy climbs through in-plane elastic dissipaters. Such a mechanism is inactive when the adhesive is peeled in the opposite direction, and easy detachment is experienced. The underlying physics is elucidated via theoretical and numerical analyses and verified through experiments by using hydrogel adhesives with different elastic moduli and geometric parameters. The asymmetric adhesion can be further enhanced over soft substrates or by designing hierarchical structures – increases by up to 22 folds in strength and 7 folds in energy have been observed. The proposed mechanism is universally applicable to various intermolecular interactions and different loading modes, and can pave the way to engineering new adhesives with superior yet controllable adhesion performance.