Improve Hydrogel Adhesion by Introducing Pillar Structures at the Interface

Introducing inelastic dissipaters can enhance the adhesion of hydrogels. However, the adhesion energy enhanced by inelastic dissipaters dramatically decreases when the adhesion interface is loaded repeatedly. Here, we achieve tough adhesion of hydrogels by introducing a structure of a pillar array to the adhesion interface as elastic dissipaters. Each pillar undergoes large deformation before debonding. Once debonded, all the elastic energy stored in the pillars is released, and the adhesion energy is greatly improved. As a proof of concept, we adhere a piece of polyacrylamide hydrogel to a piece of polyacrylic acid hydrogel and measure the adhesion energy by a 90-degree peel test. The adhesion energy is 56 J/m² for the adhesion without structures and 249 J/m² for the adhesion with structures. We apply the pull-off test on a pillar unit and estimate the adhesion energy enhanced by the pillars using a simplified model, which is in good agreement with the experimental results. We conduct experiments to study the influence of the height and width of the structures on the adhesion energy. The mechanism of enhancement as well as the influence of geometric parameters is further studied by finite element method. The proposed mechanism provides a simple method of structural design to enhance hydrogel adhesion.