Drying-Induced Bending of Hydrogel Disks

Abstract

Smart reconfigurable hydrogels that undergo programmable shape deformation hold promise for a myriad of common applications ranging from soft robotics to biomedical devices and optics. To encode shape morphing abilities, thin hydrogel layers presenting different properties are typically bound together and submerged, subsequently inducing differential swelling. However, many applications of such hydrogel structures occur in air, preventing swelling from occurring. Here, we report a new technique based on differential drying to induce programmable shape morphing into three-dimensional structures. By directly visualizing the drying of hydrogel disks on substrates with different water affinity, we are able to observe different delamination processes, reminiscent of the drying-induced bending of colloidal suspensions. We develop a mechanistic model which quantifies the interplay of geometry, surface energy, and elastic strains. Such an approach not only opens the door for the design of complex hydrogel origami used in air, but also decouples the effect of surface energy and elastic energy, a common hurdle in the drying of colloidal suspension community.