Photomechanical Hydrogels from Visible Light Responsive Supramolecular Complexes

Stimuli-responsive hydrogels are an attractive material platform to create functional devices with applications that include soft robots and biomedical materials. Light-responsive hydrogels are of interest due to the fine spatiotemporal control that light affords. There has been considerable work in this area focused on inclusion of photothermal particles in a thermoresponsive hydrogel matrix, and, while these materials do achieve significant volume change upon light exposure, they suffer from decreased resolution and nonpersistent response due to heat dissipation in the system. Leveraging photochemical response in hydrogels alleviates these issues, however, this is typically achieved using either azobenzene, which relies on a relatively small change in polarity upon isomerization to drive volume change, or spiropyrans, which generally have narrow pH ranges in which they operate. Our group has previously addressed these shortcomings by including photoswitchable supramolecular complexes between azobenzene and cyclodextrin, which enable rewritable shape changes in hydrogels using spatially patterned light. Here, we build upon that work by developing supramolecular hydrogels that include visible-light responsive photoswitches. We characterize the resulting host-guest interactions and demonstrate photochemically driven shape change using only visible light, which increases penetration depth and improves compatibility with biological materials.