(Photo-)thermally induced formation of dynamic surface topographies in polymer hydrogel networks

In this Article, we report on our approaches to creating responsive hydrogel coatings with surfaces that can be switched between a close to flat state and a state with a predesigned topographic pattern. The trigger is either temperature or, indirectly, light. The hydrogel coatings are based on the known thermal responsive poly(N-isopropylacrylamide) utilizing its solubility change at its lower critical solution temperature (LCST) at around 32 °C. Using this material in combination with controlled cross-linking, we developed three fabrication strategies. Thermally switching symmetric surface topographies were created by careful and spatial control of the cross-link density. Sensitivity to light was created by patterns of tin oxide converting absorbed light into local heat. And to broaden the application range, we introduced a method based on volumetric effects created by a corrugated substrate. The latter method allows for the formation of asymmetric or slanted surface structures.