Single-composition three-dimensionally morphing hydrogels

We describe an approach to create pH responsive films that can transform from a flat state to a pre-described deformation. Our approach to fabricate these films is based on the use of a monomeric mixture of acrylic acid and a diacrylate crosslinker. Upon UV initiated free-radical polymerization the different monomers have different reactivities, which enables polymerization induced diffusion during spatially modulated UV intensity gradients. By means of this process the crosslink density within the film can be tuned spatially both in-plane and over the film thickness. The crosslink density determines the degree of swelling upon actuation of the formed hydrogel by a pH change. We demonstrate this effect by pH-switchable systems which are either substrate-attached exhibiting surface topologies upon actuation or freestanding that can undergo geometrical changes in the form of bending, curling or morphing into even more complex shapes.