Programming 3D shapes from 2D hydrogel sheets with patterned metric and curvature

Hydrogels are capable of undergoing large strains via swelling/deswelling in response to a variety of stimuli, making them ideal candidates for shape morphing systems. A number of recent studies have shown how patterning variations in swelling within the plane of thin sheets can be used to define complex 3D shapes with prescribed Gaussian curvatures. However, few methods exist to controllably break degeneracy between nearly isometric states in these materials. Here, we rely on photocrosslinking of pendent benzophenone groups to pattern the crosslinking density and swelling degree of a poly(diethylacrylamide) (PDEAm) by UV irradiation. Using a digital micromirror array device (DMD), we pattern differential swelling in PDEAm thin films by maskless photolithography, successfully programming the shape morphing from 2D flat films to non-Euclidean surfaces in 3D. Furthermore, we introduce gradients in crosslinking through the film thickness by introducing a UV absorber, thus defining a preferential buckling direction during shape morphing of PDEAm films. With double-sided lithographic exposure, we control both in-plane and out-of-plane differential swelling in the films and demonstrate the patterning of buckling directions of each repeating unit in a corrugated surface.