In this paper by M. Guvendiren et al, a simple and robust method is used to generate a range of osmotically-driven surface patterns in hydrogels, including random, lamellar, peanut, and hexago- nal structures. The patterns are fabricated by exposing a photocurable formulation to light while open to air and then swell- ing, using oxygen inhibition of the radical polymerization at the surface to create a gradient of crosslinking with depth. HYDROGEL PATTERNING