Gel sheets morph into different three-dimensional forms in response to various stimuli, such as changes in pH or salt concentration, according to researchers in Canada and colleagues in the US. The University of Toronto’s Eugenia Kumacheva, Zhihong Nie of the University of Maryland, and their teams have programmed a polymer hydrogel to adopt multiple shapes. To make their mighty morphing material, the team made a thin layer gel with one type of monomer and added a second monomer solution together with a cross-linker. A photoinitiator is also added to trigger polymerization under UV light. A mask can be used to control the pattern of exposure. The approach thus allowed the team to make a multiple different stimuli-responsive polymer networks within the same object.