Almost all solid materials expand when heated - only in rare instances do certain materials buck this trend and shrink with heat. An interdisciplinary research team led by MIT mechanical engineers has now manufactured tiny, star-shaped structures out of interconnected beams, or trusses, that quickly shrink when heated to about 540 degrees Fahrenheit. Each structure’s trusses are made from typical materials that expand with heat. The researchers realized that these trusses, when arranged in certain architectures, can pull the structure inward. The researchers consider the structures to be "metamaterials" - composite materials whose configurations exhibit counterintuitive properties not normally found in nature. Such materials could have applications in computer chips, which can deform when heated for long periods of time. The research team had pioneered a 3D printing technique called microstereolithography, in which light from a projector is used to print very small structures in liquid resin, layer by layer. “We can now use the microstereolithography system to create a thermomechanical metamaterial that may enable applications not possible before,” says Christopher Spadaccini of Lawrence Livermore National Laboratory.