Two-dimensional patterns that can self-fold into 3-D objects using only light have generated a breakthrough that could have applications in manufacturing processes or packaging. The technique takes a prestressed plastic sheet — made from the same polystyrene material used in the popular 1980s toy Shrinky Dinks — and runs it through a conventional ink-jet printer that stamps it with bold black lines. The material is then cut into a pattern and placed under an infrared source, such as a heat lamp. The printed lines absorb more energy than the rest of the material, causing the plastic to contract and creating a hinge that folds the sheets into 3-D shapes. The technique can be used to create a variety of objects, such as cubes or pyramids, without ever having to physically touch the material. By changing the width of the black lines, or hinges, researchers also can change how far each hinge folds; e.g., they can create a hinge that folds 90º for a cube or one that folds 120º for a pyramid. The wider the hinge, the further it folds. Wider hinges also fold faster because there is more surface area to absorb energy. The new technique, developed at North Carolina State, can be used to create a variety of objects, such as cubes or pyramids, without ever having to physically touch the material. (Video: Michael Dickey, North Carolina State University) “You can also pattern the lines on either side of the material, which causes the hinges to fold in different directions,” said Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at North Carolina State University. “This allows you to create more complex structures.” The process works only when the surface temperature of the hinge exceeds the glass transition temperature of the material — the point at which it starts to soften. The heat also must be localized to the hinge for quick folding. “This finding stems from work we were doing on shape memory polymers, in part to satisfy our own curiosity. As it turns out, it works incredibly well,” Dickey said. The research was published in Soft Matter; Dickey was co-author. For more information, visit: www.ncsu.edu