4D Printing Creates Shape-Shifting Materials

Scientists at Georgia Institute of Technology and Singapore Univ. of Technology and Design have developed a way to 3D-print objects that can easily change shape when they are heated. The process could enable a new approach to product design, in which a single component is designed to embody multiple configurations.

The new process is considered four-dimensional (4D) printing, a recently coined term that refers to the integration of 3D printing with smart materials to form printed components that can switch among multiple configurations in response to an environmental stimulus. Hydrogels and shape-memory polymers (SMPs) are the two most common materials used in 4D printing.

For 4D-printed components based on hydrogels, the hydrogel is combined with a nonswelling polymer. When the printed structure is immersed in a solvent, the hydrogel swells while the nonswelling polymer does not, creating mismatched strains between the two materials that cause the component to change shape. Although this approach is simple and does not require programming, it has drawbacks. Hydrogels are soft, so the printed object typically lacks stiffness that is needed in many applications. Because the shape-shift is based on diffusion, the change happens very slowly. And, the actuated shape is not stable and will change as the environmental conditions change.

SMPs, on the other hand, offer the advantages of a relatively stiff structure and fast...