Ulsan National Institute of Science and Technology (UNIST): Multicolor 4D Printing of Shape-Memory Polymers
Researchers from Ulsan National Institute of Science and Technology (UNIST) take 3D printing to the next level, releasing findings from their study in the recently published ‘ Multicolor 4D printing of shape-memory polymers for light-induced selective heating and remote actuation .’
While the miracles of 3D printing continue to abound, 4D printing allows users to work with materials that respond to their environment, deforming accordingly—and then reverting to their initial, natural shapes. In this study, the authors 4D print multicolor shape-memory polymers (SMPs) and demonstrate how light absorption and subsequent heating of the material cause remote actuation.
Previous studies have tended to focus on how SMPs deform in the presence of heat or moisture, but here light is used as a powerful force in causing stimuli-responsive changes. Selective heating was allowed due to choices in color of light, also resulting in color-dependent structural transformations.
“4D printing can allow the complex geometries of multicolor composites with predesigned responses,” stated the authors. “In addition, SMPs can be reused multiple times by conducting thermomechanical programming again. Therefore, multicolor 4D printing of SMPs can offer unique merits for light-induced structural changes and remote actuation.”
For the study, the authors created a light-activating structure measuring L = 40 mm, w = 5.5 mm, t = 2 mm, a = 0.4 mm, and made of three materials:
Yellow (Veroyellow)
Blue (Verocyan)
Sky-blue matrix (Tango +)
A 3D printed light-activating structure. (a) Schematic for the multicolor SMP structure. (b) Side view of the structure. (c) Thermomechanical programming and bending behavior (the dotted line in the figure is an eye guide).
Light was able to reach both the yellow and blue fibers due to strategic positioning of the fibers. After 3D printing and post-processing, the structure was bent downward, reverting to its initial shape after being exposed to blue light. Through continued experimentation with color dependent selective heating, the researchers realized that they could manipulate actuation through sequences of light.
Bending behavior of the multicolor sample. A thermomechanically programmed structure bends to a n-shape under red illumination. After bending, the structure can recover to an initial flat state with blue illumination. In case of illuminating blue light first, the structure bends to a U-shape. It can also recover to the initial state with red-light illumination. (a) is the schematic for dual-step actuation, while (b) is the experimental result.
“Applying red light later caused the entire structure to retain its initial flat state. However, when the structure was heated in hot water (instead of selective heating with colored light), the change in shape of our sample was insignificant (data is not shown here). In the hot...
