The Harvard team came up with hydrogel composites -- think jello -- that contain cellulose fibrils derived from wood and are similar to the tiny structures that allow plants to change their shape.
"They respond to water. As they hydrate, they begin to swell," Lewis said. The 3-D printer was programmed to give some parts of the structure more stiffness, and other parts flexibility. The difference in flexibility makes the entire flower curl up like a real one when dropped in water.
4-D Printer Makes Shape-Shifting Wood
"We can locally encode changes in swelling behavior which give rise to a lot of complexity to have bending, rustling and twisting," said Lewis, who conducted the research along with co-lead authors A. Sydney Gladman, a graduate research assistant and Elisabetta Matsumoto, a postdoctoral fellow, both at Wyss.
The secret to the folding orchid is the design of the special ink that contains the hydrogels. The composite ink that the team uses flows like liquid through the printer head, yet solidifies once printed.
"We can swap one hydrogel for another, or swap cellulose fibrils for carbon nanotubes or metal nanorods," Lewis explained. "It opens the ability to create scaffolds for tissue engineering or for tissue repair." The video below shows how it work.