Researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University and the Harvard John A. Paulson School of Engineering and Applied Sciences have unveiled a new 4D printing technique, capable of producing structures that change upon immersion in water.
“This work represents an elegant advance in programmable materials assembly, made possible by a multidisciplinary approach,” said Jennifer Lewis, Sc.D., senior author on the new study, published in Nature Materials. “We have now gone beyond integrating form and function to create transformable architectures.”
Inspired by the dynamic morphologies of the plant world, the 4D-printed hydrogel structures contain wood-derived cellulose fibrils, which are similar to the microstructures that enable shape changes in plants, and have been programmed to exhibit precise, localized swelling behaviours.
By aligning cellulose fibrils during printing, the hydrogel composite ink is encoded with anisotropic (directionally dependent) swelling and stiffness, which can be patterned to produce intricate shape changes. The anisotropic nature of the cellulose fibrils gives rise to varied directional properties that can be predicted and controlled.
Whenever immersed in water, the hydrogel-cellulose fibril ink undergoes differential swelling behavior along and orthogonal to the printing path, making it behave like a real plant.
The new printing method, combined with a proprietary mathematical model developed by the team to predict how a 4D object must be printed to achieve prescribed transformable shapes, could open up many new and exciting potential applications for 4D printing technology, including smart textiles, soft electronics, biomedical devices, and tissue engineering.
“What’s remarkable about this 4D printing advance made by Jennifer and her team is that it enables the design of almost any arbitrary, transformable shape from a wide range of available materials with different properties and potential applications, truly establishing a new platform for printing self-assembling, dynamic microscale structures that could be applied to a broad range of industrial and medical applications,” Donald Ingber, M.D., PhD and Founding Director of the Wyss Institute.