Scientists from Wyss Institute for Biologically Inspired Engineering at Harvard University have managed to take micro-scale 3D printing technology to the next dimension – time.
The research was inspired by natural structures such as plants that respond and modify their form as per environmental stimuli. The team unveiled ‘4D-printed’ hydrogel composite structures which change their shape when immersed 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. “We have now gone beyond integrating form and function to create transformable architectures.”
Plants have unique tissue compositions and microstructures which result in dynamic morphologies that alter as per the environment. The 4D-printed hydrogel composites contain precise localized swelling behaviors. The hydrogel composites also contain cellulose fibrils derived from wood, which are similar to the microstructures that change the shape of plants.
The cellulose fibrils are aligned during printing and the hydrogel composite ink is encoded with anisotropic swelling and stiffness, which can then be patterned to produce intricate shapes. The anisotropic trait of cellulose fibrils results in varied directional properties which can be predicted and controlled.
This allows wood to be split easily along the grain rather than across it. When immersed in water, the hydrogel-cellulose fibril ink undergoes differential swelling behavior along and orthogonal to the printing path. The researchers developed a proprietary mathematical model to predict how the 4D object must be printed to achieve the predetermined transformable shapes.
“Using one composite ink printed in a single step, we can achieve shape-changing hydrogel geometries containing more complexity than any other technique, and we can do so simply by modifying the print path,” said Sydney Gladman, co-lead author of the study. “What’s more, we can interchange different materials to tune for properties such as conductivity or biocompatibility.”
The composite ink flows like liquid through a printhead but solidifies rapidly once printed. A variety of hydrogel materials can be used interchangeably which results in different stimuli-responsive behaviors. The cellulose fibrils can also be replaced with other anisotropic fillers, including conductive fillers.
The new technique opens up exciting potential applications for 4D printing technology in the fields of smart textiles, soft electronics, tissue engineering and biomedical devices.
“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,” said Wyss Institute Founding Director Donald Ingber.
Excerpts and image courtesy of Wyss Institute at Harvard University