3D printed flower-like objects that change in time based on a pre-programmed pattern have been created by American researchers.
The researchers described the technology as adding a fourth dimension to 3D printing. In its essence, the technology does exactly what plants and flowers do in nature – they change their shapes based on external stimuli. And similarly to plants, the key ingredient for the 4D-printed hydrogel composite structures to change their shape is water.
"This work represents an elegant advance in programmable materials assembly, made possible by a multidisciplinary approach," said Jennifer Lewis from the Wyss Institute for Biologically Inspired Engineering at Harvard University, who led the research.
"We have now gone beyond integrating form and function to create transformable architectures."
To enable the 3D printed objects to mimic flowers, the scientists had to go deeper and create a material that actually acts in a similar fashion to the natural tissues of plants. They incorporated cellulose fibrils into the hydrogel that have a similar microstructure to the tissues of leaves, tendrils and blossoms. This microstructure allows the plants to promptly change their shape based on environmental factors such as temperature or humidity.
The cellulose fibrils were incorporated into the objects already during the 3D printing process. These fibrils make the hydrogel swell or become stiff based on the external factors. Elaborate mathematical modelling enabled the researchers to precisely control the swelling and stiffness.
"Our mathematical model prescribes the printing pathways required to achieve the desired shape-transforming response," said Elisabetta Matsumoto, a postdoc researcher at the Wyss Institute. "We can control the curvature both discretely and continuously using our entirely tuneable and programmable method."
In future, the team hopes, the technology could be used to create smart textiles and soft electronics with novel capabilities or serve for the development of innovative biomedical devices.
"What's remarkable about this 4D printing advance 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.
The research was described in an article published in the latest issue of the Nature Materials journal.