Teams from the Wyss Institute for Biologically Inspired Engineering at Harvard University and the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have moved 3D printing into the 4^th dimension with 4D printed hydrogel composite structures that respond to environmental stimulus and can change shape when submerged in water.

Harvard researchers take shape shifting into the 4th dimension The materials are printed using a mathematical model the team created. The model predicts how the material will swell in water, mimicking nature’s dynamic morphology in response to stimuli. The technique aligns cellulose fibrils during the printing process with a hydrogel composite ink that has been encoded with anisotropic swelling and stiffness – designed to result in a variety of intricate directional properties that can be predicted as well as controlled.

The properties of the composite ink, along with the mathematical model, determine how the object should be printed to achieve the desired transformable shapes. The researchers say they believe this new method could be used in a variety of 4D applications, from textiles and electronics, to tissue engineering and biomedical device creation.

The process also allows the researchers to add other materials during the printing to incorporate mechanical properties, such as biocompatibility or conductivity. The greatest challenge the model overcomes, the researchers say, is the “inverse problem.” This is the ability to predict what the printing toolpath must be in order to achieve the proper encoding, resulting in the desired shape after swelling. The researchers believe the process establishes a new platform to print dynamic, self-assembling structures.