"4D Printing" Creates Objects That Change Shape

ADDING ANOTHER DIMENSION TO 3D

Drawing inspiration from how plants change shape in response to environmental stimuli, Harvard scientists from the Wyss Institute and John A. Paulson School of Engineering and Applied Sciences have developed a novel approach in 3D printing that allows the printed objects to also shift their structures.

Wherein most 3D printers are designed to create objects that have to remain rigid in structure and shape, 4D printing, as it is called, allows the 3D printed objects to change their shape and structure through time thus adding the additional dimension, time. A demonstration of this technology using hydrogel composite structures, a type of structure that adheres to water, shows that it changes shape upon immersion in water.

In their study in Nature Materials, the authors were able to utilize real life examples of plants' leaves, tendrils, and flowers responding to external factors to develop a mathematical framework on how the 4D printed objects will respond in water.

Aside from this, the object was able to change its structure by aligning cellulose fibers in the composite ink during printing. This technique allows for the object to have anisotropic properties which means that, instead of having uniform properties throughout the object, it instead has directional properties similar to that of wood.

This quality of anisotropy, which allows wood to be chopped easier along the grain rather than across it, is also what provides the flexibility of the 4D printed objects to swell and change shape.

TRANSFORMING 3D PRINTING

While the current demonstration simply showed an object swelling like an orchid in water, the potentials are endless. In a Harvard Gazette report, A. Sydney Gladman, a co-lead author of the study, emphasized the techniques adaptability. By utilizing a composite ink, this allows the technique to be easily adapted in current 3D printers with minimal modifications.

“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 Gladman. “What’s more, we can interchange different materials to tune for properties such as conductivity or biocompatibility.”

The mathematical modelling also resolves the "inverse problem" of 3D printing which is determining the printing toolpath or the process of the object will be printed. By using 4D printing and their model, they are instead able to reverse engineer the needed properties of the object to attain its final shape. The authors expect that 4D printing may hold potential applications smart textiles, biomedical devices, and even tissue engineering.