10 March 2021

Objects with shapeshifting superpowers sound like the stuff of science fiction, but materials that change shape with the right stimulus are already here.

Complex objects that respond to external signals by changing shape can be created using 3D printing techniques combined with smart or active materials – introducing a fourth dimension. The signals that can be used to trigger shapeshifting include changes in temperature, humidity or light.

Materials scientists and engineers from Scion and the University of Waikato report successfully printing 3D objects that change shape with temperature in a recent paper.

Lead author, Maxime Barbier, describes the process: “First, cellulose was added to modify the flow properties of a biopolymer that exhibits shape memory ability but also to provide a paste that could be 3D printed. The cellulose also added some structural stability to the 3D printed object before we set (cured) the print with heat.

“The shape-changing objects were printed in their permanent state. Then we deformed them into their temporary state by freezing them under strain. The temporary state is maintained by a change in the chemical or physical structure that can be reversed.

“When we apply heat, the strain involved in locking in the temporary shape is released. We saw up to 98% of shape recovery.

“This study has given us an insight into how we might target specific triggering temperatures, says Maxime. “One small piece of a giant puzzle with wide potential applications in the fields of biomedical, aerospace and robotics.”

How shape memory polymers work

The shape changing polymers contain a “switching” phase that stores the temporary shape and is sensitive to the trigger and a non-sensitive phase responsible for recovery of the permanent shape. With heat, the switching phase goes through a transition, in this case from a hard (glassy) to a viscous/rubbery state. The non-sensitive phase includes an interpenetrating network structure with “netpoints” or cross linkages that store the permanent shape.

This work was funded by the New Zealand National Science Challenge: Science for Technological Innovation—Kia kotahi mai—Te Ao Putaiao me Te Ao Hangarau as part of the Spearhead Project: ‘‘Additive manufacturing and 3D and/or 4D printing of bio-composites’’

Barbier, M., Le Guen, M. J., McDonald-Wharry, J., Bridson, J. H., & Pickering, K. L. (2021). Quantifying the Shape Memory Performance of a Three-Dimensional-Printed Biobased Polyester/Cellulose Composite Material. 3D Printing and Additive Manufacturing. https://doi.org/10.1089/3dp.2020.0166