The two-way shape memory effect
IV: "We now know about the one-way shape memory effect, but how can we now think of the two-way shape memory effect?"
Dr. Pretsch: "The approach pursues the idea of producing "programmable" materials that are capable of thermo-reversibly changing their shape. We always speak of a two-way shape memory effect when the manufactured printed object repeatedly adapts its shape through the raising or lowering of the ambient temperature. We call this switching back and forth between two shapes 'thermal actuation'.
After 4D printing, an actuation-capable object is thus available. For this, we programme the information on thermo-responsiveness into the polymer structure. The material behaviour is then dependent on the ambient temperature. As long as a critical temperature is not exceeded, actuation then takes place."
IV: "Are there already applications that illustrate this effect?"
Dr. Pretsch: "We built grippers in the course of researching the two-way shape memory effect. These could grip a small glass vial as the inner diameter of the gripper was designed to be larger than the outer diameter of the vial. The circular gripper was heated to the upper switching temperature, whereupon it shrank onto the vial so that it could then transport it. Lowering the temperature then caused the vial to be released again (https://onlinelibrary.wiley.com/doi/pdf/10.1002/mame.202200214).
In another example, we used a lever mechanism to actuate the wings of an artificial butterfly. The technology has potential applications as a sunshade or privacy screen, for example.
At the moment, we are working on laying the foundations for making thermal actuation as useful as possible in new areas of application."