Contactless reversible 4D-printing for 3D-to-3D shape morphing

4D printing provides a means to create dynamic structures for self-actuating devices fabricated by additive manufacturing techniques. Most existing 4D printing processes are only capable of one-way shape morphing using a single mechanism for stimulation. In the limited successful reversible 4D-printing studies, most only demonstrate 2D-to-3D shape morphing. This study introduces a contactless shape setting mechanism to empower reversible 4D printing using a combination of stimuli. The forward shape programming is realised by asymmetric swelling with heated ethanol, and the shape recovery is accomplished by dry heating. The shape morphing can be predicted using a simulation model. Several designs are 4D-printed to achieve different forms of morphing to obtain 3D-to-3D shape morphing. The entire shape morphing cycle could be completed within as short as 3 min. The capability of 3D-to-3D shape morphing and reversibility of our 4D-printing process promise great potential for different applications such as biomimetics and soft robotics.