Researchers from SUTD, along with research collaborators, made reversible 4D printing possible.

While 3D printing is receiving all craze and 4D printing is the trending buzzword, researchers have already started working on reversible 4D printing. A team from Singapore University of Technology Design (SUTD) did a collaborative research project with Nanyang Technological University (NTU), resulting in a 3D printed material changing its shape and back again numerous times without any electrical input. While 3D printing is widely used across many industries, the rapid development of additive manufacturing and advances in shape-memory materials have fueled the progress of 4D printing.

4D printing is an emerging approach in which 3D objects are produced whose shape changes over time. Like 3D printing, this technology is also based on Stereolithography (SLA). However, a 4D printed object has the ability to react to environmental changes like temperature, pressure, humidity variation, and adjust to them accordingly. Meanwhile, reversible 4D printing is an upgrade. In the case of 4D print, the initial changes in shape are usually caused by either heat or water, but the reversion often requires manual input in the form of stretching or pulling, which can be time-consuming and arduous. This is because the process involves the use of hydrogel as a stimulus. These hydrogels lack mechanical strength, and they become a limitation when used for load-bearing applications.

Fortunately, the new project aims to solve this issue. The researchers used two widely available and compatible materials, VeroWhitePlus and TangoBlackPlus, for printing in a 3D polyjet printer compared to using a hydrogel. In the process, researchers used ethanol to cause the elastomer to swell, which—like the hydrogel in other similar processes—creates stress on the transition material, they said. Then, when heated, the transition material changes its shape to a second shape. The process then requires drying the ethanol out of the elastomer and heating the transition material again, which allows it to revert to its original shape, researchers said. Simultaneously, the elastomer pulls the transition material back due to elastic energy stored in it after drying. The team cites that the elastomer plays a dual function in this whole process. It was used both to induce stress in the programming stage and store elastic energy in the material during reversion. Further, the shape morphing can be predicted using a simulation model. This model also helped in attaining control over the bending and studying the degree of curvature. The team hopes, this understanding of the curvature will provide a great degree of control over the reversible 4D-printed structure.

The whole findings are published in the journal Engineering as a study titled ‘Preliminary Investigation of the Reversible 4D Printing of a Dual-Layer Component’. It is co-authored by Chee Kai Chua ( lead researcher and Head of Engineering Product Development in SUTD) Amelia Yilin Lee, Jia An, and Yi Zhang. The study also concluded that the reversion was more precise when using the present method than manually forcing the object to revert. Reversible 4D printing is very much in its early stages, but the collaborative project provided great insight into automated reversible 4D printing mechanisms. The team hopes to carry on trialing the technique with new materials.

Professor Chua said while reversible 4D printing in itself is a great advancement, using a more robust material while ensuring a more precise reversal during shape change is revolutionary as it allows us to produce complex structures that cannot easily be achieved through conventional fabrication. He further added that relying on environmental conditions instead of electricity makes it a game-changer across various industries, completely changing how we design, create, package, and ship products.

You can study more about the research here.