Just as 4D cinema brings films to life through motion and physical effects, 4D printing infuses 3D-printed objects with the ability to bend, fold or transform in response to stimuli such as heat or electrical activation. In the long run, such materials could support various industrial applications, from aerospace and space technologies to healthcare, medicine and advanced electronics.
Current 4D printing approaches use specialised shape-memory polymers that require a separate mechanical programming step. At the A*STAR Singapore Institute of Manufacturing Technology (A*STAR SIMTech), Senior Principal Scientist Sharon Nai, Scientist Thang Quyet Tran and colleagues are exploring whether the desired shape-changing behaviour could be programmed directly using a widely available thermoplastic, acrylonitrile butadiene styrene (ABS).
By evaluating the properties of starting filaments and the resulting structures, the researchers observed that reheating the ABS materials after printing led to shrinkage. During filament production and printing, polymer chains can become stretched and tense. Cooling then locks some of this internal tension or stress into the finished material. When reheated, the chains return to a more relaxed arrangement, much like a stretched rubber band returning to its original shape. As this internal stress is released, the printed material shrinks.
Rather than treating this shrinkage as a printing defect, the researchers turned it into a driving force for movement. They printed two ABS materials with contrasting shrinkage behaviours as bonded layers. Upon heating, one tries to contract more than the other, but the two layers cannot shrink independently.
“The difference in shrinkage creates an internal imbalance that causes the whole structure to bend,” said Tran. “In this way, the ABS filament combination and printed architecture act as the programming mechanism that directly creates the shape-changing behaviour of the final material.”
By varying the heating temperature as well as the thickness, pattern and orientation of the ABS materials, the researchers could control where and how much the structure would bend. Further experiments showed that heating at 130 degrees Celsius produced the largest bending response, while layers of approximately equal thickness generated the greatest curvature.
The team also sees potential beyond simple heat-triggered bending. For example, initially flat structures could potentially be induced to form folds, curves, spirals and other complex shapes. Incorporating electrically activated fillers in certain regions of the structure could also enable precisely triggered transformations when an electrical current is applied.
“By combining readily available thermoplastics with thoughtful design and material placement, we may be able to create cost-effective structures that transform themselves when activated,” remarked Nai. As the approach can be implemented using conventional 3D printing technologies, the researchers hope it can provide a simpler and more accessible route to producing 4D-printed materials.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Singapore Institute of Manufacturing Technology (A*STAR SIMTech).
