4D printing technique speeds up "shape-shifting" of objects

A new technique for 4D printing could make objects shift shape quicker, say scientists.

Researchers at the Georgia Institute of Technology, Singapore University of Technology and Design (SUTD) and Xi'an Jiaotong University in China have developed a so-called 4D printing method that allows 3D-printed components to change shape when heated.

The technology could be useful for applications that require components to morph into multiple configurations and “self-assemble without human intervention” during operation, said Peter Walters, a 3D printing expert at the Centre for Fine Print Research at the University of the West of England in Bristol, who was not involved in the research.

The new approach can greatly reduce printing time and save a lot of material, said Jerry Qi, a materials scientist at Georgia Tech and one of the paper's authors. "This completely eliminates time-consuming mechanical programming from the design and manufacturing workflow."

The term '4D printing' was first coined by a Massachusetts Institute of Technology computer scientist Skylar Tibbits in 2013, when he pioneered it in collaboration with the 3D printing company Stratasys, using hydrogels to make objects shape-shift.  

But the team led by Georgia Tech eliminates the use of hydrogels, which usually slow down transformation time and lead to unstable shapes, according to the researchers.

Another team from SUTD attempted a similar 4D printing method last year by using shape memory polymers, but the stiff material required a series of programming steps - such as heating, mechanical loading, cooling and removal of load - after printing to transform.

This time around, the three universities overcame the issue by incorporating these steps into the printing process. The researchers printed a laminated strip of shape memory polymer with a built-in soft elastomer that put an internal strain on the material. After applying heat – by immersing the strip in hot water – the strain on the elastomer loosened and gave the strip a permanent arrangement of waves. 

The scientists then reshaped the material into several other configurations upon heating, including a model flower with bent petals and a lattice-shaped object "that could expand nearly eight times its original size," said Qi.

The technology could make way for products to be stacked or rolled to save storage space and be expanded once in use, or allow components to respond to temperature and light. 

One potential example is the manufacture of “adaptive wing flaps on aircraft or stents in the medical world,” said Phill Dickens, manufacturing technology expert at the University of Nottingham. He added that 4D printing is currently used to control exhaust gas systems in aeroengines.

The paper is published in the journal Science Advances.