In what is described as a world first, researchers in Australia and New Zealand have developed a 3D-printing process that is compatible with “controlled polymerization,” using visible light to control the makeup of polymers and “tune” their mechanical properties. The new process also enables 4D printing, by which the 3D-printed object can change shape or its chemical and physical properties can be altered to adapt to its environment. Advancing the recycling and reuse of plastics and supporting biomedical breakthroughs are among the potential applications.

Dial showing create and improve

Research teams from the University of New South Wales (UNSW) in Australia and the University of Auckland in New Zealand collaborated in the successful merging of 3D and 4D printing and photo-controlled, or “living,” polymerization. The method uses visible light to “create an environmentally friendly ‘living’ plastic or polymer [that] opens a new world of possibilities for the manufacture of advanced solid materials,” writes Caroline Tang in an article published on the UNSW website.

The research builds upon the 2014 discovery of PET-RAFT polymerization (Photoinduced Electron/energy Transfer-Reversible Addition Fragmentation Chain Transfer polymerization) at the UNSW Sydney Boyer Lab. Described as a new way to make controlled polymers using visible light, the technology was not compatible with 3D printing. “The rates of typical controlled polymerization processes are too slow for 3D printing, where the reaction must be fast for practical printing speeds,” explained Cyrille Boyer, lead author of a paper describing the research in Angewandte Chemie International Edition. Two years of research and hundreds of experiments eventually bore fruit with the development of a 3D-printing system that enabled the PET-RAFT polymerization technique.

By using visible light, the researchers are able “to control the architecture of the polymers and [to] tune the mechanical properties of the materials prepared by our process,” said Boyer. “This new process also gives us access to 4D printing and allows the material to be transformed, or functionalized, which was not previously possible.”

“With 4D printing, the 3D-printed object can change its shape and chemical or physical properties and adapt to its environment,” explained UNSW’s Nathaniel Corrigan, co-first author of the paper.

“In our work, the 3D-printed material could reversibly change its shape when it was exposed to water and then dried. For example, the 3D object starts as a flat plane and when exposed to certain conditions, it will start to fold—that’s a 4D material. So, the fourth dimension is time.”

The researchers envisage multiple potential groundbreaking applications for the new technology. The material could negate the need to recycle or discard plastics in some cases because the “new living material will be able to repair itself,” explained Boyer. As a “living” object, the plastic part can continue to grow and expand, he said. It would also enable advanced biological applications, such as tissue engineering, added Boyer.

“Current 3D printing approaches are typically limited by the harsh conditions required, such as strong UV light and toxic chemicals, which limits their use in making biomaterials,” Corrigan explained in the news release. “But with the application of PET-RAFT polymerization to 3D printing, we can produce long polymer molecules using visible light rather than heat. Using heat above 40 degrees kills cells, but for visible light polymerization we can use room temperature, so the viability of the cells is much higher.”

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