Living polymerization takes 3D printing into fourth dimension

Repairing and reusing plastics and delivering cancer drugs more effectively are only two of many potential applications of a new 3D/4D printing technology developed by researchers at the University of New South Wales (UNSW) Sydney in Australia and the University of Auckland in New Zealand. In a paper in Angewandte Chemie International Edition, the researchers report the successful merging of 3D printing and photo-controlled/living polymerization – a chemical process for creating polymers. In 4D printing, a subset of 3D printing, the printed object can transform its shape in response to certain conditions. The new controlled polymerization method, in which the researchers use visible light to create an environmentally friendly ‘living’ plastic or polymer, opens a new world of possibilities for the manufacture of advanced solid materials. The research built upon PET-RAFT (photoinduced electron/energy transfer-reversible addition fragmentation chain transfer) polymerization, a new way to make controlled polymers using visible light. These polymers can be reactivated for further growth, unlike traditional polymers which are ‘dead’ after being made. Since this development, the technology has expanded and proven useful for making well-controlled molecules for many applications, including drug delivery. Lead author Cyrille Boyer at UNSW Sydney said that his team's latest breakthrough involved the development of a new 3D printing system that takes advantage of PET-RAFT polymerization to allow 3D printed materials to be easily modified after printing. "Controlled polymerization has never been used in 3D and 4D printing before, because the rates of typical controlled polymerization processes are too slow for 3D/4D printing, where the reaction must be fast for practical printing speeds," Boyer said. "After two years of research and hundreds of experiments, we developed a rapid process compatible with 3D printing. "In contrast to conventional 3D printing, our new method of using visible light allows us to control the architecture of the polymers and tune the mechanical properties of the materials prepared by our process. This new process also gives us access to 4D printing and allows the material to be transformed or functionalized, which was not previously possible." UNSW's Nathaniel Corrigan, co-first author of the paper with UNSW PhD candidate Zhiheng Zhang, said a bonus advantage of their new system was the ability to finely control all molecules in the 3D-printed material. "4D printing is a subset of 3D printing. But with 4D printing, the 3D-printed object can change its shape and chemical or physical properties and adapt to its environment," Corrigan said. "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 are hopeful that their new 3D/4D printing process will lead to the production of functional materials able to solve many of the problems facing society today. According to Boyer, the new method has a multitude of applications for everyday items – particularly if a deformed or broken object needs to be repaired or modified. "The main application is of course recycling, because instead of using a plastic object once, it can be repaired and reused," he said. "For ordinary recycling you take the materials away and have to reconstruct them, but for the new 'living' material it will be able to repair itself. For example, if you want to put the UNSW logo on a mug, you can modify the surface of the object and grow the polymers to show UNSW because the object is not dead; it's a living object and can continue to grow and expand." Corrigan said that another major benefit of the new process was its compatibility with biomedicine, as it didn’t require extreme conditions. "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," he said. "But with the application of PET-RAFT polymerization to 3D printing, we can produce long polymer molecules using visible light rather than heat, which is the typical polymerization method. Using heat above 40°C kills cells, but for visible light polymerization we can use room temperature, so the viability of the cells is much higher." Objects made through this new process could more easily be used in advanced bio-applications, such as tissue engineering, where a tissue structure is used to form new, viable tissue for medical purposes. "Our new method targets small scale, niche applications in fields like microelectronics and biomedicine – a huge area for us – that require very advanced polymers," Boyer said. Boyer added that their new technique would allow commercial and non-expert operators to produce materials with seemingly endless properties and applications. "We want to explore our system to find and address any limitations to allow for better uptake and implementation of this technology," he said. "There is so much we can do by combining 3D and 4D printing with controlled polymerization to make advanced and functional materials for many applications to benefit society." This story is adapted from material from UNSW, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.