A research team at the University of Texas at Austin has developed a new 3D printing process that, for the first time, precisely combines soft and hard material properties within a single component—without mechanical weaknesses at the transition zones. The method uses two different wavelengths of light to locally control the mechanical properties of a specially formulated photopolymer resin matrix. The results were published in Nature Materials.
At the heart of the process is a dual-exposure technique: while violet light triggers an elastomeric (soft) crosslinking reaction, higher-energy UV light induces a rigid, thermoplastic-like hardening. By selectively exposing the material to each wavelength, seamless transitions between soft and hard regions can be created—all within a single printing operation. The key chemical mechanism relies on a molecule that contains two different functional groups, enabling controlled reactions at the interfaces.
“What really motivated me and my research group is looking at materials in nature,” said Zak Page, an assistant professor of chemistry at UT Austin and corresponding author. “Nature does this in an organic way, combining hard and soft materials without failure at the interface. We wanted to replicate that.”
“This approach could make additive manufacturing more competitive for higher-volume production compared with traditional processes like injection molding. Just as important, it opens up new design possibilities,” said Keldy Mason, lead author of the latter study and a graduate student in Page’s lab. “This gives engineers, designers and makers more freedom to create.”
According to Page, potential applications range from medical prosthetics to flexible electronic components. One demonstrator—a functional knee joint with elastic ligaments and rigid bone-like structures—shows the method’s promise.
“We built in a molecule with both reactive groups so our two solidification reactions could ‘talk to each other’ at the interface,” Page said. “That gives us a much stronger connection between the soft and hard parts, and there can be a gradual transition if we want.”
“Honestly, what surprised me most was how well it worked on the first try. That almost never happens with 3D printing resins,” Page said. “We were also shocked by how different the properties were. The soft parts stretched like a rubber band and bounced back. The hard parts were as strong as plastics used in consumer products.”
“It could be used to prototype surgical models, wearable sensors or even soft robots,” Page said. “There’s so much potential here.”
Another prototype featured a stretchable circuit with a gold-coated wire that remains flexible in one region while providing structural support in another. In addition to high precision, the process offers rapid curing and relies on relatively simple hardware, making it suitable for research labs or medical applications. A patent has been filed. The project received funding from the U.S. Department of Defense and the National Science Foundation, among others.
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