Dual-light 3D printing technique enables seamless blending of flexible and rigid materials

Inspired by how nature blends toughness and flexibility, such as the rigid structure of bone surrounded by pliable cartilage, all with elegant and precise geometric properties, researchers at The University of Texas at Austin have developed a fast, precise new 3D printing method that seamlessly merges soft and hard properties into a single object using different colors of light.

This advance could pave the way for next-generation prosthetics, flexible medical devices and stretchable electronics that move naturally with the body, much like a human joint or ligament. The process is described in a paper published today in Nature Materials.

“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.”

A related paper published May 29 in ACS Central Science from Page and other authors, describes adjacent work, which the journal’s editors praised in a “First Reactions” commentary, saying the work represents “the future of 3D printing” and showcases “how light─not merely as a tool for curing resin, but as a finely tuned sculptor─can drive the next generation of additive manufacturing.”

“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.”

One of the biggest challenges in creating objects with vastly different physical properties is that materials tend to fail at the interface, or the point they come in contact. Think about how the rubber sole of a running shoe will separate over time from the softer mesh cloth above it.

The new 3D printing method uses a custom-designed liquid resin and a dual-light printing system that activates different chemical reactions depending on the color of light used. By shining violet light, the resin cures into a stretchy, rubber-like material. But in areas hit with higher-energy ultraviolet light, it becomes rigid and strong. The result is an object with distinct zones of softness and hardness crafted in a single print.

“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.”

The team demonstrated the system by printing a small but functional knee joint with flexible ligaments and rigid bones that move together smoothly. They also created a prototype stretchable electronic device with a gold wire mounted on a strip that could bend and stretch in parts, but with a more rigid section to prevent the circuit from breaking.

“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.”

The process also works faster and with better resolution than previous approaches. And because the printer setup is relatively simple and affordable, the technology could become accessible to researchers, hospitals and educators.

“It could be used to prototype surgical models, wearable sensors or even soft robots,” Page said. “There’s so much potential here.”