3D printing: special resin combines strong and soft material properties

A team of scientists at the University of Texas has developed a method with which a specially developed resin can be printed in such a way that it takes on either solid or soft material properties. An object printed with this resin can therefore have a soft outer shell, for example, but still be stable at its core.

The inspiration for the printing process came from nature, according to Zak Page, assistant professor of chemistry and one of the authors of the study “Hybrid epoxy-acrylate resins for wavelength-selective multimaterial 3D printing”, which has been published in Nature Materials.

Nature combines hard and soft materials at their interface without error, says Page. This is exactly what the researchers wanted to imitate. To achieve this, they developed a special liquid resin for a printing process that uses ultraviolet light (UV light) to harden the individual layers.

Light color determines the material properties

However, instead of using UV light in only one light color, as is conventionally the case, the scientists use two different light colors. Depending on the wavelength of the light, different chemical processes are triggered in the printing resin. Under bright violet light, the resin takes on a rubbery consistency. However, if it is exposed to more energetic ultraviolet light, it hardens into a solid plastic-like material during 3D printing. As the original material is the same, the printed elements can be easily combined with each other despite their different properties, without any durability problems occurring at the seams. This means there are no weak points.

“We have incorporated a molecule with both reactive groups so that our two solidification reactions can 'communicate' with each other at the interface,” explains Page.

To test the process, the researchers used their new 3D printing method to print an artificial knee joint consisting of soft ligaments and hard bones. The joint could be moved without any material fractures or subsequent signs of fatigue at the interfaces.

The scientists themselves were surprised by how well the resin worked. “The soft parts stretched like a rubber band and bounced back. The hard parts were as stable as a plastic used in consumer goods,” says Page.

The scientists also tried out the process on an electrical switch. One part of the switch is soft and movable so that an integrated electrical contact could be switched. In contrast, another area is difficult to prevent the switch from breaking.

The researchers at the University of Texas were themselves surprised that the resin had the desired properties straight away. This “hardly ever happens” with newly developed 3D printing resins.

(olb)