Newly developed 3D printing resin can produce single-piece products with moderate hardness and softness

Apart from bones, our bodies are almost entirely made up of soft biological tissue. And items like medical implants or wearable electronics almost always contain at least some rigid components. While more and more devices are being developed for use on or in our bodies, these devices tend to not be very... "body-like."

Even though these devices do contain some softer synthetic materials, there is always a clear line where soft and hard materials connect to each other. These boundaries can cause discomfort, reduced function, and mechanical failure when stressed.

In nature, biological tissues often avoid such abrupt boundaries by gradually transitioning from low to high stiffness as they are stretched from one point to another. For example, tendons provide a smooth transition from relatively soft muscle tissue to hard bone.

A new type of 3D printing resin could change that by giving individual objects varying hardnesses.

Scientists at Lawrence Livermore National Laboratory (LLNL) and MetaCorp have now replicated this property in a "one-pot" thiol-ene-epoxy 3D printing resin. Like other photosensitive resins, this resin changes from a viscous state to a solid state when exposed to light. By projecting these patterns into clear side cavities of resin, objects are created.

In this case, though, the intensity of the light determines the solid's hardness. Thus, by strategically varying the intensity of light throughout the making process, it is possible to make a single object gradually transition from softness in one area to hardness in another. The material's toughness also increases by up to 10 times throughout the gradient.

In a demonstration of the technology, scientists used it to print an all-in-one finger-mounted device that can convert text messages into Braille. When attached to an air pump, the wearable device pushes air in and out of a pad that presses against the user's fingertips, replicating the sensation of touching raised Braille characters.

"This work has been investigating whether we can engineer a continuous mechanical gradient from soft to stiff in a single resin system," said lead scientist Dr. Sijia Huang of LLNL. "Here we are printing everything we see, just using light dose to control the modulus."

A paper on the research was recently published in the journal Matter.