UT researchers published a
paper
in Nature Materials on June 30 describing a resin
3D printing process
that creates structures with hard and soft properties in a single object. This finding can help with the manufacturing of stretchable medical and electronic devices, according to the news release.
The resin 3D printing process can improve efficiency in the manufacturing of these devices, said Ji-Won Kim, first author who worked on the paper as a postdoctoral research assistant.
“The manufacturing process could be very multi-step and then time-consuming,” Kim said. “We want to make it single-step to make everything at the same time.”
The process creates multi-material structures, which are single structures composed of more than one mechanical property, Kim said. Multi-material structures are found in nature, such as a human foot with bones and skin.
“The way that (biological structures) combine those multiple materials, such as hard and soft components that you see in things like wood and bone, is in a manner that allows the two materials to operate synergistically,” principal investigator Zachariah Page said.
These structures are made using a resin 3D printing process called photopolymerization, which uses light to solidify liquid photo resin. Kim said resin is composed of a monomer, which is a molecule that reacts with other molecules. It is also composed of an initiator, which acts as a catalyst for a reaction. When the monomer reacts, she said it builds a larger molecule called a polymer.
A common issue with 3D printing is failure at the interface between different monomers, Page said. The interface is the point where different properties, such as hard and soft, come into contact, according to the news release.
“How do we combine, in a synthetic manner, multiple different materials and have them not just simply fail at the interface when you apply some stress to the structure?” Page said.
To solve this issue, Kim said the researchers created a hybrid monomer of epoxy and acrylate, which are two monomers used to create multi-material structures. By creating a resin that uses a hybrid epoxy-acrylate monomer, she said every polymer would incorporate the same hybrid monomer, solving the interface failure issue.
“Everything is about the chemistry,” Kim said.
Conventional resin 3D printing also uses ultraviolet light. Page said the team designed photosystems in the resins, which absorb different colors of light. The printing process uses the spectral control of ultraviolet and violet light to determine if the material will be hard or soft, Kim said.
Page said the lower energy violet light activates a process to produce soft material with fewer connections. Meanwhile, the higher energy ultraviolet light would activate a secondary reaction that produces more connections and a rigid material.
“A big theme of our research group in general has been expanding the toolbox of photochemistry and 3D printing,” said graduate research assistant Keldy Mason, first author on a related
research paper
that Page and Kim also worked on. “We’ve had quite a bit of development in visible wavelengths and how we can tune the reactivity depending on the color of light.”
The researchers also created a prototype of a stretchable electronic device, which protected the electronic component with hard material, while having soft material attached to make it bendable.
Page said there are biomedical applications with surgical models and prosthetic devices. Page said the Nature Materials paper provided proof-of-concept applications, including a knee joint with ligaments and bones that move together.
Mason said multi-material printing could become a larger part of additive manufacturing or 3D printing.
“It feels like we’re at the cutting edge of 3D printing and polymer science,” Mason said. “It’s very exciting to think about how our system could directly solve some problems in 3D printing or additive manufacturing.”
