CRAFT controls crystallinity during 3D printing and varies hardness and transparency pixel by pixel

Researchers at the University of Texas at Austin and Sandia National Laboratories present CRAFT, a 3D-printing process that controls material properties at pixel-level resolution via grayscale light. Using just a single cyclooctene-based resin, a DLP/LCD printer can create hard, opaque regions and soft, transparent regions—such as for realistic hand models for surgical training or shock-absorbing protective parts.

The process is called Crystallinity Regulation in Additive Fabrication of Thermoplastics, or CRAFT for short. Technically, it is based on DLP or LCD projection printers that expose not only binary masks but grayscale images. This varies the local light dose layer by layer while a build platform moves through a resin bath. The starting material is cyclooctene, which converts under exposure into a thermoplastic polymer; the exposure parameters influence the ordering of the polymer chains and thus the crystallinity in the resulting volume.

“We can control molecular level order in three-dimensional space, and in doing so, completely change the mechanical and optical properties of a material,” said Zak Page, a UT associate professor of chemistry and author on the paper. “And we can do that all from a really simple, inexpensive feedstock by just changing the light intensity. It’s the simplicity at the heart of it that’s really exciting.”

As applications, the authors cite anatomical training models in which bone-, ligament-, and soft-tissue equivalents come together in a single print job, as well as vibration- and shock-damping structures for protective components. According to UT Austin, the study was supported in part by the U.S. Department of Energy, the National Science Foundation, and the Robert A. Welch Foundation.

“DLP or LCD 3D printing, which this method is compatible with, are some of the cheapest printers that you can buy,” Page said. “You can get one of these printers with the capability to do grayscale projection for $1,000 or less and be off to the races printing.”

The work was led by Alex J Commisso and Samuel Leguizamon; both were previously at Sandia, Leguizamon now works at the Savannah River National Laboratory, and Commisso at Azul 3D. In practice, what will be decisive is how reproducible the crystallinity profiles remain with part size, thermal management, and post-processing—and what material limits cyclooctene-based systems impose in industrial use.