Newswise — Researchers at Lawrence Livermore National Laboratory (LLNL) have co-developed a new way to precisely control the internal structure of common plastics during 3D printing, allowing a single printed object to seamlessly shift from rigid to flexible using only light.
In a paper published today in Science, the researchers describe a technique called crystallinity regulation in additive fabrication of thermoplastics (CRAFT) that enables microscopic control over how plastic molecules arrange themselves as an object is printed. The work opens new possibilities for advanced manufacturing, soft robotics, national defense, energy damping and information storage, according to the researchers. The team includes collaborators from Sandia National Laboratories (SNL), the University of Texas at Austin, Oregon State University, Arizona State University and Savannah River National Laboratory.
The team demonstrated that by carefully tuning light intensity during printing, they could dictate how crystalline or amorphous a thermoplastic becomes at specific locations within a part. That molecular arrangement determines whether a material behaves more stiff and rigid, or as a softer, more flexible plastic — without changing the base material. CRAFT builds on that principle by allowing researchers to control crystallinity spatially during printing, rather than uniformly throughout a part.
“A classic example of crystallinity is the difference between high-density polyethylene —picture a milk jug — and low-density polyethylene, like squeeze bottles and plastic bags. The bulk property difference in these two forms of polyethylene stems largely from differences in crystallinity,” said LLNL staff scientist Johanna Schwartz. “Our CRAFT effort is exciting in that we are controlling the crystallinity within a thermoplastic spatially with variations in light intensity, making areas of increased and decreased crystallinity to produce parts with control over material properties throughout the whole geometry.”
A key challenge, however, was translating this new materials capability into practical manufacturing instructions that could be used on real 3D printers, according to LLNL engineer Hernán Villanueva. Villanueva joined the project after early discussions with Schwartz and former SNL scientists Samuel Leguizamon and Alex Commisso identified a missing link: a way to convert any three-dimensional computer-aided design (CAD) into the detailed light patterns needed to print parts using the CRAFT method.
Villanueva said he drew on prior work in a multi-institutional team focused on lattice structures and advanced manufacturing workflows. In that effort, he developed software that rapidly converted complex, topology-optimized designs into printing instructions by parallelizing the process on LLNL’s high-performance computing (HPC) systems — reducing turnaround times from days to hours or minutes.
Applying that same computational approach to CRAFT, Villanueva adapted the workflow to encode “changes in light” rather than changes in material. He was soon able to convert 3D CAD geometries directly into CRAFT printing instructions, cutting instruction-generation time from hours — or even a full day — down to seconds, making rapid design iteration and demonstration of the method practical.
“This work is a natural extension of the Lab’s strengths in advanced manufacturing and materials by design,” Villanueva said. “As part of the CRAFT effort, we have evolved a tool that connects materials science with computational workflows and advanced printing, enabling us to move directly from a 3D design to a part with spatially varying properties.”
The team’s method relies on a light-activated polymerization process in which exposure level governs the stereochemistry of growing polymer chains, researchers said. Lower light intensities favor more ordered crystalline regions, while higher intensities suppress crystallization, yielding softer, more transparent material. By projecting grayscale patterns during printing, the team produced parts with smoothly varying mechanical and optical properties.
The demonstrated ability to tune properties by changing a light’s intensity rather than swapping materials could significantly simplify additive manufacturing (3D printing), Schwartz explained.
“If you can get many different properties from one vat of material, printing complex multi-material or multi-modulus structures becomes much easier,” she said.
The researchers demonstrated the CRAFT technique on commercial 3D printers, fabricating objects that combine multiple mechanical behaviors in a single print. Examples included bio-inspired structures that mimic bones, tendons and soft tissue, reproductions of famous paintings, as well as materials designed to absorb or redirect vibrational energy without adding weight or complexity. Among the most striking demonstrations was the ability to encode crystallinity through transparency differences, according to Schwartz.
“Being able to visualize the differences easily spatially, to the point of generating the Mona Lisa out of only one material, was incredibly cool,” Schwartz said.
LLNL’s Villanueva said the work reflects the Lab’s long-standing investments in HPC and in integrating modeling, design tools and novel manufacturing processes. He added that future work could integrate topology optimization directly into the CRAFT framework, enabling researchers to optimize light patterns themselves — rather than material layouts — to achieve desired performance.
Because the process works with thermoplastics — materials that can be melted and reshaped — printed parts remain recyclable and reprocessable, an important advantage for manufacturing sustainability. The findings suggest a future where 3D-printed plastic components can be tailored at the molecular level for specific functions, bridging the gap between material science and digital manufacturing.
From an applications standpoint, Schwartz said the technology could have broad and near-term impact.
“Energy dampening and metamaterial design are the most exciting use cases to me,” she said. “From space to fusion to electronics, there are so many industries that rely on energy and vibrational dampening control. This CRAFT printing process can access all of them.”
