Researchers at Northwestern University have developed a hybrid 3D printing method that combines extrusion of thick, particle-filled inks with projection-based crosslinking, aiming to close the gap between the materials functional parts require and the speed and resolution of light-based processes. The technique, called direct ink additive lithography (DIAL), was led by Pranav Kaarthik and published in Science Advances.
The work addresses a split between two established approaches. Digital light processing can pattern features quickly but depends on low-viscosity, weakly scattering resins. Direct ink writing can handle functional yield-stress inks, yet its throughput is limited by filament deposition and by nozzle diameter. "In 3D printing, manufacturers have had to choose between the materials they need and the printing speed, resolution, and scale they want," said Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern. "With DIAL, we lay a foundation for eliminating that compromise."
In DIAL, each layer begins with a slot die that extrudes ink onto the substrate. A doctor blade then spreads the deposit into a sheet as thin as 25 microns. A 405-nanometer projector travels over that sheet and crosslinks only the selected regions, leaving uncured ink in place to support subsequent layers. Because light passes through a thin sheet rather than a deep vat, opaque and heavily filled inks remain printable. The projector's 50-micron pixel pitch sets the planar resolution.
Using a model ink of polyurethane-based resin thickened with fumed silica, the team printed a 60 mm by 40 mm log-pile structure in 30 minutes, compared with 124 minutes for direct ink writing, along with fins about 150 microns thick. Rastering the projection across overlaid ink sheets produced a multimaterial lattice covering four times the projector's illumination area.
The researchers also printed interlocking chain mail with struts roughly 250 microns thick, 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run, and hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids.
The authors described their reported print times as conservative, noting that tool changes had not been tuned for speed. They also said the absence of the suction and peel forces associated with vat-based printing should make it easier to expand build area and volume.
"Rebuilding American manufacturing will depend on new ways to make advanced materials," Truby said. "Because DIAL can print many complex, functional parts at once, we see a path toward scaling it from the lab to larger-volume manufacturing of architected materials for applications spanning robotics, aerospace, healthcare, and much more." Kaarthik and Truby are listed as coinventors on a U.S. provisional patent application. Funding came from the National Science Foundation, the Air Force Office of Scientific Research and Northwestern's McCormick School of Engineering.