Researchers at Northwestern University have developed a hybrid additive manufacturing process that combines extrusion-based ink deposition with projection lithography, aiming to print thick, particle-filled functional inks at resolutions and speeds closer to light-based methods. The method, called direct ink additive lithography (DIAL), was led by Pranav Kaarthik and published in Science Advances.
DIAL addresses a trade-off between digital light processing and direct ink writing. According to the researchers, DLP requires low-viscosity, weakly scattering resins, while DIW can handle functional yield-stress inks but is slowed by filament deposition and constrained by nozzle diameter.
In the DIAL process, a slot die extrudes ink onto a substrate for each layer. A doctor blade then spreads the material into a sheet as thin as 25 microns. A 405-nanometer projector moves over the sheet and crosslinks selected regions; uncured ink remains in place and acts as support. Because the light passes only through a thin sheet, opaque and heavily filled inks remain printable, the team reported. The projector's 50-micron pixel pitch defines planar resolution.
Demonstrations and measured gains
Using a model ink made from polyurethane-based resin thickened with fumed silica, the researchers printed a 60 mm by 40 mm log-pile structure in 30 minutes. The same structure took 124 minutes with DIW, according to the paper. The team also produced fins about 150 microns thick.
By rastering projection over overlaid ink sheets, the researchers made a multimaterial lattice with an area four times the projector's illumination area. They also printed interlocking chain mail with struts about 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.
Manufacturing implications
Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern, said manufacturers have had to choose between needed materials and desired speed, resolution, and scale. "With DIAL, we lay a foundation for eliminating that compromise," he said in a statement.
The authors described their reported print times as conservative because tool changes had not been tuned for speed. They also said the absence of suction and peel forces seen in vat-based printing should make it easier to expand build area and volume.
Truby linked the process to broader manufacturing goals. "Rebuilding American manufacturing will depend on new ways to make advanced materials," he said, adding that DIAL's ability to print many complex functional parts at once suggests a path from lab-scale work toward larger-volume manufacturing of architected materials for robotics, aerospace, healthcare, and other applications.
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.