Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography, or DIAL, that is designed to print thick, particle-filled extrusion inks at speeds and resolutions closer to those of light-based processes. The work, led by Pranav Kaarthik, was published in Science Advances.
The team framed DIAL as a response to a trade-off in additive manufacturing. Digital light processing can pattern features quickly, but it needs low-viscosity resins that scatter light weakly. Direct ink writing can handle functional inks with yield-stress behavior, yet its filament-by-filament deposition limits speed, and nozzle diameter constrains resolution.
DIAL divides each layer into two steps. A slot die extrudes ink onto the substrate, and a doctor blade spreads it into a sheet as thin as 25 microns. A 405-nanometer projector then moves over the sheet and crosslinks only the selected regions. Ink that is not exposed remains in place and acts as support. Because the light only passes through a thin sheet, the process can use opaque inks with heavy particle loading. The projector's 50-micron pixel pitch defines planar resolution.
Benchmark prints and functional parts
Using a model ink made from a polyurethane-based resin thickened with fumed silica, the researchers printed a 60 mm by 40 mm log-pile structure in 30 minutes. They reported 124 minutes for the same structure with direct ink writing. The DIAL process also produced fins about 150 microns thick.
By rastering projection across overlaid ink sheets, the team made a multimaterial lattice covering four times the projector's illumination area. It printed interlocking chain mail with struts about 250 microns thick and produced 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run. The researchers also fabricated hydrogel cell-culture inserts containing 0.5-mm-deep inverted pyramids.
The authors described their reported print times as conservative because tool changes had not been optimized for speed. They also noted that DIAL avoids the suction and peel forces associated with vat-based printing, which they said should make it easier to expand build area and volume.
From lab demonstration to manufacturing
Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern, said manufacturers have faced a choice between needed materials and desired speed, resolution and scale. In the paper's account, DIAL is intended as a foundation for removing that compromise.
Truby also linked the process to broader manufacturing goals. He said rebuilding American manufacturing would depend on new ways to make advanced materials, and that DIAL's ability to print many complex functional parts at once offers a path from the lab toward larger-volume production of architected materials. He named robotics, aerospace and healthcare among potential application areas.
Kaarthik and Truby are listed as coinventors on a U.S. provisional patent application. The work received funding from the National Science Foundation, the Air Force Office of Scientific Research and Northwestern's McCormick School of Engineering.