Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography (DIAL) that is designed to pattern thick, particle-filled inks at resolutions and speeds closer to those of light-based printing. The work, led by Pranav Kaarthik, was published in Science Advances.
The method addresses a trade-off between two established approaches. Digital light processing requires low-viscosity resins that scatter light only weakly, while direct ink writing can handle functional yield-stress inks but is slowed by filament deposition and constrained by nozzle diameter.
Ryan Truby, a materials science and engineering professor at Northwestern, said manufacturers have had to choose between the materials they need and the printing speed, resolution and scale they want. The researchers present DIAL as a foundation for removing that compromise.
In DIAL, a slot die extrudes ink onto a substrate for each layer, 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 selected regions. Uncured ink remains in place and acts as support. Because light passes only through a thin sheet, opaque inks with heavy filler loading remain printable. The projector's 50-micron pixel pitch determines planar resolution.
Using a model ink made from a 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, and produced fins about 150 microns thick. Rastering projection over overlaid ink sheets yielded a multimaterial lattice four times the projector's illumination area.
The researchers 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.
The authors described their print times as conservative because tool changes had not been tuned for speed. They also noted that DIAL avoids the suction and peel forces associated with vat-based printing, a characteristic they expect to make it easier to expand build area and volume.
Truby said the ability to print many complex, functional parts at once points to a path for scaling the process from the laboratory to larger-volume manufacturing of architected materials. He cited potential applications in robotics, aerospace and healthcare. 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.