Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography (DIAL), 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.
DIAL combines extrusion with projection lithography. For each layer, a slot die deposits ink onto a substrate, and a doctor blade spreads it into a sheet as thin as 25 microns. A 405-nanometer projector then travels over the sheet and crosslinks selected regions. Ink that is not cured remains in place and acts as support. Because light passes only through a thin sheet, opaque inks with heavy particle loading remain printable, the researchers report. The projector's 50-micron pixel pitch sets the planar resolution.
Addressing a materials and process trade-off
The method targets a trade-off described by the team. Digital light processing requires low-viscosity, weakly scattering resins, while direct ink writing can handle functional yield-stress inks but is slowed by filament deposition and limited by nozzle diameter. Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern University, said manufacturers have had to choose between the materials they need and the printing speed, resolution and scale they want, and that DIAL lays a foundation for eliminating that compromise.
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 using direct ink writing, and produced fins about 150 microns thick. Rastered projection over overlaid ink sheets produced a multimaterial lattice four times the projector's illumination area.
Printed demonstrations
The researchers printed interlocking chain mail with struts about 250 microns thick and 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run. They also produced hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids.
The authors called their print times conservative because tool changes had not been tuned for speed. They added that the lack of suction and peel forces seen in vat-based printing should ease expansion of build area and volume.
Truby said that rebuilding American manufacturing will depend on new ways to make advanced materials. Because DIAL can print many complex, functional parts at once, the team sees a path toward scaling it from the lab to larger-volume manufacturing of architected materials for applications spanning robotics, aerospace, healthcare and more, he said.
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.