Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography (DIAL), built to print thick, particle-filled extrusion inks at speeds and resolutions closer to light-based processes. The work, led by Pranav Kaarthik, was published in Science Advances.

Digital light processing needs low-viscosity, weakly scattering resins, while direct ink writing handles functional yield-stress inks but is slowed by filament deposition and limited 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. With DIAL, we lay a foundation for eliminating that compromise,” said Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern University.

For each layer, a slot die extrudes ink onto the substrate and a doctor blade scraps it into a sheet as thin as 25 microns. A 405-nanometer projector then travels over the sheet and crosslinks selected regions, with uncured ink left in place as support. Since light only has to pass through a thin sheet, opaque, heavily filled inks remain printable. The projector’s 50-micron pixel pitch sets planar resolution.

With 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, against 124 minutes with DIW, and fins about 150 microns thick. Rastered projection over overlaid ink sheets produced a multimaterial lattice four times the projector’s illumination area.

The researchers 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 called their print times conservative, since tool changes had not been tuned for speed, and said the lack of suction and peel forces seen in vat-based printing should ease expansion of build area and volume.

“Rebuilding American manufacturing will depend on new ways to make advanced materials. 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,” Truby said.

Kaarthik and Truby have been 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.