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.
The method targets a long-standing trade-off. 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 constrained 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,” said Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern University. “With DIAL, we lay a foundation for eliminating that compromise.”
How a layer is formed
For each layer, a slot die extrudes ink onto the substrate and a doctor blade scrapes it into a sheet as thin as 25 microns. A 405-nanometer projector then travels over the sheet and crosslinks selected regions, leaving uncured ink in place to act as support. Because light has to pass only through a thin sheet, opaque, heavily filled inks remain printable. The projector’s 50-micron pixel pitch sets the planar resolution.
Parts printed and measured times
With a model ink of polyurethane-based resin thickened with fumed silica, the team reported the following results:
- A 60 mm by 40 mm log pile structure printed in 30 minutes, against 124 minutes with direct ink writing.
- Fins about 150 microns thick.
- A multimaterial lattice four times the projector’s illumination area, produced by rastering projection over overlaid ink sheets.
- Interlocking chain mail with struts roughly 250 microns thick.
- 15 gyroid structural electrolyte lattices printed from an ionogel ink in a single 15-minute run.
- Hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids.
Outlook
The authors described their reported print times as conservative, noting that tool changes had not been tuned for speed. They also said the absence of the suction and peel forces seen in vat-based printing should make it easier to enlarge build area and volume.
“Rebuilding American manufacturing will depend on new ways to make advanced materials,” Truby said. “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.”
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.