Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography (DIAL), which 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 method addresses a trade-off between two established approaches. Digital light processing relies on 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. Ryan Truby, the June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern, said manufacturers have had to choose between needed materials and desired printing speed, resolution and scale. He described DIAL as a foundation for removing that compromise.
How each layer is formed
For every layer, a slot die extrudes ink onto a substrate, and a doctor blade spreads it into a sheet that can be as thin as 25 microns. A 405-nanometer projector then moves over the sheet and crosslinks selected regions. Ink that is not cured remains in place and acts as support. Because light passes through only a thin sheet, opaque inks with heavy filler loading can remain printable. The projector's 50-micron pixel pitch determines planar resolution.
Demonstrations and measured performance
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. The process also produced fins about 150 microns thick. By rastering projection over overlaid ink sheets, the researchers made a multimaterial lattice four times the projector's illumination area.
The team also demonstrated several other structures:
- Interlocking chain mail with struts about 250 microns thick.
- Fifteen 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.
The authors described their reported print times as conservative because tool changes had not been tuned for speed. They also said the absence of suction and peel forces that occur in vat-based printing should make it easier to expand build area and volume.
Outlook for manufacturing
Truby linked the method to broader manufacturing goals, saying that rebuilding American manufacturing will depend on new ways to make advanced materials. He said that 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 robotics, aerospace, healthcare and other applications.
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.