Researchers at Northwestern University have developed a hybrid 3D printing method, 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 addresses a trade-off between two established approaches. 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.
Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern, 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 removing that compromise.
How the process works
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, with uncured ink left in place to act as support. Because light only has to pass through a thin sheet, opaque and heavily filled inks remain printable. The projector's 50-micron pixel pitch sets the planar resolution.
Printed demonstrations
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 for direct ink writing, and produced fins about 150 microns thick. Rastered projection over overlaid ink sheets yielded a multimaterial lattice four times the projector's illumination area.
- 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 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 expand build area and volume.
Truby said rebuilding American manufacturing will depend on new ways to make advanced materials, and that because DIAL can print many complex, functional parts at once, the team sees a path to scaling it from the lab toward 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. Funding came from the National Science Foundation, the Air Force Office of Scientific Research and Northwestern's McCormick School of Engineering.