Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography, or DIAL, that aims to print thick, particle-filled 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. Direct ink writing can handle functional yield-stress inks, but its speed is limited by filament deposition and its feature size by nozzle diameter. DIAL instead combines extrusion with projection patterning.
How the process works
For each layer, a slot die extrudes ink onto the substrate. A doctor blade then scrapes the deposit into a sheet as thin as 25 microns. A 405-nanometer projector travels over the sheet and crosslinks selected regions. Ink that is not exposed remains in place and serves 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.
Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern, said manufacturers have faced a choice between the materials they need and the printing speed, resolution and scale they want. He said DIAL lays a foundation for eliminating that compromise.
Demonstrations and measurements
The team used a model ink made from a polyurethane-based resin thickened with fumed silica. It 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. By rastering projection over overlaid ink sheets, the researchers made a multimaterial lattice four times the projector's illumination area.
The paper also reports interlocking chain mail with struts about 250 microns thick. In a single 15-minute run, the team printed 15 gyroid structural electrolyte lattices from an ionogel ink. It additionally produced 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 found in vat-based printing should make it easier to expand build area and volume.
Path toward manufacturing
Truby linked the process to broader manufacturing goals. He 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 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.