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 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. DIAL is designed to combine the material range of extrusion with the patterning speed and resolution of projection.
Layer formation and patterning
For each layer, a slot die extrudes ink onto a substrate, and a doctor blade spreads it into a sheet as thin as 25 microns. A 405-nanometer projector then moves over the sheet and crosslinks selected regions. Uncured ink remains in place and acts as support. Because light passes only 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 had to choose 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
With 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 using direct ink writing. The process also produced fins about 150 microns thick. Rastered projection over overlaid ink sheets yielded a multimaterial lattice four times the projector’s illumination area.
The researchers also printed interlocking chain mail with struts about 250 microns thick and 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run. They produced hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids. These examples indicate that the process can handle functional, particle-filled formulations and several part types within one build sequence, although the reported demonstrations remain laboratory results.
Speed and scale-up
The authors described their 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. Those points are expectations about scale-up rather than demonstrated production performance.
Truby said rebuilding American manufacturing will depend on new ways to make advanced materials. Because DIAL can print many complex, functional parts at once, he 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.