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 extrusion 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 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. DIAL combines elements of both.
For each layer, a slot die extrudes ink onto the substrate, and a doctor blade scrapes the deposit into a sheet as thin as 25 microns. A 405-nanometer projector then travels 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, heavily filled inks remain printable. The projector's 50-micron pixel pitch sets planar resolution.
Using a model ink made from 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. They 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 printed interlocking chain mail with struts about 250 microns thick. In a single 15-minute run, they produced 15 gyroid structural electrolyte lattices from an ionogel ink. They also made 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 associated with vat-based printing should make it easier to expand build area and volume.
Ryan Truby, 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 said DIAL lays a foundation for eliminating that compromise. Truby also said the ability to print many complex, functional parts at once offers a path toward scaling the process 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. Funding came from the National Science Foundation, the Air Force Office of Scientific Research and Northwestern's McCormick School of Engineering.