Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography, or DIAL, designed 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 needs low-viscosity, weakly scattering resins. Direct ink writing can handle functional yield-stress inks, but filament deposition slows the process and nozzle diameter limits resolution.
A sheet-based hybrid process
In DIAL, each layer begins with a slot die extruding 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, while uncured ink remains in place as support. Because light passes only through the thin sheet, opaque, heavily filled inks remain printable. The projector’s 50-micron pixel pitch sets planar resolution.
Ryan Truby, the 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.
Printed demonstrations
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. It 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, 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run, and hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids.
The authors described their print times as conservative because tool changes had not been tuned for speed. They added that the absence of 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. Because DIAL can print many complex, functional parts at once, he said 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. Funding came from the National Science Foundation, the Air Force Office of Scientific Research and Northwestern’s McCormick School of Engineering.