Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography (DIAL) for thick, particle-filled extrusion inks. The process is intended to print at speeds and resolutions closer to light-based processes while accommodating opaque, heavily filled formulations. The work, led by Pranav Kaarthik, was published in Science Advances.
The development targets 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, 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.
Layer formation and projection
For each layer, a slot die extrudes ink onto a substrate, and a doctor blade scrapes 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 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.
Demonstrations
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 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.
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.
Speed, scale and next steps
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.
Truby said that rebuilding American manufacturing would depend on new ways to make advanced materials. He said DIAL's ability to print many complex functional parts at once offered a path from laboratory work 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.