Researchers at Northwestern University have developed a hybrid additive manufacturing method called direct ink additive lithography (DIAL), which is designed to print thick, particle-filled inks at resolutions and speeds 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 resins that scatter light only weakly, while direct ink writing can handle functional yield-stress inks but is limited by filament deposition and nozzle diameter. DIAL combines extrusion with projected light so that opaque, heavily filled inks can be patterned.
How the process works
For each layer, a slot die deposits ink onto a substrate, and a doctor blade spreads it into a sheet as thin as 25 microns. A 405-nanometer projector then moves across the sheet and crosslinks selected regions. Uncured ink remains in place and serves as support. Because the light passes through only a thin sheet, opaque, heavily filled inks remain printable. The projector's 50-micron pixel pitch defines planar resolution.
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. The process also 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.
Other demonstrations included interlocking chain mail with struts about 250 microns thick, 15 gyroid structural electrolyte lattices printed 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 optimized for speed.
Potential for scaling
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 removing that compromise.
The researchers also noted that DIAL avoids the suction and peel forces associated with vat-based printing, which they said should make it easier to expand build area and volume. Truby added that the ability to print many complex functional parts at once could provide a path from laboratory demonstrations 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.