Researchers at Northwestern University have introduced a hybrid additive manufacturing process that pairs slot-die extrusion of particle-filled inks with projection lithography, aiming to remove the usual trade-off between the material a part requires and the speed or resolution at which it can be printed. The method, called direct ink additive lithography (DIAL), was led by Pranav Kaarthik and reported in Science Advances.
The team frames the problem as a split between two established approaches. Digital light processing needs low-viscosity resins that scatter light only weakly, while direct ink writing can handle functional yield-stress inks but is slowed by filament-by-filament deposition and limited by nozzle diameter. DIAL forms each layer mechanically and then patterns it optically.
How each layer is formed
For every layer, a slot die extrudes ink onto the substrate and a doctor blade spreads it into a sheet as thin as 25 microns. A 405-nanometer projector then travels over the sheet and crosslinks only the selected regions. Ink that is not exposed stays in place and serves as support for subsequent layers. Because light has to pass through only a thin sheet, opaque and heavily filled inks that would otherwise be difficult to process remain printable. Planar resolution is set by the projector's 50-micron pixel pitch.
Demonstrated parts and timings
Using a model ink made from a polyurethane-based resin thickened with fumed silica, the researchers printed a 60 mm by 40 mm log-pile structure in 30 minutes; the same geometry took 124 minutes with direct ink writing. They also produced fins roughly 150 microns thick. By rastering the projection across overlaid ink sheets, the group built a multimaterial lattice covering 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.
What the authors say
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, and that DIAL lays a foundation for eliminating that compromise.
The authors described their reported print times as conservative, noting that tool changes had not been tuned for speed. They also argued that the absence of the suction and peel forces seen in vat-based printing should make it easier to expand build area and volume. Truby said that because DIAL can print many complex, functional parts at once, the group sees a path toward scaling the process from the lab to larger-volume manufacturing of architected materials for applications spanning robotics, aerospace, healthcare and beyond.
Status and funding
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.