Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography, or DIAL, for forming thick, particle-filled inks at speeds and resolutions closer to those of light-based processes. The work, led by Pranav Kaarthik, was published in Science Advances.
The team positions DIAL between two established approaches. Digital light processing needs low-viscosity resins that scatter light only weakly. Direct ink writing can handle functional yield-stress inks, but filament deposition slows it down and nozzle diameter limits its resolution. DIAL is intended to reduce that trade-off by combining extrusion with projected light.
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 described DIAL as a foundation for eliminating that compromise.
Layer-by-layer sheeting and projection
For each layer, a slot die extrudes ink onto a substrate, and a doctor blade spreads 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 serves as support. Because light passes through only a thin sheet, opaque inks with heavy filler loading remain printable, and the projector's 50-micron pixel pitch sets planar resolution.
Demonstrations and measured output
With 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, compared with 124 minutes using direct ink writing. They also produced fins about 150 microns thick. Rastering projection over overlaid ink sheets yielded a multimaterial lattice covering four times the projector's illumination area.
The group further 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 inverted pyramids 0.5 mm deep. These examples show the process being applied to both structural and biological-interface geometries.
Scale-up outlook
The authors called their reported print times 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 tied the method to production of advanced materials, saying that DIAL can print many complex functional parts at once and offers a path from laboratory demonstrations toward larger-volume manufacturing of architected materials. The researchers point to robotics, aerospace and healthcare among possible application areas.
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.