Researchers at Northwestern University have developed a hybrid 3D printing method, direct ink additive lithography (DIAL), that is 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 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.
Deposition and light patterning
For each 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 selected regions. Uncured ink stays in place and acts as support.
Because the light passes only through a thin sheet, opaque and heavily filled inks remain printable, according to the researchers. The projector's 50-micron pixel pitch determines planar resolution.
With 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 researchers also produced fins about 150 microns thick. Rastered projection over overlaid ink sheets yielded a multimaterial lattice four times the projector's illumination area.
Printed parts and scale-up
- The team printed interlocking chain mail with struts about 250 microns thick.
- It produced 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run.
- It made 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 also said the lack of suction and peel forces seen in vat-based printing should make it easier to expand build area and volume.
Ryan Truby, a materials science and engineering professor at Northwestern, said manufacturers have had to choose between the materials they need and the printing speed, resolution and scale they want. DIAL, he said, lays a foundation for eliminating that compromise.
Truby also linked the process to manufacturing scale-up. He said rebuilding American manufacturing will depend on new ways to make advanced materials, and that DIAL's ability to print many complex, functional parts at once offers a path from the lab toward larger-volume production of architected materials for robotics, aerospace and healthcare.
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.