Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography, or 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.
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. DIAL is intended to avoid that trade-off by separating material deposition from light-based patterning.
Thin ink sheets, patterned by projection
For each layer, a slot die extrudes ink onto the 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. Ink that is not cured remains in place and acts as support.
Because the light only has to pass through a thin sheet, opaque and heavily filled inks remain printable. The projector's 50-micron pixel pitch sets the planar resolution. The process therefore uses a dense, functional ink rather than a low-viscosity photopolymer, while still defining features optically.
Demonstrations show speed and material range
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 process also produced fins about 150 microns thick. In another demonstration, rastered projection over overlaid ink sheets yielded a multimaterial lattice four times the projector's illumination area.
- Interlocking chain mail with struts about 250 microns thick.
- Fifteen gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run.
- 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 noted that DIAL does not involve the suction and peel forces found in vat-based printing, which they said should make it easier to expand build area and volume.
Scale-up path and research support
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. He said DIAL lays a foundation for eliminating that compromise. Truby also linked the method's ability to print many complex, functional parts at once to a path from the lab toward larger-volume manufacturing of architected materials for robotics, aerospace, healthcare and other applications. He argued that rebuilding American manufacturing will depend on new ways to make advanced materials.
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.