Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography, or DIAL, for thick, particle-filled inks. The process is designed to bring extrusion-based materials closer to the speed and resolution of light-based printing. The work, led by Pranav Kaarthik, was published in Science Advances.
The team frames DIAL as a response to a materials-versus-throughput trade-off. Digital light processing requires low-viscosity, weakly scattering resins. Direct ink writing can handle functional yield-stress inks, but filament deposition and nozzle diameter constrain speed and feature size. DIAL combines elements of both.
Layer-by-layer patterning
For each layer, a slot die extrudes 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. Ink that is not cured remains in place and serves as support. Because the light passes through only a thin sheet, the process can handle opaque, heavily filled inks that would be difficult for vat-based light printing. The projector's 50-micron pixel pitch determines planar resolution.
Ryan Truby, a materials science and engineering professor at Northwestern, said manufacturers have had to choose between needed materials and desired printing speed, resolution and scale. He said DIAL provides a foundation for removing that compromise. That is the team's stated aim.
Printed structures and performance
Using a model ink made from polyurethane-based resin thickened with fumed silica, the researchers printed a 60 mm by 40 mm log-pile structure in 30 minutes. The same structure took 124 minutes with direct ink writing, according to the paper. They also produced fins about 150 microns thick. By rastering projection across overlaid ink sheets, they made 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. These examples show the method across several material and geometry types, but they remain laboratory demonstrations.
Speed, scale and next steps
The authors describe their reported print times as conservative because tool changes had not been tuned for speed. They also say the absence of suction and peel forces associated with vat-based printing should make it easier to expand build area and volume. The authors present these as expectations based on the process design.
Truby linked the work to broader manufacturing goals, saying that rebuilding American manufacturing will depend on new ways to make advanced materials. He said DIAL's ability to print many complex functional parts at once offers a path from the lab toward larger-volume manufacturing of architected materials for robotics, aerospace, healthcare and other applications. The authors present the work as a foundation for further scaling rather than a finished manufacturing process.
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.