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 inks with speed and resolution closer to light-based printing. The work, led by Pranav Kaarthik, was published in Science Advances.
The method addresses a trade-off between digital light processing and direct ink writing. According to the researchers, DLP requires low-viscosity, weakly scattering resins, while DIW can handle functional yield-stress inks but is slowed by filament deposition and limited by nozzle diameter. 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; DIAL aims to remove that compromise.
How the process works
For each layer, a slot die extrudes ink onto a substrate. A doctor blade then spreads the material into a sheet as thin as 25 microns. A 405-nanometer projector moves over the sheet and crosslinks selected regions. Ink that is not cured stays in place and supports the structure. Because light passes only through a thin sheet, opaque and heavily filled inks remain printable. The projector’s 50-micron pixel pitch sets the planar resolution.
Using 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 DIW. It also produced fins about 150 microns thick. By rastering projection over overlaid ink sheets, the researchers made a multimaterial lattice four times the projector’s illumination area.
Demonstrations and outlook
The researchers printed interlocking chain mail with struts about 250 microns thick. They produced 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run, and hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids.
The authors described the reported print times as 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 linked the work to manufacturing of advanced materials, saying DIAL can print many complex functional parts at once and offers a path to scale from the lab to larger-volume production of architected materials for robotics, aerospace, healthcare and other applications.
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.