Northwestern University engineers have developed a 3D-printing technique that combines the speed and detail of light-based printing with the ability to use thick, functional inks typically associated with extrusion-based methods.
The process, called direct ink additive lithography (DIAL), spreads paste-like ink into thin layers and uses patterned light to harden selected areas. Repeated layer by layer, this approach can create detailed, free-standing objects without printing temporary support structures. It can also work with particle-filled inks that scatter light and are difficult to process with conventional light-based printers.
Combining speed and material flexibility
Traditional extrusion printing pushes ink through a nozzle, building objects line by line. It accommodates many materials but can be slow, and small nozzles used for fine details may clog. Light-based printing is generally faster and more precise, but usually relies on thin materials that let light pass through.
DIAL uses a slot-die nozzle to apply thick ink onto a flat surface. A blade spreads it into a uniform layer about 50 microns thick, after which a projector hardens the desired pattern. The printer repeats these steps to build the object. Because it hardens broad sections at once, DIAL can print faster than line-by-line extrusion, with detail determined mainly by the projector’s pixel size and the thickness of each layer.
The ink is formulated to hold its shape after being spread. Researchers add fumed silica nanoparticles to a light-curable resin, giving it a yield-stress property: it flows when the blade moves across it, then quickly stiffens again. The surrounding unhardened ink supports delicate features during printing and can be washed away afterward. Excess ink can be collected and reused.
Faster prints and more complex structures
In testing, DIAL produced a porous grid-like structure in 30 minutes, compared with 124 minutes using conventional extrusion. It also printed lattices with walls as thin as 150 microns, as well as delicate forms that extrusion printing could not reproduce. In some comparisons, light-based printing could make similar structures only with additional supports.
The team also printed multiple objects at once and combined different inks across successive layers. By moving the projector over overlapping sheets, the researchers created a honeycomb-like structure spanning nearly four times the projector’s illuminated area. Because DIAL does not operate inside a vat of resin, the researchers say the method may be easier to scale to larger build areas.
To demonstrate the range of materials, the team printed structures using a polymerizable ionic-liquid electrolyte and a hydrogel. The electrolyte ink was used to produce 15 porous lattices in a 15-minute run, suggesting potential applications in energy storage. The hydrogel was used to make small containers modeled on cell-culture inserts, with microscopic surfaces designed for growing cells and organoids.
The researchers see possible uses for DIAL in aerospace, robotics, batteries, tissue engineering and custom medical devices. The study, “Rapid, voxel-based 3D printing with yield-stress fluid inks,” is due to appear in Science Advances.