Northwestern's DIAL method prints a porous grid over four times faster than extrusion

Engineers at Northwestern University have developed direct ink additive lithography, or DIAL, a 3D printing method that combines patterned light with thick, paste-like inks. The work was published on 4 November in Science Advances. The senior author is Ryan Truby; the lead author is Pranav Kaarthik doi.orgScience Advancesdoi.orgOpen source ↗. In a side-by-side test, DIAL printed a porous, grid-like structure in 30 minutes, while conventional extrusion needed 124 minutes doi.orgScience Advancesdoi.orgOpen source ↗.

How DIAL works

The printer first deposits a large amount of ink through a long, narrow slot-die nozzle onto a flat surface. A blade then spreads the ink into a uniform sheet 50 microns thick. A projector shines patterned light onto the sheet and hardens selected areas, and the cycle repeats layer by layer doi.orgScience Advancesdoi.orgOpen source ↗.

Because whole regions harden at once instead of being traced line by line, printing is faster than with conventional extrusion. Resolution depends mainly on the projector's pixel size and the layer thickness, not on the nozzle size, according to the authors doi.orgScience Advancesdoi.orgOpen source ↗.

The model ink is a light-curable resin mixed with fumed silica nanoparticles, which gives it a yield stress: it holds its shape until force is applied. The blade makes it flow briefly, then it stiffens again. The unhardened ink around a printed feature supports the object during fabrication, so no scaffolding is printed. Afterwards the remaining ink is washed away, and excess ink left on the print surface can be collected and reused doi.orgScience Advancesdoi.orgOpen source ↗.

Test structures and materials

The team printed lattices with walls as thin as 150 microns, which conventional extrusion could not produce, and interlocking chainmail. A desktop light-based printer could make the delicate lattices only with added supports doi.orgScience Advancesdoi.orgOpen source ↗.

To test material range, the researchers printed structures from two functional inks: structural electrolytes being developed for batteries, and hydrogels inspired by laboratory devices for growing cells and engineering tissues doi.orgScience Advancesdoi.orgOpen source ↗. The study also compared DIAL with digital light processing (DLP) and direct ink writing (DIW) and evaluated how ink rheology affects printing, using model inks with kilopascal-scale yield stresses doi.orgScience Advancesdoi.orgOpen source ↗.

The authors state that DIAL can print light-scattering, particle-filled inks, which conventional light-based printers handle poorly. Truby said the method can produce parts that have been difficult or impossible to make with other 3D printing methods doi.orgScience Advancesdoi.orgOpen source ↗. The results come from laboratory experiments.