For decades, people using 3D printers have faced a tough decision: print quickly, print parts with fine features or print materials that meet performance requirements. Light-based 3D printers are fast and precise but limited in what materials they can use. Extrusion-based techniques can handle a wider range of functional materials but sacrifice speed and fine details.
Now, Northwestern University engineers have developed a new 3D printing method that brings all these capabilities together.
The study will be published on Wednesday (Nov. 4) in the journal Science Advances.
Called direct ink additive lithography, or DIAL, the new method combines the speed and precision of light-based 3D printing with the broad ink compatibility of extrusion-based printing. Rather than slowly depositing materials one line at a time, DIAL spreads thick, paste-like inks into thin sheets. Then, patterned light selectively hardens the ink into precise designs.
By repeating this process layer by layer, DIAL rapidly builds complex, finely detailed, free-standing 3D objects without the need for co-printed scaffolding typically needed to support overhanging features. DIAL also can print with thick, particle-filled inks — even those that scatter light, which conventional light-based printers struggle to handle. This capability opens new possibilities for printing materials with a wide range of specialized functions.
"DIAL can produce parts that have been challenging if not impossible to make with other 3D printing methods," said Northwestern's Ryan Truby , the study's senior author. "From aerospace to robotics to medicine, the technologies of the future will require materials with structures we've never achieved before. Getting there means fundamentally rethinking how we turn functional materials into useful forms. This new printing method opens up an entirely new design space, giving us the freedom to create materials and architectures that were previously out of reach."
Truby is an assistant professor of materials science and engineering and of mechanical engineering, and the June and Donald Brewer Junior Professor at Northwestern's McCormick School of Engineering , where he leads the Robotic Matter Lab . Pranav Kaarthik, a Ph.D. candidate in mechanical engineering and a member of the Robotic Matter Lab, is the paper's lead author. Northwestern co-authors Michael Bayer, EunBi Oh and Alexander Kane also contributed to the work.
In side-by-side tests, DIAL printed porous, grid-like structures more than four times faster than possible with conventional extrusion-based printing. The resulting structures also contained sharper features and fewer defects. DIAL also printed delicate lattices that conventional extrusion printing could not replicate and that a desktop light-based printer could only make with additional supports. To further demonstrate DIAL's wide material compatibility, the team printed intricate structures using two functional inks: structural electrolytes being developed for batteries and hydrogels inspired by laboratory devices for growing cells and engineering tissues.
The advance could pave the way for faster, higher-resolution manufacturing of sophisticated materials for structural applications, robotics, energy storage, tissue engineering, custom medical devices and more.
A longstanding trade-off
Although 3D printing has transformed manufacturing, existing methods often force users to opt between speed, precision, part size and material.
One common technique, known as direct ink writing, works much like squeezing toothpaste from a tube. The printer pushes thick inks through a narrow nozzle, drawing a 3D object one line at a time. Although this method can handle a wide variety of inks, tracing every line takes time. And the tiny nozzles needed for fine details can easily clog, so researchers often resort to larger nozzles that limit resolution.
The other common technique, called light-based printing, offers a faster, higher-resolution alternative. Instead of drawing individual lines, these printers project patterned light onto liquid resins to harden exposed regions into solid features. This makes printing faster and more precise, but it generally requires thin, free-flowing materials that allow light to easily pass through.
A path to faster printing
To overcome these limitations, Kaarthik, Truby and their team developed a hybrid approach that combines elements of extrusion and light-based printing.
First, the printer deposits large amounts of thick, paste-like ink through a long, narrow opening — called a slot-die nozzle — onto a flat surface. Then, a blade sweeps across the material, spreading it into a smooth, uniform sheet just 50 microns thick — thinner than a human hair. Next, a projector shines patterned light onto the sheet, hardening selected areas into a precise design.
The printer repeats the process, stacking one layer on top of another until the object is complete. By hardening entire sections at once instead of tracing them line by line, DIAL can print much faster than conventional extrusion methods. And because its resolution depends primarily on the projector's pixel size and the thickness of each ink layer — rather than the size of the nozzle — DIAL can produce fine details in high resolution.
Ink that doubles as support
As another advantage, DIAL can print free-standing structures that don't require wasteful scaffolding. In conventional 3D printing, delicate bridges, overhangs and other complex features often require temporary support structures to prevent them from collapsing. These scaffolds consume extra material, increase printing time and can be tricky to remove.
"When you 3D print a complex part, you also have to co-print a support to hold it together," Kaarthik said. "If you don't print the scaffold, your printed object will literally fail. But then we need to figure out a way to remove the scaffold. Sometimes, removing those supports can destroy the delicate features you're trying to make."
With DIAL, the ink itself provides that support. To develop a model ink for DIAL, the team mixed light-curable resin with fumed silica nanoparticles, giving it a property called a yield stress. Much like pomade, cream cheese or toothpaste, the ink holds its shape until force is applied. When the sweeping blade scrapes the ink into a sheet, it temporarily flows. Then, after the blade passes, the ink quickly regains its stiffness and holds its shape.
By adjusting the concentration of the silica nanoparticles, the researchers fine-tuned the ink's stiffness and response to scraping. The unhardened ink surrounding each printed feature remains firm enough to support the object during its fabrication. When printing is complete, users can wash away the remaining unhardened ink to reveal the finished object. Then, they can collect and reuse the excess ink left behind on the print surface to further reduce waste.
Faster printing, finer details
To put DIAL to the test, the researchers printed a variety of challenging structures. In one demonstration, the team printed a porous, grid-like structure. DIAL completed the object in 30 minutes, while conventional extrusion required 124 minutes — more than four times as long.
They also used DIAL to print lattices with walls as thin as 150 microns, which could not be printed with conventional extrusion, as well as interlocking chainmail that is difficult to make with either extrusion or light-based printing. By streamlining how DIAL switches among tools, the team expects it to achieve even faster print times.
The team also demonstrated that DIAL can print multiple objects simultaneously and combine different inks in successive layers. In one example, they fabricated a honeycomb-like structure spanning an area nearly four times larger than the projector's illumination area by moving the projector across overlapping ink sheets. Most light-based 3D printers operated inside a vat, or container filled with liquid resin. Because DIAL is not confined to a vat, the researchers expect it to scale to larger build areas more readily than most light-based methods.
From batteries to biomedical research
Beyond demonstrating speed and precision, the team wanted to show that DIAL can manufacture materials with useful functions. To do so, they developed two additional ink formulations.
One ink was a structural electrolyte made from a polymerizable ionic liquid — a liquid salt that Truby's lab synthesizes for soft, iontronic sensors and devices. Using this electrolyte-based ink, the researchers printed 15 intricate, porous lattices in a single 15-minute run. The structures were approximately the size of small coin-cell batteries. The ability to print electrolytes into precisely controlled 3D architectures eventually could support the development of new energy-storage devices.
For the second demonstration, the researchers developed a hydrogel ink. Soft, water-rich hydrogels can mimic certain properties in biological tissues. Using this material, the team printed small containers modeled after cell culture inserts used in biomedical and tissue engineering labs. The containers featured arrays of microscopic, inverted pyramids that resemble the specialized surfaces used to culture cells and organoids, or small, laboratory-grown organ-like constructs.
"To print these types of materials, we don't just need new software capabilities, new hardware or new inks," Truby said. "We need all three, working in concert. Pranav and our team have been able to achieve that with DIAL. We're now working to DIAL print materials and structures that can be used to withstand extreme environments for space travel, as flexible body parts for robots, as medical devices and even as tissue culture environments for biomanufacturing. We're going to be able to 3D print materials that have not been 3D printed before."
The study, "Rapid, voxel-based 3D printing with yield-stress fluid inks," was supported by the National Science Foundation through the Northwestern Materials Research Science and Engineering Center (award number DMR-2308691), the Air Force Office of Scientific Research (award number FA9550-22-1-0218) and the Ryan Family Fellowship at Northwestern, administered by the International Institute for Nanotechnology.
