November 17, 2022
Engineers have designed a new material for nanoscale 3D printing that is able to absorb twice as much energy as other materials of similar density and could be used to create better lightweight shielding networks.
By Laura Castañon
Science fiction envisions rapid 3D printing processes that can quickly create new objects from any number of materials. But in reality, 3D printing is still limited in the properties and types of materials that can be used, especially when printing at very small scales.
Tiny but strong Stanford logo made using nanoscale 3D printing. (Image credit: John Kulikowski)
Stanford researchers have developed a new material for nanoscale printing – creating structures that are only a fraction of the width of a human hair – and used it to print tiny lattices at the both strong and light. In an article published in Science, the researchers demonstrated that the new material is able to absorb twice as much energy as other 3D-printed materials of comparable density. In the future, their invention could be used to create better lightweight protection for fragile parts of satellites, drones and microelectronics.
“There is currently a lot of interest in designing different types of 3D structures for mechanical performance,” says Wendy Gu, assistant professor of mechanical engineering and corresponding author of the paper. “What we’ve done additionally is develop a material that resists forces really well, so it’s not just the 3D structure, but also the material that provides really good protection.”
Presentation of metallic nanoclusters
To design a better material for 3D printing, Gu and his colleagues incorporated metallic nanoclusters — tiny clumps of atoms — into their print medium. The researchers print with a method known as two-photon lithography, where the print material is hardened by a chemical reaction initiated by laser light. They found that their nanoclusters were very good at starting this reaction and ended up with a material that was a composite of the polymer print medium and the metal.
“Nanoclusters have very good properties for absorbing laser light and then converting it into a chemical reaction,” says Gu. “And they’re able to do that with multiple polymer classes, so they’re even more versatile than I expected.”
The researchers were able to combine metal nanoclusters with acrylates, epoxides and proteins – several common classes of polymers used in 3D printing. Additionally, the nanoclusters helped speed up the printing process. By combining the nanoclusters with proteins, for example, Gu and his colleagues were able to print at a speed of 100 millimeters per second, which is about 100 times faster than previously achieved in printing proteins at the nanometric scale.
The researchers tested their new material with several different lattice structures, favoring the ability to carry a heavy load in some and the ability to absorb impact in others. With the nanocluster-polymer composite, all structures demonstrated an impressive combination of energy absorption, strength and recovery capability – essentially the ability to crash and rebound.
“The truss structure is definitely important, but what we’re showing here is that if the material it’s made of is optimized, it’s more important for performance,” Gu says. “You don’t have to worry about the exact nature of the 3D structure if you have the right materials to print on.”
Copy the natural world
In some ways, Gu and his colleagues attempt to emulate what nature has already perfected. Bone, for example, derives its resilience from the combination of a hard exterior, nanoscale porosity, and small amounts of soft material. This combination of a 3D structure and several well-designed materials allows our bones to transfer energy without breaking (most of the time) while remaining relatively light. Ideally, 3D printed protective structures would also contain multiple types of materials, some harder and some softer, to better disperse an impact and resist crushing.
“Since nanoclusters are able to polymerize these different classes of chemicals, we may be able to use them to print multiple materials in a single structure,” says Gu. “That’s something we would like to aim for.”
Additional Stanford co-authors of this research include postdoctoral fellows Qi Li and Ottman A. Tertuliano; and graduate students John Kulikowski, David Doan and Melody M. Wang. Other co-authors come from Northwestern University. Gu is also a member of Stanford Bio-X.
This work was funded by the National Science Foundation, the American Chemical Society Petroleum Research Fund, and a Stanford Graduate Fellowship.
To read all of Stanford’s science stories, subscribe to the bi-weekly Stanford Scientific Summary.