Researchers at Stanford have developed a new material for printing at the nanoscale – capable of creating structures that are a fraction of the width of a human hair. It has been used by the researchers to create tiny lattices that can be both strong and lightweight. Researchers published their findings in Science. They showed that the new material absorbs twice as much energy than other 3D printed materials. Their invention could be used in the future to provide lightweight protection for fragile parts of satellites, drones and microelectronics.
“There’s a lot of interest right now in designing different types of 3D structures for mechanical performance,” said Wendy Gu, an assistant professor of mechanical engineering and a corresponding author on the paper. “What we’ve done on top of that is develop a material that is really good at resisting forces, so it’s not just the 3D structure, but also the material that provides very good protection.”
Metal nanoclusters
Wendy Gu and her collaborators used metal nanoclusters (tiny clusters of atoms), to create a better material for 3D printers. The researchers are printing with two-photon lithography – where the printing material is hardened through a chemical reaction initiated by laser light. The researchers discovered that nanoclusters are very effective at jumping-starting the reaction. This resulted in a material composed of both metal and the polymer printing medium.
“The nanoclusters have very good properties for taking in the laser light, and then converting that to a chemical reaction,” said Wendy Gu. “And they’re able to do this with several classes of polymers, so they’re even more versatile than I expected.”
The Stanford researchers were able to combine metal nanoclusters with acrylates, epoxies, and proteins – several common classes of polymers that are used in 3D printing. The nanoclusters helped speed up the printing process. By combining the nanoclusters with proteins, for example, Wendy Gu and her colleagues were able to print at a rate of 100 millimeters per second – about 100x faster than had previously been achieved in nanoscale protein printing.
The researchers tested their new nanoscale material with several different lattice structures – prioritizing the ability to carry a heavy load in some and the ability to absorb an impact in others. With the nanocluster-polymer composite, all the structures demonstrated an impressive combination of energy absorption, strength, and recoverability – the ability to squish and spring back, to put it simply.
“The lattice structure certainly matters, but what we’re showing here is that if the material it’s made out of is optimized, that’s more important for performance,” said Wendy Gu. “You don’t have to worry about exactly what the 3D structure is if you have the right materials to print with.”
Imitating the natural world
Wendy Gu and her coworkers are trying to imitate what nature has done. The combination of a hard outer, small amounts of porosity, and soft material gives bone its strength. The combination of a 3D structure with multiple well-designed materials allows bones to transfer energy efficiently and not break (most of all). It is also relatively light. 3D printed protective structures could also contain multiple types of material, including softer and harder, to disperse impact better and resist crushing.
“Since the nanoclusters are able to polymerize these different classes of chemicals, we may be able to use them to print multiple materials in one structure,”said Wendy Gu. “That’s one thing we’d like to aim for.”