3D microstructure fabricated from nanoparticles.
3D microstructure fabricated from nanoparticles.

Complex three-dimensional Meccano-like constructions can be built from nanoparticles without the need of templates or supporting scaffolds, according to researchers at Washington State University [Saleh et al., Science Advances 3 (2017) e1601986].

Rahul Panat and his team were inspired by the way that petal-shaped gypsum crystals known as ‘desert roses’ that form through the condensation of sulfur compound-containing fog in the dry heat of the desert. In an analogous manner, the researchers created a ‘fog’ from droplets containing silver nanoparticles dispersed in a solvent (ethylene glycol) using the Aerosol Jet technique. When the aerosolized nanoparticle fog encounters a heated substrate, the liquid evaporates leaving a complex three-dimensional structure behind.

“The method allows the arrangement of nanoparticles in three-dimensional space,” explains Panat. “This means we can maintain the nanoscale beneficial properties of materials, while building a total minimum volume required for real, practical devices.”

The intricate architectures consist of trusses of fused nanoparticles at different angles to each other arranged in a regular pattern, separated by spaces or voids or sizes ranging from 100 microns to 1 mm. The trusses themselves can be as thin as 20 microns in diameter and of variable porosity depending on the size of the nanoparticles and the degree of sintering.

Varying the fabrication conditions produces different structures or architectural geometries up to a few millimeters in size. The range of possibilities is impressive, from highly porous periodic three-dimensional lattices to stretchy bridge-like structures, which could be used as flexible electrodes, to hollow pillars and spirals.

“Our three-dimensional printing method arranges nanoparticles in space at micro- and nanoscales to build large structures,” says Panat. “The method rapidly creates and precisely controls the material’s architecture from the nanoscale to centimeters.”

The approach is also open to the use of different materials, since any nanoparticle that can be dispersed in a solvent could be synthesized into complex structures.

“This method creates structures that fill critical gaps in existing applications and opens up new applications that we have not even thought about before,” adds Panat.

The complex three-dimensional lattices could find application as lightweight structural materials, believe the researchers, because of their high strength-to-density ratio over a range of densities. The porous nature of the materials could also be useful as scaffolds for tissue engineering and biomedical applications, as well as in batteries, supercapacitors, microfluidic devices, and catalytic converters. The periodic regularity of the structures could also be useful in microelectronics and optoelectronics.

“I am highly excited about this discovery,” says Panat. “This is a groundbreaking advance in the three-dimensional architecturing of materials at nano- to macroscales with many applications.”

This article was originally published in Nano Today (2017), doi: 10.1016/j.nantod.2017.04.005.