Nature inspires 3D-printed lightweight structures with exceptional stiffness

A team in the US has developed a new method to 3D print materials with independently tuneable macro-and microscale porosity using a ceramic foam ink.

The approach - from researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), the Wyss Institute for Biologically Inspired Engineering at Harvard University, and MIT - could be used to fabricate lightweight structural materials, thermal insulation or tissue scaffolds.

They were said to be inspired by natural cellular structures such as those in grass, which allow it to support its own weight, resist strong wind loads, and recover after being compressed. The research is published in the Proceedings of the Natural Academy of Sciences.

"By expanding the compositional space of printable materials, we can produce lightweight structures with exceptional stiffness," said Jennifer Lewis, Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS and senior author of the paper. Lewis is also a Core Faculty Member of the Wyss.

The ceramic foam ink used by the Lewis Lab is said to contain alumina particles, water, and air.

"Foam inks are interesting because you can digitally pattern cellular microstructures within larger cellular macrostructures," said Joseph Muth, a graduate student in the Lewis Lab and first author of the paper. "After the ink solidifies, the resulting structure consists of air surrounded by ceramic material on multiple length scales. As you incorporate porosity into the structure, you impart properties that it otherwise would not have."

By controlling the foam's microstructure, the researchers tuned the ink's properties and how it deformed on the microscale. Once optimised, the team printed lightweight hexagonal and triangular honeycombs, with tuneable geometry, density, and stiffness.

"This process combines the best of both worlds," said Lorna Gibson, the Matoula S. Salapatas Professor of Materials Science and Engineering at the Massachusetts Institute of Technology, who co-authored the paper. "You get the microstructural control with foam processing and global architectural control with printing. Because we're printing something that already contains a specific microstructure, we don't have to pattern each individual piece. That allows us to make structures with specific hierarchy in a more controllable way than we could do before."

"We can now make multifunctional materials, in which many different material properties, including mechanical, thermal, and transport characteristics, can be optimised within a structure that is printed in a single step," said Muth.

While the team focused on a single ceramic material for this research, printable foam inks can be made from many materials, including other ceramics, metals, and polymers.

"This work represents an important step toward the scalable fabrication of architected porous materials," Lewis said in a statement.