A close-up image of one node of the triangular honeycomb. The structure, which consists of air surrounded by ceramic, can be designed with a specific porosity. Image: James Weaver/Wyss Institute.
A close-up image of one node of the triangular honeycomb. The structure, which consists of air surrounded by ceramic, can be designed with a specific porosity. Image: James Weaver/Wyss Institute.

Nature does amazing things with a limited range of materials. Grass, for example, can support its own weight, resist strong wind loads and recover after being compressed. The plant's hardiness comes from a combination of its hollow, tubular macrostructure and porous microstructure; these architectural features work together to give grass its robust mechanical properties.

Inspired by these natural cellular structures, a team of US researchers has now developed a new method for 3D printing materials with independently tunable macro-and microscale porosity using a ceramic foam ink. Their approach, which is described in a paper in the Proceedings of the Natural Academy of Sciences, could be used to fabricate lightweight structural materials, thermal insulation or tissue scaffolds. The researchers come from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), the Wyss Institute for Biologically Inspired Engineering at Harvard University and the Massachusetts Institute of Technology (MIT).

"By expanding the compositional space of printable materials, we can produce lightweight structures with exceptional stiffness," said Jennifer Lewis, 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 developed by the Lewis Lab is made of alumina particles, water and air. "Foam inks are interesting because you can digitally-pattern cellular microstructures within larger cellular macrostructures," explained 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 optimized, the team printed lightweight hexagonal and triangular honeycombs, with tunable geometry, density and stiffness.

"This process combines the best of both worlds," said Lorna Gibson, professor of materials science and engineering at MIT, 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 optimized 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," said Lewis.

This story is adapted from material from the Harvard John A. Paulson School of Engineering and Applied Sciences, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.