Inspired by natural cellular structures, researchers at Harvard and the Massachusetts Institute of Technology have developed a method to 3-D print materials with independently tunable macro- and microscale porosity using a ceramic foam ink.

Their approach could be used to fabricate lightweight structural materials, thermal insulation or tissue scaffolds.

The research is published in the Proceedings of the Natural Academy of Sciences.

Researchers 3D-printed lightweight hexagonal and triangular honeycombs with tunable geometry, density, and stiffness using a ceramic foam ink. By expanding the compositional space of printable materials, researchers can produce lightweight structures with exceptional stiffness, says Jennifer Lewis, Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS and senior author.

The ceramic foam ink contains alumina particles, water and air. According to researchers, foam inks are interesting because cellular microstructures can be digitally patterned within larger cellular macrostructures.

After the ink solidifies, the resulting structure consists of air surrounded by ceramic material on multiple length scales. As porosity is incorporated into the structure, properties are imparted that otherwise would not have existed.

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.

Because researchers are printing something that already contains a specific microstructure, they did not have to pattern each individual piece. That allowed researchers to make structures with specific hierarchy in a more controllable way than before.

Researchers 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.

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.

According to researchers, this work is an important step toward the scalable fabrication of architected porous materials.