Recreating Nature's Designs with 3D Printing and Ceramic Foam Ink

Harvard and MIT researchers 3-D printed lightweight hexagonal and triangular honeycombs (pictured here), with tunable geometry, density, and stiffness using a ceramic foam ink. Their approach could be used to fabricate lightweight structural materials, thermal insulation or tissue scaffolds. (Image courtesy of James Weaver/Wyss Institute.)

Some of the most resilient and ingenious designs that exist can be found in the natural world; designs which humans continue to emulate. Now, inspired by cellular structures found in nature, a research team has discovered a way to 3D print materials using independently tunable macro- and micro-scale porosity with ceramic foam ink.

This approach, developed by researchers from Harvard’s 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 as a single-step process to fabricate everything from lightweight structural materials to thermal insulation to tissue scaffolds.

“By expanding the compositional space of printable materials, we can produce lightweight structures with exceptional stiffness,” explained Jennifer Lewis, senior author of the study and professor of engineering at SEAS.

The key to this new method is the ceramic foam ink, which contains alumina particles, water and air. By controlling the foam’s microstructure, the researchers were able to tune the ink’s properties and adjust how it deformed on a micro scale. After this process was optimized, the team could print lightweight hexagonal and triangular honeycombs, complete with tunable geometry, density and stiffness.

"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."

According to Lorna Gibson, a professor of materials science and engineering at MIT, this process “combines the best of both worlds,” through a marriage of the microstructural control of foam processing and the global architectural control of 3D printing.

“Because we're printing something that already contains a specific microstructure, we don't have to pattern each individual piece,” Gibson said. “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," added Muth.

Close up image of one node of the triangular honeycomb. The structure, which consists of air surrounded by ceramic, can be designed with specific porosity. (Image courtesy of James Weaver/Wyss Institute.)

The team focused on a single ceramic material for the purposes of their research, but printable foam inks can be made from any number of materials, including other ceramics, metals and polymers–thus increasing the potential applications for this process exponentially.

This new process is another example of the nature-inspired designs out there, like smart concrete designed with biomaterials and suction-based adhesive inspired by octopuses.

For more information, check out the paper, "Architectural cellular ceramics with tailored stiffness via direct foam writing," published in the journal Proceedings of the National Academy of Sciences.