3D Printing Used to Mimic Nature's Cellular Architectures

With limited design materials, nature achieves phenomenal things. For instance, grass is capable of supporting its own weight, recovering after being compressed, and resisting strong wind loads.

Grass gets its hardness from a combination of its porous, or cellular, microstructure, and its hollow, tubular macrostructure. These architectural features work together to bestow grass with its strong mechanical features.

Taking inspiration from nature’s cellular structures, a team of 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 have developed a new technique to 3D print materials with individually tunable macro-and microscale porosity using a ceramic foam ink.

This process could be applied to fabricate lightweight structural materials, tissue scaffolds, or thermal insulation.

The research findings have been published in the Proceedings of the Natural Academy of Science.

“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 that the Lewis Lab used had alumina particles, air, and water.

Foam inks are interesting because you can digitally pattern cellular microstructures within larger cellular macrostructures. 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.

Joseph Muth, Graduate Student, Harvard SEAS

The researchers were able to tune the ink’s properties and the way it deformed on the microscale by manipulating the microstructure of the foam. Once perfected, the team began printing lightweight triangular and hexagonal honeycombs, with tunable density, geometry, 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 coauthored 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.

Joseph Muth, Graduate Student, Harvard SEAS

Although the team worked with a single ceramic material for this research, printable foam inks can be created from several materials, including other metals, ceramics, and polymers.

“This work represents an important step toward the scalable fabrication of architected porous materials,” said Lewis.

This research was coauthored by Patrick G. Dixon and Logan Woish. It received support from the National Science Foundation and the Harvard Materials Research Science and Engineering Center.

How to make ceramic foam ink (Video courtesy of Lori Sanders/Harvard University)