When it comes to design, there is likely no better teacher than nature. While humans have produced an impressive number of gadgets, devices, and systems, most of them are far less efficient and require far more in the way of inputs than nature’s designs do. Even the simplest organisms have the ability to grow and to do so, they must rely on readily available nutrients in their environment. This often boils down to one ingredient, from which a dazzling array of properties can be produced, often by making changes to structure at a very small scale.
Until recently, humans have been unable to do this and have therefore relied on a wide variety of materials, from which to obtain the required properties. This can result in products with materials sourced from literally around the world, an expensive proposition, to say the least.
The advent of 3D printing has changed all that, allowing for the possibility of producing objects, with continuously variable properties from a single feedstock. Beyond that, researchers are now finding that by combining materials development and material placement, you can combine properties in a variety of ways. A lot of work has been done on this with fibers and fiber reinforced materials .
|Close-up image of one node of the triangular honeycomb, consisting of air surrounded by ceramic particles. Image source: Wyss Institute|
Comparatively little efforts have focused on porous materials or foams. However, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), the Wyss Institute for Biologically Inspired Engineering at Harvard, and MIT, recently extended this concept to foams. They developed a new method to 3D print bioinspired ceramic materials with independently tunable macro-and microscale porosity using a ceramic foam ink.
“We wanted to know if we could make cellular structures with multiple length scales in a scalable way,” said Joseph Muth, lead author of the paper entitled, Architected Cellular Ceramics with Tailored Stiffness via Direct Foam Writing . Prior work up to this point has primarily used a single length that had to be built up from the smallest scale, which is very time-consuming. “If you can demonstrate control of the cellular microstructure with ink development, letting the material assemble itself into microscale architectures, then you can pattern at much larger scales and get the small length scale for free,” he said.
What this allows is for variable properties to be produced within a part as it is made from a single material. In demonstrating that capability, the team wanted to know, “what kind of property space can we navigate?”
In their work, they varied stiffness, but Muth said, other properties like strength, thermal conductivity, or porosity could also be manipulated in this way.
Asked what kinds of applications might utilize this capability, Muth mentioned bone tissue scaffolds using variable stiffness, or battery electrodes, filters, or catalyst supports that employ porosity gradients. Mechanically robust insulation is another. Several companies have expressed interest.
In addition to varying the properties through material placement, they can also change the properties of the foam itself to achieve