Lightweight Ceramics Inspired by Natural Hierarchical Cellular Structures

Innovation: Academia

Harvard

2017

Image: Ochir-Erdene Oyunmedeg / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Manage Impact

An impact is a high force or mechanical shock that happens over a short period of time, such as a hammer hitting a nail rather than a hand pushing slowly against a wall. Because of their speed and force, impacts don’t allow materials to slowly adjust to the force, which can lead to cracks, ruptures, and complete breakage. Therefore, living systems have strategies that can absorb, dissipate, or otherwise survive that force without the need to add large amounts of material. For example, the Toco toucan’s large beak is very lightweight, yet can withstand impacts because it’s made of a composite material with rigid foam inside and layers of a hard, fibrous material outside.

Search this Function

Manage Tension

When a living system is under tension, it means there is a force pulling on it, like a person pulling on a rope tied to a horse. When applied to a living system, unless the system is completely rigid, the result is that it gets stretched. If stretching exceeds the strength of the living system’s material, it can damage it. Living systems manage tension using materials that are flexible and stretchable enough to survive most tension that occurs in their environment. The ocean’s intertidal zone offers a good example. The waves and incoming and outgoing tides put tension on soft-bodied organisms. Mussels resist tension with flexible threads that hold them onto rocks; in contrast, large algae have stretchy fronds.

Search this Function

Manage Compression

When a living system is under compression, there is a force pushing on it, like a chair with a person sitting on it. When evenly applied to all sides of a living system, compression results in decreased volume. When applied on two sides, it results in deformation, such as when pushing on two sides of a balloon. This deformation can be temporary or permanent. Because living systems must retain their most efficient form, they must ensure that any deformation is temporary. Managing compression also provides an opportunity to lessen the effects of other forces. Living systems have strategies to help prevent compression or recover from it, while maintaining function. For example, African elephant adults weigh from 4,700 to 6,048 kilograms. Because they must hold all of that weight on their four feet, the tissues of their feet have features that enable compression to absorb and distribute forces.

Search this Function

Ceramic material from Harvard is composed of a closed-cell porous structure that mitigates impact forces.

Benefits

Scalable
Fracture-resistant
Durable

Applications

Electronics
Bridge and building design

UN Sustainable Development Goals Addressed

Goal 9: Industry Innovation & Infrastructure

The Challenge

Developing resource-efficient design methods will be essential as we transition into a sustainable society. Due to the limited properties of many materials, buildings and products are often designed to be high in weight, with added material to increase structural strength. Developing stronger and lighter materials could reduce the costs of our creations, both financially and environmentally.

Innovation Details

The cellular ceramic material is made of a 3D-printed ceramic foam ink. During the 3D-printing process, engineers can tune the macro- and microscale porosity, which determines the ‘stiffness’ of the material—the tendency for an element to return to its original form after being subjected to external forces. Up close, the closed-cell pores are shaped as hexagonal and triangular honeycombs. This organization allows for efficient distribution of pressure, making the material incredibly strong. Cellular ceramics could find potential applications in numerous fields, including lightweight structures, thermal insulation, tissue scaffolds, supports, and electrodes.

Biomimicry Story

Biological hierarchical structures have to do with the assemblages of molecular units or their aggregates, where a similar feature reoccurs at different scales. There are many types of hierarchical structures in nature: bird feathers, bones, wood, stems, and more. For example, grass has a hollow, tubular macrostructure and a porous microstructure that enables the plant to bounce back after being stepped on. With intention down to microscopic arrangement, nature designs efficiently and beautifully by utilizing hierarchical structures, and so can we.

See Related Content

a person holds a brazil nut seed pod with nuts from the seed pod

Biological Strategy

The Toughest Nuts to Crack

Brazil nut

Brazil nut seed pods hurtle down from tall treetops, but their complex structure deters them from cracking open.

close up photo of seven pomelo citrus fruits, one with exposed orange flesh

Biological Strategy

Hierarchical Organization of Peel Confers Impact Resistance

Pomelo

The pomelo fruit has excellent damping properties due to the hierarchical organization of its composite peel

References

Journal article

Architected cellular ceramics with tailored stiffness via direct foam writing

PNAS

embedly preview

AskNature