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Bio-inspired Materials: The Conch Shell

Posted on October 12th, 2017 by in Chemical R&D

From the very first wheel, the process of engineering has always been deeply inspired by nature. The Wright brothers, for example, spent hours studying the flight of birds before designing their airplane.

And nature probably has more to offer materials science than most fields. We’ve been gifted with an optimization process which has been running for millions of years. Why not make the most of it?

The Conch

One material that has been recognized as special in various cultures and religions for a long time is the conch shell. Conch shells house and protect a marine snail and are known for their toughness and resistance to cracks. Researchers around the world have been exploring what makes the conch so tough, and recently at MIT, a series of drop-tower tests on 3-D printed conch shell prototypes found some answers.

Toughness-By Architecture

In making a protective material, we often think of finding the strongest substance possible. However, it’s common for strong materials to be brittle and easily crack. To compensate, a shock-absorbing layer like a flexible liner for a helmet is commonly used.

In a conch shell, however, what gives the material its toughness is not the substance itself (which is 95% calcium carbonate, the same material as a soft stick of chalk) but the structure of the shell.

The shell has three levels of hierarchy in its structure, and a complex criss-crossed internal structure, with the grain of each layer oriented in a different direction. This complexity means that if a crack were to occur, it would be hard for it to propagate through the material’s zigzag, mazelike structure.

If we’re able to replicate the toughness of the conch shell, the potential applications of such a material could be numerous. One of the obvious uses is body armor, since this is essentially what a conch shell has evolved to do; protect the soft marine animal inside.

While the structure of the conch shell has been known for a while, until recently it has been very difficult to recreate in a synthetic material. But with advances in 3D printing technology, a team at MIT were able to print a composite material with a structure similar to that of a conch shell.

With the exact structure of the material tightly controlled and replicated over many samples, the team found that under test, the performance of the material matched that of previous computer simulations.

Testing found that material with a “conch-like” structure was 85% better than the base material at preventing crack propagation. It also performed 70% better than a more traditional fibre composite.

3-D Printed Protection

The structure of the material, with its layers of criss-crossed grains, naturally lends itself to 3-D printing. This method of fabrication also opens up the possibility of personalizing each piece, which could give tangible benefits if implemented in some sort of body armor.

For example, a model could be tailored to produce a helmet which takes into account the contours of an individual skull.  Personalizing the material in this way could further enhance the protection given to the person wearing it.

The development of 3D printing means that the “toughness-by architecture” design of the conch, which had been described earlier only in theory, could now be replicated in the laboratory.

While the conch shell is made from materials available to nature, we’re moving closer and closer to being able to fabricate structures with a similarly intricate architecture with bespoke materials.

Perhaps one day, we’ll even be able to improve on nature’s work. 

All opinions shared in this post are the author’s own.

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