Why is mother-of-pearl so hard?

Few natural materials are as hard as mother-of-pearl. In search of answers, scientists have finally figured out how the microscopic layers of nacre can make it so hard.

You’ll find mother-of-pearl on the outer coating of pearls and inside some mollusk shells, but scientists didn’t really understand how it worked at the nanoscale before, because of this coating. resistant to extreme shocks.

The secret was finally revealed in the way the surface of the material came together like a tile . Upon impact this structure allows it to spread the pressure. By the time the surface is no longer under pressure, it will change again.

Why is mother-of-pearl so hard?
The structure of nacre.

This finding is remarkable because it could lead to the development of super-strong materials inspired by the best that nature has to offer.

“It’s unbelievable that one mollusk, not the most intelligent organism, is building so many structures on so many different scales,” said materials scientist Robert Hovden from the University of Michigan. .

In previous work, the scientists identified a brick-like nacre structure – nanoscale aragonite glued together with organic material, which looks like a brick wall if you stand close enough.

Most surprising and unusual is that mother-of-pearl does not lose any resistance during impact . Tests show that its level of recovery does not decrease, even under repeated impact of up to 80% of its yield strength.

If the surface develops cracks, the nacre can isolate where the crack occurred, so it doesn’t affect the rest of the surface.

Researchers even consider nacre to be “nature’s hardest material”. Of course, that really depends on the different reference scale.

“We humans can create harder materials, but we can’t replicate the kind of nanoengineering that mollusks have achieved,” says Hovden.