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One of the toughest materials known to science is made not by humans, but by nature... and it's inside of oysters.

Hosted by: Stefan Chin

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Sources:
https://news.umich.edu/cracking-the-mystery-of-natures-toughest-material/
https://www.nature.com/articles/s41427-018-0009-6
https://www.google.com/books/edition/Fundamentals_of_Materials_Science_for_Te/UumaDwAAQBAJ
https://ceramics.org/wp-content/uploads/2014/05/McKittrick-article.pdf
https://www.e-education.psu.edu/matse81/node/2105
https://newscenter.lbl.gov/2008/11/25/mother-of-pearl-secret-revealed/
https://www.pbs.org/wgbh/evolution/library/01/3/l_013_06.html
http://ams.cstam.org.cn/article/2018/0567-7718-34-1-143.html
https://www.cambridge.org/core/journals/journal-of-materials-research/article/platelet-interlocks-are-the-key-to-toughness-and-strength-in-nacre/74323E967B18BF539E91008B98C5A5DC
https://www.nature.com/articles/s41467-019-12743-z
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https://www.sciencedirect.com/science/article/abs/pii/S0928493116311997

Image Sources:
https://www.istockphoto.com/photo/white-mother-of-pearl-pinctada-maxima-oyster-gm917436656-252399392
https://www.istockphoto.com/photo/close-up-image-of-organic-pearl-in-a-shell-gm1133373675-300783030
https://www.istockphoto.com/photo/vascular-stent-inside-the-vein-gm517751816-89662509
Intro: Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to check out their course, The Chemical Reaction. [ ♪INTRO ]. One of the toughest materials known to science is made not by humans, but by nature. And it’s the shiny stuff oysters use to get rid of something that’s bugging them: nacre, also known as mother-of-pearl.

And nacre is, surprisingly, some of the toughest stuff on earth. So, here’s what makes this beautiful, iridescent material the envy of materials scientists everywhere. As a material, nacre is more than the sum of its parts.

Two different substances in combination mean nacre itself can take a serious beating without splintering into pieces. Now, if you have much up-close-and-personal experience with pearls, you might be going, “Hold up…. They get scratched up if you so much as look at them the wrong way!

And that’s true. Nacre isn’t super hard, which in materials science terms means it’s easy to scratch its surface. But hardness isn’t the only way we judge the overall oomph of a material, and nacre can withstand a lot more than you might think.

For one thing, it’s stiff, meaning it’s rigid and hard to bend. And it’s also strong in the sense that a pearl has to experience a lot of force before breaking. And finally, it’s tough, meaning that even if you can put a crack in a pearl, it’s super hard to make that crack grow bigger.

That toughness is what nacre is really known for. In fact, it’s 3000 times more break-resistant than aragonite, the mineral that makes up 95% of nacre! So how is that possible?

Well, scientists don’t know everything about what makes nacre so tough, but one important factor is that it’s not a solid sheet of aragonite. Rather, it’s made up of overlapping, roughly hexagonal plates. The aragonite plates are laid down in layers with a softer organic material in between — very much like the layers of bricks and mortar in a brick wall.

The alternating structure gives nacre strength and support. But while these plates are often described as a “brick and mortar” structure, they aren’t spaced quite as regularly as brick. They’re offset, which actually helps them interlock and makes the structure more resilient.

And the plates have rough surfaces, which adds friction and helps them remain in place. They may even have small mineral deposits or bridges hooking them together. So it’s really hard to pull nacre apart.

But then there’s the mortar-like material, which helps compensate for one of aragonite’s flaws: on its own, it’s fairly brittle. This gluey stuff is a complex organic mixture made up of a handful of components — like chitin, which is found in crab shells. If a predator chomps on the shell, the soft, cushiony “mortar” gets squeezed out, which helps dissipate stress, and prevents any cracks from spreading too far.

And if that predator stops chomping, it can all spring back into place — bricks, mortar… everything! Scientists have been inspired by this amazing stuff to create super-tough synthetic materials, as well as trying to make nacre from scratch. For example, we can design artificial nacre to be biocompatible, meaning it won’t set off our bodies’ alarms.

So it would be perfect for things like stents, which are little tubes that are inserted into the body to hold passages open, like a weak artery, for example, and thus have to be durable enough to last a long time in our bodies without being rejected by our immune systems. But we’ve got a ways to go before these materials are ready for use by the public. So, until then, we’ll just have to admire the amazing engineering that nature is capable of.

Outro: Now, if we’ve piqued your chemistry curiosity with this episode, you might enjoy Brilliant’s course on The Chemical Reaction. It’s all about how one thing transforms into another, and it uses puzzles and patterns to teach you to predict how molecules behave. Brilliant offers tons of courses in science, engineering, math, and computer science, and its courses are designed by professional educators and lifelong learners to help you sharpen your skills. If you’re interested, you should check them out.

The first 200 people to sign up at Brilliant.org/SciShow will get 20% off an annual Premium subscription to Brilliant. [♪OUTRO].