Three-layered shell of deep-sea snail could inspire next-gen body armour

Deep beneath the ocean's surface lie the "black smokers", undersea chimneys channelling superheated water from below the Earth's crust. Completely devoid of sunlight, they are some of the most extreme environments on the planet. Any creature that can survive their highly acidic water, scorching temperatures and crushing pressures still has to contend with assaults from predatory crabs. What better place, then, to look for the next generation of body armour technology?

i-dc76e7a1d42221cdbe5c0ecf14f9f55a-Scalyfoot-snail.jpgThe scaly-foot gastropod (Crysomalion squamiferum) was discovered just 9 years ago at an Indian black smoker and it may have one of the most effective animal armours so far discovered. Its shell is a composite, made of three layers, each with different properties and made of different minerals. Together, they form a structure that's completely unlike any known armour, whether natural or man-made. It can protect the animal from the searing heat of its habitat, stop its precious minerals from dissolving away in the acidic water and resist the crushing, penetrating, peeling claw-attacks of predatory crabs.

Animals have been protecting themselves with armour long before humans starting shaping steel and Kevlar. To create a protective covering, human designers must account for a mind-boggling array of physical traits including thickness, geometry, strength, elasticity and more. But evolution can take all of those factors into account without the guiding hand of a designer, putting thousands of structures through the test of natural selection and weeding out the best combinations. The results are the culmination of millions of years of research and development and they are striking in their effectiveness.

Haimin Yao from MIT works in the lab of Catherine Ortiz, a group that has been studying the defences of animals including sea urchins, chitons, a group of marine molluscs, to the Senegal bichir, a type of armoured fish.  

Yao discovered the secrets behind the snail's shell by slicing through it in cross-sections and studying its structure at a nanometre level. He even attacked it with a diamond-tipped probe, to simulate the crushing attacks of the crabs that frequent the black smokers. Using this data, Yao created a virtual simulation of the shell and put it through a digital crash-test, crab claws and all.

The outer layer is the thinnest but also the toughest. It's rich in iron sulphide nanoparticles and the snail is the only animal known to use these minerals to build a shell. There's good reason for this - the water around the black smokers is absolutely teeming with iron sulphides, so the snail has plenty of mortar for its construction needs.

When crushed by a crab claw, the outer layer cracks but that's all part of the plan. The cracks are tiny and jagged. They dissipate the energy from the attack and prevent larger cracks from forming - those could cause the entire shell to shatter. The tough iron minerals can also grind and erode the crab's claw - it's a defence that also weakens the attacker's weapon.

The middle layer is organic with no minerals to speak of. It's much thicker than the other one but it's also soft and spongy. It also helps to absorb the force from the crab's blows, dissipating their energy before it reaches the inner layer.  The boundary between the outer and middle layers is wavy rather than flat, which reduces the risk that the two will simply disconnect and slide off one another.

Only when you get to the inner layer do you find calcium carbonate, the building material that most snails use to construct their shells. In the acidic water of a black smoker, an uncovered calcium carbonate shell would rapidly dissolve away, leaving behind a naked and vulnerable snail. Again, the three-layer armour comes into its own, with the outer and middle layers protecting the inner one from the acidic water, and from the frequent bursts of intense heat.

The rigid inner layer isn't useless though. It adds structural support and prevents the shell from bending. That foils one of the crab's main tactics - shoving its claw into the shell's opening and peeling off small chunks until it can reach the animal inside.

Yao says that this multi-layered armour could help to inspire the next generation of man-made defences. Potential uses aren't just limited to armour for people or vehicles, but sporting equipment or coverings for pipelines that are frequently hit by rocks. In particular, he's intrigued by the snail's use of an outer layer of iron nanoparticles as a sacrificial structure, designed to trap cracks and dissipate energy. That's an original idea as far as human design goes and one that the group will be eagerly following up.


Reference: Yao et al. 2010. Protection mechanisms of the iron-plated armor of a deep-sea hydrothermal vent gastropod. PNAS

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So we drag these snails out of the depths of the ocean and murder them in order to learn how better to murder fellow members of our species.

How very human of us.

By mad the swine (not verified) on 19 Jan 2010 #permalink

Allow me to explain the concept of *armour*. It is a thing that stops pointy things from making you go ow. Clearer?

And if you're trying to murder people USING body armour, you're doing it wrong.

Great post, Ed!
I was wondering: do you know how the snail protects its fleshy parts during such processes as feeding, traveling and mating - or can it easily handle short-term exposures of its more vulnerable sides to the acidic water and high heat of its environment?

Just don't beat anyone to death with a giant snail...

That's seriously fascinating, though. Remind me to email this to the next person who asks what practical use the study of nature is...

Great post as always, and thanks to Mad the Swine I am now trying to work out how you could even *use* body armour as a weapon short of hitting someone over the head with it. They should add it to cluedo: "Reverand Green, in the ballroom, with the full suit of body armour" :)

Well exactly. I've got (a) just bludgeoning people with it, (b) smothering or (c) stabbing *yourself* with a bladed weapon so that it bounces off into someone else.

As I said, doing it wrong.

Ferris - sadly no. Didn't see any reference to this in the paper (but it *was* incredibly dense, so I may have missed something).

Tracey - try The Gecko's Foot too. Awesome book on biomimetics.

How about (d), you give it to a US soldier or Blackwater mercenary, who then is able to last longer under fire and so rack up a higher body count.

Any improvement in the technology of warfare leads to more dead people. Better armor just shifts the casualties to the other side.

By mad the swine (not verified) on 19 Jan 2010 #permalink

@mad the swine

Unfortunately, even basic science research such as this can result in uses not intended or even foreseen by the researchers involved. People do not typically begin careers in marine biology with the aspiration of killing people, and it is rather asinine of you to focus on this singular application when other uses (such as sporting equipment) were mentioned and many more can easily be conceived. Your inability to look beyond your social/political opinions* to appreciate this study of a truly remarkable creature or to simply move along to a different blog belies your prejudices - and your immaturity.

* Guess what, I'm vegan, and I don't believe war is the answer, either.

@Ed Yong

As always, a fascinating post.

"So we drag these snails out of the depths of the ocean and murder them in order to learn how better to murder fellow members of our species.

How very human of us."

I think, what MAD THE SWINE is trying to imply is that protecting ourselves largely involve MURDERING as well. Well, we can very well see that defense never existed without offense. Nevertheless, this issue rocks! Keep this up!

Re: Comment 1 - there's a pervasive belief that any research that is funded by or used by the military is inherently evil. The line of thought for armor goes: "If US soldiers get better body armor, then they are a more effective fighting force and so the government will be more likely to use them, leading to more war. Therefore any aid to military = more war = evil.
Call me crazy, but I think of research that reduces death and promotes health to be a good thing, regardless of who is helped by it.

Great post....and i'll have to check that biomimetics book.

By Daniel J. Andrews (not verified) on 19 Jan 2010 #permalink

can we conceive of shells for laptops or impact zones for cars/trains/planes from this information, or are we simply relegated to killing people with it *because* that is a foreseeable option? ;) rock on, good article.

The improvements in body armor from this research do not address momentum-transfer trauma caused by stopping the heavier, more energetic round. the Marine or soldier who is struck may survive on the battlefield but then must endure unknown physical effects for years and the all too well-known psychological trauma. Also any moderate advance in body armor will not defeat any round that will be introduced that utilizes enhanced incendiary/reactive chemical components. In fact this may well spur the introduction of these component based rounds into general infantry use. This would be counterproductive and increase suffering even beyond the use of Willy Pete white phosphorus.

Its shell is a composite, made of three layers, each with different properties and made of different minerals. Together, they form a structure that's completely unlike any known armour, whether natural or man-made.

If the uniqueness is in the use of different layers with very different properties rather than the exact materials used, then this isn't really unique. Modern tank armour has made use of similar layering using various different steels, ceramics, dead space, depleted uranium slabs and polymers (like Kevlar spall linings) for the last 30 years or so. Most modern tank armours are of layered construction. The processes they inflict on penetrators are similar to what's described above (the outer iron sulphide later sounds like it works like the ceramics in modern armours, including some body armours). And with all due respect to the gastropod, a crab claw is not a 10kg tungsten bolt travelling a kilometre and a half per second. Not to say there's nought to be learned from Mother Nature here, but it does seem they're being a bit excitable.

Now, has anyone put that Crysomalion squamiferum up against a hungry Odontodactylus scyllarus for a real test?

By Mike from Ottawa (not verified) on 22 Jan 2010 #permalink

Great post.

Small point, Ed. You say: "But evolution can take all of those factors into account without the guiding hand of a designer, putting thousands of structures through the test of natural selection and weeding out the best combinations." I think you might mean, either, 'ferreting out' or 'weeding out weak combinations, and retaining the best ones'.

Do the snails repair their shell after being attacked? If they did, studying the repair mechanism might provide some pretty interesting insights.

If they don't, is that because they don't get attacked often? I'd assume that a snail with a weakened shell would be pretty vulnerable, even if it did survive the initial attack.

By Reviewer 3 (not verified) on 30 Jan 2010 #permalink

Another Darwinian triumph. I think this is exactly what Darwin noticed with the parallelism of environment and the development of features to adapt to it.