Science

Fish's piranha-proof scales could lead to tough, flexible body armor

Fish's piranha-proof scales co...
The piranha-bite-proof scales of the Arapaima fish could serve as the inspiration for body armor that is tough yet flexible (Photo: Jeff Kubina)
The piranha-bite-proof scales of the Arapaima fish could serve as the inspiration for body armor that is tough yet flexible (Photo: Jeff Kubina)
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The corrugated surface keeps the scales' thick mineralized surface intact while the fish flexes as it swims
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The corrugated surface keeps the scales' thick mineralized surface intact while the fish flexes as it swims
A close-up of two Arapaima scales, overlapping as they would in nature
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A close-up of two Arapaima scales, overlapping as they would in nature
The corrugations, the soft but tough internal layer and the hydration of the scales all contribute to their ability to flex while remaining strong
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The corrugations, the soft but tough internal layer and the hydration of the scales all contribute to their ability to flex while remaining strong
Marc Meyers, a professor of mechanical and aerospace engineering at the Jacobs School of Engineering at UC San Diego, holds two overlapping Arapaima scales
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Marc Meyers, a professor of mechanical and aerospace engineering at the Jacobs School of Engineering at UC San Diego, holds two overlapping Arapaima scales
The razor-like teeth of the piranha trap the skin and muscle of its prey in a guillotine-like bite
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The razor-like teeth of the piranha trap the skin and muscle of its prey in a guillotine-like bite
An Arapaima scale rests on the bottom half of Meyers' testing apparatus
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An Arapaima scale rests on the bottom half of Meyers' testing apparatus
A piranha tooth is mounted on the top half of Meyers' testing apparatus
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A piranha tooth is mounted on the top half of Meyers' testing apparatus
The razor-like teeth of the piranha trap the skin and muscle of its prey in a guillotine-like bite
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The razor-like teeth of the piranha trap the skin and muscle of its prey in a guillotine-like bite
Arapaima gigas scales have a highly mineralized outside layer, and an internal layer of collagen fibers stacked in a "plywood" formation for maximum toughness
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Arapaima gigas scales have a highly mineralized outside layer, and an internal layer of collagen fibers stacked in a "plywood" formation for maximum toughness
The piranha-bite-proof scales of the Arapaima fish could serve as the inspiration for body armor that is tough yet flexible (Photo: Jeff Kubina)
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The piranha-bite-proof scales of the Arapaima fish could serve as the inspiration for body armor that is tough yet flexible (Photo: Jeff Kubina)
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Here's a question - if piranhas are so ferocious and will attack anything, why aren't they the only fish in the Amazon? Well, in some cases, it's because other fish possess bite-proof armor. The 300-pound (136-kg) Arapaima is just such a fish. In the dry season, when water levels get low, Arapaima are forced to share relatively small bodies of water with piranhas. Their tough-but-flexible scales, however, allow them to remain unharmed. A scientist from the University of California, San Diego is now taking a closer look at those scales, with an eye towards applying their secrets to human technology such as body armor.

Mechanical and aerospace engineering professor Marc Meyers first became interested in the Arapaima on an expedition to the Amazon basin, several years ago. Now, he has an Arapaima scale-testing rig set up in his UC San Diego lab. The device is not unlike an industrial-strength hole punch, with piranha teeth mounted on the top, which are pressed down into Arapaima scales on the bottom - the scales are laid over soft rubber, to simulate the fish's underlying flesh.

Upon first examining the scales, they were found to have a hard mineralized outer coating, with a layer of softer, more flexible collagen fibers underneath. Using his device, Meyers found that while the teeth could partially penetrate that outer coating, they cracked before they could penetrate all the way through the inner layer. This was apparently because the fibers in that layer are stacked in alternating directions (like the wood chips in plywood), thus spreading the bite force out instead of allowing it to squeeze through.

Marc Meyers, a professor of mechanical and aerospace engineering at the Jacobs School of Engineering at UC San Diego, holds two overlapping Arapaima scales
Marc Meyers, a professor of mechanical and aerospace engineering at the Jacobs School of Engineering at UC San Diego, holds two overlapping Arapaima scales

It was also noted that the hard outer layer is corrugated, alternating between thicker and thinner ridges. This allows the scales to bend without cracking, as the fish moves. Manmade ceramics that are of a uniform thickness, by contrast, are put under strain when forced to follow a curved surface.

The Arapaima's "hard on the outside but pliable underneath" strategy is employed by a number of organisms, that need to be agile while remaining protected. Meyers believes the principle could find use in flexible ceramics, that could in turn be applied not only to soldiers' body armor, but also fuel cells, insulation or aerospace technology.

"We have used our ingenuity to the maximum, but one way to overcome that is to look at nature," he suggested. "The materials that nature has at its disposal are not very strong, but nature combines them in a very ingenious way to produce strong components and strong designs."

Source: University of California, San Diego

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2 comments
chidrbmt
Nature will give all the answers if we don\'t destroy it first. How much has already been lost by extinction caused by humans?
Gregg Eshelman
There\'s already a body armor like that, Dragonscale. The military tests have been rigged and/or they\'ve lied about the results, same as was done when the old fogeys tried to stop the M-16 from being bought by the US Army.