Fish with piranha-proof scales inspire new body armour designs

Good fences may make for good neighbours, but as a team of U.S. researchers has discovered, when your neighbours are a school of voracious piranha, adding a suit of armour helps a lot more.

There's a large, ponderous species of fish swimming in the Amazon River, called Arapaima gigas, that's already earned a reputation both as one of the largest freshwater fish in the world, and as a living fossil. However, what's particularly interesting to some researchers is the fact that this species has survived this long living alongside the piranha. Examining the scales of this fish down to the microscopic level, a team of scientists from Lawrence Berkeley National Laboratory, in Berkeley, California, have found a unique structure that they believe can be turned into armour that can protect against both bullets and knife attacks.

The scales of this fish are overlapped by about 60 percent, already making an effective 'suit of armour' against attacks. However, each scale in that 'suit of armour' is made up of two layers for added protection.

The outer layer is hard, but brittle, is roughly half a millimetre thick, with corrugated ridges across its surface, and serves to turn aside most bite attempts. The inner layer is twice as thick as the outer layer, and is made up of flexible, but tough collagen arranged in long strands with a 'spiral staircase' shape. If a bite manages to break through the hard outer layer, the strands inside the inner layer are able to roll inward with the tooth as it penetrates, absorbing the energy of the bite and slowing it down so that it can't break all the way through. The overlapping of the scales provides even more defence, since any particularly 'enthusiastic' bite that can make it through one scale will have another to contend with right underneath.

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This isn't the first time that fish scales have been used for this kind of inspiration, of course. Armourers have been producing suits of mail with overlapping scales, using leather, bronze, iron and even paper, for centuries. However, modern science and engineering has been turning to nature more and more lately, seeking 'biomimicry' solutions to a host of different problems.

The texture of shark skin has been used to develop a film that helps keep surfaces free from bacteria. Researchers have looked at how mussels stick to wet surfaces to produce better glues. They've used how trees turn carbon dioxide into fibres to make plastics, and they've produced cement from carbon dioxide and sea water in the same way that corals use those materials to build up their structures. An architect has even drawn inspiration from how human cells combine to form tissues to produce 'pneumocells', which can be used to make shelters and other structures.

Technology has often been seen as the antithesis of nature, but moving forwards, we may be turning more and more back to nature to provide us with inspiration for the technologies of the future.

(Image courtesy: Wikimedia Commons, Ritchie et alia/Nature Communications)

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