Piranha-Proof Fish May Build Better Body Armor

Scientists hope to replicate the fish scales of a tough, ancient Amazonian fish that repels predators' bites.

- The arapaima can grow to nearly 8 feet long and weigh more than 500 pounds.

- The arapaima's outer scales are mineralized bio-material, while the inner ones are made of collagen fibers that form a flexible laminate, almost like a woven cloth.

An ancient Amazonian fish with thick piranha-proof scales may hold the secret to building better bullet-proof body armor, puncture resistant gloves or even safety goggles and CD cases.

Researchers at several institutions have been looking engineering new materials that contain some of the same properties as these fish scales; they're light, flexible and often transparent. Now some are taking a step forward and actually building these materials.

At the University of California, San Diego, materials science professor Marc Meyers has been studying the scales on the massive freshwater arapaima, which use two layers of scales to repel bites from the predatory piranha.

Piranha normally don't attack the arapaima, which can grow to nearly 8 feet long and weigh more than 500 pounds, however when food supplies are low and water levels drop in the Amazon basin, everything in the water is considered a meal, Meyers said.

"The arapaima is called the cod of the Amazon," Meyers said. "When there is not a lot of food, the piranha will attack anything that is in trouble."

Meyers likes to go fishing in the Amazon, and once hooked a 100-pound arapaima. At his lab in San Diego, Meyers used a special device to press a piranha tooth into the arapaima scales to measure the force it took to penetrate them. But the piranha tooth failed to penetrate into two layers and broke when it was pulled out.

"What arapaima have are fairly thick triangular ridges that other fish don't have," Meyers said. "It can bend at same time, like a ceramic that would be flexible."

The outer scales are mineralized bio-material, while the inner ones are made of collagen fibers that form a flexible laminate, almost like a woven cloth.

Meyers experiments were published in this month's Advanced Engineering Materials.

In Canada, scientists are using a scales of a more common fish, the striped bass, as inspiration for new materials that could even change the shape and form of airplane wings.

Francois Barthelat, assistant professor of mechanical engineering at McGill University, has tried to puncture the much lighter and weaker bass scales with a sharpened steel needle, which simulates the shape of a tooth used by predators.The results showed the scales were stronger than protective plastics used for CD cases, biomedical equipment and safety goggles.

Barthelat said it's the formation and pattern of the scales, rather than their intrinsic properties that make them tough. Now he's used this research on scales to build a composite material that he one day hopes will be worn by both soldiers and athletes.

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"We actually made a large scale material inspired by the scales that can duplicate its properties," Barthelat said. "Once we have proof of concept in the lab, then we can put more effort into fabrication. I don't think it's very far down the road."

Barthelat is also considering an idea to match the flexible bio-armor with something called morphing materials that change shape. Rather than using fixed-wings on aircraft, for example, he envisions a scale-coated rubber wing that would constantly alter its shape for improved aerodynamics as it flies. "The wing would be inspired from birds," Barthelat said. "And it would have protection on top from fish scales."

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