A gigantic fish from the Amazon has incredibly tough scales—and materials scientists are looking to them for bulletproof inspiration. Christopher Intagliata reports.
Deep in the Amazon lives one of the world's largest freshwater fish: the legendary Arapaima. It tips the scales at hundreds of pounds, making it a coveted catch for extreme anglers, like Jeremy Wade from the show River Monsters.
[CLIP: River Monsters audio]
After a dramatically scored struggle, he catches one. It takes two guys to hold it up!
[CLIP: “There it is. Look at that for a fish! Look at that massive female Arapaima; about 150 pounds.”]
Speaking of scales, this giant fish has another superlative quality: “It has these very impressive armored scales on its body, which prevent penetration by predators teeth yet still makes the fish quite flexible and nimble in the water.”
Robert Ritchie, a materials scientist at U.C. Berkeley. The predators he’s talking about are piranhas. But the mighty Arapaima has them beat with its scales—one of the “toughest flexible biological materials,” according to Ritchie’s team.
After subjecting the scales to stress tests and electron microscopy in the lab, they figured out the scales’ secrets. For one, they have a hard, mineralized layer on the outside.
“You need the hard layer at the surface to prevent the thing from penetrating. But if the whole scale was made of this hard layer, it would just shatter, like if you tried to penetrate a piece of glass.”
And so the scale then has a layer of softer but tougher collagen on the inside—more resistant to cracking in a piranha’s bite. Materials scientists have already figured out this trick—to build materials with a hard layer on the outside and a tough layer on the inside. But the secret of the Arapaima scales is how exquisitely they transition from the hard to the tough.
“We would love to do that in synthetic materials; it’s just very hard to make materials like that. Maybe 3-D printing in the future can do this. Nature does this rather cleverly because it builds materials from the bottom up, from the atoms and molecules up to the macro scale.”
Photos and details are in the journal Matter. [Wen Yang et al., Arapaima fish scale: One of the toughest flexible biological materials]
So who cares about a fish’s scales? Well, the Air Force Office of Scientific Research does—they funded the study—because Kevlar and other body armors are incredibly heavy. And this piranha-proof fish could be the key to a lighter load.
[The above text is a transcript of this podcast.]