Crustacean’s claw may be suited for battle
Researchers have figured out how a tiny tropical crustacean packs an outsized punch. And they are using that knowledge to engineer super-durable materials that could protect troops in the line of fire, among other useful applications.
The peacock mantis shrimp, scientific name Odontodactylus scyllarus, isn’t actually a peacock, a mantis or a shrimp.
It’s a stomatopod, a member of a group of aggressive ocean-dwellers that use outsized appendages to smash, slash or spear their heavily shelled prey.
It gets its name because of its colorful, shrimp-like appearance and speedy, mantis-like “feeding strike,” said David Kisailus, a professor of chemical and environmental engineering at UC Riverside, who runs the lab that is studying the animal.
And what a strike that is: When unleashed on a potential meal like a crab or a snail, the peacock mantis shrimp’s 2/10-inch-wide fist accelerates faster than a .22-caliber bullet, reaching speeds of 45 mph underwater and smacking its prey with 200 pounds of force.
The punch packs a double-wallop. By accelerating so quickly, the animal’s club actually boils the water surrounding it, creating bubbles that implode upon prey, landing a second strike.
This pounding can penetrate mollusks’ shells in a matter of seconds and bust holes through glass. (The peacock mantis shrimps in Kisailus’ lab are housed in aquariums made of more-durable plastic.) But it doesn’t seem to damage the stomatopod.
“We were impressed that this guy can impact its prey tens of thousands of times over a period of three to four months without breaking its own hand,” Kisailus said. “For decades people have studied snails as the benchmark of impact resistance. Here’s the stomatopod that eats those guys for dinner.”
To figure out how the peacock mantis shrimp pulls off this feat, Kisailus and his team examined the creature’s dactyl clubs using electron microscopy, X-ray diffraction, spectroscopy and computer simulations. They discovered that the hammers’ extraordinary strength comes from a complex interaction between three distinct sections within.
The outer part of the club, or the “impact region,” is made of a crystalline mineral material that can withstand compressive forces more effectively than engineered ceramics forged at extreme temperatures.
The center, or “periodic region,” is made of spiraling layers of sugar-based chitin fibers, reinforced by a different mineral material, that absorb impact energy and prevent cracking.
Finally, the stomatopod depends on the “striated region,” another layer of chitin fibers that wraps around the entire club. Kisailus said these fibers compress the minerals in the appendage, which also keeps fractures from propagating.
The combination gives the peacock mantis shrimp its power, he said. The results of the study were published online this week in the journal Science.
“This research is really cool,” said Sheila Patek, a biologist at the University of Massachusetts Amherst who studies mantis shrimp mechanics. “They didn’t just discover one thing — they discovered a constellation of features that make this appendage so damage resistant.”
Kisailus said he would like to develop materials that mimic the components of the peacock mantis shrimp’s super-tough fists, perhaps for use in lighter, tougher types of body armor. (His work is funded in part by the Air Force Office of Scientific Research.)
Engineers in Kisailus’ laboratory have already started making composite materials based on the tiny creature’s biology, he said, forging substances that are similar to the tissue in the periodic region and forming them into sheets measuring about one foot square and less than an inch thick.
Some of Kisailus’ students took a few of the squares out to the desert and fired at them with high-velocity rounds.
The squares cracked a bit but survived, with energy from the impact dissipating laterally into the material.
The bullets were flattened.
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