Shrimp Fight Club: ‘Holy Grail For Materials Engineers’
Engineers at the University of California, Riverside are looking to nature for inspiration in creating stronger vehicle frames and body armor. They may have found a key structure in the club-like claw of the sea floor-dwelling mantis shrimp, according to a report published online this week in the journal Science.
The 4-inch crustacean, also known as a stomatopod, uses its claw with the deadly speed of a 22-caliber bullet to crack open everything from crab exoskeletons to driver’s thumbs to aquarium glass.
“This club is stiff, yet it’s light-weight and tough, making it incredibly impact tolerant and interestingly, shock resistant,” said David Kisailus, the study’s co-author and an assistant professor at UC Riverside’s Bourns College of Engineering. “That’s the holy grail for materials engineers.”
The shrimp, which molts and replaces its claws every few months, uses its deadly appendage to strike its prey of mollusks and crabs. Every iteration of the claw strikes tens of thousands of times in an attempt to crack open the hard shells and exoskeletons of its victims.
In examining these claws, researchers found that the shrimp can fire them at speeds of 75 feet (23 meters) per second and with 200 pounds (91 kg) of force. An amazing feat considering that the creature’s modest weight class and length. These hooks and jabs also cause a process called cavitation, which shears the water and creates bubbles that strike the target with about half the force of the initial strike.
“We have been studying these other organisms when we should have been studying this guy because he literally eats them for breakfast,” Kisailus said.
The researchers found that the mantis shrimp’s claw is a highly complex structure, comprised of three specialized regions that work together to create a structure tougher than many engineered ceramics.
Using electron microscopy and other techniques, Kisailus and his colleagues delved deep into the claw’s structure.
“The team we put together was excellent: having experts in zoology, mechanics, modeling and synchrotron x-ray characterization gave us multiple views of the same problem, making it a very thorough investigation,” Kisailus said.
The first region, located at the impacting surface, contains a high concentration of a mineral called hydroxyapatite, also found in human bones, which supports the impact when the mantis shrimp strikes.
Further inside, highly organized and rotated layers of chitin fibers are stacked at different orientations and act as a shock absorber. The intricate structure makes long fissures in the claw difficult, as any crack that does form has to change directions multiple times to progress further into the appendage.
Finally, the club is encapsulated on its sides by tightly oriented chitin fibers, which wrap around the claw. These fibers act like tape around a boxer’s fingers, keeping the appendage compact during these high velocity impacts.
Using funding from the Air Force Office of Scientific Research to continue work with the shrimp, researchers said they want to use their research to design materials inspired by the claw’s structure. Kisailus said the potential applications for structural materials they develop are widespread because the final product could be lighter and more impact resistant than contemporary products.
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