Turning a shrimp's claw into better body armor

June 18, 2012

Material engineering research has regularly turned to the natural world for inspiration in recent years, a process generally known as biomimetics or biomimicry. But researchers at the University of California at Riverside have taken this tendency in an interesting direction, adapting one of the more formidable weapons found under the sea to make what could prove to be a very power defensive tool for the nation's military.

One tough shrimp

The huge diversity of creatures under the water use a wide array of weapons to protect themselves and secure their next meal, from sharp teeth to deadly poisons to the pistol shrimp's sonic gun, which can stun larger fish. But a team led by UC Riverside assistant professor of engineering David Kisailus instead looked at the humble club of the so-called peacock mantis shrimp.

Though they are not technically shrimp, nor do they resemble peacocks or mantises, these crustaceans sport an impressive set of fist-like clubs in place of claws that they use to beat assailants and prey. These clubs can reach astounding speeds in excess of 1,000 feet per second and often make quick work of the resilient exoskeletons that many materials engineers have used as bases for their own research.

"We have been studying these other organisms when we should have been studying this guy because he literally eats them for breakfast," said Kisailus.

Taking as well as its giving

But while the force and strength of the these clubs is impressive in itself, especially coming from a half-foot crustacean, what ultimately drew the attention of Kisailus' and Harvard University researcher James Weaver, who did post-doctoral work with Kisailus, was its resilience.

Over the course of a mantis shrimp's life, its clubs could survive more than 50,000 impacts, each one of which carries a force more than 1,000 times the shrimp's weight. Each club strike is comparable to the impact of a .22-caliber bullet.

"This club is stiff, yet it’s light-weight and tough, making it incredibly impact tolerant and interestingly, shock resistant," Kisailus explained. "That’s the holy grail for materials engineers."

Upon investigating the structure of the club, Kisailus' group found that they were an interesting combination of layers that help distribute the shock of impact while providing a solid structure.

According to DiscoveryNews, the toughest point, where the club makes contact with enemies, incorporates a mineral called hydroxyapatite arrayed in supporting pillars perpendicular to direction of the blow. Hydroxyapatite also helps provide strength to human bones.

Beneath these support pillars is a layer of sugar-based fibers known as chitosan, part of the chitin in many crustacean shells, which is arrayed at slightly varied angles to distribute stress more broadly and prevent fractures along seams.

The last level uses similar fibers wrapped around the club, keeping it under pressure and acting in a sense like the tape around a boxer's knuckles.

From seabed to the sky

This intricate combination of chitin and minerals, arranged specifically to provide the greatest possible support while also minimizing the risk of catastrophic failure, could provide a blueprint for dramatically increasing the durability of many materials while also potentially reducing their weight.

The principles found within the shrimp's club could be applied to a broad range of technologies. Aircraft and motor vehicles could benefit from lighter frames to increase fuel consumption, or potentially better adopt technologies like electric engines. However, Kisailus' team has targeted the potential for their research to improve the effectiveness of military body armor, which can add as much as 30 pounds to equipment that already includes weapons, ammunition, supplies and a variety of other gear. In turn, the Air Force Office of Scientific Research has chosen to further fund the research.