Punching mantis shrimp inspires super-tough composites

A new lightweight, super strong material has been discovered thanks to one of nature’s most violent sociopaths. The peacock mantis shrimp may look like a colorful, reasonably mild-mannered aquarium dweller, but its claws have the punch of a .22 bullet. A team of researchers led by University of California, Riverside, has developed a carbon composite that imitates the claw’s structure. The result is a promising new material that may one day be used to build cars and airplanes.

At 4 to 6 in (10 to 15 cm) long, the peacock mantis shrimp isn't the biggest crustacean in the sea, but it is the meanest. It mixes the attitude of an underwater Tasmanian devil with claws so deadly they can stun or kill prey without even touching them. The characteristic clicking sounds that they and other mantis shrimps make as they snap their claws while hunting or communicating with one another (usually saying “stay away”) is a common noise heard by sailors sitting in tropical harbors while trying to sleep at night.

That clicking is also the sound of one of the oddest weapons in the animal arsenal. The mantis shrimp uses its claws to punch prey, other mantis shrimp, or anything else that it thinks is looking at it the wrong way. What’s unusual about this is that the club-like claw cocks back like a pistol hammer and as it snaps closed, it accelerates faster than a .22-caliber bullet, generating a force more than 1,000 times the shrimp’s own weight. That’s about 200 lb (91 kg).

To give some idea of how powerful a hit that mantis shrimp can swing, it’s notoriously frustrating for aquarium owners to keep because its punch can shatter a pane of glass, so they have to be kept in a special tank.

Another remarkable thing about the mantis shrimp’s claw is that it snaps shut so fast that it literally boils the water in it at a temperature of 4,000⁰ C (7,200 ⁰ F). This creates a sonic shock wave as the bubble expands and a second as it collapses an instant later. This shock wave is so strong that it stun or kill small prey at short distances.

But what caught the attention of the University of California team is that the mantis shrimp can punch other sea creatures thousands of times without breaking its claw. The question is, why?

In previous studies, the team established that the claw’s covering, called cuticle, is made up of several layers, the innermost of which is the endocuticle. This is comprised of a spiraling arrangement of mineralized fiber layers, each of which is laid at a slightly rotated angle to the next that forms a complete spiral and acts as shock absorber.

Taking what they’d learned from the shrimp, the team formed a similar spiral using carbon fiber-epoxy composites. This spiral was made with the fibers set at three different angles ranging from 10 to 25 degrees to the previous layer.

These were compared to two spirals that acted as a control; one in a simple one-way spiral and the other with each layer placed at a quarter turn to the previous one. They were then subjected to tests used to determine the strength of aircraft materials by dropping weights on them, then studying the damage using ultrasound.

The results showed that the control materials did very badly with the one-way spirals failing completely and the quarter-turn material punctured and damaged. On the other hand, the team says that the material based on the mantis shrimp, while showing some damaged fibers, stood up to the beating with as little as 20 percent of the damage as that of the quarter turn version.

This is because the spiral pattern of the shrimp-based material spread the damage throughout the structure rather than letting concentrate in one spot. This property also allowed the material to stand up to compression tests.

According to the team, the new composite material could have applications in the fields of aerospace and car manufacturing, as well as improved body armor and football helmets. In addition, computer modelling of the shrimp’s claw covering could provide new insights into improving synthetic imitations.

“The more we study the club of this tiny crustacean, the more we realize its structure could improve so many things we use every day,” said David Kisailus, a Kavli Fellow of the National Academy of Science and the Winston Chung Endowed Chair of Energy Innovation at the UC Riverside’s Bourns College of Engineering.

The team’s findings were published in Acta Biomaterialia.

The video below shows the mantis shrimp in action.

Source: University of California, Riverside