Mantis shrimp ‘fist’ could inspire new body armour

by Dr Jonathan D Sarfati

Published: 17 July 2012 (GMT+10)

This is the pre-publication version which was subsequently revised to appear in Creation 36(4):40–41.

Credit: Jenny, Wikipedia.org

The mantis shrimp (aka stomatopod), has one of the strongest ‘punches’ in nature. A specimen only an inch (2.5 cm) long can draw blood if they hit a human finger, and bigger ones have caused severe injuries. Considering how some can grow a foot (30 cm) long, and one has even reached 15 inches (38 cm) long, they are not to be messed with! 13

With an intricate catapult mechanism, its ‘fist’ (called a dactyl) can accelerate up to 10,600 g1 (a greater acceleration than a 22-calibre bullet—while underwater—and hundreds of times what humans can stand2), high enough to induce a mini-explosion called cavitation.3 If kept in captivity, this punch can shatter the glass walls of their tanks. And in the wild, it breaks the shells of its prey, which are often marvels of engineering toughness in their own right.4

We also noted its amazing colour vision, with 12 primary colours receptors—four times as many as humans.5 Later we noted how DVD makers wanted to copy the shrimp eye’s ability to change the polarization over multiple colours.6

There are actually three different regions of the club that cooperate ‘to create a structure tougher than many engineered ceramics.’

But back to its powerful punch: it raises the question of how the ‘fist’ itself can survive. We noted that it moults frequently to regenerate. But frequent moulting could not be the whole story. It could not be frequent enough to withstand 50,000 high-speed strikes against hard prey shells in its lifetime.

Recently, a research team at the University of California, Riverside’s Bourns College of Engineering, discovered what makes its club so damage-resistant.7

There are actually three different regions of the club that cooperate “to create a structure tougher than many engineered ceramics.”8

The outer region that actually contacts the prey is mineral rich, like our bones. But this intrinsically brittle material is buttressed by the next layer, comprising “highly organized and rotated layers of chitin … fibers dispersed in mineral”. (Chitin is a complex polymer, i.e. made from smaller molecules joined together, in this case modified sugars. It is the main component of the outer “skeleton” of many invertebrates, and we have used it to make a strong biodegradable material called “shrilk”.9) In the mantis shrimp club, the arrangement of its tough chitin fibres enables them to absorb the energy of stress waves from the impacts. And the third region comprises “oriented chitin fibers, which wrap around the club,” which holds it together.

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

The three layers allow small cracks to form, but the differences in hardness and orientation prevent the cracks propagatins. Researcher David Kisailus, “who studies the structures of marine animals for inspiration to develop new materials,” says:

It’s counterintuitive: Mother Nature prevents catastrophic failures by allowing local failures. It’s that architecture that makes them so strong.10

That is, as with so many biological materials, it’s not only the chemistry, but also the fine structure that makes them extremely strong. Kisailus also said:

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

Indeed, a summary article said the shrimp club “has a much higher specific strength and toughness than any synthetic composite material.”11 He sees the immense applications if we can reproduce this design. The reduced weight could cut fuel consumption in electric cars and airplanes, and the increased impact resistance should reduce repair bills. Dr Kisailus also hopes to help soldiers, because at present body armour adds about 10 kg (over 20 lb) to his load. Armour based on this design could be just as strong for a third of the weight.

Dr Kisailus and colleagues received $590,000 in funding from the Air Force Office of Scientific Research to continue their great research. But given the high-class science of making the imitation material, what does it say about the Maker of the original?12