The powerful, hammer-like rounded claws of the mantis shrimp are incredibly strong, making them ideal for cracking open the hard shells of clams and crabs (its favoured prey), and for warding off predators. Now those claws are also inspiring scientists keen on building super-strong materials to make tougher body armour and football helmets. Mantis shrimp SMASH! Image: Klaus Stiefel on flickr.
There are two types of mantis shrimp (AKA stomatopods): "spearers" (that spear the prey) and "smashers" (that smash the prey). A team of researchers from the University of California, Riverside, and Purdue University has been studying the multilayered structure of the "smasher" variety of this colourful creature, and recently discovered a unique herringbone structure in the outer layer. They describe their work in a new paper in Advanced Materials.
The outer layer of a mantis shrimp's claw has a unique herringbone strutter. Image: University of California, Riverside
"The smasher mantis shrimp has evolved this exceptionally strong and impact-resistant dactyl club for one primary purpose — to be able to eat," UCR's David Kisailus, who heads the Bourns College of Engineering, said in statement. "However, the more we learn about this tiny creature and its multilayered structural designs, the more we realise how much it can help us as we design better planes, sports equipment, and armour."
Back in 2012, Kisailus' group published a paper in the journal Science, describing the interior region of the mantis shrimp's claw. It is very energy-absorbent, which helps to dissipate impact forces — like when the colourful creature pounds mercilessly, Hulk-like, on would-be predators. That so-called "periodic region" is made partly of chitin (a common compound in the shells of crustaceans) and partly of calcium phosphate and calcium carbonate, entwined together like a spiral staircase.
The current paper deals with the outer layer of the claw, or "impact region", which is very tough and resistant to cracking. It too contains chitin fibres, only this time surrounded by calcium phosphate (found in human bone), forming a tight herringbone pattern. There's also a thin coating around the surface that serves to further dissipate the stress of impact.
The researchers first ran computer simulations replicating that unusual herringbone structure, and then tested those findings by 3D printing a composite material based on that pattern. This confirmed that the structure really does effectively distribute force of impact to minimise stresses on the claw during use.
The next step is to learn more about the underlying mechanism by which such a unique herringbone structure forms. In the meantime, Kisailus's team has already used 3D printing to make composite materials mimicking the properties of mantis shrimp's claws.