Microscopy adds to understanding mantis shrimp strength

The mantis shrimp uses its two dactyl clubs to strike prey at over 50mph without appearing to incur any damage.

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Now, University of California, Irvine materials science researchers discovered that the clubs have a uniquely designed nanoparticle coating that absorbs and dissipates energy. Their findings have been published in Nature Materials.

"Think about punching a wall a couple thousand times at those speeds and not breaking your fist," said David Kisailus, UCI professor of materials science & engineering. "That's pretty impressive, and it got us thinking about how this could be."

He and postdoctoral scholar Wei Huang used transmission electron and atomic force microscopy to examine the nanoscale architecture and material components of the clubs' surface layer. They determined that the nanoparticles are bicontinuous spheres, made of intertwined organic (protein and polysaccharide) and inorganic (calcium phosphate) nanocrystals.

The 3D inorganic nanocrystals are mesocrystalline with small orientational differences where they join. According to UCI, the crystalline interfaces are crucial to the resilience of the surface layer, because they fracture and break during high-speed impact, decreasing the penetration depth by half.

"The high-resolution TEM really helped us understand these particles, how they're architected and how they react under different types of stress," Kisailus said in a statement. "At relatively low strain rates, the particles deform almost like a marshmallow and recover when the stress is relieved."

He noted that the behaviour of the structures under high-strain impact is much different. "The particles stiffen and fracture at the nanocrystalline interfaces," Kisailus said. "When you break something, you're opening up new surfaces that dissipate significant amounts of energy."

The team, which included researchers from Purdue University, Oxford Instruments and Bruker Corp, was also able to measure and characterise the damping capabilities of the coating.

"The stiff inorganic and soft organic materials in an interpenetrating network confer impressive damping properties to the coating without compromising stiffness. It's a rare combination that outperforms most metals and technical ceramics," Kisailus said.

He added that he's now focused on translating these findings to new applications in a variety of fields: "We can imagine ways to engineer similar particles to add enhanced protective surfaces for use in automobiles, aircraft, football helmets and body armour."