Body Armor Inspired by Piranha-Proof Scales

A complex fish scale architecture that's impervious to piranha teeth could be mimicked to provide flexible composites with a hard ceramic surface for applications like body armor or prosthetics.

The architecture, revealed by a research team at the University of California, San Diego's Jacobs School of Engineering, includes a very hard exterior and a tough but flexible interior and helps the scales resist razor-sharp piranha teeth.

The Amazonian Arapaima gigas fish is the only animal that lives in the same environment as piranhas and doesn't get eaten by them. Its scales, which can measure up to four inches long, combine a heavily mineralized outer layer with a layered internal structure made of stretchy protein material.

The research team, led by Marc Meyers, a professor of mechanical and aerospace engineering, set up a lab experiment to study the Arapaima scale. The experiment used a sensor-equipped machine that resembles an industrial-strength hole punch. The researchers mounted piranha teeth on the top part of the punch. On the bottom part, the team placed Arapaima scales embedded in a soft rubber surface to emulate the fish's soft, underlying muscle.

When the top part of the punch was pressed down into the scales, the piranha teeth partly penetrated the scales but cracked before they could puncture the rubber.