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THE PEACOCK mantis shrimp Odontodactylus scyllarus is native to the Indo-Pacific from Guam to East Africa. A large shrimp growing to 7 in. long, it has feelers that are so club-like they can shatter glass aquarium walls. These natural hammers are helping engineers formulate better and stronger composite structures. This, from my weekly Science magazine, Vol. 336, 8 June 2012, published by the American Association for the Advancement of Science.
These shrimp clubs have evolved as a composite of three separate parts. The outer shell, the “impact region,” consists of calcium phosphate, a compound also found in tooth enamel. It’s hard, yet derives its fracture resistance from interlayering of another material, chitosan, a natural polymer.
This thin outer shell is backed by a “periodic region.” Here, additional chitosan polymers are stacked at angles rotating through 180 degrees, this directionality giving excellent fracture resistance. (Any crack is forced to change direction, thus retarding its spread.)
Last, the periodic region is supported at its edges by a “striated region” contributing resiliency.
Materials engineers have fabricated composites along these multi-layered lines. And to really good effect: By interlacing titanium dioxide, TiO2, with a softer polymer, they’ve devised a nanocomposite that’s more than four times as tough as monolithic TiO2. Enhanced armor, lighter, yet more protective, could be one application.
In fact, Roman soldiers predated this biomimicry with their testudo, or tortoise, formation. Overlapping shields provided the outer shell. What’s more, each shield had layers with wood grains alternating between vertical and horizontal.
Alas, the soldiers themselves were expected to provided the elastic substructure.
© Dennis Simanaitis, SimanaitisSays.com, 2012