Amazonian freshwater fish, Arapaima gigas

Tough as scales

April 14, 2020
This article appeared in Berkeley Engineer magazine, Spring 2020

scales of the Amazonian freshwater fish, Arapaima gigas

• The scale has a hard outer layer of mineral and collagen — similar to bone, but even harder. This highly mineralized surface is the initial line of protection.
• The scale’s soft, thick inner layer is composed of parallel collagen fibrils arranged in a twisted spiral pattern. If the outer layer is cracked, these fibrils deform, containing the crack and preventing the scale from breaking.
• The outer and inner layers of the scales are bound by collagen and grow together as a graded structure in one solid piece, which further strengthens the scales.
• After subjecting the scales to force, the researchers found the A. gigas scales to be one of the toughest flexible materials in nature. They hope their study can be used to develop improved lightweight armor.

Even the razor-sharp teeth of piranhas can’t penetrate the scales of the Amazonian freshwater fish, Arapaima gigas. Now, a new study from Robert Ritchie, professor of materials science and engineering and of mechanical engineering, working in collaboration with researchers at UC San Diego, has determined exactly what makes these scales so incredibly tough, yet still lightweight and flexible.