The design principles of the protective outer scales of fish are reported online this week in Nature Materials. This knowledge could be applied in the fabrication of human body armour, as well as provide an understanding of how fish evolved, in particular, to survive predatory biting attacks from other animals.
The individual scales of fish are made up of four distinct layers that all have a reinforcing influence and unique ways of deforming and dissipating energy to enhance the scales\\\' strength. The four layers - ganoine, dentin, isopedine and a basal bone plate - are made up of organic-inorganic nanocomposites.
With methods used to test the mechanical properties of materials, Christine Ortiz and colleagues found that the outer ganoine layer is the hardest and most resistant to sharp ‘teeth-like’ penetration. The underlying dentin is softer and dissipates energy via plastic deformation. The isopedine layer has a plywood-like structure, which provides a second line of defence for deeper penetration.
The sequence and thickness of the layers, and the junctions in between them, were all found to be critical in the preservation of mechanical toughness and penetration resistance, but maintain a low weight to ease the fish’s mobility.