Structure and Mechanical Performance of Teleost Fish Scales

Abstract

In this work, we have studied the structure and mechanics of fish scales from striped bass (Morone saxatilis). This scale is about 200–300 μm thick and consists of a hard outer bony layer supported by a softer cross-ply of collagen fibrils. Puncture tests with a sharp needle indicated that a single fish scale provides a high resistance to penetration which is superior to polystyrene and polycarbonate, two engineering polymers that are typically used for light transparent packaging or protective equipment. Under puncture, the scale undergoes a sequence of two distinct failure events: First, the outer bony layer cracks following a well defined cross-like pattern which generates four “flaps” of bony material. The deflection of the flaps by the needle is resisted by the collagen layer, which in biaxial tension acts as a retaining membrane. Remarkably this second stage of the penetration process is highly stable, so that an additional 50% puncture force is required to eventually penetrate the collagen layer. The combination of a hard layer that can fail in a controlled fashion with a soft and extensible backing layer is the key to the resistance to penetration of individual scales.