Structural Insight into Coexistence of Flexibility and Toughness in Ctenoid Fish Scales

Scales of fish primarily protect them from their predators and also provide hydrodynamic advantages by reducing dynamic friction, allowing them to move easily while they are swimming. Unlike the continuously mineralized morphology in cycloid scales, the ctenoid scales possess two conflicting properties: strength and flexibility. The present work aims to understand the structural origin of the simultaneous presence of these two conflicting properties in ctenoid scales. Spatially evolved anisotropic small-angle X-ray scattering across a scale reveals that, unlike Bouligand architecture in cycloid scales, the spatially rotating oriented-strand-board-like nanopatterning in ctenoid scales provides the strength as well as flexibility. These scales also show good temperature stability at least up to 100 °C, and the laminated collagen-network remains intact even in a strong acidic environment.