The elasmoid scales of teleosts: from structure to bioinspired materials
The elasmoid scales of teleosts, remarkable by the diversity of their aspect and ornamentation, nevertheless present a similar structural organization. Each scale is composed of three superimposed layers. At the outer surface, the limiting layer, which may be absent in the anterior field, is the most mineralized of the three layers; it consists of a random meshwork of acidic glycoproteins. Collagen fibrils are the main component of the other two layers. The external layer is made up of thin collagen fibrils (30 nm in diameter) organized into a loose meshwork. This layer is the first to be formed and to be mineralized. Apatitic crystals are not coaligned with the thin collagen fibrils. The most extended part of the scale is the basal plate made up of thick collagen fibrils (about 100 nm in diameter), which are organized into a plywood-like structure. Apatitic crystals appear to be oriented in parallel to the direction of elongation of the fibrils, but they do not penetrate deeply within the fibrils. Most of the crystals are located in the interfibrillary matrix. Knowledge of the elasmoid scale structure may enable pathways to design bioinspired materials for various applications. Elasmoid scales are considered as a source of inspiration for biomimetic composites that would provide resistance, flexibility and lightweight. Because of their transparency and their composition in type I collagen, elasmoid scales are considered as a biomaterial useful for the repair of bone and cornea.