Natural Flexible Dermal Armor

Abstract

Fish, reptiles, and mammals can possess flexible dermal armor for protection. Here we seek to find the means by which Nature derives its protection by examining the scales from several fish (Atractosteus spatula, Arapaima gigas, Polypterus senegalus, Morone saxatilis, Cyprinius carpio), and osteoderms from armadillos, alligators, and leatherback turtles. Dermal armor has clearly been developed by convergent evolution in these different species. In general, it has a hierarchical structure with collagen fibers joining more rigid units (scales or osteoderms), thereby increasing flexibility without significantly sacrificing strength, in contrast to rigid monolithic mineral composites. These dermal structures are also multifunctional, with hydrodynamic drag (in fish), coloration for camouflage or intraspecies recognition, temperature and fluid regulation being other important functions. The understanding of such flexible dermal armor is important as it may provide a basis for new synthetic, yet bioinspired, armor materials.

Structure and mechanical properties of selected protective systems in marine organisms

“…Non-stoichiometric hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ), where 4-6% of the phosphate groups are replaced by carbonate groups [52], constitutes the biomineral phase of bone, teeth and most fish scales [13,[53][54][55][56]. Given its presence in the bones and teeth of humans, it has garnered a significant amount of research in the biomedical field, producing a number of bioinspired designs with a focus on biomedical materials and implants [9,[57][58][59][60][61].…”

“…Fish scales provide protection from a variety of predators by integrating highly ordered type I collagen fibers with hydroxyapatite biomineral [13,179,180]. Scales are composites that are composed of multiple layers.…”

“…These generally include mineralized collagen and enamel-like (or bony) layers (example shown in Fig. 25a) [13,[180][181][182]. When a collagen layer is formed, it often has a Bouligandlike structure in order to provide increased toughness and strength in many directions [44,183].…”

“…When a collagen layer is formed, it often has a Bouligandlike structure in order to provide increased toughness and strength in many directions [44,183]. Scales are most commonly arranged in overlapping sheets that allow for smooth motion of the body for locomotion while ensuring full coverage for protection from predators [13,180]. This overlapping pattern minimizes drag to ease swimming by regulating wave propagation about the body [184][185][186].…”

“…2 shows some examples) offer an amazing array of traits and properties due to the design of their complex biological materials. The lessons learned from the structural biological materials of marine organisms have stimulated a number of bioinspired designs including high toughness materials inspired by abalone nacre [9], fiber optic wires inspired by sea sponge spicules [10,11] and body armor inspired by fish scales [12,13]. Given the complex structures that have already been discovered and the immense number of organisms that have yet to be investigated, the study of structural biological materials of marine organisms offers much interest to the scientific community.…”