Chitin in the Exoskeletons of Arthropoda: From Ancient Design to Novel Materials Science

Abstract

The Arthropoda use chitin and various proteins as basic materials of their cuticle which is forming their exoskeletons. The exoskeleton is composed of skeletal elements with physical properties that are adapted to their function and the eco-physiological strains of the animal. These properties are achieved by forming elaborate microstructures that are organized in several hierarchical levels like the so-called twisted plywood structure, which is built by stacks of planar arrays of complex chitin-protein fibres. Additionally, the properties are influenced by variations in the chemical composition of the cuticle, for instance by combining the organic material with inorganic nano-particles. From a materials science point of view, this makes the cuticle to a hierarchical composite material of high functional versatility. The detailed investigation of microstructure, chemical composition and mechanical properties of cuticle from different skeletal elements of the crustacean Homarus americanus shows that cuticle can combine different design principles to create a high-performance anisotropic material. Numerical modelling of the cuticle using ab initio and multiscale approaches even enables the study of mechanical properties on hierarchical levels where experimental methods can no longer be applied. Understanding and eventually applying the underlying design principles of cuticle bears the potential for realization of a completely new generation of man-made structural materials.