Microstructure and crystallographic texture of the chitin–protein network in the biological composite material of the exoskeleton of the lobster Homarus americanus

The exoskeleton of the lobster Homarus americanus is a multiphase biological composite material which consists of an organic matrix (crystalline α-chitin fibers and various types of non-crystalline proteins) and minerals (mainly calcite). In this study we discuss experimental data about the mesoscopic structure and the crystallographic texture (orientation distribution) of the α-chitin–protein fiber network in this material. The synchrotron measurements reveal very strong crystallographic textures of the α-chitin. According to these data, a large fraction of the α-chitin lattice cells is arranged with their longest axis parallel to the normal of the surface of the exoskeleton. Additionally, a smaller fraction of the α-chitin cells is oriented with their longest axis perpendicular to the cuticle surface. These structural investigations reveal the pronounced role of crystallographic orientation distributions in mineralized biological composite materials which may be of relevance for an improved understanding of biological and bio-inspired nano-composites.