Discovery of a honeycomb structure in the twisted plywood patterns of fibrous biological nanocomposite tissue

Electron microscopy and synchrotron Bragg diffraction were used for the investigation of the structure of the exoskeleton of the lobster Homarus americanus. The study reveals a pronounced microstructure hierarchy and a strong crystallographic and topological texture of the α-chitin-protein network underlying the twisted plywood (Bouligand) structure. The results suggest that the classical picture of such structures must be refined. Instead of a smoothly misoriented stacking sequence of its constitutive nanofibrous chitin-protein planes, two major and two minor orientation branches of the fibers perpendicular to a common 〈0 2 0〉 crystallographic axis pointing towards the surface of the cuticle were found. This crystallographic texture confirms the microscopical observation that the chitin-protein arrays which form the structural subunits of plywood patterns assume the form of planar honeycombs.