Structural and mechanical properties of the arthropod cuticle: comparison between the fang of the spider Cupiennius salei and the carapace of American lobster Homarus americanus.

Most biological materials are nanocomposites characterized by a multi-level structural hierarchy. Particularly, the arthropod cuticle is a chitin-based composite material where the mechanical properties strongly depend on both molecular chitin/protein properties, and the structural arrangement of chitin-fibrils within the protein matrix. Here materials properties and structural organization of two types of cuticle from distantly related arthropods, the wandering spider Cupiennius salei and American lobster Homarus americanus were studied using nanoindentation and X-ray diffraction. The structural analysis of the two types of cuticle including the packing and alignment of chitin-fibrils is supported by Monte Carlo simulations of the experimental X-ray data, thereby regions of parallel and rotated fibril arrangement can be clearly distinguished. The tip of the spider fang which is used to inject venom into the prey was found to be considerably harder than the lobster carapace, while its stiffness is slightly lower.