Microstructure and Mechanical Anisotropy of Crab Cancer Magister Exoskeletons

Abstract

In this study, the microstructure and mechanical anisotropy of a crab Cancer magister exoskeleton – including both the claw and body shell - were studied by using systematic scanning electron microscopy, energy dispersive x-ray analysis, and nanoindentation. The exoskeleton was observed to have a layered microstructure on the cross sections with hierarchically stacked chitin-protein fibrous planes, and porous structures on the in-plane sections. The elastic modulus and hardness decrease with increasing distance from the exoskeleton surface. When comparing the same cuticle layer, higher mechanical properties were measured in the claw than the body shell. A pronounced mechanical anisotropy is observed between the in-plane and cross-section directions – higher modulus and hardness on the in-plane sections than the cross sections, with the exception for the claw endocuticle which shows significantly higher mechanical properties on the cross-sections. Possible mechanisms leading to the observed microstructural and mechanical anisotropy were discussed.