Structure and mechanical properties of pincers of lobster (Procambarus clarkii) and crab (Eriocheir Sinensis)

The structure and mechanical properties of the pincer exoskeletons (cuticles) of lobster (Procambarus clarkii) and crab (Eriocheir Sinensis) were investigated, respectively. The microstructures and inorganic materials of the pincer exoskeletons were observed and determined using a scanning electron microscope and X-ray diffraction. The mechanical properties of the pincer exoskeletons were evaluated by nano-indentation tests and tensile tests under different conditions. The results showed that the inorganic materials in the lobster claw exoskeleton exhibited an amorphous structure, while those in the crab claw exoskeleton were crystallized as calcium carbonate with a calcite crystal structure and were stable at the temperature below 250 °C. The surfaces of the pincers were biologically unsmooth. Many concave valleys with setae near the tip and many convex domes far off the tip were observed on the surface of the lobster pincer, while many micro-spines were seen on the surface of crab pincer. The microstructures of the pincer exoskeleton exhibited highly mineralized chitin–protein fibers arranged in a twisted plywood structure. The surface hardness and elastic modulus of the crab claws were 0.33 GPa and 8.18 GPa, respectively, higher than those of the lobster claw (0.27 and 5.44 GPa). The transition in the mechanical properties and structure between the exocuticle and the endocuticle was discontinuity. The tensile strength of the crab pincer was two times higher than that of the lobster pincer, and the dry specimen was fractured more easily than the fresh specimen.