Metal ions dependent material density and mechanical properties of the chela spines in the scorpion Androctonus bicolor

Scorpions are distributed almost all over the world and inhabit rainforests, deserts, mountains, and littoral zones. Their multifunctional chelae play a key role in their biology. The chela is the pincer that has originated from the last two segments of the pedipalp. Many previous studies have focused on the morphology of the chela and the overall pincer force. The knowledge about the material properties of scorpion chelae remains rather poor. In particular, little is known about the spines located on the grasping edge of the chela. In this study, we use a combination of nanoindentation, micro-computer tomography, confocal laser scanning microscopy, scanning electron microscopy and energy-dispersive X-ray elemental analysis, to examine the mechanical properties, relative density, sclerotization level, microstructure and biomineralization of both the regular cuticle and the spine cuticle of the chela in the scorpion Androctonus bicolor . Our results show that the mechanical property values of the spine cuticle are significantly higher than those of the regular cuticle. This can reduce the risk of damage to the chela, increase the chance of indentation into the prey tissue and is very likely to result from both higher sclerotization level and biomineralization due to the accumulation of zinc. The specialized microstructure of the cuticle could contribute to the enhancement of the stiffness, strength and toughness of the chela. This study aids in better understanding the material structure, composition and properties of the scorpion chela cuticle.