THE EXOSKELETON OF SCORPIONS PINCERS: STRUCTURE AND MICRO-MECHANICAL PROPERTIES

Along with the marine crustaceans - lobsters and crabs - scorpions belong to the phylum of arthropods, invertebrate animals having an external skeleton consisting of a stiff and strong material - the cuticle. Arthropod’s cuticle has become a fundamental topic of study in the field of bioinspired materials due to its multifunctionality. Moreover, the cuticle structural configuration, comprising stiff chitin fibers embedded in a tough protein matrix, has emerged as a novel approach in the preparation of innovative structural composite materials. The mechanical properties of the chela cuticle are affected not only by its composition, but also by how the chitin fibers are spatially arranged, resulting in specific bio-mechanical functionalities such as defense, prey handling, and excavation among others, which lead to the development of a variety of types and distributions of mechanical stresses. Here, we provide new comparative data on the hierarchical structure and mechanical properties of the chela cuticle in two scorpion species: Scorpio Maurus Palmatus (SP) that has a large chela and Buthus Occitanus Israelis (BO) that has a slender chela. We have found different cuticular arrangements between the two scorpions species, which are also different from the morphologies present in lobster or crabs cuticles. Nanoindentation measurements on the scorpion chela cuticle show that the Bouligand structure is isotropic in-plane and also, reveal the effect of fiber orientation on the mechanical properties of the scorpion chela cuticle. These structural variations and their effect on the mechanical properties of the chela are discussed. The chela cuticle structure appears to be a key factor towards the decision of the scorpion whether to choose to sting or use the chela for other mechanical functions.