Comparative Trans-specific studies of calcitic bio-mineralization processes

RISSO, PABLO; DE ARANZAMENDI, MARÍA CARLA; ÁVALOS, MARTINA; LÓPEZ, ANALÍA; BOLMARO, RAÚL; TARTALINI, VANINA; GORDILLO, SANDRA

Cancún

Congreso; XXVII International Materials Research Congress; 2018

Material Research Society

Bio-mineralization processes have evolved along eons, allowing to generate organs, protection systems and general mineralized tissues. Such evolution is driven not only by the possibilities of genetic mechanisms but also by the external evolution pressures.Among the bio-synthesized minerals, the carbonates, either in the form of calcite or aragonite, are the most extensively distributed among genera, families and/or species. One of the main characteristics of calcitic microstructures is the preferential growing of [0001] directions along aparticular direction of the organ or individual. The most tempting speculation would be that the preferential orientation favored an improvement of the mechanical strength of the macroscopicstructures built by those minerals and a consequent comparative advantage against the intentional or accidental damage inflicted by the environment. Alternatively, such preferred orientation could beonly due to an intrinsic limitation of the bio-mineralization process.In the current work we analyze the preferred orientations of the calcitic structures of three different species, belonging to two classes (avian and gastropoda-limpets) and one phylum (brachiopoda).The comparison of preferred orientations in avian eggs and mollusk and brachiopoda shells allows the evaluation of the possible influence of external solicitations and growing directions on preferential orientations. From such comparisons we can infer the relative influence of biochemicalreactions and competitive advantages produced through a given growing process.Texture studies were performed by Electron Back Scattering Diffraction (EBSD) with a TSL OIM-EDAX system in a SEM-FEG Quanta 200.The samples were cut from bio-mineralized tissues, polished with decreasing grit size papers and alumina plus colloidal silica.The texture is characterized by [0001] direction along the growing direction, normal to the surface of avian eggs and radial in the case of limpets and brachiopods.The compressive external solicitations due to their own weight, avian weights or predation actions of other species, etc. are expected to be always perpendicular to the eggs or shell thicknesses. We can infer that the external solicitations have no decisive influence on the preferred orientation.Instead, the crystal growing direction is commanded by the bio-chemistry and probably the need for a faster growing process.