COMPARATIVE TRANS-SPECIFIC STUDIES OF CALCITIC BIO-MINERALIZATION PROCESSES.

V. TARTALINI; C. ARANZAMENDI; R. BOLMARO; P. RISSO; S. GORDILLO; M. AVALOS; A. LOPEZ

Cancun

Congreso; XXVII INTERNATIONAL MATERIALS RESEARCH CONGRESS; 2018

International Material Research Society

Bio-mineralization processes have evolved along eons, allowingto generate organs, protection systems and general mineralized tissues. Suchevolution is driven not only by the possibilities of genetic mechanisms butalso by the external evolution pressures.Among the bio-synthesized minerals, the carbonates,either in the form of calcite or aragonite, are the most extensivelydistributed among genera, families and/or species. One of the maincharacteristics of calcitic microstructures is the preferential growing of [0001]directions along a particular direction of the organ or individual. The mosttempting speculation would be that the preferential orientation favored animprovement of the mechanical strength of the macroscopic structures built bythose minerals and a consequent comparative advantage against the intentionalor accidental damage inflicted by the environment. Alternatively, suchpreferred orientation could be only due to an intrinsic limitation of thebio-mineralization process.In the current work we analyze the preferredorientations of the calcitic structures of three different species, belongingto two classes (avian and gastropoda-limpets) and one phylum (brachiopoda). Thecomparison of preferred orientations in avian eggs and mollusk and brachiopodashells allows the evaluation of the possible influence of external solicitationsand growing directions on preferential orientations. From such comparisons wecan infer the relative influence of biochemical reactions and competitiveadvantages produced through a given growing process.Texture studies were performed by Electron BackScattering Diffraction (EBSD) with a TSL OIM-EDAX system in a SEM-FEG Quanta200.The samples were cut from bio-mineralized tissues, polished with decreasinggrit size papers and alumina plus colloidal silica.The texture is characterized by [0001] direction alongthe growing direction, normal to the surface of avian eggs and radial in thecase of limpets and brachiopods.The compressive external solicitations due to theirown weight, avian weights or predation actions of other species, etc. areexpected to be always perpendicular to the eggs or shell thicknesses. We caninfer that the external solicitations have no decisive influence on thepreferred orientation. Instead, the crystal growing direction is commanded bythe bio-chemistry and probably the need for a faster growing process.