Comparative Studies on Trans-specific Characteristics of Bio-mineralized Calcite

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

Darmstadt

Congreso; Materials Science and Engineering Congress 2018; 2018

FEMS - TMS

Bio mineralization processes have evolvedthrough eons, producing organs, protection systems and general mineralizedtissues. All those processes find limitations, other than in the inheritedgenetic, in the external evolutionary pressures. Given certain environmentalrequirements, a particular genetic pool may have or not the capacity to evolutionaryrespond to the needs of the organism. As a golden rule, technically, living organism do what they can and not what they should towithstand an external requirement and facilitate its survival or improve itsreproductive advantages and competitiveness.Among the bio-synthesized minerals,calcite and aragonite are the most extensively distributed between genera,families and/or species.We analyze the preferential orientationsof calcite structures of three different species, belonging to three differentclasses (avian, bivalves and gastropods) and a separate phylum (brachiopods).The comparison between preferred orientation in avian and snail eggs as well asin mollusks and brachiopod shells allows to evaluate the possible influence ofexternal solicitations, growing direction and preferred orientations. From suchcomparisons, we can infer the relative influence of the biochemical reactioncapabilities and the competitive advantages conferred by a given preferredorientation.The orientational studies have beenperformed by Electron Back Scattering Diffraction (EBSD), using TSL OIM-EDAX ina SEM-FEG Quanta 200. Samples cut from a few individuals were polished withpaper, alumina and colloidal silica.There is a marked [0001] preferred crystaldirection in the growing direction, close to normal to the surface in the caseof eggs (avian and gastropods) and coplanar with the shells in the case of limpetsand brachiopods. One may speculate whether such preferential orientation wouldfavor a better mechanical resistance of the macroscopic structures built withthose bio-minerals or, alternatively, such preferential orientation might justbe due to some limitations of the bio-mineralization process.The compressive external solicitations,due to mechanical actions because of gravity, avian weights, crush attempts byother predator species, etc., are mostly perpendicular to the shells of eggsand valves. A prime conclusion would be that the growing process is commandedmainly by the biochemical limits rather than based on a selective pressuregiven by external accidental or predatory actions.