The co-operate influence of Agar polymeric matrices and reagent solution concentrations on gel incorporation and crystal organization in hydrogel-mineral composite aggregates

Trabajo presentado en el 14th International Symposium on Biomineralization (BIOMIN XIV) from Molecular and Nano-structural Analyses to Environmental Science, celebrado en Tsukuba (Japón), del 9 al 13 de octubre de 2017Organisms exert precise control over the architecture and material properties of their biomineralized tissues through the presence of biopolymers which organize the texture and microfabric of the mineral. The understanding of this control has considerable potential for the development and optimization of bioinspired man-made materials. Hydrogel matrices are adequate substrates for biomimetic crystallization as their characteristics can be fine-tuned to reproduce a wide range of biomineralization conditions. Hydrogels consist of a threedimensional network of fibrils and interconnected pores filled with an aqueous solution. We report results of CaCO3 crystallization experiments carried out with agar gel using two different solid contents (0.5 and 2 wt%) and two concentrations for the counter-diffusing reactants (0.1M CaCl2-0.1M Na2CO3; 0.5M CaCl2-0.5M Na2CO3). We find that, for the same concentration of Agar in the gel, the waiting time for the appearance of the first visible crystals decreases with higher concentration of the reactant solutions and/or lower concentration of agar in the gel. This dependence can be related to changes in supersaturation threshold. The calcite crystals incorporate the gel. The density of the intracrystalline gel matrix varies according to defined patterns, with oscillations in the amount of incorporated gel. Almost independent of the concentration of the counter-diffusing reactants, agar gel solid content determines the mode of calcite organization within the composite. As EBSD measurements show, in the presence of a weak gel (0.5 wt% agar solid content) the calcite of the composite is almost a single crystal, while textured polycrystals are obtained when strong gels (2 wt% agar solid content) are used. The amount of occluded gel is relevant for explaining differences in mechanical properties. It can be changed and the mechanical properties of a mineral-gel composite can be tuned at the micrometric scale by the combined change of gel solid content and reagents concentration.Peer reviewe