Patterns of mineral assembly in hybrid gelatin/agarose hydrogels: Similarities and/or discrepancies between bioinspired and biological biopolymer-carbonate composite materials

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 2017Mineralized structures generated under biological control consist of a biopolymer matrix reinforced by mineral, where matrix membranes form grid structure, that subdivides space and influences the morphology of mineral units in the hard tissue. These membranes are composites of biopolymers and only as such are sufficiently strong scaffolds for the hard tissue. Gelatin and agarose are fibrous hydrogels. Each of them forms a 3D network of fibres, confine water content in pores, enable that their compositions and solute concentrations to be tuned, and with this, mimic biopolymer matrices where biomineral formation occurs. Gelatin and agarose can be mixed to chemically approach the gel composition of that of biopolymers in biominerals, rendering them especially appropriate model systems for understanding the directing influence of biopolymers in biologically formed hard tissues. Here we discuss the influence of Mg-free and Mg-bearing gelatin-agarose gel composite networks (gelatin:agarose ratios = 1:1, 1:2, 2:1) on calcite crystallization and aggregate organization. We find that, relative to gelatin:agarose 1:1, an increase in agarose, with and without Mg in the growing solution, induces an increase in co-orientation of the mineral within the aggregate. In contrast, an increase in gelatin induces the formation of subunits, with most of these being further structured internally. Thus, addition of gelatin lowers the pattern of co-orientation of calcite in the aggregate and induces hierarchy. The presence of Mg in the growth medium, further lowers co-orientation, increases the number of subunits and promotes hierarchical organization. A most significant difference between biomimetic hydrogel-carbonate composite systems and biological biopolymer-carbonate hard tissues concerns the fabric and mode of co-assembly of the polymeric matrix, which is highly co-organized in biological hard tissues but lacks co-organization in hydrogel systems. This difference reflects characteristics of biomimetic gel-calcite aggregates, which, in contrast to biological hard tissues, do not show shape-regulated mineral unit formation.Peer reviewe