Influence of Gelatin–Agarose Composites and Mg on Hydrogel-Carbonate Aggregate Formation and Architecture

Abstract

Hydrogels are adequate systems for investigating biological structural material formation as they mimic a wide range of biomineralization conditions. Previous studies focused on the influence of single-component gel systems in the growth of calcite aggregates and their microstructure characteristics. In this work, we investigate the effects of hydrogel mixtures (gelatin/agarose), in the presence and absence of Mg in the growth medium, on calcite aggregate formation, hydrogel incorporation in the calcite, mode of crystallite assembly, and hierarchical mineral organization. We find marked differences between aggregates developed in gel mixtures with increased content of either gelatin or agarose. The presence of Mg, in addition to the gel incorporation, strongly influences the local lattice deformation within the aggregates. The mode of local deformation (homogeneous or localized) is closely related to the size, distribution, and crystallographic co-orientation of subunits within the aggregate. An increase in agarose induces homogeneous distribution of local deformation within the aggregates and formation of a graded mineral arrangement (archetypical spherulites), while an increase in gelatin leads to differentiation of the center and rim portions within the same aggregate. On a higher hierarchical level, when all subunits of an aggregate are considered, both agarose and gelatin evoke the formation of polycrystals.