Effect of Hydrogel Matrices on Calcite Crystal Growth Morphology, Aggregate Formation, and Co-Orientation in Biomimetic Experiments and Biomineralization Environments

Abstract

We investigate the effect of gelatin, agarose, and silica hydrogel with and without magnesium in the growth medium on calcite single crystal growth and aggregate formation. We characterize the hydrogel and the mineral by cryo-scanning electron microscopy (SEM), high-resolution SEM, and electron backscatter diffraction (EBSD). We image the pristine hydrogel fabric and the fabric of hydrogel incorporated into the mineral. We visualize the hydrogel–mineral interface and investigate the effect of the hydrogels on calcite micro- and mesostructure in the gel/calcite composits. We compare hydrogel fabrics in biomimetic hybrid composites with biopolymer matrices and networks in biological carbonate tissues of bivalves, gastropods, brachiopods, and corraline red algae. In Mg-free environments, silica gel has very little effect on crystal morphology and arrangement; the gel/calcite composite that forms is a single gradient mesocrystal. Agarose and gelatin hydrogels influence mineral organization in gel/calcite aggregates, and these consist of very few subunits separated by hydrogel membranes. With Mg added to the growth medium, large and small angle boundaries highly increase in number: silica gel/calcite aggregates consist of partial spherulites with mesocrystalline subentities; agarose, gelatin gel/calcite aggregates are regular spherulites, and their subentities are single crystals. Thus, calcite crystal organization is influenced by accumulative split growth provoked by incorporation of magnesium.