(481g) Modeling Crystallization in Hydrogels Under Double-Diffusion Conditions

In nature, the deposition of biominerals usually takes place in gel-like extracellular matrix environments where the transport of ions to growth sites is regulated. These matrices play an important role in controlling the nucleation, growth, and the final morphology of biominerals. Hydrogels can serve as excellent matrix models for biomineralization. The hydrogel matrix provides a template for crystallization, while at the same time controls the diffusion of ions, regulates the nucleation and growth rates, and directs the hierarchical organization of the minerals. In this work, we investigate the crystallization of calcium oxalate, the primary mineral constituent of kidney stones, in hydrogels. We employ a double-diffusion experimental set-up in which a hydrogel (serving as the crystallization medium) is brought in contact with calcium and oxalate ion reservoirs that serve as sources for the reactants, thus allowing for counter diffusion of the reactant ions across the hydrogel column and precipitation of calcium oxalate in the gel. We study the nucleation, growth, polymorphic outcome and morphological evolution of the calcium oxalate crystals as affected by the gel density, reservoir concentrations, molar stock solution ratios, and additives. The experimentally observed precipitation patterns (time and location within the gel) in the calcium oxalate-gel systems are in very good agreement with theoretical predictions based on the relative diffusion coefficients of both ions. Such understanding of the diffusion and precipitation processes can aid in predicting the time scales of nucleation and growth of the crystals and can facilitate further use of gel matrices as templates for biomineral formation or for development of bio-inspired materials.