Crystal Growth and Morphology Control of Calcium Oxalate Grown in Hydrogels
Suryadevara, Kali Ananth
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Biominerals found in living organisms have diverse biological functions and unique properties arising from the particular structure, orientation, and morphology of the constituent minerals. A systematic investigation toward studying the formation mechanisms of biominerals in an extracellular matrix-like environment is essential for understanding biomineralization processes and for developing bio-inspired materials. The main objective of this thesis is to investigate the crystallization of calcium oxalate, the primary mineral constituent of kidney stones, in gelatin hydrogels. Hydrogels serve as excellent matrix models for biomineralization media and can provide ways for regulating the local supersaturation levels by controlling the diffusion rate of the reactant ions. We employed a double-diffusion experimental set-up in which a hydrogel (serving as the crystallization medium) is brought in contact with two 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. An experimental set-up of this kind can provide insight into different growth conditions in a single experiment. The morphology of calcium oxalate crystals that precipitated in the hydrogels was quite different from that of crystals grown in aqueous solutions. In addition, the morphology of the particles was dependent on their location of appearance inside the hydrogel column (and their corresponding proximity from the source reservoirs). We studied the nucleation, growth, and morphological evolution of calcium oxalate crystals by varying the hydrogel density and the reservoir ion concentrations. The observed outcomes of the gel-mediated crystallization of calcium oxalate were rationalized on the basis of gel-crystal/lattice ion pair interactions. Gelatin hydrogels did not seem to influence the polymorphic form of calcium oxalate (only the thermodynamically stable monohydrate was formed). However, gelatin was incorporated in the growing crystals, thus affecting the morphologies and creating organic-inorganic composites. The morphology and physical properties of the calcium oxalate-gelatin composites produced in this study bear strong resemblance to the biogenic crystalluria. We further evaluated the basic precipitation behavior in the context of fundamental diffusion phenomena.