The Effects of Alginate Additives on Calcium Phosphate Mineralization
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Nature produces a variety of highly functional composite structures by the combination of organic and inorganic constituents and these composites stand as a central source of interest and inspiration for tissue engineering applications. In order to highlight the controlling mechanisms used by nature and employ these strategies to design efficient synthetic materials for clinical use, it is vital to study the interactions between organic and inorganic components. In this context, the purpose of this work has been to investigate the effects of alginate additives on different stages of calcium phosphate mineralization. The motivation for this study was founded on a model system composed of alginate hydrogel with calcium phosphate mineral content which has been comprehensively explored in our group as a potential scaffold material for bone tissue engineering applications. The intermolecular interactions of alginate with calcium phosphate minerals were investigated by using compositional variations of alginate in terms of block structure and molecular weight so that the operative interactions between the molecules and minerals could be assessed. The mineralization processes and regulatory roles of alginate additives were systematically studied by use of the complementary experimental techniques that combine monitoring of solution chemistry with material characterization. Detailed studies were conducted on brushite crystallization where the growth rates were determined quantitatively and the effects of alginate additives on growth mechanisms were investigated. By coupling of growth data and spontaneous precipitation experiments information on nucleation kinetics were also deduced. The kinetics of brushite transformation to hydroxyapatite in the presence of alginate was investigated in detail and the rate-determining reaction mechanisms were determined. Hydroxyapatite formation was also investigated via the amorphous calcium phosphate precursor. The course of reaction was studied in detail where the steps of hydroxyapatite formation and the operating mechanisms were discussed as well as the effects of varying alginate additives on these processes. The findings in this study may improve the understanding of the roles of additives with similar structure and functionality during mineralization such as other polysaccharides that are known to have regulatory roles in biomineral formation and contribute to the design of better controlled composite model structures.