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Comparison of dynamic light scattering and laser diffraction study of early stages of amorphous calcium phosphate formation

Excellent biological properties of amorphous calcium phosphate (ACP), precursor of crystalline calcium phosphates (CaPs), as well as its major role in the normal and pathological biomineralization of vertebrates continues to motivate interest in elucidating its formation. Crucial part of ACP formation mechanism is aggregation at different scales, i.e. calcium and phosphate ions associate forming prenucleation clusters, which aggregate to spherical ACP nanosized particles, which in turn aggregate to chain-like aggregates. The aim of this study was to apply dynamic light scattering and laser diffraction, two widely used techniques for particle size’s determination, in order to follow aggregation kinetics of ACP particles at nano to micron scale at two different supersaturations. Precipitation of ACP was initiated by fast mixing of equimolar reactant solutions. Induction time for nucleation of crystalline phase, i.e. time needed for the commencement of ACP transformation, was determined from potentiometric measurements. Furthermore, formed ACP was characterized by FT-IR spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). During induction time spherical particles and their chain like aggregates characteristic for ACP were formed, as confirmed by FTIR, AFM and TEM. The initial formation rates, as well as the size of the particles, depended on the initial supersaturation. Although the precipitation conditions differed in DLS and laser diffraction studies (mode of mixing, reaction volume), a general conclusion that aggregation of ACP particles is a process which simultaneously takes place at different length scales leading to highly polydisperse precipitate, can be drawn. This points to a possible way of controlling ACP formation by controlling aggregation on chosen scale.

dynamic light scattering ; amorphous calcium phosphate ; laser diffraction

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