Biomineral formation in vivo is a complex process regulated by functional molecules. Highlighting the mechanisms underlying biomineralization is necessary for a better understanding of in vivo processes and for enhanced in vitro model systems. Here, the effect of alginate and its well-defined oligomers with M- or G-block structure on brushite nucleation and growth is investigated by seeded and unseeded experiments. Growth kinetics were studied by seeded experiments, and it was shown that molecular weight and functionality of alginate additives affect the crystal growth rates and the growth mechanisms. Growth retardation was most prominent when G-block additives were present. Growth proceeded by surface nucleation when alginate and G-block oligomers were added in the crystallization medium, whereas in the presence of M-block oligomers parabolic rate laws were obtained. By decoupling the seeded and unseeded experiments, information was deduced on the effects of additives on brushite nucleation. In the presence of alginate and G-block oligomers, nucleation was inhibited; however, M-blocks did not show a similar effect. Possible modes of interactions between the mineral and polymer additives are discussed by the evaluation of final crystal morphologies.
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