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Functional biominerals formed in living organisms require high control of inorganic phase crystal polymorphs, morphology, size, and orientation. Such control is often governed by both soluble and insoluble functional molecules, where the soluble ones usually are highly negatively charged proteins and polymers. Here, the effect of alginate and well-defined alginate oligomers on calcium carbonate crystallization is explored, by seeded and unseeded experiments, to separate the effects of the additive on the crystal growth process from the effect on nucleation. The experiments were done at well-defined activity-based levels of supersaturation, controlled pH and temperature. In the seeded experiments, crystal growth of calcite, aragonite, and vaterite were studied separately, and the observations were used to explain a switch in polymorphism when alginate oligomers were present during the crystallization process. Unseeded experiments showed that low concentrations of G-blocks (oligomers of α-l-guluronic acid) ...

Structural biocomposites found in nature often have a well-defined organization on the nanometer scale. For mineralized materials, interactions between organic and inorganic phases are important fo...