Alginate-controlled formation of nanoscale calcium carbonate and hydroxyapatite mineral phase within hydrogel networks

A one-step method was used to make nanostructured composites from alginate and calcium carbonate or calcium phosphate. Nanometer-scale mineral phase was successfully formed within the gel network of alginate gel beads, and the composites were characterized. It was found that calcite was the dominating polymorph in the calcium carbonate mineralized beads, while stoichiometric hydroxyapatite was formed in the calcium phosphate mineralized beads. A combination of electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis and powder X-ray diffraction showed that alginate played an active role in controlling mineral size, morphology and polymorphy. For the calcium phosphate mineralized beads, alginate was shown to modulate stoichiometric hydroxyapatite with low crystallinity at room temperature, which may have important applications in tissue engineering. The results presented in this work demonstrate important aspects of alginate-controlled crystallization, which contributes to the understanding of composite material design.