Alginate-Intervened Hydrothermal Synthesis of Hydroxyapatite Nanocrystals with Nanopores

This study reports the preparation of dispersive hydroxyapatite (HA) nanocrystals with nanopores based on hydrothermal reactions of Ca- and phosphate-containing aqueous solutions in the presence of alginate. Compared with the conventional hydrothermal HA nanocrystals, very fine rodlike HA nanocrystals were obtained; e.g., the average measures were 13 nm for diameter and 34 nm for length when the nanocrystals were hydrothermally synthesized in the presence of 1.6 wt % alginate. Systematic X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, transmission electron microscopy (TEM) and high-resolutuion TEM, and Brunauer-Emmer-Teller results indicate that alginate-intervened hydrothermal synthesis caused alginate concentration-dependent effects on HA crystallization, agglomeration, particle size, and nanopore formation. In contrast to the generally mentioned roles of polymers as growth modifiers, alginate as well as its depolymerized products under hydrothermal conditions was found to exert synergic and enhanced modulating effects on the preparation of dispersive HA rodlike nanoparticles with numerous nanopores. These HA nanocrystals are promising for applications for various biomedical purposes.