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Hydroxyapatite ( HAp) hollow microspheres with hierarchically porous structure and nanorice-like architecture units were synthesized by the composite-hydroxide approach. NH4 H2 PO4 was first reacted with hydroxides to form a hydroxide-insoluble M3 PO4 (the term M represents either Na or K). The diffusing M3 PO4 at the liquid-solid interface then reacted with the Ca( OH)2, forming insoluble HAp hollow spheres by Kirkendall process. Results show that when reaction time is increased from 3 to 12 h, the average diameter of the microspheres increased from 2.64 to 4.16 μm. In addition, the size homogeneity of the hollow microspheres was improved gradually due to Ostwald ripening. The prepared hollow microspheres were treated by ultrasound, and nanorice-like component units with a large mass of mesopores (<10 nm) were displayed. These prepared HAp hollow microspheres might be expected to apply to ion adsorption and drug delivery. [ABSTRACT FROM AUTHOR]

Abstract: We prepared hydroxyapatite/alumina (HA/Al2O3) porous composite materials by the in situ growth of HA on lamellar Al2O3 ceramics. The procedure comprises two steps. First, lamellar Al2O3 ceramics with aligned pore channels were obtained by freeze casting Al2O3 slurry. Second, as-prepared monoliths were used as scaffolds and subjected to hydrothermal treatment in the HA precursor solution. We characterized the microstructure, chemical composition, and mechanical properties of synthesized HA/Al2O3. Experiment results show that the addition of H2O2 into the reaction solution plays an important role in controlling the microstructure of the cultivated HA. The formation of HA has no obvious influence on the lamellar architecture of Al2O3 ceramics. The prepared composite materials exhibit superior compressive strength. Combination of the high strength of lamellar Al2O3 with the excellent biological properties of HA increases the potential of obtained HA/Al2O3 for load-bearing biological applications. [Copyright &y& Elsevier]