The Preparation And Solubility Research Of Hydroxyapatite Nanopowder With Trace Element Doping

Hydroxyapatite (HA) has been widely used in biomedical field such as bone substitutes or non-stress areas due to its similar structure and composition with human hard tissue (bones, teeth, etc.). However, its applications are limited because of the low degradation rate after implantation. Moreover, the solubility of HA can be adjusted by doping trace elements, such as magnesium and zinc, etc.In this paper, HA powder doping with different contents of magnesium or zinc were prepared by sol-gel method, and DSC-TG, XRD, SEM were used to analyze the crystallization and decomposition temperatures, crystalline phases, crystallinity, crystal sizes, lattice parameters, microstructures. The biodegradation of HA powders were performed in phosphate buffer solution (PBS) to determine the solubilities.The results implied that the main crystalline phase of HA powder doping with 1.00-8.00 mol.% MgO after heat treatment at 550℃was Mg-substituted HA (MgHA). Meanwhile, the entry of magnesium into the crystal lattice of HA promoted the decomposition of HA to doped beta-tricalcium phosphate (β-MgTCP) and Ca₇Mg₂P₆O₂₄. When coming to solubility, Mg-containing HA was more soluble than pure HA. Moreover, the solubilities of HA increased with MgO content when MgO content was no more than 5.00 mol.%, while the solubility dropped with MgO content when greater content of MgO was doped, depending on the relative contents of MgHA,β-MgTCP and Ca₇Mg₂P₆O₂₄.Similarly, when doping with zinc oxide, the substitution of calcium by zinc in HA lattice resulted in the changes of crystal sizes, crystallinity, lattice parameters, microstructures, etc. Also, the incorporation of ZnO stimulated the thermal decomposition of HA, leading to the production ofβ-ZnTCP and Ca₁₉Zn₂(PO₄)₁₄, thereby improved the solubility of HA. Simultaneously, when ZnO content was in the range of 1.00-3.00 mol.%, the more ZnO was introduced, the more soluble the Zn-containing HA was, while the solubility of HA doping with 3.00-8.00 mol.% ZnO decreased with ZnO content. In addition,β-ZnTCP was more soluble comparing with Ca₁₉Zn₂(PO₄)₁₄ according to the experimental results. The solubility of magnesium-containing HA was different with that of zinc-containing HA, and the former had higher solubility.