The Preparation And Performance Research Of Fluorine-substituted Hydroxyapatite/Zirconia Compound Ceramics

Nowadays, with the growing need for biomaterials, Hydroxyapatite (HA) hasreceived extensive attention due to its direct bonding capability to the surroundingtissues and the excellent osteoconductivity property, as well as its chemical andbiological similarity to the human hard tissues. Nevertheless, the HA-based implantscan not be used in non-load-bearing areas alone because of their intrinsic lowmechanical properties. Therefore, for full utilization of bioactive HA-based implants,improvements in the mechanical properties are necessary. A well-known method isto synthesize the composites consisted of HA and zirconia in order to achieve thenecessary mechanical strength and bioactive properties at the same time. However,when mixed with zirconia, the decomposition temperature of HA to tricalciumphosphate (β-TCP) will be reduced. The decomposition of HA results in the changesin physical and chemical properties of the material, which would increase thesolubility and then reduce the long-term effectiveness after implantation. In thisstudy，a amount of fluorine is added into70wt%HA/30wt%ZrO2(H7Z3) matrix.Effects of fluorine content on the phase and crystal structure of the compositeceramics are studied. In addition, the dissolution and biological activity in vitro arealso investigated.The composite nanopowders consisted of hydroxyapatite/zirconia containingvarious amount fluorine Ca10(PO4)6Fx(OH)2-x/ZrO2were successfully synthesizedusing a precipitation method, in which the x values were equal to0,1,2,(namely:F0H7Z3, F1H7Z3F2H7Z3). XRD analyses showed that the composite powders wereconsist of HA and t-ZrO2. In addition, with the increasing of the fluorine content, thelattice parameter a decreased from0.94119nm to0.93690nm, while the latticeparameter c do not significantly changed. XPS results showed that the actualfluorine content of F1H7Z3and F2H7Z3were0.9078and1.8658, respectively.The line shrinkage rate and density increased with the fluorine content, whichrevealed that the addition of fluorine increased the density and reduced the porosity.SEM analysis revealed that t-ZrO2grains (280-400nm) were uniformly distributedin the HA matrix, which showed polygons (0.5-0.8μm). The significantdecomposition temperature of the F0H7Z3, F1H7Z3, F2H7Z3composite ceramicswere1300℃,1400℃and1500℃, respectively, which revealed a remarkableimprovement of the thermal stability of HA with the increase of the fluorine content.The dissolution of the composite ceramics were studied in CPBS. The Ca ionconcentrations changing with immersion time in the CPBS were investigated by ICP-AES. The results showed that the dissolution and dissolution rate increasedwith the increase of immersion time. And the dissolution rates of ceramics sinteredat1400℃were in the order as F2H7Z3>F1H7Z3>F0H7Z3. Ca ion concentration was146.88mg/mL, and the weight loss was1.37%after28d of immersion for F2H7Z3ceramic sintered at1400℃. At the same immersion time, the F2H7Z3ceramicsshowed best stability, which was suitable for the oral implant material.The in vitro biological activity evaluations of the composite ceramics wereperformed in SBF. The SEM showed that the new apatite phase was shown on thesurface, which was the patch of carbonate hydroxyapatite sheet (HCA). With theextension of soaking time, HCA gradually grew up. The results showed that theprepared FxH7Z3composite ceramics had good biocompatibility. At the sameimmersion time, the F1H7Z3composite ceramics showed best biological activity,which was suitable for the bone implant material.