Preparation And Property Of Hydroxyapatite/Zirconia Biocomposite

Hydroxyapatite is one of the most extensively used synthetic calciumphosphates for restoring of defects of bone and teeth as well as bone tissueengineering materials. Human bone apatites are characterized by a variety ofionic substitutions, such as K+、Na+、Mg+、CI一、F一and CO2一3which replacesthe Ca2+and OH-in apatite and plays a very important role in the biologicalprocesses in the human body. Human bone apatite structure is about40-60nm inlength and20nm in width and the basic unit is a needle-like or rod-like boneapatite crystals, which consists of a variety of orientation and arrangement and ishelpful for transfer of nutrients. Furthermore, three-dimensional porous structureof interconnected can allow cell attachment and proliferation which providesaccess for biological fluids. New bone tissue can along the pore walls of theporous structure into the hole, constituting osseointegration. Applications ofsynthetic calcium phosphates using as bone tissue engineering materials arelimited because of their poor strength and toughness for the load-bearing parts.The purpose of this study is to imitate bone apatite from the compositionand structure, so glass modified titanium-doped hydroxyapatite coating/porouszirconia composite was designed and fabricated to meet the demand of bonetissue engineering materials. Hydroxyapatite nanopowder was synthesized bychemical precipitation doped by tetrabutyl titanate which changed the latticestructure of hydroxyapatite and improved its thermal stability. Furthermore, theaddition of Tween80induced to obtain nanorods hydroxyapatite.Three-dimensional interconnected porous zirconia was fabricated by gel-formingmethod on which glass modified titanium-doped hydroxyapatite coating wascoated by coating-sintering. Morphology and phases on interface, mechanicaland biological properties were studied systematically. Some important andcreative conclusions were made as follows:(1) Hydroxyapatite nanopowder was synthesized by chemical precipitationmethod doped by tetrabutyl titanate. The results showed that the addition of titanium to hydroxyapatite had a great influence on thermal stability、grain sizeand morphology. When sintered at1000℃-1200℃,0.8wt%titanium-dopedhydroxyapatite did not decompose and hydroxyapatite did not react withtitanium either, which demonstrated that titanium-doped hydroxyapatite didrestrain the decomposition and improved the thermal stability of hydroxyapatite.Titanium-doped hydroxyapatite restrained the grain growth during the sintering.The grain size of0.8wt%titanium-doped hydroxyapatite was much smaller thanthat of pure hydroxyapatite.(2) Hydroxyapatite/zirconia doped by titanium restrained the thermalreaction between hydroxyapatite and zirconia. The results showed that with thetitanium doped to hydroxyapatite/zirconia composite, titanium iron entering thestructure of hydroxyapatite, when sintered at1000℃-1200℃, the main phases of0.8wt%titanium-doped hydroxyapatite/zirconia composite were alwayshydroxyapatite and zirconia which had the combination of good bioactive ofhydroxyapatite and high strength of zirconia.(3) Nanorod hydroxyapatite was synthesized by chemical precipitationmethod induced by Tween80. The results showed that Tween80had asignificant effect on crystal growth and morphology of hydroxyapatite. Withoutaddition of Tween80, hydroxyapatite crystals were lamellar with a wide range ofgrain size distribution between100-300nm. With6.5g/ml addition of Tween80,hydroxyapatite was rod-like morphology and grain size distribution was narrowaround about60nm. More addition of Tween80had no more significant effecton the morphology of synthetic hydroxyapatite.(4) Hydroxyapatite generated self-assembly on the surface of Na2O-CaO-SiO2glass. The results showed that the crystallinity and morphology ofhydroxyapatite depended on the concentration of Na2HPO4、 soaking time andthe content of CaO in the Na2O-CaO-SiO2glass. Morphology of synthetichydroxyapatite showed “pine leaf-shape” multilayer structure.(5) Porous zirconia was fabricated by gel-forming method. Three-dimensional mesh interconnected structure was obtained with controlled porosityand pore size.(6) The glass modified titanium-doped hydroxyapatite coating was coatedon porous zirconia by coating-sintering method. The results showed that this composite still had three-dimensional interconnected structure with controlledporosity and pore size. Compared with pure porous hydroxyapatite, thecompressive strength of this composite improved and the maximum valuereached27MPa. The glass modified titanium-doped hydroxyapatite coating andporous zirconia combined tightly and there were no lamination and cracksbetween them. The maximum bonding strength between them was about53MPa,which was twice of pure hydroxyapatite coating. Simulated body fluid showedthat the apatite layers generated quickly on the glass modified0.8wt%titanium-doped hydroxyapatite coating/porous zirconia composite, whichdemonstrated that this composite had good biological activity. Cytotoxicity testshowed that this composite was not toxic to osteoblasts and the morphology ofosteoblasts was spindle. In vitro test showed that this composite could supportthe attachment and growth of osteoblasts. On the seventh day culture, osteoblastscultured on the glass modified0.8wt%titanium-doped hydroxyapatite coatingwere more bioactive than that of pure hydroxyapatite coating, which indicatedthat the glass modified0.8wt%titanium-doped hydroxyapatite coating couldpromote cell proliferation.