The Controllable Lanthanum Ion Released From Ca-P Coating Fabricated By Laser Cladding And Its Inhibition On Osteoclast

In this paper,a gradient Ca-P ceramic coating doped with rare earth oxide La₂O₃ was fabricated on titanium alloy Ti6Al4V by laser cladding.It was expected that the microstructure and phase composition of the coating could be changed by controlling the doping amount of La₂O₃ and the aim of controllable release of La³⁺from the coating could be achieved.Meanwhile,the controllable release of La³⁺was also used to control the number of osteoclasts,which provided a feasible method for prevention and treatment of debris disease of artificial joint.The metallographic microscope,micro-hardness tester,scanning electron microscope,energy dispersive spectroscopy,X-ray diffractometer,inverted fluorescence microscope,MTT analysis were used to study the combination of the coating between the substrate,the microhardness,the surface morphology,the changes of the phase and the toxicity of the coating.At the same time,plasma mass spectrometry was used to investigated the law of release of La³⁺from the coating and the relationship between the concentration of La³⁺and osteoclastogenesis.In the process of the study,some improvements were made to decrease the coating deficiencies.The inhibitory effect of the coating on osteoclastogenesis was optimized by doping a certain amount of SiO_2.The specific conclusions obtained in the above studies are as follows:（1）When the doping amount of La₂O₃ is 0.6 wt.%,there is no obvious transverse cracks in the area of the coating between the substrate,and the coating is of best bonding to the substrate.The number of wide cracks and holes in the coating is also minimal,while the micro cracks in the coating also can provide favorable conditions for the rapid growth of new bone.The results of coating microhardness study show that the coating is of the highest average hardness when the doping amount of La₂O₃ is 0.6 wt.%.（2）The coating mainly contains HA,TCP,CaTiO₃,TiO and other phases.When the doping amount of La₂O₃ is 0.4⁰.6 wt.%,the amount of HA+TCP reaches maximum.Due to the high content of HA+TCP,the proliferation and activity of osteoblast MG63 is better,and the most abundant and active cells can be observed on the surface of the coating.The cells are evenly situated on the surface of the coating and tightly adhered to the surface of the coating and these proved that the coating is not toxic to cells.（3）Ca-P ceramic coating is immersed in the simulated body fluid（SBF）and with the degradation of TCP,honeycomb structure appeared on the surface of Ca-P ceramic coating,and carbonated apatite was formed in some areas of the coating surface.According to the study on La³⁺release from ceramic coatings with different amount of La₂O₃ in SBF,the concentration of La³⁺in the coating increases first and then decreases gradually with time.Because there is almost no wide cracks in Ca-P ceramic coatings doped with 0.6 wt.%La₂O₃,the excellent structure makes the decrease of the concentration of La³⁺in the coatings smoothly,and the time for the continuous release of La³⁺from coatings increases.At the same time,the amount of TCP in the coating and the formation of bone-like apatite on the surface of the coating also affect the release of La³⁺.The average daily release concentration of La³⁺in the coating ranges from 9.3±0.9 to 11.2±0.7 PPB.The mathematical model is used to show the relationship between the concentration of La³⁺and time,and it is predicted that the release time of La³⁺is between 51 and 190 weeks.（4）When La³⁺concentration is 20 PPB,La³⁺could significantly promote the formation of osteoclasts,but when La³⁺is at other concentrations,La³⁺is of inhibitory effects on osteoclastogenesis.Since the maximum daily release concentration of La³⁺from the coating is 11.2 PPB,at this concentration,La³⁺is of an inhibitory effect on the formation of osteoclasts,and the duration of sustained inhibition is approximately 51 to 190 weeks.Beyond this time range,the effect of La³⁺on the formation of osteoclasts is not clear.（5）After doping 10 wt.%SiO₂ on the basis of Ca-P ceramic coating with 0.6 wt.%La₂O₃,the coating guarantees a certain amount of HA,the content of Ti on the coating surface is obviously reduced.A large amount of Ca₂SiO₄ is formed in the coating,and the amount of CaTiO₃ is reduced,which makes the ceramic coating is of better inhibitory effect on the activity of the osteoclast precursor.