Studies On Bioactive Coatings On Porous Implants Made Of A New β Titanium Alloy

Joint replacement is one of the most clinically successful operations. It can relieve pain and reconstruct joint function in patients suffering from end-stage arthritis or injuries from accidents. More than 1000,000 joint replacements(mainly hip and knees) are undertaken annually all over the world. The number is expected to rise exponentially with the increase of populations’ age and serious traffic accident. Current research focuses not only on extending implant longevity, but also on improving function to meet the increased demands of today’s patients, who are likely to be younger and more active than their predecessors two decades ago. The success and lifetime of a prosthesis is mainly dependent on the degree of osseointegration between the implant and bone. Potential research areas in porous joint implant include metallic materials, coating materials and coating methods.1. Preparation of HA and HA-BMP composite coating on porous implants made of a new titanium alloy.Objective:To analyze the composition and surface morphology of HA and HA-BMP composite coatings produced respectively by micro-arc oxidation(MAO) and dialysis-lyophilization technique. Methods:HA coatings were made on the surface of porous titanium alloy implants by means of MAO technique. Then HA-BMP composite coatings were made on some of the implants by means of dialysis-lyophilization technique. XRD analysis was used to identify the composition of the coatings prepared by MAO. The surface structure of these coatings was observed by the ESEM. Results:XRD results affirm the existence of HA in the coatings prepared by MAO. The HA coating layer is uniform and has a satisfactory binding strength. Many well-distributed porous structure was observed(1-10μm).Flocculation of BMP particles was observed on the HA-BMP composite coatings. Conclusion:MAO performed well on the new β titanium alloy as a coating method, which can produce a HA coating with wonderful surface structure. BMP can be combined to the surface of HA coatings by means of dialysis-lyophilization technique.2. An animal experiment of HA-coated porous implants made of a new β titanium alloy.Objective:To evaluate the bone formation of the two groups, and explore the clinical application of MAO as a new method of surface modification. Methods:HA coated and uncoated porous implants were implanted into dog’s bilateral femoral. After 4、12、24 week, the new bone tissues around the implants were observed by gross observation and histology and the formation rate of new bone was calculated and analyzed. Coating degradation was observed by ESEM. Results:Both two surface coatings had good biocompatibility. HA coating can significantly improve the bone formation around the implant. There was significant difference in the formation rate of new bone between the two groups at different time(P<0.05). Most of the HA coating still existed on the surface of porous implants. Conclusion:HA-coated group showed better osteoconductivity and a good prospect for clinical application.3. An animal experiments of HA-BMP coated porous implants.Objective:To evaluate the new bone formation of the two groups, and explore the composite coating method of BMP. Methods:HA coated and HA-BMP coated porous implants were implanted into dog’s bilateral femoral. After 4、12、24 week, the new bone tissues around the implants were observed by gross observation and inverted microscope. The formation rate of new bone was calculated and analyzed. Results:In the early stage(4w,12w), BMP can significantly promote bone formation around the implant. There were statistical difference in the average formation rate between the two coating groups(P<0.05). But In the later stage(24w), there was no significant differences(P>0.05). Conclusion:HA-BMP composite coating showed better osteoconductivity in the early stage. And its biological activity decreased with the degradation in vivo.4. Biomechanical test of the three implant-bone interfaces.Objective:To assess the biomechanical performance of the three implant-bone interfaces at different time. Methods:Implant-bone blocks from the animal experiments above were placed in the ESEM with a mechanical device,and a pull-out test was carried out. Results:In the early stage(4w,12w), The HA-BMP-coated group showed the best mechanical performance of implant-bone interface,HA-coated group the middle,none-coated group the worse. In the later stage(24w), there were no significant difference between the HA-BMP-coated and HA-coated group. Conclusion:HA and BMP can significantly enhance the biomechanical performance of the implant-bone interface. But in the later stage(24w), the HA-BMP-coated group lost its superiority due to the degradation of BMP, compared with HA group.