Preparation,Mechanism And Performance Investigation Of High Bioactive Coatings Containing Ca,mg And P On Medical Titanium Alloys

Titanium alloys have been widely used as biologic implant materials due to their low density and elastic modulus,excellent mechanical properties,good biocompatibility and corrosion resistance.However,the lack of bioactivity on the surface of the titanium alloy prevents the titanium implant from tightly bonding with the bone tissue.Therefore,it is very meaningful to prepare a highly bioactive coating on the surface of titanium alloys by choosing a suitable surface treatment method.Micro-arc oxidation（MAO）can produce ceramic coatings on titanium alloys with a controllable chemical composition and a rough porous structure,which can facilitate cell adhesion and proliferation.Phosphorus（P）is one of the basic elements of the human and cells,which promotes the mineralization of bone cells.Calcium（Ca）is an important element in the composition of human bones.Magnesium（Mg）can promote osteoblast differentiation and bone tissue healing.Although MAO can significantly enhance the surface properties of titanium alloys,it generates a large amount of industrial wastewater.Therefore,it is of great importance to choose environmentally friendly electrolytes.In this thesis,the environmentally friendly phytic acid（IP6）and sodium phytate(Na₁₂Phy)were used as phosphorus-containing electrolytes.In addition,calcium gluconate（CaGlu₂）,magnesium gluconate（MgGlu₂）and calcium glycerophosphate（Ca-GP）,which are commonly used in the food and pharmaceutical industries,were separately selected as the calcium and magnesium sources in the coatings.In a near-neutral solution,phsopshorus-containing bioactive MAO coatings were fabricated and their bone formation property was investigated.The entrance mechanism of calcium and magnesium elements into MAO coatings developed in the solution containing CaGlu₂ and MgGlu₂ was investigated by an orthogonal experiment.In addition,the effects of Ca-GP concentrations were studied and highly bioactive MAO coatings with Ca-Mg-P were successfully prepared.The main research work of this paper is as follows:（1）In order to balance coating properties and environmental friendliness,a neutral solution composed of natural organic IP6 and Na₁₂Phy was selected to prepare MAO coatings containing 8.75 at%,9.83 at%and 10.79 at%P on Ti-6Al-4V alloys by adjusting the electrical parameters.The results show that anodic coatings are mainly composed of titanium,anatase and Ti P₂O₇.In addition,three coatings exhibit good hydrophilicity,and the rougher the coatings,the better the hydrophilicity.MAO coatings exhibit good cytocompatibility and osteoinductive properties.Especially,P-9.83 at%and P-10.79 at%are found to significantly promote osteogenic differentiation at both early and late stages.（2）In the basic solution composed of CaGlu₂ and MgGlu₂,the effects of Ca-GP,Na₁₂Phy,phosphoric acid（H₃PO₄）and voltage on the performance of MAO coating were investigated by an orthogonal experiment with four factor and three levels.The results show that the MAO coating with a Ca/P ratio of 1.35 and a high bioactive hydroxyapatite（HA）phase can be successfully prepared by one-step MAO treatment under appropriate conditions by adjusting the process parameters.Constant voltage is the most important factor to adjust Ca and Mg content in MAO coating,in which Ca²⁺and Mg²⁺ions enter MAO coating through electromigration and diffusion.H₃PO₄ is an effective film-forming agent and the increased concentration significantly decreases both the Ca and Mg amounts.Sole Ca-GP or CaGlu₂ cannot significantly improve the Ca amounts,while Ca-GP and CaGlu₂ can synergistically improve the Ca amount in MAO coatings.（3）Based on the previous experimental results,the effects of 8,10 and 12 g/L Ca-GP on properties of the oxide film were further investigated.The results indicat that with the increase of Ca-GP concentration the Ca content in the coating also increase,indicating that the Ca can enter the MAO coating by diffusion.The MAO coatings are mainly composed of Ti,anatase and rutile.There are Ti P₂O₇,Mg₃（PO₄）₂ and HA in anodic coatings prepared in the solution containing 12 g/L Ca-GP（MAO-12）,and the Ca/P ratio is close to 1.67.The results obtained through immersion experiments in simulated body fluids show that a large amount of granular HA is formed on the surface of the coated MAO-12,indicating that the high Ca/P ratio,surface roughness,pore size distribution and Mg content of MAO-12 contribute to induce the formation and deposition of HA phase.