| Most of the traditional bio-implantation materials are inert materials,but the long-term safety and reliability of inert materials still have obvious deficiencies.Biomagnesium alloys have higher safety,degradability,and the most bone-like density and Young's modulus of elasticity,demonstrating the potential to be an ideal biodegradable biomaterial.However,magnesium alloys degrade too quickly in human environments containing Cl-ions,limiting their use.In order to improve the mechanical properties,corrosion resistance and biocompatibility of magnesium alloys,methods such as high purification,fine crystallization and alloying are generally used.In addition,the bio-coating on the surface of magnesium alloy not only improves the biocompatibility of the implant,but also promotes the direct chemical bonding between the implant and the bone tissue,which helps to shorten the healing period after surgery and can delay the substrate in body fluids.In this paper,7kinds of Mg-Ca biodegradable magnesium alloys were prepared with good biocompatibility of alloying elements.The calcium salt pretreatment on the surface of magnesium alloy was innovatively developed.The mechanical properties,corrosion resistance and biocompatibility of Mn-Ca phosphate conversion coating and“organic silicone polymer pretreatment+conversion coating+electrophoretic polymer coating”of magnesium alloy was developed and evaluated through mechanical tests,electrochemical and immersion tests in SBF.In vitro cell culture tests were also carried out for the cell viability rate.The main research results of this paper are as follows:1.Novel Mg-5Zn-1Ca and Mg-5Zn-1.5Ca as-cast alloys have been studied.The Mg-5Zn-1.5Ca alloy has been found to poccess finer crystalline structure through experimental analysis,and its grain boundary contains more corrosion resisting Mg2Ca composition.Electrochemical corrosion analysis shows that it has a smaller corrosion current;2.Calcium salt pretreatment coating was prepared on the surface of Mg-5Zn-1.5Ca alloy to make the phosphate chemical coating deposition more uniform.A highly corrosion-resistant Mn-Ca phosphate conversion coating was developed and compared to CaP conversion coating.The coating obtained from the 0.05 mol/L Mn2+solution contained MnHPO4·3H2O,Ca3?PO4?2,and CaHPO4·2H2O.The crystal structure is needle-like alternately with the columnar crystals.The corrosion potential of the coating obtained from the 0.05 mol/L Mn2+solution was the most positive in the coating among coatings obtained from phosphating solutions containing 0-0.07 mol/L Mn2+,which was-1.305V/SCE;the corrosion current was the lowest,which was 7.414×10-7 A/cm2,2 orders of magnitude lower than other coating samples.At the same time,the total surface resistance of this coating sample was 36273?cm2,and the corrosion resistance was better.3.Five novel biomagnesium alloys were prepared by gravity casting and rolling,Mg-0.5Ca-Sr-4Zr,Mg-0.5Ca-1.5Sr-1.5Zr,Mg-0.5Ca-1.5Sr-4Zr,and Mg-0.5.Ca-3Sr-0.5Sn and Mg-0.5Ca-1.5Sr-0.5Sn.XRD analysis shows that the first three alloys were mainly composed of?-Mg,?-Zr and Mg17Sr2,and the latter two alloys mainly consisted of?-Mg,?-Zr,Mg17Sr2 and CaMgSn.Metallographic analysis showed that the Mg17Sr2 phase in Mg-0.5Ca-1.5Sr-0.5Sn homogenizes the distribution of CaMgZn phases.The mechanical properties of the five rolled alloys were much higher than those of pure magnesium,and the compressive strength was more than twice higher than that of pure magnesium.The Mg-0.5Ca-1.5Sr-0.5Sn alloy has a tensile strength of 180 MPa and a compressive strength of 340 MPa.4.Mn-Ca phosphate conversion coating was prepared on Mg-0.5Ca-1.5Sr-0.5Sn alloy.XRD analysis showed that the main components of the coating were MnHPO4·3H2O,CaHPO4·2H2O.The Mn-Ca phosphate conversion layer prepared from 0.07mol/L manganese solution also contains Mn2P2O7·5H2O.Polarization curves and immersion tests in human simulated liquids show that the corrosion resistance of the Mn-Ca phosphate conversion coating prepared from the 0.07 mol/L manganese solution was the best.Immersion test showed that Mg-0.5Ca-1.5Sr-0.5Sn had the least amount of hydrogen evolution in simulated body fluids,even lower than that of pure magnesium,and showed the lowest corrosion current and corrosion rate in electrochemical tests.The corrosion current was 25%of pure magnesium,and its hydrogen evolution rate was 0.68 m L/?cm2d?;5.A pretreatment+conversion coating+electrophoretic polymer coating was prepared on the surface of Mg-0.5Ca-1.5Sr-0.5Sn alloy.The use of an organosilicon sealant to pretreat the magnesium alloy provided the conversion coating uniform surface.A novel composite silicate accelerator accelerates the progress of the conversion coating,and a dense Mn-Ca phosphate conversion coating having a thickness of about 1?m was prepared in a solution containing an accelerator.The composition of the coating layer was mainly Mg3?PO4?2,MnHPO4·3H2O and CaHPO4·3H2O,provided electrophoretic coatings with a100%adhesion quality transition layer.The mechanism of"chemical coating-forming and electrochemical coating-forming"of Mn-Ca phosphate conversion coating and accelerating mechanism of accelerator were studied.The cathodic epoxy electrophoresis polymer coating after pretreatment and conversion coating treatment had good adhesion.The polarization curve corrosion current of the electrophoretic coating with a thickness of 20?m had icorr6.404×10-7A/cm2.Magnesium alloy substrate was two orders lower of magnitude.At the same time,the total res istance of 20?m thick electrophoretic coating coating was Rtotalotal 43269?cm2,which was 18 times that of magnesium alloy substrate,which provides good protection to magnesium alloy.6.The CVR of SaOS2 osteoblasts cultured on the surface of Mg-0.5Ca-1.5Sr-0.5Sn magnesium alloy substrate for 5 days was evaluated by MTS method.It was found that the Mg-Ca alloys prepared in this study had an effect on osteoblasts.Alloy's proliferation have reached Grade 1 or above according to GB/T 16886.5.Among them,the CVR of Mg-0.5Ca-1Sr-1.5Zr alloy and Mg-0.5Ca-1.5Sr-0.5Sn alloy was over 90%.CCK-8 method was used to evaluate the L929 mouse fibroblasts on magnesium alloy substrate,Mn-Ca phosphate conversion coating and epoxy electrophoresis coating.After three days of cell survival test on the surface of the layer,it was found that the Mn-Ca coating had the best biocompatibility;the cells had an 80%survival rate on the third day,followed by more than45%of the epoxy electrophoresis coating layer.The Mn-Ca phosphate conversion coating and the“pretreatment+conversion coating+electrophoretic polymer”coating prepared on the alloy greatly improved cell viability. |
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