| Recently,with the science and technology advancement and the economic growth,functional requirements for biomedical materials are constantly improving.In orthopedics,where bearing loads is required,metal-based biomaterials have the advantages that other materials cannot replace.Traditional metal materials such as stainless steel,cobalt-chromium alloy and titanium alloy can meet the requirements of mechanical properties.However,a second operation is needed to remove the plant after recovery.The second operation not only increases the financial burden of the patient,but also brings additional pain to the patient.In addition,since the elastic modulus of most metal materials is much higher than that of bone,it will produce a"stress shielding"effect,which is not conducive to the recovery.Based on this,the degradable metal materials become one of the most potential biomaterials.Magnesium alloy can be naturally degraded in vivo,by which the second surgery can be avoided.The magnesium ions released by the degradation of magnesium alloy are non-toxic and harmless,and can promote the healing of bone.Simultaneously,excess magnesium ions can be excreted through the kidney.Magnesium is a light metal,and its elastic modulus is closest to that of bone among metal-based biomedical materials currently studied,therefore the"stress shielding"effect can be eliminated.However,the corrosion rate of magnesium alloy is too fast.They often lose their mechanical integrity before recovery.Moreover,hydrogen produced by magnesium alloy corrosion is also unfavorable to the recovery.Therefore,the current research focus on how to improve the corrosion resistance of biodegradable magnesium alloys.There are two main methods to improve the corrosion resistance of biodegradable magnesium alloys,including alloying and surface modification.Surface modification is favored by researchers for simple operation and wide application.In addition to reducing the corrosion rate,surface modification can enhance the biocompatibility and the antibacterial property.Surface modification includes many kinds of methods,such as micro arc oxidation,ion implantation and so on.In this paper,AZ31 magnesium alloy was used as substrate,and a variety of composite coatings were prepared by electrodeposition,biomimetic deposition,chemical conversion,etc.to enhance the corrosion resistance and in vitro biocompatibility.The morphology,structure and composition of the composite coating were observed and characterized by scanning electron microscopy,X-ray diffraction and so on.The corrosion resistance,in vitro biocompatibility and antibacterial property of the composite coating were evaluated by electrochemical tests,cell experiments,in vitro antibacterial effect test,and so on.The film forming mechanism and corrosion behavior were also explored and disscussed.The main studies are as follows.（1）Chitosan（CS）/polylactic acid（PLA）composite coating was prepared by electrodeposition and dip coating.CS can enhance the binding strength of PLA and the substrate,and PLA can seal the holes of CS to improve the corrosion resistance.The results show that the pores of the CS/PLA composite coated sample are covered.The corrosion resistance and in vitro biocompatibility of the CS/PLA composite coated sample are also improved.（2）The silane（SCA）/calcium phosphatite dihydrate（DCPD）composite coating was prepared by biomimetic deposition using SCA induced deposition of DCPD,and the the composite coating was treated with stearic acid（SA）and sodium stearate（SS）,respectively.Both stearic acid treatment and sodium stearate treatment can make the composite coating hydrophobic without damaging the porous structure.As a result,the corrosion resistance is improved and the biocompatibility is not affected.The results showed that both stearic acid treatment and sodium stearate treatment could make the composite coating hydrophobic,improve the corrosion resistance and in vitro biocompatibility,among which,the effect of stearic acid treatment is better than that of sodium stearate treatment.（3）The SCA/Calcium carbonate（CC）composite coating was prepared by biomimetic deposition by changing the composition of the solution,and the the composite coating was still treated with stearic acid and sodium stearate,respectively.The results showed that the effect of sodium stearate treatment is better than that of stearic acid treatment for the SCA/CC composite coating.（4）DCPD/polycaprolactone（PCL）composite coating was prepared by chemical conversion and spin coating,in which hydrothermal synthesised copper-doped anhydrous calcium hydrophosphate（Cu-ADCP）nanoparticles were added.DCPD can enhance the binding strength of PCL and the substrate,and PCL can seal the pores of DCPD to improve the corrosion resistance.Cu-ADCP nanoparticles embedded in PCL made the sample antibacterial by slowly releasing Cu2+.The results show that the DCPD/PCL/Cu-ADCP composite coating is smooth and uniform.The corrosion resistance and in vitro biocompatibility of the DCPD/PCL/Cu-ADCP composite coated sample is improved,and show a significant broad-spectrum antibacterial effect. |
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