Fabrication Of Biodegradable Coating On Magnesium Alloy And Its Properties Study

Magnesium have recently been considered as promising biological implants,as its high specific strength,appropriate Young's modulus and good biocompatibility.However,the demonstrated drawback of magnesium,such as rapidly degradation and speedy corrosion rate in human fluid environment,still limits the application in biomedical implant materials.Local pH remark elevated,and hydrogen sharply release carried out by excessive degradation will cause infection and even required secondary removal procedure.In order to get over difficulties mentioned above,surface modification like fabricating polymer coatings on the surface of magnesium is a well-established strategy which have been extensively investigated.However,the commonly used degradable polyester(such as polylactic acid,polycaprolactone)are difficult to synthesize because of its harsh synthetical conditions and limited monomers.Free radical polymerization is a simple polymerization method.The functional design of polymer can be realized by adjusting the type and proportion of monomer.Therefore,in this paper,a series of degradable functional polymers were prepared via free radical polymerization.Then,the degradable coatings were prepared on the surface of magnesium alloy via dip coating method and electrodeposition.The basic properties of the coatings(such as hardness,adhesion),in vitro degradation,corrosion resistance and cell compatibility were investigated.The specific research content are as follows:1.Synthesis of biodegradable polymer and preparation of coatings on magnesium alloy via dip coating.First,monomers 2-methylene-1,3-dioxane(MDO)and coumarin derivatives 7-(2-methacryloyloxyethoxy)-4-Methyl coumarin(MAC)were synthesized,vinyl acetate(VAc)was selected as a comonomer,and copolymer P(MAC-co-VAc-co-MDO)(PMVO)was synthesized via free-radical ring-opening polymerization.The results of ~1H NMR showed that the monomers MDO,MAC and copolymer PMVO were successfully prepared,and UV absorption spectrum showed that PMVO had the same characteristic UV dimerization behavior as coumarin MAC.Furthermore,PMVO coating was prepared on the surface of magnesium alloy via dip coating method.The basic properties of the coating,such as thickness,weight of per unit film,water contact angle,hardness,adhesion and initial corrosion resistance,were characterized.The best conditions for the preparation of the coating by dip coating method were as follows:3 times of dip coating,concentration of polymer solution 30 mg/ml,ambient temperature 40°C,ultraviolet irradiation time 6 min.Potentiodynamic polarization curve suggested that the corrosion resistance of PMVO coating magnesium alloy was stronger than bare magnesium alloy,and the simulated degradation experiment in vitro further proved that PMVO coating could effectively reduce the degradation rate of magnesium alloy.Finally,the results of cell experiments show that the degradation products of magnesium alloy coated with PMVO coating had low toxicity to cells.2.The preparation and properties of biodegradable coating on magnesium alloy via electrodeposition.Catechol group was further introduced into the PMVO structure and the coating was prepared by electrophoretic deposition to increase the adhesion and corrosion resistance of coating.Firstly,the monomer dopamine acrylamide(DOPA)was synthesized,and the quaternary copolymer P(MAC-co-VAc-co-MDO-co-DOPA)(PMVOA)was synthesized by free radical ring opening polymerization.The structure of DOPA and PMVOA was proved by~1H NMR.PMVOA colloidal particles were prepared by slowly dropping isopropanol(IPA)into DMSO solution of PMVOA.The effects of initial concentration of PMVOA and ion concentration on the morphology,size and potential of colloidal particles were studied by transmission electron microscopy(TEM)and zeta potential and particle size analyzer.The results show that the PMVOA colloidal particles are spherical and negatively charged,and the particle size is 30-120 nm under different influence factors.Furthermore,the electrodeposition method was used to prepare coatings on the surface of magnesium alloy.The effects of deposition time,deposition voltage and concentration of deposition solution on the basic performance and initial corrosion resistance of coating were studied.The best conditions of electrodeposition were obtained as follows:4 min of electrodeposition time,100 V of deposition voltage and 30 mg/ml of deposition solution concentration.The potentiodynamic polarization curves showed that PMVOA coating had better corrosion resistance than PMVO coating,and the electrochemical impedance spectroscopy(EIS)showed that the magnesium alloy coated with PMVOA still had strong corrosion resistance within 8 hours.Through the simulated degradation experiment in vitro,it is found that PMVOA coating has stronger ability to inhibit the degradation of magnesium alloy than PMVO coating,and effectively controlled the change of pH in the liquid environment.The results of cell experiment showed that the degradation products of PMVOA coating had lower cytotoxicity than that of bare magnesium alloy.Before and after degradation experiment,the cells could directly adhere to the surface of PMVOA coating and continue proliferation,which proved that PMVOA coating could provide a better growth environment for cells.