Study On Surface Modification Of AZ81 Magnesium Alloy By Micro-arc Oxidation And Coating's Drug Release

Magnesium alloy is a kind of potential implant biomaterial due to their good biocompatibility and biodegradability; it is possible to develop a new type of coronary artery stent. This research taking into account the dual controlled release of drug and magnesium ions, a new type of coating on magnesium alloys was designed to meet these requirements, and the release property was studied systematically.In this study, micro-arc oxidation was used to modify the magnesium's surfaces; a preliminary study of oxidation mechanism was taken by the contrast of the modified effect of the samples which were treated with different oxidation current density. Electrochemical tests in Hank's simulated body fluid and immersion test were used to characterize the modification effect. SEMs showed that there were many pores on the surface of the modified samples, and with the oxidation current increased, the number of the pores decreased, the pores'diameter increased. Then the polarization and impedance spectroscopy tests showed that compared to the bare samples, the modified ones had a certain increase in corrosion resistance, showed a trend that first increased and then decreased.XRD test showed the modified ceramic layer was comprised of the phases such as MgO and Mg2SiO4 mainly. Immersion test showed that the magnesium release rate of the modified ones can be maintained at a stable level relatively, it can achieve the target of controlled degradation of magnesium alloy in some way.By use of PLGA as drug-loaded coating, Taxol as drug,the drug release profile was studied. DSC and infrared spectral of the drug-loaded coating showed that Taxol can be dispersed in the polymer system evenly when the concentration of drug ranged from 8% to 12%. In static drug release experiment, the results showed Taxol could be gradually release in a long time, and the cumulative release rate after 50 days reached approximately 30%. The study of release mechanism showed that the paclitaxel release in first stage was dominated by diffusion, and then shifted to degradation-controlled stage.The influence on the drug release by the addition of PEG as plasticizer was investigated. The results showed that PEG was indeed able to accelerate the degradation of PLGA films, and with the increasing of the content of PEG, the rate of drug release increased. Different LA: GA ratio of PLGAs were used as the controlled release layer, drug release experiments showed that the controlled release layer can significantly reduced the release rate of paclitaxel, and the controlled-release effect was weaker as the proportion of PGA increasing.The platelet adhesion experiment was used to evaluate the blood compatibility of PLGA drug-carrying film, the results showed that there were no large-scale platelet aggregation on the surface of PLGA film with the adding of the paclitaxel, the number of adhesion platelets was significantly reduced and no severe deformation was found , showing that the drug-carrying film's good blood compatibility...