چكيده به لاتين
Magnesium implants are preferred because of their unique characteristics compared to ordinary stainless steel, titanium, and cobalt chromium implants. The similarity of the mechanical properties of magnesium to the bone, its biodegradability, and the reduction of the stress shield effect are the most important of these properties. Despite its many advantages, magnesium's relatively high corrosion rate creates the possibility of failure and problems before the complete healing process. In addition, due to cyclic loading in the lower limb, these materials are exposed to the simultaneous effect of corrosion and fatigue. Magnesium reinforced by bioceramic particles shows excellent improvement in its fatigue, corrosion, and corrosion-fatigue properties. However, the high decomposition rate of magnesium, especially in the early stages, still causes problems. Implant coating is one of the effective ways to further control corrosion and increase fatigue strength in the corrosive environment inside the body. The studies conducted in the field of corrosion and corrosion-fatigue behavior of coated magnesium biocomposites are limited. In this thesis, after the fabrication of a magnesium composite with 2.5% HA, its microstructure and mechanical properties were assessed. Then the coating of the composite was done by electrospinning PCL and PCL/HA fibers with optimal parameters, and the surface of the samples was characterized. In the next step, polarization and in vitro corrosion tests, mechanical integrity, fatigue, corrosion-fatigue, and biocompatibility tests were performed on the samples. The results indicate a decrease in grain size and proper strength in the composite compared to pure magnesium. Electrospinning of fibers has dramatically reduced the corrosion current density. Also, the PCL/2.5%HA coating has lessened the corrosion rate of the composite by 81% to 0.98 mm/year in the 14-day immersion interval. The results of the mechanical integrity test confirm the improvement in the performance of this sample compared to the uncoated one. Based on the results of the corrosion-fatigue test in SBF, a life of more than 1 million under 60 MPa stress has been obtained for coated and uncoated composite samples. In addition, these results show an increase in fatigue resistance in the PCL/2.5%HA coated sample compared to the uncoated composite sample, especially at low stress levels. Furthermore, the biocompatibility results reveal an increase in the viability of MC3T3-E1 cells on the surface of this sample. The protection effect of the passive layer, scaffold, and the absorbed Ca-P layer can decrease the corrosion rate and thus improve the performance under fatigue load in the SBF environment.
