Biodegradation And Biocompatibility Evaluation Of Mg-3Sn-0.5Mn Alloy

Magnesium alloys have attracted great attention as a new class of biodegradablebiomedical metallic materials, due to the combination of good mechanical property,degradability and biocompatibility. The majority medical magnesium alloys which areresearched are commercial magnesium.Scholars realize that the alloying elementsaluminum and rare earth seem not to be the best adding elements, because they are not toxicfree.In the present work, we rule out disputable elements and select beneficial elements asalloying element to develop a new kind of medical Mg-Sn-Mn alloys,we take theMg-3Sn-0.5Mn alloys with excellent performance to evaluate its biodegradation andbiocompatibility.Mg-3Sn-0.5Mn alloys fabricated under rolling and extrusion could significantly refinethe grains and improve its mechanical properties.The UTS and elongation of as-cast (129.7MPa and14.7%) and as-solution treated Mg-3Sn-0.5Mn alloy (154.7MPa and20.6%)were largely improved after hot rolling (233.5MPa and24.9%) and hot extrusion (243.4MPa and25.2%). The hematolysis rate of as-cast Mg-3Sn-0.5Mn alloy (4.5%) was largelyreduced after fabricating under rolling (2.7%) and extrusion (2.7%).Their hematolysis ratewere less than5%, showing good biocompatibility.Evaluated the corrosion properties by electro-chemical method and immersion corrosiontest in SBF.Electrochemical testing indicated that the biodegradation rate order ofmagnesium alloys was: as-cast> as-rolled> as-solution treated> as-extruded. Immersioncorrosion test showed that, after immersion for720h, as-extruded magnesium alloy showeda lower weight loss (6.95%), and the other three showed a greater weight loss. However, asimmersion proceeded, all of them showed the same changes in trends: during the early stageof exposure, the degradation rate was fast, and as immersion proceeded, the degradation ratewas much lower than those during earlier stage. The in vitro degradation behaviour ofas-extruded Mg-3Sn-0.5Mn alloys was studied by electrochemical techniques andimmersion corrosion test in the presence of albumin. Electrochemical testing indicated thatthe addition of BSA significantly suppressed the corrosion reaction and the higher thealbumin concentration was, the higher the inhibitive effect was. The experimental results of soking in SBF with albumin showed that the corrosion behaviors of as-extrudedMg-3Sn-0.5Mn alloys were strongly affected by the addition of albumin through thecombined effects of adsorption and chelation. The quickly adsorbed albumin served as aneffective protective layer, resulting in a much slower corrosion rate at the initial stage. Withincreasing immersion time, a higher corrosion rate was observed since the chelation effectexerted more significant acceleration effects on the removal of the passivation layer.In order to investigate both the influence and the degradation behavior of magnesiumalloys in animals, the rabbits were underwent surgery to implant as-extrudedMg-3Sn-0.5Mn alloys into the dorsal abdominal region and the femoral. The hydrogen gasbubbles appeared in the early implantation time and disappeared later. The magnesiumconcentration in the blood was within the normal range during the experiment. The internalorgans of animals (heart, liver, kidney and spleen) were made into sections forhistomorphology analysis and no obvious abnormalities were observed. It meant thatpostoperation of the alloy in rabbits did not show negative influence on the recirculating,immune and urinary systems of them. Implantation in vivo showed that the degradation rateof Mg-3Sn-0.5Mn alloys could be different when contacting with different tissues, and thefastest was in the femoral. The biocorrosion products on the surface were rough andcrumbly and the main component of them was C, O, Mg, P, Ca, N. The X-ray diffractionpattern and FT-IR spectra showed that the biocorrosion products were Mg(OH)2and a smallamount of hydroxyapatite.