Degradation Performance And Surface Modification Of Magnesium For Interventional Medical Applications

There are a increasing number of studies have investigated magnesium?Mg?and its alloys as most promising biodegradable implant materials for clinical use due to their good mechanical properties,biosafety and biocompatibility.However,in terms of the interventional stents filed,most of them focused on the applications of Mg and its alloys used as coronary stents,but a few about the applications in other body parts.In our research,we have selected high-purity magnesium wires?HP-Mg?as materials,m-SBF,artificial urine and human bile as simulated physiological fluids to investigate the feasibility of Mg for urinary and biliary stents.Electrochemical measurements and immersion test in vitro were conducted to compare the differences on corrosion behavior of HP-Mg in three physiological fluids.Furthermore,surface modification was carried out to improve the corrosion resistance of HP-Mg in artificial urine and we performed a series of experiments to characterize the performance and biocompatibility of surface coating on materials.This work achieved the materials with uniform microstructures and good mechanical properties.The grain size is about 10³0?m,the tensile strength reaches 176 MPa,and the elongation is 7%of HP-Mg wires in1.00 mm diameter.We showed that HP-Mg corroded more uniformly and much slower in bile than in m-SBF and artificial urine,slower corrosion rate resulting in a small amount of corrosion products which are mainly amorphous probably will not cause problem such as biliary occlusion,suggesting Mg and its alloys may be a potential material for biliary stents.In terms of corrosion products,crystalized minerals such as Mg₂CO₃?OH?₂·3H₂O,CaHPO₄·2H₂O and hydroxyapatite which may be the precursors of ureteral stones were deposited on HP-Mg after immersion in artificial urine,but not in bile or m-SBF,which suggested a potential risk of urolithiasis when using the bared HP-Mg as a urinary stent.Surface modifications may be one of the most effective ways to improve corrosion resistance of Mg and its alloys in some specific corrosive mediums.A layer of MgF₂ coating with a uniform,dense and integral surface was achieved after hydrofluoric acid treatment,whose thickness is about 2?m.The protection period of MgF₂ coating was about 5 days.Both the electrochemical measurements and immersion tests revealed that hydrofluoric acid treatment can effectively improve the corrosion resistance of HP-Mg in artificial urine,and greatly reduce the corrosion rate,which was very likely to reduce the risk of urinary stones formation.Cells direct culture assays proved that compared with unhealthy cell response to bared HP-Mg,both two kinds of cells proliferated and migrated very well on the surface of HP-Mg after hydrofluoric acid treatment,and there are a increasing number of cells and pseudopods were appeared with incubation time prolonging,suggesting a good biosafety and biocompatibility of MgF₂ coating.Unfortunately,few of normal A7r5 cells were observed after 48 hours incubation on bared HP-Mg surface.Our results could provide useful information for better design of Mg and its alloys as biliary and urinary stents.