Study On The Biodegradable Magnesium Alloys Used For Laparoscopic Surgery Hemostatic Clip

The main purpose of this study is developing laparoscopic surgery hemostatic clips of degradation characteristics.According to the service requirements of hemostatic clip,namely the required mechanical and degradation properties,magnesium alloys with good biological compatibility and biodegradable properties were selected for composition designing,material preparation,processing and molding,and studying microstructure, mechanical properties and degradation behavior. The main research includes:Mg-3.0wt%Zn-0.8wt%Zr alloys and Mg-xwt%Zn-0.2wt%Ca alloys(x=3.0, 4.0) were prepared by vacuum melting,the as-cast samples were then extruded to sheets. Their microstructures, mechanical, electrochemical and in vitro degradation properties were characterized. The as-cast Mg-Zn-Ca alloy was deformed by equal channel angular extrusion(ECAE) in different passes in route A, and the microstructure,texture and electrochemical properties of the as-ECAEed samples were studied preliminary.The Mg-3wt%Zn-0.2wt%Ca alloy sheet of good comprehensive properties was selected to make the hemostatic clip. The results of the research are as follows:1.The grain size of the as-cast Mg-Zn-Ca alloy is slightly larger than the as-cast Mg-Zn-Zr alloy. After extruding,the grain size of two alloys reduced obviously,the grain size of latter is reduced by 10 times,and former nearly 30 times.Tensile strength and yield strength of extruded Mg-Zn-Ca alloy sheet is 290 MPa and 211 MPa,higher than Mg-Zn-Zr alloy sheet(282MPa and 199MPa),and the elongation is 29.4%.The corrosion resistance of the extrusion Mg-Zn-Ca alloy sheet a little poorer than Mg-Zn-Zr alloy sheet.After 2 weeks’ immersion,latter generated some Mg instead calcium phosphates,the corrosion of former is more serious,the generated corrosion products are mainly Mg(OH)2 and HA.2.The ECAE process can effectively refine the grain size of as-cast Mg-Zn-Ca alloy, and with the increase of deformation passes, alloy microstructure is more homogeneous. Using the path A deformation after 4 times, the average grain size was refined to 20μm; The texture with most(002) plane is inclining 39° to ED, at the same time there are a few(002) plane paralleled to ED; TD of the alloy has the best corrosion resistance; After immersion in SBF for 36 h, the impedance values of ND and TD cross section were increased gradually, and impedance values of ED cross section first increased then decreased.3.Microstructure of Mg-Zn-Ca alloy laparoscopic surgery hemostatic clip is composed of fine equiaxed grains and curse incompletely recrystallized grains, the grain size is about2.5μm. After closed, a large number of twins and about 200μm micro-cracks appeared in the microstucture. The hardness of hemostatic clip’s closed part present a rule of low in the middle and high on the edge. Surgical hemostatic clips were clipped on the rubber pipe, after2 weeks immersion, hemostatic clips failured gradually, the weight lost quickly at first then slowly. Maintaining hemostatic clip’s mechanical integrity is the problem to be solved.