Microstructure,Corrosion Pruduct And Biocompatibility Evaluation Of Novel Mg Alloy For Orthopedic Application

Magnesium and its alloys are considered to be biodegradable orthopedic materials of great potential.For further use,however,we still need to study effects that were given by corrosion process on cells.Magnesium alloy material biocompatibility has to be evaluated for multiple times and we need to study patterns of alloy’s corrosion products and its influence on cells.The evaluation results provide evidence for the surface modification of process improvement in order to meet replacement requirements for organs or tissues in human body.Therefore,magnesium alloy biocompatibility reserach becomes pivotal and crucial.This thesis mainly concerns the characterization of alloy and its extract on cell proliferation and differentiation behaviour respectively,illustrating Mg-Zn-Y-Nd-Zr alloy biocompatibility.First,we use optical microscope(OM),scanning electron microscope and energy spectrometer(SEM&EDS)and X-ray diffraction(XRD)to perform characterization analysis of substrate materials,which reveals alloy’s basic characters of microstructure and phase composition.Mg-Zn-Y-Nd-Zr alloy was studied in simulated body fluid(SBF)and the medium(DMEM)to observe its corrosion products and surface variation.By comparing proliferation and differentiation performance change of cells in the alloy surface and its extract,the preliminary biocompatibility of the alloy was investigated.The research provides a scientific basis for further optimizing the Mg-Zn-Y-Nd-Zr alloy process and for medical performance.This thesis compared microstructures of as-cast and extrusion Mg-Zn-Y-Nd-Zr alloy and studied the microstructure and corrosion resistance change created by extrusion process.After extrusion processing,alloy’s grain size has been cut down to about 10 times,the second phase that was originally distributed on grain boundary has been broken and distributed into the substrate in average.The extrusion process also resluts in simple silk texture,but the alloy phase composition has not changed.Corrosion current density of Mg-Zn-Y-Nd-Zr alloy was reduced by 40% after extrusion process,and its corrosion rate in SBF has been significantly lower too.This thesis discusses corrosion process on the surface of Mg-Zn-Y-Nd-Zr alloy in SBF.In the process of immersion,corrosion products of as-cast alloy shows such behaviour as “nucleation-debris fall off-grewup-covered-chunk off-continue to spread”.Corrosion products of extrusion alloy shows such behaviour as “nucleation-growth-dense-covered-layer overlay-small pieces fall off-continue to grow-covered”.Graduated,cells are more likely to proliferate on the surface of extrusion alloy due to slower growth change of corrosion products.MTT cell toxicity test shows that alloy extract produces non-poisonous influence on cells proliferation.RGR in extrsusion extract of lower concentracion is higher while it goes another way in higher concentration extract.Cell differentiation in extrusion alloy extract shows better performance and can produce significant Ca/P sedimentation phenomenon.Pretreatment comparation SEM results show that alloy has a flat surface topography when 2 hours was selected as pretreatment time,and its surface corrosion products consists of rich amount of Ca and P elements.In co-culture span,cell adhesion rate on alloy and co-culture wells rises at first and keeps going down as time goes by.It shows that cells would perform normal proliferation on alloy to some extent.