Study On The In Vitro Degradation Behavior And Biocompatibility Of Iron-based Alloys

Biodegradable medical metal materials have attracted wide attention due to their unique properties,especially in clinical vascular stent implantation and orthopaedic implants.Among the developed biodegradable medical metals,iron-based alloys have caught much attention because of their excellent mechanical properties and biocompatibility.However,the degradation rate of iron-based alloys currently developed is not enough to meet the actual needs of clinical application.Therefore,how to accelerate the corrosion rate of iron-based alloys has become an important issue for biodegradable medical Fe-based alloys.Based on this,this paper focuses on the mechanical properties,corrosion properties and biocompatibility of degradable FeMn alloys.Fe-30Mn-XAg?X=0,1,2,5,10?series alloys were fabricated by the rapid solidification using copper mold suction casting.The microstructure of the alloy was characterized by X-ray diffraction?XRD?and Scanning Electron Microscope?SEM?.It was found that the alloys consisted of austenite phase with face-centered cubic structure and martensite phase with dense hexagonal structure.The precipitated particles in Fe-30Mn-5Ag alloy were further studied by transmission electron microscopy?TEM?.It was found that the precipitated particles were Ag₃Fe₂ phase.The results of compression experiments showed that the mechanical properties of Fe-30Mn-XAg series alloys were significantly improved compared with pure iron.The yield strength increased with the increase of silver content,which was mainly attributed to the combined effect of precipitation of silver-rich particles at grain boundaries and refinement of grain size.The static immersion test in simulated body fluid Hank's solution was carried out.It was found that the degradation rate of Fe-30Mn-XAg alloy is higher than that of pure iron and Fe-30Mn alloy,which was caused by the micro-galvanic corrosion between Ag₃Fe₂ phase precipitated at grain boundary and Fe-Mn alloy matrix results in the formation of micro-galvanic corrosion.However,the degradation rate of Fe-30Mn-XAg series alloys did not increase with the increase of silver content,and the degradation rate was the fastest when the silver content was 5 wt%.Staphylococcus aureus and Escherichia coli were used to test the bacteriostasis of Fe-30Mn-1Ag alloy,and the results showed that it had no obvious bacteriostasis effect.For the cytotoxicity of Fe-30Mn-XAg alloy,human umbilical vein endothelial cells?HUVEC?were used.The cell viability was evaluated by diluted alloy extract.The results showed that the other alloys had no obvious cytotoxicity except Fe-30Mn-1Ag alloy after one day of culture.After 2 and 4 days of incubation in the extract,although the cell activity declined,the cell activity was still higher than 75%,and the ionic concentration released by the solution of static immersion experiment was far below the range that might be harmful to human body.The wettability of deionized water on the surface of Fe-30Mn-XAg alloy was studied by contact angle measuring instrument.The contact angle of the series alloys is in the range which is benifical for cell adhesion.The magnetic susceptibility of the series alloys is much lower than that of pure iron,which is equivalent to that of stainless steel.It shows that the series alloys developed at present have good nuclear magnetic compatibility.Fe-30Mn-1C-XP?X=0,1,2,3,4?series alloys were also prepared by vacuum arc melting furnace in argon atmosphere.The results of XRD and SEM showed that with the increase of P content,the single austenite phase was transformed into austenite phase and martensite phase.The compressive yield strength of these alloys were much higher than that of Fe-30Mn alloy.Moreover,the compressive yield strength of Fe-30Mn-1C-XP alloys increased with the increase of P content.When P content was 4%,its compressive yield strength reached 755 MPa.The results of electrochemical test in Hank's solution showed that the degradation rate of Fe-30Mn-1C-XP alloy was significantly higher than that of Fe-30Mn-1C alloy,and increased with the increase of P content.After adding 4%P,the degradation rate of Fe-30Mn-1C-1P alloy was about twice a s fast a s that of Fe-30Mn-1C-1P alloy.Cytotoxicity of Fe-30Mn-1C-XP series alloy was tested by Mouse Fibroblasts?L929?cultured in 10%diluted extract.After 1,2 and 4 days of culture,the cell vitality was above 70%,which proved that Fe-30Mn-1C-XP alloys had no obvious toxicity.The static contact angle of Fe-30Mn-1C-XP series alloys was measured.It showed that the contact angle of Fe-30Mn-1C-XP alloys ranged from 60-70°,and was in an appropriate range,which was benificial to cell adhesion.Therefore,the Fe-30Mn-XAg and Fe-30Mn-1C-XP alloys developed in this paper are expected to be used as new biomedical degradable metal materials.