Studies On The Microstructure And Properties Of The Biomedical Ti-Mn Alloy

Ti-Mn alloys with different Mn content (2,5,8,10wt.%) were developed in the presentwork and various experiments have been carried out to investigate the microstructure andphase composition，tensile properties, in vitro electrochemical corrosion in simulated oralenvironment and bile environment, ion release behavior and the in vitro cytotoxicity, withpure titanium as control. The purpose of the study was to explore the feasibility of Ti-Mnalloys used as potential dental materials and biliray stent materials. Optical microscope,scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to studythe evolvement of microstructure and phase composition with the alloying element content.Tension property was investigated with universal materials testing machine. Microhardnessand wear resistance had been studied with digital hardness tester and ball-on-flat tribometer.Electrochemical behaviors in the artificial saliva were analyzed by methods of open circuitpotential (OCP), electrochemical impedance spectroscopy and dynamic polarization potential.The immersion corrosion behaviors of the alloys in artificial saliva had also been studied withInductively Coupled Plasma Optical Emission Spectrometer（ICP-OES）, SEM and XRD.Furthermore, the in vitro toxicity of the alloys to L929and MG63cell lines had beenevaluated by MTT method.The microstructure of as-cast Ti-Mn alloys changes from single-Ti phase to-Ti+TiMn precipitation phase with the increase of Mn content, and Ti0.48Mn0.52phase wasobserved when Mn content arrived10wt.%. The yield strength and fracture elongation ofas-cast Ti-Mn alloy first increased and then decreased with the increase of Mn content, whilethe tensile strength, microhardness and wear resistance increased with the increase of Mncontent. Compared with the wear loss under dry condition, the wear loss of Ti and as-castTi-Mn alloy decreased under the wet condition with artificial saliva as lubricant, indicatingthe improved wear resistance. Compared with the as-cast Ti-5Mn alloy, the grain size ofhot-rolled Ti-5Mn alloy increased, and the microhardness and wear resistance of hot rolledTi-5Mn alloy was improved, while the tensile property decreased, especially the fractureelongation of hot-rolled Ti-5Mn alloy decreased by65%. The best combination of tensilestrength and elongation lies in Ti-Mn alloy with the composition point at5wt.%.The electrochemical tests indicated that Ti-Mn alloys showed similar corrosionresistance like pure Ti in artificial saliva without any addition, while in the fluorinatedartificial saliava, Ti-Mn alloys didn’t show obvious deterioration like pure Ti. However, Ti-Mn alloys, after the breakdown of the passivation at around1.2Volts, fail to repassivatelike pure Ti. After immersion in the different artificial saliva for7d, Ti ions and Mn ionsreleased from the substrate due to the damage of the passivation coating. The released amountof Ti ions was maximum in artificial saliva with addition of NaF and lactic acid. Pure Ti andTi-5Mn alloy were passivated in human bile environment, and the passive current density wasmore than0.1mA/cm2, indicating better corrosion resistance. The corrosion resistance ofas-cast Ti-5Mn alloy was similar to pure Ti in human bile with pH6.8and pH7.0, and it wasbetter than pure Ti in weakly alkaline human bile with pH7.4, which exhibited higher selfcorrosion potential.The contact anglesof Ti-Mn alloy with different Mn contents were less than90°whencontact with water and glycerol, suggesting hydrophilic property. The contact angle increasedwith increasing Mn content. The surface energy of as-cast Ti-5Mn alloy was least in the fourkinds of Ti-Mn alloys, which was similer to that of pure Ti. After the immersion of Ti andTi-5Mn alloy in human bile, the UV spectra showed the characteristic absorption peak,suggesting that there was no aggregation and adherence of the detached bilirubin and calciumbilirubinte on the surface of Ti and Ti-5Mn alloy and little influence on the composition ofbile. After immersion in human bile for3d, pure Ti and Ti-5Mn alloy had no effect on the thephospholipid of human bile, while with the increase of immersion time (7d), the alloysinteracted with the phospholipid of human bile, resulting in the change of characteristic peakof phospholipid on FT-IR spectra. The drug-loading paclitaxel/PLGA (PTA/PLGA)composite coating was prepared on pure Ti and Ti-5Mn alloy by sprying method, the surfaceof which was uniform and exhibited some directivity. The contact angle of Ti and Ti-5Mnalloy with drug-loading paclitaxel film didn’t change, indicating that there was no influenceof drug-loading film on the hydrophilicity. After immersion in human bile for3d and7d,PTX/PlGA drug loaded coating exhibited no effect on the composition of human bile, such asbilirubin and phospholipid. The in vitro cytotoxicity test shows that the in vitro cytotoxicitygrade of Ti-Mn alloys for L929fibroblast cells and MG63osteosarcoma cells is1grade,namely mild toxicity. Moreover, it has been found that the inhibition of the cell growthaggravates with the increase of Mn content in the testing alloys, which indicates slighttoxicity of Mn to the cultured cells.