Dissertation > Medicine, health > Basic Medical > Medical science in general > Biomedical Engineering > General issues > Biomaterial

Preparation of Bio-materials of Mg-4.0Zn-1.0Sr and Mg-4.0Zn-2.0Sr Alloys with HA-coated and the Studies on Its Degradation Performance and Biocompatibility

Author KongXianJun
Tutor CuiTong
School Northeastern University
Course Materials Science
Keywords Mg-Zn-Sr alloy HA coated degradation biocompatibilit
CLC R318.08
Type Master's thesis
Year 2012
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In recent decades, biomedical metallic material is in the continuous development and innovation, and many new materials are developed successfully. Because there are many advantages as biomedical implant materials, the study on magnesium alloys as one of attracted material become imperative. It is well known that the density and the elastic modulus of magnesium physical properties are very close to human bone tissue, as well as the magnesium ion is one of necessary trace elements of human body. Hydroxyapatite (HA) is the main ingredients of bone, tooth dentin and enamel etc. hard tissue essence. If HA is coated on the magnesium alloy surface, the composite material not only keeps good mechanical properties but also has excellent biocompatibility. This topic is dependent on biocompatibility, biomechanical compatibility, degradability, Mg-4.0Zn-1.0Sr and Mg-4.0Zn-2.0Sr alloy sheet were self-designed.Mg-4.0Zn-1.0Sr alloy is as the research object, After the HA coated on the Mg-4.0Zn-1.0Sr and Mg-4.0Zn-1.0Sr alloy sheet surface was prepared, the degradability and biocompatibility of the material were analyzed. Main results were as follows:(1) Optimal designed Mg-4.0Zn-1.0Sr and Mg-4.0Zn-2.0Sr alloys ingot was prepared to lmm thickness sheet through hot rolling between the anneal temperature of300℃-400℃from high temperature to low temperature after homogenizing. The reduction in very pass was controlled in10~20%. It had good mechanical properties after reasonable aging treatment, whose tensile strength can reach to253MPa, hardness can reach to69.78HV and elongation rate can reach to13.3%.(2) The compared tests of corrosion resistance capability of Mg-4.0Zn-1.0Sr and Mg-4.0Zn-2.0Sr alloys sheet were carried out. In the SBF solution immersion test, their average corrosion rates were1.163g/(m2·h) and1.244g/(m2·h) respectively; corrosion current density values were275μA/cm2and438μA/cm2respectively.(3) In the SBF solution immersion test, the corrosion law of Mg-4.OZn-1.0Sr alloy sheet was the cycle process of pitting corrosion→horizontal expansion of pitting corrosion→local corrosion. The main reason is that the second-phase precipitates could improve the corrosion resistance capability of alloy sheet. The second-phase is mainly MgZn phase. The corrosion potential of MgZn is higher than Mg, and MgZn phase could reduce the corrosion current of the whole systerm properly, and then strengthened the corrosion resistance of magnesium alloys.(4) The Mg-4.0Zn-1.0Sr alloy sheet were used for the matrix by directly electro-deposition and pre-alkali heat treatment+electro-deposition+latter alkali heat treatment process, flat-elongated particles HA was prepared,whose main composition is Ca3(PO4)2·nH2O, and it is turned into HA by heat treatment. In37℃, the voltage was accurate controlled within3V, then the coated surface is smooth and dense. The flat-elongated particles of HA is80μm in length、34μm in broad、10μm in thickness.(5) The compared tests of degradability of Mg-4.0Zn-1.0Sr and HA-Mg-4.0Zn-1.0Sr alloys sheet were carried out.The corrosion rate of non-HA Mg-4.0Zn-1.0Sr is rest on1.139g/(m2-h) after8days,then the corrosion rate of HA-Mg-4.0Zn-1.0Sr is0.957g/(m2·h) after12days.It proved the initial corrosion resistance is improved. HA coating could reduce the corrosion current of the whole systerm, and then strengthened the corrosion resistance.(6) It took hemolysis rate test to study biocompatibility of Mg-4.0Zn-1.0Sr alloy sheet and Mg-4.0Zn-1.0Sr alloy sheet with HA coated. The hemolysis ratios of Mg-4.0Zn-1.0Sr and HA coating alloy sheet were4.70%and3.52%respectively, and the hemolysis ratios Mg-4.0Zn-2.0Sr and HA coating alloy sheet were4.60%and3.51%respectively. The hemolysis ratios were all lower than5.0%, which has a higher anti-hemolysis ability. Then hemolysis ratios of the HA coated alloys were increased through HA coating, which satisfied the requirement of bio-materials.(7) In3ds cytotoxicity test indicated that the cell toxicity of Mg-4.0Zn-1.0Sr, Mg-4.0Zn-2.0Sr and the HA coated alloy sheet were approximately at level one. The values of RGR of four materials were among90to100by means of MTT metabolism, which also prove all of the materials were approximately at level one. The cytotoxicity of Mg-4.0Zn-0.5Sr alloy with coating is decreases slightly.

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