| 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, and self-designed Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet. Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet is as the research object, and Mg and Mg-Ca alloy as contrastive materials, compared to their degradative situations. After the HA coated on the Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet surface was prepared, the degradative situations and biocompatibility of the material were analyzed. Main results were as follows:(1) Optimal designed Mg-4.0Zn-1.0Ca-0.6Zr alloy, and the Mg-4.0Zn-1.0Ca-0.6Zr alloy ingot was prepared to1mm 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 to320MPa, hardness value can reach to71.2HV and elongation rate maximum can reach to19.2%.(2) The compared tests of corrosion resistance capability of pure Mg, Mg-0.6Ca, Mg-1.0Ca alloy and Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet were carried out. In the SBF solution immersion test, their average corrosion rates were1.208g/(m2·h),1.172g/(m2·h),1.263g/(m2·h) and0.907g/(m2·h) respectively; corrosion current density values were1.670 mA/cm2,1.523mA/cm2,1.848mA/cm2and1.238mA/cm2respectively. Their corrosion resistance capability were Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet>Mg-0.6Ca alloy>Mg>Mg-1.0Ca alloy.(3) In the SBF solution immersion test, the corrosion law of Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet was the cycle process of pitting corrosion→local corrosion→pitting 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 and Mg6Ca2Zn3phase. The activity of Zn itself is lower than Mg, and Zn could increase the corrosion potential of magnesium alloy properly, and then strengthened the corrosion resistance of magnesium alloys.(4) The Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet were used for the matrix by pre-alkali heat treatment+electro-deposition+latter alkali heat treatment process, and then the HA coating with the thickness about31.575μm was prepared. In50℃, the voltage was accurate controlled within10V, then the coated surface is smooth and dense. The HA grain is fine and its Ca/P (1.72) is close to human bone Ca/P (1.67).(5) The initial free corrosion potential of HA coating Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet shifted positively by200mV through electrochemical curve. It proved the initial corrosion resistance is improved. And in the SBF solution immersion test, the initial corrosion rate was lower than the uncoated alloy sheet.(6) It took hemolysis rate test and cytotoxicity test to study biocompatibility of the HA coated Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet. The hemolysis rate was4.35%, which satisfied the requirement of biocompatibility. In3d cytotoxicity test indicated that the cell toxicity of the HA coatd Mg-4.0Zn-1.0Ca-0.6Zr alloy sheet was approximately at1level, and the value of RGR was90～100, which satisfied the requirement of cell toxicity bio-materials. |
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