Study On The Synthesis And Properties Of Mg-4.0Zn-2.5Sr Alloy With HA Coating Prepared By Electrochemical Deposition

In recent decades, biomedical materials have experienced a series of development and innovation, and a variety of new materials have been successfully developed. magnesium alloys as biomedical implant materials have much better performance than other materials. For example, the density of the magnesium, the elastic modulus and other physical properties are close to human bone tissues, magnesium ion is one of the trace and necessary elements for the human body. Hydroxyapatite (HA) is the main component of bone, dentin and enamel which are considered as the hard tissues. If we Put this two kind of properties together, the good mechanical properties of metal materials and excellent biological compatibility of HA that is coated on the surface of magnesium alloy will be obtained.According to the request of the mechanical properties, biodegradability and biocompatibility which are very important factors of biological materials, we decided the composition of alloys that is Mg-4.0Zn-2.5Sr. First Alkali heat treatment is as a method to activate the surface of magnesium substrate. Hydroxyapatite (HA) is prepared by means of electrochemical deposition method on the surface of as-cast Mg-4.0Zn-2.5Sr magnesium alloy, and determining the optimization parameter. After alkali heat treatment can promote the transformation of HA. And compare the Biodegradability and biocompatibility between Magnesium alloy with HA coating and without HA coating. The main results are as follows:(1)The change of corrosion rate of Magnesium alloy without coating in Hank’s solution is fast at the initial corrosion state, then gradually decreased, and finally tends to be stable as the corrosion rate is0.264g/(cm2·h). The change of corrosion rate of magnesium alloy without coating in Hank solution is similar with magnesium alloy without coating, finally tends to be stable, the corrosion rate is0.163g/(cm2·h). (2)The optimum parameters for the deposition of HA coatings is that the voltage is5V, the temperature is50℃lasting2h.(3) Corrosion potential without coatings on magnesium alloy is-1.326V in Hank’s solution. And the corrosion current density is about1.120×10-6A/cm2. Corrosion potential with coating on magnesium alloy is-0.801V and the corrosion current density is about5.293×10-7A/cm2. Because of the protection of HA coating, the corrosion potential increased about525mV and corrosion current was reduced to0.591μA. The presence of HA coating improves the corrosion resistance of Mg-4.0Zn-2.5Sr alloy, as the same as immersion test results.(4) The hemolytic rate of Mg-4.0Zn-2.5Sr alloy is4.75%, but the hemolytic rate of HA coated on Mg-4.0Zn-2.5Sr is3.30%, They are all less than5%. HA coating can reduce the hemolytic rate, which has better anti-hemolytic property.(5)Cell relative proliferation rate in cell extracts of Mg-4.0Zn-2.5Sr alloy with coating increased as time increased, and so does the Mg-4.0Zn-2.5Sr alloy without coating. Moreover, both of them increase more than96%. The cell relative proliferation of Mg-4.0Zn-2.5Sr alloy with coating increases up to109%, while the cell relative proliferation of Mg-4.0Zn-2.5Sr alloy without coating reaches a maximum of105%. In hence, the HA coating can transform cytotoxicity from level1to level0. The cell morphology after culture observation prove that the HA coating can make cytotoxicity reduce slightly.