The Study On The Magnesium Alloy Composites Used For Biodegradable Intravaseular Stents

Magnesium-matrix material would dissolve easily in the solution which contains chloride ion, and the corrosion products are necessary to the human body. Due to they have both the mechanical properties of metals and the degradability of polymeric materials, the magnesium-matrix materials will have bright future for intravascular stent in clinic. Firstly, the corrosion behavior of different magnesium-matrix materials:Mg-0.5vol%MgO, Mg-1vol%CNT and AZ80A were investigated in the simulate body fluid(SBF). Then the Mg-3wt%Zn-0.8wt%Zr and Mg-5wt%Zn-0.8wt%Zr alloys were prepared and studied. The nano-hydroxyapatite(HA) was mixed in the alloy which has the best mechanical properties and the Mg-3wt%Zn-0.8wt%Zr-1wt%HA composites was prepared. The effects of HA on microstructure, mechanical properties and corrosion behavior of alloy were investigated. At the same time, Mg-3wt%Zn-0.8wt%Zr-1wt%HA and Mg-3wt%Zn-0.8wt%Zr were treated by immersion in hydrofluoric acid (HF) and the surface coatings were characterized. The influence of HF treatment on the corrosion behavior was investigated by immersion in the SBF. In addition, the biocompatibilities of them were evaluated in vitro . The results are listed as follows:1 Compared to the commercial magnesium alloy (AZ80A) , the corrosion rate of Mg-0.5vol%MgO and Mg-1vol%CNT composites which were synthesized using the disintegrated melt deposition method were more quickly. The corrosion products of the three are the same, namely: a large amount of Mg₂Cl(OH)₃·4H₂O and a small quantity of MgCl₂.2 Compared to Mg-3wt%Zn-0.8wt%Zr alloy, the Mg-3wt%Zn-0.8wt%Zr-1wt%HA composites which prepared by melting method we concluded that the growth of grain would be restricted by HA. The results of tensile tests indicated that the ultimate tensile strength and elongation of Mg-3wt% Zn-0.8wt%Zr-1wt%HA composites were higher than that of Mg-3wt%Zn-0.8wt%Zr alloy. We studied the corrosion resistance of the two materials by the electrochemical tests and immersion tests in simulation body fluid, the result showed that HA can markedly improve the corrosion resistance of the magnesium alloy.3 Fluoride conversion coating was synthesized on Mg-3wt%Zn-0.8wt%Zr alloy and Mg-3wt%Zn-0.8wt%Zr-1wt%HA composites by immersion treatment in hydrofluoric acid (HF) for 24 hours. The coating was mainly composed of magnesium fluoride (MF2), the thickness about 1μm. The results of immersion test and electrochemical test showed that the coating have improved the corrosion resistance. The electrochemical test results showed that the coating giving an highest improvement about 16 times.4 The magnesium- matrix materials were nontoxic to osteoblast. The materials treated by HF with higher corrosion resistance, were more suit osteoblast to live for long time.