Preparation Of Functional Biological Coatings On Magnesium Alloy

As a lightest structural metal, magnesium and its alloys have been widely used in the fields of auto-motive industry, aerospace, electronics, telecommunication, computer manufacturing for their outstanding physical and mechanical properties, such as good vibration, shock adsorption and high damping capacity. Besides, the specific density and Young’s modulus are close to human body’s bone makes it quite suitable for using as bone repairing materials. Moreover, Mg2+ is an essential element to human metabolism and was reported to stimulate the growth of new bone tissue. Compared with other applicable implantable metals such as stainless steels, titanium and its alloys, tantalum, cobalt-chromium-based alloys, the magnesium alloys are able to degrade relatively safely within the body. The limitations of these metallic implants involve a possible release of toxic ions and/or particles through corrosion or wear processes. Furthermore, being xenogenic, all metals evoke a physiological response that results in formation of a fibrous capsule, thus isolating the implants from the body. However, the applications of magnesium alloys are limited by their poor corrosion resistance, especially in the environment of body fluid and blood plasma. How to improve the corrosion resistance of magnesium alloys in the body fluid environment is an essential research topic. Among the present researches, the improvements of modification on magnesium alloy were investigated. In this article, we used the dip-coating, hydrothermal method, anodic treatment, and pre-corrosion method to prepare a series of novel functional composite coatings on magnesium alloys.Firstly, we prepared a novel functional MgO/PCL/ZnO composite coating on magnesium for enhancing the bioactivity and biocompatibility of the implant by using anodic treatment and dip-coating technique. The adhesion tests suggested that the adhesion strength between the coating and magnesium were strong enough to protect the magnesium after anodic treatment. SEM images showed that the composite coatings were with low porosity and the ZnO powders dispersed in PCL uniformly. Besides, immersion tests in vitro for corrosion were conducted from the viewpoint of electrochemical polarization. The results of corrosion tests demonstrated that the composite coating had good corrosion resistance and zinc ion was released in SBF after immersion.Then a novel and functional hyperbranched polyphenylene sulfide/poly(ε-caprolactone)/ZnO composite coating (HPPS/PCL/ZnO) was prepared on magnesium alloy by using dip-coating method in methenyl trichloride containing coating solution on the basis of the previous research. The surface of the coated sample was with lower porosity and high uniformity. The electrochemical tests and immersion tests suggested that the corrosion resistance of the sample coated HPPS/PCL/ZnO composite coating was higher than that of the PCL coated alloy. After 20 days’immersion in SBF, the sample coated composite coating was still smooth and hardly changed. Therefore, the HPPS/PCL/ZnO composite coating can protect the magnesium more efficiently.After that, we prepared the hydroxyapatite/pefloxacin mesylate composite coating (HA/PFLX) on magnesium using hydrothermal method and impregnation method. Hydroxyapatite (HA) is a bioactive coating that widely applied to improve the bone response in dental and orthopedic implants. In vivo hydroxyapatite forms strong chemical bonds with bone, because its chemical composition is similar to the apatite of the nature bone. HA coating of implant materials improves the corrosion resistance by forming a barrier against the dissolution of metal ions from the magnesium substrate at the same time as promoting its bone bonding ability. Pefloxacin (PFLX) is an antibiotic fluoroquinolone group drug with a broad spectrum of activity against bacteria. Pefloxacin is also used as corrosion inhibitor for metal materials in the corrosive medium. The electrochemical polarization tests demonstrated that the composite coating had good corrosion resistance for magnesium in SBF. The SEM micrograph of HA coating showed that the surface of sample were globular structures which were structed by lamellar hydroxylapatite. After immersed in PFLX solution, the micrograph of HA coated magnesium showed that the holes formed by gas escaping in the reaction process became less and more unconspicuous. After all, the HA/PFLX could improve the corrosion resistance of magnesium and also could release PFLX against bacteria.