| Magnesium is a kind of light metal, its density is only1.7g/cm3,its specific strengthand stiffness is superior to steel and aluminum. The modulus of elasticity, yield strengthand fracture toughness of magnesium alloy is close to human bone tissue compared withthe traditional medical implant materials of stainless steel and titanium alloys, so it canavoid stress shielding effect. Studies have shown that human bone tissue has magnesiumions, so magnesium is not only play an important role in metabolism but also promotethe growth of new bone tissue. When traditional metallic implant materials implanted invivo, it is possible to release toxic metal ions or particles in wear or corrosion processthat can lead to inflammation and tissue damage and resulting in lower materialbiocompatibility. When the fracture healed, magnesium alloy can be completelydegraded in vivo, reducing the risk of the patient’s medical and health care costs.However, magnesium alloys is corroded quickly in physiological environment,resulting in implant materials destructed before fracture healing, and the hydrogenproduced in the corrosion process, that will lead to the accumulation of human skinbubbles and block some fluids and tissues contact, influencing wound healing. In thispaper, in order to improve the corrosion resistance of magnesium alloy, we use tanninsand phytic acid which extracted from natural plant as the main film-forming agent,preparation conversion of tannins and phytic acid on the AZ60magnesium alloys. Todetermine the optimum parameters for preparing conversion coatings, we useelectrochemical test methods and SEM. The components of conversion coatings andforming process are used by EDS, XPS and FTIR testing methods. The biologicalproperties of conversion coatings are used by immersion test and biological properties invitro test.1. The optimum process parameters of tannic acid conversion coating: pH value of3.5, time is10min and temperature of20℃. The optimum process parameters of phytic acid conversion coating: pH value of4, time is20min, temperature of20℃and phyticacid concentration of5g/L.2. XRD, EDS and FTIR analysis showed that the composition of tannic acidconversion coating is tannins–magnesium complexes as well as a small amount of MgF2,the composition of phytic acid conversion coating is phytic acid magnesium, MgO, Mg(OH)2and a small amount of Al2O3.3. Electrochemical tests in simulated body fluid showed that the corrosion currentdensity and corrosion potential of tannins conversion coating and phytic acid conversioncoatings were far superior to AZ60magnesium alloy, enhance the corrosion currentdensities are two orders of magnitude and three orders of magnitude, the film resistorsare33times and48times of the substrate.4. Immersion test results show that the two conversion coating immersed in SBF for7days, the surface only in localized corrosion, corrosion position covered by a layer richin Ca, P and other elements of the corrosion products. Hydrogen evolution test and pHtest show that the two conversion coating can effectively control the rate of hydrogenevolution of the samples in simulated body fluid, slow the rate of change of pH value andnarrow the range of pH changes.5. Biological properties in vitro test results show that the cytotoxicity grade oftannic acid conversion coating is two with a slight cytotoxicity, the cytotoxicity grade ofphytic acid conversion coating is one with no cytotoxicity. There is no significantdifference between the cells grown on the phytic acid conversion coating with thenegative control group. The morphology of the cells grown on the tannic acid conversioncoating is not well. |
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