| The density, elastic modulus of magnesium is similar to human bones. The most important thing is that magnesium has excellent compatibility with the human body, the dissolved magnesium ion is one of essential element of human body. The early clinical application confirmed the truth of the biocompatibility of magnesium as well as the possibility of biomedical materials use. Magnesium can degrade in human body gradually by form soluble, non-toxic oxide. These oxides will be absorb by human body and then excreted as urine through the body's metabolic balance system.Therefore, magnesium alloy is a potential human implant. Usually, the corrosion behavior of target biological materials should be researched in simulated body fluid SBF before the clinical experiments. The degradable behavior of a patented magnesium alloy–Mg-Nd-Zn-Zr (refer to JDBM) was studied by comparing with that of pure magnesium and AZ91D alloy in SBF in the present research. By metallographic observation,corrosion weight loss test,PH value analysis, X ray diffraction analysis, hydrogen evolution rate test,scanning electron microscopy morphology analysis,electrochemical measurements, the corrosion behavior of magnesium and magnesium-based alloy in SBF were studied.At the same time,the cell toxicity and hemolysis tests were carried to research the biological properties of the samples. Experimental results were summariged as the follows:In solution state, the average corrosion rate of JDBM in the Hank's simulated body fluid could achieve 0.25mm/year, a little higher than that of pure Mg (0.20mm/year), much lower than that of AZ91D (2.64mm/year); The pH value variety of the SBF containing JDBM was much similar to AZ91D, changing form 7.4 to 8.6 in the initial 120 h, while the AZ91D reached 10.2 at last. Therefore, the implant of JDBM would not cause huge pH value change at the implant site; The main components of the corrosion products on the surface of these three kinds of magnesium alloys were Mg(OH)2 and a small amount of hydroxyapatite (Ca10(PO4)6(OH)2) and (Ca,Mg)3(PO4)2. The presence of hydroxyapatite could improve the biocompatibility and bone-binding capacity; Pure magnesium and JDBM corroded in the way of uniform corrosion, the degradation film had a structure of network, and there would re-generate a new layer of protective film in the film-off site, but the corrosion manner of AZ91D was proved to be pitting; impedance spectroscopy and potentiodynamic polarization curves have also demonstrated that the corrosion resistance ability of these three kinds of materials increased in order of AZ91D, JDBM and pure magnesium; The cell toxicity experiments showed that these three kinds of magnesium alloys had not cytotoxic (Р>0.05), JDBM had the lowest hemolysis, 55.2%, but still did not meet the requirement of standard GB/T16886.4-2003.In the extrusion state, the degradation rate was shown to be significantly reduced to 0.14mm/year by grain refinement produced by mechanical processing, much lower than that in solution state. Hydrogen evolution rate also decreased. The erosion surface was still smooth as the corrosion mode was still uniform corrosion.In the (MAO) state, there was a layer of protective porous ceramic coating on the surface of each sample. It was beneficial to bone cell attachment, bone tissue ingrowth on the surface morphology, improving biocompatibility of implant materials, realizing the combination of the advantages of metal and ceramic. In the simulated body fluid immersion test process, the hydrogen evolution rate of MAO treated specimen was almost zero. The impedance spectral data also showed that the corrosion resistance of materials has been greatly improved by MAO. |
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