| Biomaterials not only have important social effect in bettering the living quality of human beings, improving their health and saving their lives, but also become a new growth point in economic and scientific-technological areas. The potential worth of magnesium in biomaterials field has caused great interests of research, for its excellent biocompatiblity and similar mechnical properties to bone. Moreover, magnesium-based materials can become novel degradable biomaterials making use of its corrodibility.In this paper, the corrosion degradation process and mechanism of 4N-Mg and Mg-Ca alloys in SBF were studied. In order to improve the corrosion behavior and biological activity of Mg-based materials, surface modification of self-assembled monolayers (SAM) using of stearic acid was studied, meanwhile the mechanism of SAM and the corrosion behavior of samples were studied. To evaluate the biocompatibility and behavior of bone healing of Mg-based materials, the biocompatibility tests in vitro such as hemolysis ratio, cytotoxicity, and systemic acute toxicity and in vivo test were taken.Methods:①Simulated body fluid (SBF) which closed to inorganic composition of human plasma was used to immerse casting 4N-Mg alloy which contains 99.99 % magnesium and casting Mg-Ca alloys. Electronic balance, Scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) and digital electronic pH meter and atomic absorption spectrometry were used to analysis the corrosion process, corrosion rate and mechanism.②Modification treatment was carried out for 4N-Mg and Mg-0.88Ca alloy by stearic acid alcohol solution SAM. Firstly, pre-treatment method, concentration of stearic acid, the time immersing in stearic acid solution were determined by orthogonal test. Secondly, high concentration and short time immersing method was compared with traditional low concentration and long time immersing one, and corrosion resistant property was also compared for the samples being SAM modified and by supersonic cleaned. 4N-Mg and Mg-0.88Ca alloy was modified by SAM method and the corrosion process of samples were studied.③According to ISO 10993.4 standard to test the rate of hemolysis of 4N-Mg and Mg-0.88Ca alloy with and without modified by SAM, and the relationship between pH value and concentration of Mg2+ ion with hemolysis were analysis..④L929 fibroblast and Osteoblast cell were employed to co-cultrue with the extracts of 4N-Mg and Mg-0.88Ca alloy, and MTT cytotoxicity tests were done and the concentration of Mg2+ ion is measured. Cytotoxicity of Mg-based materials was further evaluated by direct contact method, 4N-Mg and Mg-0.88Ca alloy SAM modified before and after were cultured with Osteoblast cell, and the effects of material on reproduction and activity of cell were discussed.⑤Acute toxicity test was done by extracts of 4N-Mg with and without SAM modified. The experiment was carried out on mice, and they were injected into the abdominal cavity. Symptom, moving state and weight change of mouse were observed and recorded within 7 days after injection.⑥In vivo test was carried on white rabbit's, and the 4N-Mg and Mg-0.88Ca alloy with and without SAM modified were embedded in thigh bone. Examination by X ray method and the concerntration of Mg2+ ion in blood were done after 2, 6, and 12 weeks, respectively. The specimens were analyzed by SEM and EDS, and tissue slices were observed by optical microscope.Conclusions:①Research on untreated 4N-Mg and Mg-Ca alloy1) 4N-Mg alloy had better corrosion resistance property than Mg-Ca alloy. And Mg-0.88Ca has the lowest corrosion speed among Mg-0.88Ca, Mg-1.42Ca and Mg-2.0Ca. The form of crrosion mainly exhibited the corrosion pit and the crack.2) Though the analyse of the E-pH chart, only when the pH is higher than 11.38 the magnesium come into the passive region.The anion such as HCO3-,HPO42- in the SBF also could induce the corrosion of magnesium.3) The rate of hemolysis of 4N-Mg and Mg-0.88Ca alloy was not qualified, and cytotoxicity of 4N-Mg and Mg-0.88Ca alloy meet the demand of biomaterial.②The SAM which formed on 4N-Mg and Mg-0.88Ca in the 0.5 mol/L ethanol slution of stearic acid after soaked 1.5h had the best effect to the behavior of anti-corrosion to the samples. The SAM which formed in the higher concentration of stearic acid slution after little soaking time excelled in the one which formed in the lower concentration of stearic acid slution after long soaking time, and showed better bioactivity. The hemolysis and cytotoxicity of those samples treated by SAM were qulified,and had not iduced acute toxicity. ③In my test, the extract which pH under 10.61 and concentration of Mg2+ ion not exceed 42 mg/L, the hemolysis rate was qualified, and the exacts while the concentration of Mg2+ ion equal to 202.5mg/L met the cytotoxicity requirement, while no more than 156.2mg/L promoted the cell proliferation.④In vivo study, the magnesium concentration in blood of two groups of animal subjects were in the normal scale, Mg-based materials have good bone inducement and showed better capabilty of contact with bone. The new bone mineralizes obviously on the interface. And on the new bone, the osteoclast cells array orderly. Untreated magnesium corroded faster than SAM treated magnesium-based materials. All results indicated that Mg-based materials showed better biocompobility and the capacity of inducing new bone, proved that SAM had an effect on controlling corrsion rate of Mg-based materials.
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