| Magnesium and its alloys have great advantages and potential in the field of biomaterials due to their good biocompatibility,biodegradability and excellent mechanical properties.However,the degradation rate of magnesium alloys in the human environment containing chloride ions is too fast.In view of this problem,surface modification is currently considered as one of the most effective methods to control corrosion or degradation of magnesium alloys,and it also plays an important role in improving biological activity and biocompatibility of materials.In this work,a Ca-Mg-P composite coating was prepared on AZ31 magnesium alloy substrate via hydrothermal method.The effects of hydrothermal temperature,hydrothermal time,pH value of solution and the amount of doped zinc in the reactant on the coating composition,morphology,bonding strength and electrochemical properties were studied by scanning electron microscope（SEM）,X-ray diffraction（XRD）,adhesion test and electrochemical test,and the long-term corrosion resistance and biological activity in vitro were studied though immersion test in simulated body fluid（SBF）and in vitro cell culture experiments.The experimental results showed that when the hydrothermal temperature was140°C,the hydrothermal time was 3 h,the pH value of solution was 5.5,the Zn/Ca molar ratio was 10%,the compact coating without cracks could be prepared,which consisted of a Mg（OH）2 bottom layer and aβ-TCMP upper layer with the spherical aggregated structure.The bonding strength between the composite coating and the magnesium alloy substrate was higher than 20.88±1.60 MPa,which met the requirement specified for biomedical applications in ISO 13779-2.Electrochemical testing results showed that the impedance value of the coating sample was 1197.003kΩ.cm2,which was about 2000 times that of the naked magnesium,and the corrosion current density was 0.043μA/cm2,which was about 0.001 times that of the naked magnesium,proving its excellent corrosion resistance.The results of immersion experiment indicated that the pH value of SBF solution remained within the range of7.40-7.75 during 28-day immersion,and the corrosion rate was only 0.946±0.200mg/（cm2·d）after immersion for 28 d,which confirmed the good long-term corrosion resistance.Glue-like depositions were observed on the surface of the coating after3-day immersion,meanwhile,with the immersion time prolonged to 28 d,the structure of the coating remained intact without cracks and the calcium and phosphorus ratio of the deposition was 1.44,confirming a better effect of inducing depositions.In vitro cell culture experiment used the MC3T3-E1 osteoblast line and results showed that compared with the naked magnesium,the coated samples showed significant statistical differences,and the cell proliferation rate was always at a higher level in the process of the 7-day cultivation with no significant cytotoxicity,demonstrating the good bioactivity and biocompatibility. |
PDF Full Text Request