Magnesium Fund Belongs To Compound Preparation Of Biological Materials And Its Performance Study

Magnesium and its alloys are attracting more and more attentions as implant materials for its relative close mechanical properties to natural bone and good biocompatibility. Unfortunately, magnesium alloys degrade too fast due to the positive activities in chemistry, which may cause the implantation failed. Therefore, the study on decreasing the corrosion rate of Mg alloys and Mg-based composites through adjusting the components and structure of the materials and/or adopting new fabrication technology and surface modification becomes a hotspot.In this study three kinds of Mg-based metal matrix composites (MgO/Mg, MgO/Mg-Zn/Mg and MgO/Mg-Zn/HA/Mg) were prepared by powder metallurgy, wherein, pure magnesium, a macro-element of human body, was used as matrix and MgO powder or20.21wt%ZnO or a powder mixture of20.21wt%ZnO and10wt%HA as the addition. MgO coating and MgO/PLA complex coating were fabricated on MgO/Mg-Zn/Mg composite surface, respectively, by using Anodic Oxidation and combined Anodic Oxidation and dip coating of PLA process.The mechanical properties of the composites, i.e. the tensile strength and hardness of the composite were tested. The corrosion properties of the composites with and without coatings were studied in simulated body fluid (SBF) by immersion test (weight loss test and pH value measurement) and electrochemical measurements including potentiodynamic polarization and electrochemical impedance spectra (EIS). The phases and the morphology of the polished, corrosion product and the coating of the specimens were analyzed by means of X-ray diffraction (XRD) and Scanning electron microscope (SEM) equipped with EDX, respectively. The results are summarized as follows:1) MgO/Mg composite materials containing5wt%,10wt%and20wt%MgO as reinforcement phase were fabricated by powder metallurgy. The results of SEM of these four composites show that MgO phases evenly distribute in Mg matrix. The results of immersion tests and electrochemical measurement in SBF show that MgO/Mg composite materials have similar corrosion mechanism as pure Mg metal and the distribution of MgO in Mg matrix plays an important role in the improvement of corrosion resistance of composite materials. The corrosion resistance increases with the increase of MgO addition. The MgO/Mg composite material with20wt%MgO exhibits the best enhanced corrosion resistance. However, the mechanical properties of MgO/Mg composite deteriorate with the increase in the amount of MgO.2) MgO/Mg-Zn/Mg composite and MgO/Mg-Zn/HA/Mg composite reinforced with MgO ceramics and Mg-Zn intermetallics and with MgO ceramics, Mg-Zn intermetallics and HA ceramics, respectively, were fabricated using pure magnesium powder and20.2wt%ZnO powder by powder metallurgy. The results of XRD and SEM indicate that compound of MgO and Mg-Zn or compound of MgO, Mg-Zn and HA uniformly and consecutively dispersed in Mg matrix. The results of immersion tests and electrochemical measurements in SBF are consistent, indicating that the corrosion mechanism of the composite is the same as that of pure Mg, and compared with pure Mg, the uniformly and consecutively distributed compound in Mg matrix, together with the addition of Zn element greatly contribute to the improvement of corrosion resistance and mechanical properties of the composite. Meanwhile, mechanical properties of the composites were close to those of natural bone. The research also indicates that the existence of HA in matrix was helpful to the enhancement of mechanical properties while do little to corrosion resistance.3) The as-grown Mg(OH)2coating on the surface of MgO/Mg-Zn/Mg composite was deposited under four anodic voltages. The results show that the coating deposited at0.2V was the most compact, whereas its thickness can hardly increase. After heat-treated under450℃, the compact coating was converted to multi-cracked MgO. Complex coating of MgO and PLA on composite surface was prepared by dipping the composite substrate with MgO coating into PLA solution. The PLA not only functions as a sealant, but also as a new PLA macromolecule cover on the surface of MgO. The electrochemical measurement results of composite with MgO coating and MgO+PLA complex-coating disclose that porous MgO coating can slightly protect the substrate while the complex-coating could significantly improve the corrosion resistant of the composite.