Yun Zhao

An in situ Mg-Al hydrotalcite (LDH) film was prepared using a one-step hydrothermal method on the surface of a medical magnesium alloy. The importance and influence of the reaction parameters on the corrosion resistance of the LDH coatings were optimized and investigated through an orthogonal array and range analysis. The reaction parameters included the temperature, reaction time, pH, and concentration of the aluminum source. The relationship between the parameters and corrosion resistance performance of each coating was compared with the chemical composition, electrochemical corrosion current, and hydrogen evolution rate. Suitable reaction parameters were obtained. The morphology, element distribution, adhesion strength, and electrochemical properties of the preferred coatings were further analyzed and evaluated to optimize the treatment process. The results showed that temperature had the most significant impact on the quality of the LDH coating; a suitably high temperature, a longer reaction time, a higher aluminum source concentration, and a high pH were conducive to forming high-quality LDH coatings. There was an inverse relationship between the corrosion resistance and the LDH-to-Mg(OH)₂ content ratio of the coatings. The optimal reaction parameters for this Mg-Al LDH coating on the substrate were 130 °C for 8 h at a pH of 13 using a 10 mM Al³⁺ solution.

In this study, the 10B21 steel was treated by micro-arc oxidation (MAO) in the electrolyte consisting of aluminate and phosphate to enhance its corrosion resistance. The effect of negative voltage on corrosion resistance of the MAO coating obtained has mainly been analyzed through their phase composition, microstructure, interfacial bonding strength, salt spray and electrochemical testing. The result indicates that with negative voltages applied to the MAO coating, Fe-Al transition layers arise between coating layer and matrix. Furthermore, different negative voltages bring forward different α-Al₂O₃ contents contained in the MAO coatings and when it reaches −100 V, the amount of α-Al₂O₃ appears as the largest. The surface porosity of the coating was also significantly decreased. In addition, the corrosion current density of the coating is only 3.64 μA·cm⁻², which is two orders of magnitude lower than that of the substrate. After 72 h of salt spray corrosion, it is found that the coating substrate is less corroded when the negative voltage of 100 V is applied. Therefore, −100 V has been proven as the optimum performance for improving the corrosion resistance of 10B21 steel.

As a metallic material with lightweight and high specific strength, magnesium alloy has excellent application prospects. However, the rapid corrosion rate and localized corrosion behavior of magnesium alloys limit the practical application in the automobile industry. In this study, to improve the corrosion resistance of AZ91 alloy, the film of different concentrations containing zirconium (AZR0, AZR5, AZR10, AZR15) was prepared on the surface of AZ91 alloy by micro-arc oxidation technology in the Na₂SiO₃-Na₃PO₄ system. Furthermore, the influence of electrolyte composition on the corrosion resistance of the MAO film was systematically investigated. The experimental results revealed that the ZrSiO₄ particles added in the electrolyte could enter into the MAO film and ZrSiO₄ particles were also decomposed into ZrO₂ and Mg₂Zr₅O₁₁ in the process of micro-arc oxidation. More importantly, the formation of micro-cracks and other defects in the film could be reduced after this process. The addition of 15 g l⁻¹ ZrSiO₄ in the electrolyte was contributed to the best comprehensive properties of MAO-processed AZ91 specimens, including improved Vickers hardness of 167.16 Hv, Young’s modulus of 652 MPa, and enhanced corrosion resistance (R_P = 9.82 × 10⁵ Ω cm²). This approach could provide the approach for developing Mg-based materials with high anticorrosion in industrial fields.

Biodegradable devices for medical applications should be with an appropriate degradation rate for satisfying the various requirements of bone healing. In this study, composite materials of polylactic acid (PLA)/stearic acid-modified magnesium oxide (MgO) with a 1 wt% were prepared through blending extrusion, and the effects of the MgO shapes on the composites’ properties in in vitro and in vivo degradation were investigated. The results showed that the long-term degradation behaviors of the composite samples depended significantly on the filler shape. The degradation of the composites is accelerated by the increase in the water uptake rate of the PLA matrix and the composite containing the MgO nanoparticles was influenced more severely by the enhanced hydrophilicity. Furthermore, the pH value of the phosphate buffer solution (PBS) was obviously regulated by the dissolution of MgO through the neutralization of the acidic product of the PLA degradation. In addition, the improvement of the in vivo degrading process of the composite illustrated that the PLA/MgO materials can effectively regulate the degradation of the PLA matrix as well as raise its bioactivity, indicating the composites for utilization as a biomedical material matching the different requirements for bone-related repair.

The present work focuses on the preparation of poly(l–lactide)–magnesium oxide whiskers (PLLA–MgO) composites by the in-situ polymerization method for bone repair and implant. PLLA–MgO composites were evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and solid-state ¹³C and ¹H nuclear magnetic resonance spectroscopy (NMR). It was found that the whiskers were uniformly dispersed in the PLLA matrix through the interfacial interaction bonding between PLLA and MgO; thereby, the MgO whisker was found to be well-distributed in the PLLA matrix, and biocomposites with excellent interface bonding were produced. Notably, the MgO whisker has an effect on the crystallization behavior and mechanical properties; moreover, the in vivo degradation of PLLA–MgO composites could also be adjusted by MgO. These results show that the whisker content of 0.5 wt % and 1.0 wt % exhibited a prominent nucleation effect for the PLLA matrix, and specifically 1.0 wt % MgO was found to benefit the enhanced mechanical properties greatly. In addition, the improvement of the degrading process of the composite illustrated that the MgO whisker can effectively regulate the degradation of the PLLA matrix as well as raise its bioactivity. Hence, these results demonstrated the promising application of PLLA–MgO composite to serve as a biomedical material for bone-related repair.

In this study, composite films of stearic acid–modified magnesium oxide whiskers (Sa–w-MgO)/poly-l-lactic acid (PLLA) were prepared through solution casting, and the in vitro degradation properties and cytocompatibility of the composites with different whisker contents were investigated. The results showed that the degradation behavior of the composite samples depended significantly on the whisker content, and the degradation rate increased with the addition of MgO content. Furthermore, the degradation of the composites with higher contents of whiskers was influenced more severely by the hydrophilicity and pH value, leading to more final weight loss, but the decomposition rate decreased gradually. Furthermore, the pH value of the phosphate buffer solution (PBS) was obviously regulated by the dissolution of MgO whiskers through neutralization of the acidic product of PLLA degradation. The cytocompatibility of the composites also increased remarkably, as determined from the cell viability results, and was higher than that of PLLA at the chosen whisker content. This was beneficial for the cell affinity of the material, as it notably led to an enhanced biocompatibility of the PLLA, in favor of promoting cell proliferation, which significantly improved its bioactivity, as well.

In order to make a rational design of magnesium alloys for bone repair, four kinds of Mg alloy ingots were prepared by vacuum induction furnace, namely Mg-3Zn-0.2Ca (wt.%) (ZX30), Mg-3Zn-0.8Zr (wt.%) (ZK30), Mg-3Zn-0.8Zr-0.3Sr (wt.%) (ZKJ300) and Mg-3Zn-0.8Zr-0.3Ca-0.3Ag (wt.%) (ZKXQ3000) alloys. The four ingots were extruded into bar materials through a hot-extrusion process under different temperatures with different extrusion ratios, the mechanical performances and the corrosion behaviors in the simulated body fluid (SBF) of the four alloys were investigated, and the mechanism of fracture and corrosion was characterized by scanning electron microscopy (SEM). The results showed the ultimate compressive strength (UCS) of all the alloys were found to be around 360 MPa, while ultimate tensile strengths (UTS) of ZKJ300 (334.61 ± 2.92 MPa) and ZKXQ3000 (337.56 ± 2.19 MPa) alloys were much higher than those of ZX30 (298.17 ± 0.93 MPa) and ZK30 (293.26 ± 2.71 MPa) alloys. The electrochemical noise and immersion tests in the SBF indicated that ZK30 alloy performed better in corrosion resistance.