Applying Baghdadite/PCL/Chitosan Nanocomposite Coating on AZ91 Magnesium Alloy to Improve Corrosion Behavior, Bioactivity, and Biodegradability

Abstract

Magnesium alloys have received a great amount of attention regarding being used in biomedical applications; however, they show high degradability, poor bioactivity, and biocompatibility. To improve these properties, surface modification and various types of coatings have been applied. In this study, an anodized AZ91 alloy was coated with a polymer matrix composite made of polycaprolactone/chitosan (PCL/Ch) with different percentages of baghdadite to improve its resistance to corrosion, bioactivity, and biocompatibility. The effects of different percentages of baghdadite (0 wt %, 1 wt %, 3 wt %, and 5 wt %) on the surface microstructure, corrosion resistance, roughness, and wettability were evaluated. The results indicated that the applied nano-polymer-ceramic coating including 3 wt % baghdadite was hydrophobic, which consequently increased the corrosion resistance and decreased the corrosion current density of the anodized AZ91 alloy. Coating with 3 wt % baghdadite increased the roughness of AZ91 from 0.329 ± 0.02 to 7.026 ± 0.31 μm. After applying the polymer-ceramic coating on the surface of anodized AZ91, the corrosion products changed into calcium–phosphate compounds instead of Mg(OH)2, which is more stable in a physiological environment.

Bioactivity Behavior Evaluation of PCL-Chitosan-Nanobaghdadite Coating on AZ91 Magnesium Alloy in Simulated Body Fluid

“…By applying the polymer-ceramic coating, the corrosion rate further decreased, the amount of magnesium on the surface decreased, and a peak resulting from phosphorus appeared (Figure 2f), indicating the deposition of phosphate groups on the surface. The SEM images of the surfaces of modified and unmodified samples coated with different composites were shown in our previous study [28]. The MgO layer and forsterite particles on the surface of AZ91 alloy play a protective role, improving the bioactivity of alloy, and can act as an intermediate layer for better adhesion of the coating to the substrate.…”

“…The MgO layer and forsterite particles on the surface of AZ91 alloy play a protective role, improving the bioactivity of alloy, and can act as an intermediate layer for better adhesion of the coating to the substrate. As shown in [28], a smooth and uniform layer on the surface of MAO was observed as a result of applying the PCL/chitosan polymer coating. An increase in the roughness of the specimens was observed as a result of adding different amounts of baghdadite powder.…”

“…The average wettability angle was reported, using ImageJ software (version 1.52q). In order to examine the surface roughness before and after coating, a Mitutoyo roughness meter (Model: SJ-210, Grainger, Chicago, IL, USA) was used, and the mean surface roughness (Ra) was reported [19,28]. Figure 1a shows the TEM image of the produced baghdadite nanoparticles.…”

“…Therefore, in many applications, a combination of these materials is needed to improve and adjust the properties of the final product. Based on our previous study [28], applying this polymer-ceramic composite coating on AZ91 alloy can be an effective method to control the degradation and bioactivity of the magnesium alloys for tissue-engineering applications. Moreover, it was found that the formation of a dense composite coating on the surface improved corrosion resistance and decreased corrosion rate of AZ91 substrate.…”

Recent progress in materials used towards corrosion protection of Mg and its alloys

“…The results demonstrated that the nanocomposite coating was able to act as an excellent passivation layer to prevention diffusion and corrosion so that the corrosion current decreased significantly and the charge transfer resistance increased noticeably. Soleymani et al [150] incorporated different amounts of baghdadite mineral to polycaprolactone (PCL)/chitosan (Ch) for improving the resistance to corrosion, biocompatibility, as well as bioactivity of the anodized AZ91 alloy. According to the results, the nanocomposite coating containing 3 wt % baghdadite showed hydrophobic behavior that led to decreasing the corrosion current density for the magnesium alloy and the enhancement of its corrosion resistance.…”