Effect of Zn content on cytoactivity and bacteriostasis of micro-arc oxidation coatings on pure titanium

The aim of this study is to evaluate the effect of Zn content of micro-arc oxidation (MAO) coatings for titanium on the cytoactivity of osteoblast cells (MG63) which are responsible for human bone formation and on the bacteriostasis to Streptococcus mutans (S. mutans) which causes tooth plaque. According to Zn concentration in electrolytes, treated samples were divided into four groups: low-, medium-, high-, and no-Zn group as control. Surface morphology and chemical composition of the coatings were evaluated by scanning electron microscope (SEM), profilometer, and X-ray photoelectron spectroscopy (XPS). On the coating surface, the proliferation and ALP activity of MG63s and the bacteriostatic ability to S. mutans were assayed. The results showed that pore size and surface roughness of the coatings increased with the increased Zn incorporation. XPS analysis revealed that Zn content in low-, medium- and high-Zn coatings were 0.199 at.%, 0.574 at.%, and 1.995 at.%, respectively. The MG63s cultured on low-Zn coating exhibited the best activity of proliferation and differentiation, followed by medium-Zn and control group, while the cytoactivity of osteoblast cells on high-Zn coating was inhibited. Among the four coatings, the high-Zn one showed the best bacteriostasis to S. mutans. The cytoactivity of MG63s was promoted as the Zn content of the coatings decreased, whereas the bacteriostasis was enhanced as the Zn content increased. It indicated that an environment with relatively low Zn content might be beneficial to the proliferation of osteoblast cells; on the contrary, the one with higher Zn content might be much effective in bacteriostatic property to S. mutans. From this study, the Zn content range of the MAO coating, from 0.199 at.% to 0.574 at.%, may be beneficial to balance both the cytoactivity of osteoblast cells and the bacteriostasis to S. mutans.

► The cytoactivity of zinc on MG63 cells enhanced as the zinc content decreased.
► The bacteriostasis of zinc to S. mutans was dose-dependently increased.
► Relatively lower zinc content exhibited both cytoactivity and bacteriostasis.
► The effective range of zinc content should be relatively narrow.