Grafting of the peppermint essential oil to a chemically treated Ti6Al4V alloy to counteract the bacterial adhesion

Essential oils are effective as alternative biocide molecules, but they are currently not used against bacterial contamination of surfaces for biomedical, industrial or everyday life applications. In this work, the grafting of peppermint oil to a chemically-treated titanium alloy is explored as a coating or through functionalization (soaking in an ethanol solution of the oil); a procedure for a proper characterization of this type of materials is here suggested. A homogeneous and continuous coating is obtained by polymerization of the oil on the titanium surface, as shown by fluorescence observation. It contains a prevalence of oxygenated compounds (gas-chromatographic, XPS and FTIR analysis), has a hydrophobic behavior (contact angle test and zeta potential titration) and shows strong adhesion to the substrate (tape test). On the functionalized samples, the presence of non-oxygenated grafted compounds was detected (gas-chromatographic, XPS analysis) without the formation of a coating (fluorescent observation). The characteristics of the substrate combined to the selected functionalization procedure are selective towards grafting of specific compounds even if they are minority fractions in the source peppermint oil. The coating has a bacteriostatic effect on adherent bacteria, which is lower on the functionalized samples.