Novel chitosan-based coatings containing citronella essential oil (CEO) or citronellol additives were electrophoretically deposited on titanium substrates. The chemical composition and properties of the dispersed systems used for the deposition and process parameters to obtain robust coatings were determined. The increase in oil concentration in the dispersed systems had a negative impact on the adhesion strength of the coatings. The microstructure of the coatings consisted of droplets of CEO or citronellol distributed within and on the surface of the continuous chitosan matrix. The size of the droplets increased with an increase in the concentration of oil in the dispersed systems. Interestingly, the addition of CEO and citronellol to the chitosan matrix resulted in the formation of new hydrogen bonds between the components and the chitosan matrix. The mechanisms responsible for structural changes were identified. The coatings revealed moderate roughness of the surface. The coatings containing CEO exhibited slightly hydrophobic properties. Coatings containing citronellol were hydrophilic but with contact angles close to 90 deg. The coated titanium had weak bactericidal properties against S. aureus bacteria. The surfaces tested compared to the control did not show a significant cytotoxic effect. The coatings are interesting for further development of titanium surfaces with antimicrobial performance. Graphical abstract

The work provides novel insight into the development of advanced antibacterial surfaces using the combination of essential oils, cinnamon oil, thyme oil, and tea tree oil, as well as their active compounds, including cinnamaldehyde, thymol, and terpinene-4-ol, embedded in the chitosan and sodium alginate matrix. All coatings obtained in a two-stage electrophoretic deposition process on stainless steel and titanium substrates were characterized by high adhesion strength. The microstructural differences between the coatings were mainly related to the size and location of the additives. Structural investigation showed the impact of individual oil components on intermolecular bonds between polysaccharide chains and the formation of molecular interactions in a specific spatial conformation. The surface of all coatings was minimally rough and had a hydrophilic character. A clear matrix-dependent trade-off between antibacterial efficacy and cytocompatibility was observed: alginate-based coatings achieved strong anti-Staphylococcus aureus activity (2.81 log CFU/mL) at the expense of increased cytotoxicity, while chitosan-based systems provided a more favorable cytocompatibility profile, maintaining cell viability above 70% for selected formulations. This work provides insight into the development of natural antibacterial surfaces by the combination of active compounds and shows the distinctions on many levels between the coatings with various polysaccharide matrices.

Novel chitosan coatings incorporating antibacterial additives, including essential oils (cinnamon bark, cinnamon leaf, and thyme) or their constituents (cinnamaldehyde, eugenol, thymol, and carvacrol), were electrophoretically deposited on titanium. The electrokinetic characteristics of the emulsions and deposition parameters were determined. The increase in additive concentration (from 2 to 10 mL/L) in the emulsion resulted in poor adhesion of the coatings to the substrate (0B according to the ASTM D3359-23 standard). The coatings contained droplets of additives scattered relatively homogeneously in the chitosan matrix. The amount and dimension of the droplets were affected by the content of the additive in the emulsion. It was found that all of the additives had an impact on chitosan, as they formed new intermolecular hydrogen bonds. The roughness and wettability of the coatings were significantly affected by the concentration of additives in the dispersed systems. In most cases, increasing the concentration of additives led to lowering the wettability of coatings and increasing their roughness. Electrochemical studies confirmed that all of the investigated coatings improved resistance to corrosion compared to that of the bare titanium substrate. The coatings had different bactericidal factors with respect to the additive used. Mostly, they acted actively against Staphylococcus aureus compared to Escherichia coli bacteria. The microbicidal activity of the coatings was strongly related to the time of incubation of the bacteria strains. Of all additives, cinnamon bark oil and (cinnamaldehyde) acted the strongest against both pathogens. All coatings had a high cytotoxicity factor against both the MG-63 and FaDu cell lines. Nevertheless, they are very promising for applications that require a high antimicrobial performance.