In this study, the influence of various mechanical and chemical surface treatments on the adhesion strength and surface properties of sodium alginate coatings electrophoretically deposited (EPD) on 316L stainless steel substrates was investigated. XPS and TEM results revealed the presence of oxide layers containing elements from the substrates, with thicknesses varying from 1 to 45 nm, depending on the treatment used. Most substrates exhibited high roughness and hydrophilic properties (CA with water 62.8–82.6 deg). Sodium alginate coatings with uniform morphology were deposited with the same process parameters, i.e., 5 V and 300 s. The surface topography of the coatings was closely related to that of the substrate on which they were deposited. All coatings exhibited higher hydrophilicity (CA with water 29.5–49.7 deg) compared to the substrates (CA with water 62.8–82.6 deg). The coatings on the etched and anodized substrates demonstrated the highest adhesion strength (class 4B), attributed to the very low oxide layer thickness and the specific substrate surface topography. Mechanical interlocking was identified as the primary adhesion mechanism for these coatings. This work provides insight into optimizing surface treatments for improved adhesion of sodium alginate coatings to stainless steel substrates widely used for temporary bone implants. The results obtained will also be helpful in providing high adhesion of sodium alginate-based composite coatings to steel substrates.

A novel approach consisting of surface treatment of stainless steel substrates and a two-step electrophoretic deposition process was developed to enhance the adhesion strength of sodium alginate-based coatings. A series of different single-layer and double-layer coatings incorporated in leaf and bark cinnamon essential oils, or their main constituents, eugenol and cinnamaldehyde, were successfully deposited for the first time. The processing conditions, the chemical composition, and electrokinetic properties of the dispersed systems as well as the kinetics and mechanisms of deposition of single- and double-layer coatings were studied. The coatings obtained in a two-step process, including deposition of an intermediate sodium alginate layer and an outer oil-enriched layer, were found to exhibit the highest adhesion to the chemically treated and anodically oxidized substrates. The mechanisms of interactions between the molecules of the introduced additives and the polymer chains were proposed. The surface of the coatings exhibited high roughness and a hydrophilic character. The double-layer coatings with cinnamaldehyde had the highest bactericidal activity against S. aureus. The viability of the MG-63 and FaDu cell lines for coatings with essential oils was low. The results obtained will be useful for the further development of similar coatings to enhance the resistance to bacteria and reduce the cytotoxic response of stainless steel used for temporary bone implants.

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.

The growing global burden of antimicrobial resistance (AMR) highlights the urgency of identifying new therapeutic options or adjuvant agents capable of limiting microbial growth. This study aimed to evaluate the potential applicability of selected essential oils (EOs) as alternative antimicrobial agents by assessing their biocidal activity against clinically relevant microorganisms and determining their cytotoxicity toward human cell lines. Serial dilutions of the studied EOs were prepared to determine the minimum bactericidal (MBC), minimum fungicidal (MFC), and minimum biofilm eradication concentrations (MBEC) against Staphylococcus aureus ATCC^® 25923, Escherichia coli ATCC^® 25922, Candida albicans ATCC^® 90028, and Nakaseomyces glabratus ATCC^® 15545. Cytotoxicity towards cell lines was evaluated using the MTT assay. The tested EOs displayed significant biocidal effects against studied microorganisms in both planktonic and biofilm forms. Cinnamon bark oil and cinnamaldehyde showed the highest biocidal activity against S. aureus ATCC^® 25923, E. coli ATCC^® 25922, C. albicans ATCC^® 90028, and N. glabratus ATCC^® 15545, except for S. aureus in biofilm form. For thymol, yeast strains exhibited eight-fold lower susceptibility compared to bacterial strains. Cytotoxicity of the tested EOs towards the studied cell lines was significant. EOs proved to be effective against microorganisms but at the same time showed substantial cytotoxicity, thus potentially limiting their application. Further research on formulation strategies, selective delivery, and dose optimization is required to enhance their safety profile and clinical feasibility.