Thyme oil and its monoterpenoids as potential antimicrobial compounds of sodium alginate/(hyaluronic acid) coatings for protection of steel bone implants

• Approach was used to decrease the EtOH content in the dispersed system for EPD. • Coatings adhesion strength dependent on the chemical composition of the system. • Mechanisms of interactions of the EO components and polymers were proposed. • Coatings significantly improved the corrosion resistance of the steel substrates. • Coatings with thymol showed excellent antibacterial and antibiofilm properties. Novel antibacterial sodium alginate coatings incorporated with thyme oil and their monoterpenoids (carvacrol, thymol) were obtained in one-step and two-step electrophoretic deposition (EPD) processes on stainless steel substrates. An ecological and economical approach using a larger amount of distilled water instead of ethyl alcohol and the addition of hyaluronic acid in the oil–water emulsion utilized for EPD, while maintaining the high adhesion of obtained coatings to the etched substrate, was developed. The highest adhesion strength revealed coatings deposited in two-steps using a sodium alginate base layer and then a layer rich with a bactericide agent and/or hyaluronic acid. Coatings contained oil drops well distributed in the polymers. The study outlines possible interaction pathways between polymer chains and phytochemicals derived from thyme. The surfaces of the coatings were hydrophilic and their roughness was several times higher than that of the steel substrates. The coated samples demonstrated an improvement in the corrosion resistance of the substrates in Hanks’ solution. All tested coated samples exhibited antimicrobial activity and antibiofilm properties. The potential cytotoxicity of the surfaces was confirmed. The developed coatings are promising for protecting temporary steel bone implants against bacterial biofilm formation.