Effect of tea tree oil addition on the microstructure, structure and selected properties of chitosan-based coatings electrophoretically deposited on zirconium alloy substrates

In this work, Tea Tree Oil (TTO)/chitosan coatings of different TTO concentrations were electrophoretically deposited (EPD) on Zr-2.5Nb alloy substrates. The properties of solutions and EPD kinetics of TTO/chitosan coatings and pure chitosan coatings used as a reference material were analysed. The incorporation of TTO into chitosan solutions changed their zeta potential and conductivity, as well as influencing the EPD kinetics. The microstructure of the coatings consisted of TTO droplets embedded into the chitosan matrix. The addition of TTO resulted in the formation of new hydrogen bonds between chitosan and the TTO main components. Both pure chitosan and TTO/chitosan coatings deposited from solutions containing up to 10 mL/L TTO had excellent adhesion to the rough substrates. The mechanical interlocking was indicated as the main adhesion mechanism of coatings. However, chemical bonding was not excluded. The coatings exhibited a hydrophobic character and showed about 50% lower SFE with a very low value of the polar component compared to substrates. The ob-tained results on EPD and the characterisation of microstructure, structure and selected properties show that chitosan coatings containing TTO are promising as antimicrobial coatings for metallic biomaterial substrates. However, the antimicrobial properties and cytotoxicity of coatings should be further investigated.