Tackling the challenges facing the clinical applications of pure PEO hydroxyapatite layers: Co-deposition of YSZ nanoparticles

This contribution endeavored to enhance the overall characteristics of hydroxyapatite-Yttria-stabilized ZrO2 (HAp-YSZ) composite coating deposited on the Ti6Al4V metallic implant using a plasma electrolyte oxidation (PEO) technique. The influence of the YSZ nanoparticles concentration, in the range of 0-5 g/L, in the electrolyte on the final performance of the deposits is treated. While the increased concentration of the nanoparticles had no marked effect on the phase composition, a denser and more compact layer is obtained when 3 g/L YSZ is loaded. An increase of 42.8% in microhardness and 42% in bonding strength is obtained for composite coating compared to the HAp one. The corrosion behavior of the samples was studied by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization assays. Results showed a 67% decrease in corrosion current density with the included nanoparticles. The in vitro bioactivity of the coated implants was examined after 7 days of immersion in simulated body fluid (SBF). All of the PEO coatings stimulated the apatite growth irrespective of the nanoparticles' concentration. In view of a possible application in tissue engineering, in vitro biocompatibility tests, using SAOS-2 cell line, were carried out. The obtained results show the positive influence of the added YSZ nanoparticles on the cell viability and proliferation. The antibacterial activity of the coatings against Escherichia coli pathogenic bacteria was addressed. The higher the nanoparticle loading, the larger the inhibition zone is observed. The developed metallic-ceramic hybrid system is believed to open numerous possibilities in efficient corrosion-resistant, anti-bacterial, and bioactive dental implants.