Enhanced antibacterial efficacies, corrosion resistance, and cytocompatibility of ZnO/CuO composite coatings through designed sputtering orders

To obtain an overall enhancement on corrosion resistance, antimicrobial efficacies, and cytocompatibility of titanium-based implants, the multifunctional coatings in the forms of mono, double, and co-existence based on CuO and ZnO were innovatively designed by regulating the sputtering orders under magnetron sputtering. The results showed that ZnO and CuO were pure phases, CuO grains performed large and unevenly while ZnO grains were fine and homogeneous, such grains morphology features remerged on double-layered coatings. The surface roughness (Rq) of the monolayer to the double layer and then to the co-existing one was increased from 2.58 nm to 18 nm to 22.6 nm. All multifunctional coatings helped to lower the contact angle to a minimum of 18.82°, and enhanced the corrosion potential to a maximum of −0.261 V. The released ions, grains piercing, and ROS produced by p-n junctions co-played the bactericidal roles, which equipped ZnO/CuO composite coatings with bactericidal rates of 90.24%∼100% as directly contact with the target germs in 0.5 h. Owing to the strong metal–oxygen bonding and rough surface, all coatings supported the cell viabilities of 137.92%∼145.27% through 120 h co-culturing, MC3T3-E1 cells healthily proliferated and adhered on the surface. The double-layered coating, with ZnO as the bottom layer and CuO as the upper layer, exhibited better overall properties.