Antibacterial Properties and Molecular Biocompatibility of TiO2-ZnO Nanocomposite Coatings for Dental Implants
Objectives: This study aimed to test the antibacterial properties and biocompatibility of nano-zinc oxide coatings on dental implants with and without hydroxyapatite.
Methods: Nano-ZnO was grown on annealed TiO2 nanotubes on Ti-6Al-4V discs using a hydrothermal method in the presence of zinc nitrate and hexamethylenetetramine. Nano- HA was then grown on the annealed nano-ZnO coating using a biomimetic method in simulated body fluid. Live/dead and lactate production assays as well as microscopy were used to test the antibacterial action of the titanium alloy discs with TiO2, TiO2-ZnO and TiO2-ZnO-HA in the presence of Staphylococcus aureus. The genetic expression of ALP, FAK, COX- 2, OC, RunX-2, CA-1 , SOD, IL-6, and TNF-α in primary osteoblast cells grown on the coated discs, for 4 and 10 days, was quantitatively measured using PCR in collaboration of comparative Ct.
Results: The biochemical assays confirmed the antibacterial activity of both TiO2-ZnO and TiO2-ZnO-HA with 78.0 ± 2.0 % and 69.1 ± 3.0 % bacterial cell death with respect to S. aureus growing in broth without any disc exposure as shown in Figure 1. SEM provided a visual confirmation of the latter observation . For the biocompatibility test, the expression of all the genes indicated that the osteoblast cells were able to attach, proliferate and initiate differentiation (FAK, RunX-2, ALP, OC were upregulated). The cells also showed induction of inflammatory pathways (IL-6, COX-2, TNF-α upregulated) as early as day 4; after which they successfully expressed genes involved in oxidative defences (SOD) and well as genes constitutive to the function of osteoblasts (ALP).
Conclusions: Nano-ZnO grown on TiO2 nanotubes on the surface of Ti-6Al-4V alloy was found to be antibacterial with the presence of nano HA reducing the antibacterial action of the nanocomposite coating. Both TiO2-ZnO and TiO2-ZnO-HA allowed the expression of genes corroborating a higher biocompatibility in comparison to TiO2.