Optimized titanium dioxide nanotubes for dental implants: Estimation of mechanical properties and effects on the biological behaviors of human gingival fibroblasts and oral bacteria

The long-term successes of implant restorations rely on both appropriate osseointegration and robust soft tissue integration (STI). Numerous studies have reported that titanium dioxide nanotube (TNT) arrays formed by electrochemical anodization (EA) can promote early osteogenesis, but the mechanical stability of such modifications is often ignored and remains underexplored. In addition, relatively little research has been done on their effects on soft tissues integration. In this study, we developed mechanically robust TNT arrays using an optimized EA system. Subsequently, we immobilized a peptide, specifically D-amino K122-4, onto the anodized TNTs via polydopamine (PDA) films to enhance their mechanical properties. Surface morphology and composition were characterized by scanning electron microscopy (SEM), atomic force microscopy, and X-ray photoelectron spectroscopy. Mechanical properties, including the elastic modulus and hardness of TNTs modified Ti surfaces, were assessed using the nano-indention test. The adhesive strength of TNTs films to the substrate was measured using the nano scratch test. Furthermore, we evaluated the adhesion, spreading, and proliferation of human gingival fibroblasts (HGFs) and periodontal pathogenic bacteria such as Streptococcus mutans (S.m) and F. nucleatum (F.n) on the surface. Results showed that the elastic modulus, hardness, and adhesive strength of anodized TNTs were significantly enhanced by the incorporation of the D-amino K122-4 peptide. Live-dead staining and SEM observation suggested a decreased surface colonization by both bacterial species. The antibacterial rate of S.m and F. n was 81.5% and 71.7%, respectively, evaluated by colony counting method. Additionally, results of CCK8 assay showed that modified TNTs slightly stimulated HGFs attachment and proliferation while producing enhanced fluorescence of integrin β1 and F-actin, confirmed by laser confocal microscopy observation. Thus, D-amino K122-4 biofunctionalized TNTs present significantly improved mechanical properties, and the mechanically robust structures modulate HGFs proliferation and alignment, resulting in decreased bacteria growth. This novel strategy has the potential to create a surface coating for implants that exhibits superior mechanical robustness and enhanced surface-to-implant interactions.