Synthesis and tunable properties of double-walled and single-walled zirconia nanotubes: Enhancing bioactivity for bone and dental implants with controlled local delivery of antimicrobial peptides

Abstract

This study investigated zirconia (ZrO₂) nanotubes (NTs) synthesized by anodization in electrolytes with different glycerol concentrations. High-glycerol solution (sol 1) produced double-walled NTs, whereas low-glycerol solution (sol 2) formed single-walled NTs at 60 V. Well-ordered NTs were developed within 0.5–1 h in both electrolytes, with sol 2 exhibiting faster growth and a higher initial surface area (166.00 m²/g at 1 h). Crystallographic analysis revealed mixed tetragonal and monoclinic phases, with sol 1 favoring the tetragonal phase and sol 2 favoring the monoclinic phase at extended anodization times. In simulated body fluid (SBF) tests, both NTs demonstrated strong apatite-forming ability over 28 days, achieving Ca:P ratios of 1.86 (sol 1, 3 h) and 1.94 (sol 2, 1–3 h). Notably, sol 2 promoted faster and more extensive apatite deposition compared with sol 1; however, prolonged anodization led to partial collapse of the NT structure, reducing accessible surface area. Based on bioactivity and stability, sol 2 NTs anodized for 1 h were selected for drug delivery studies using a melittin (MEL)–Poly (lactic-co-glycolic acid) (PLGA) system. Uncoated NTs released 50 % of MEL within 60 min, whereas PLGA-coated NTs provided sustained release and enhanced antibacterial activity against Staphylococcus aureus (S. aureus). The results highlight the potential of ZrO₂ NTs as biomedical implant coatings, offering tunable morphology, bioactivity, and drug release properties for improved osseointegration and infection prevention.