Development and characterization of a multilayer silver/silver-tantalum oxide thin film coating on stainless steel for biomedical applications

Stainless steel 316L (SS 316L) is widely used in biomedical applications, particularly in surgical tools. Although this class of material has good wear and mechanical properties, it still lacks in antibacterial properties. Therefore, various surface modifications such as antibacterial coatings have been developed to enhance its properties. In this study, the surface of SS 316L was engineered with a thin multi-layer of tantalum oxide (TaO) and silver (Ag) with thickness of 4.7–6.4 μm. The thin film multilayered coatings were deposited using physical vapor deposition (PVD) magnetron sputtering. In this study, Ag/AgTa₂O₅ nanocomposite thin film is developed to avoid or limit bacterial adhesion on surgical tool surfaces. The as-deposited Ag/AgTa₂O₅ nanocomposite film were thermally treated to enhance the mechanical properties of the film. The thermal annealing of the as-sputtered thin film at 400 °C induced segregated Ag microstructure, increased the crystallinity and adhesion strength by about 152% (2916 ± 147 mN). The 400 °C annealed thin film exhibited hydrophobicity (102.5°) and thermal stability properties. The superior adhesion strength of the thermally treated film reduces and slows down delamination while in use at the rugged surgical environment.     

Antibacterial activity and corrosion resistance of Ta2O5 thin film and electrospun PCL/MgO-Ag nanofiber coatings on biodegradable Mg alloy implants

Biodegradable magnesium (Mg) alloys have drawn considerable attention for use in orthopedic implants, but their antibacterial activity and corrosion resistance still require improvement. In the present work, functional Ta₂O₅ (tantalum pentoxide) compact layers and PCL/MgO-Ag (poly (ε-caprolactone)/magnesium oxide-silver) nanofiber porous layers were subsequently deposited on Mg alloys via reactive magnetron sputtering and electrospinning, respectively, to improve anticorrosion and antibacterial performance. Sputter coating of the Ta₂O₅ resulted in a thick layer (～1?μm) with an amorphous structure and high adhesive strength. The nanostructure exhibited bubble-like patterns with no obvious nano-cracks, nano-porosities, or pinholes. The electrospun PCL/MgO-Ag nanofiber coating was porous, smooth, and plain with no obvious beads. In vitro corrosion tests demonstrated the PCL/MgO-Ag nanofiber-coated alloy had greater corrosion resistance than a Ta₂O₅ sputter-coated alloy or uncoated Mg alloy. The additional electrospun PCL/MgO-Ag nanofiber coating also had greater antibacterial behavior toward Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria than the Ta₂O₅-coated or uncoated alloy specimens. Increasing the MgO-Ag concentration of the nanofibers from 1 to 3?wt% increased antibacterial activity. The combination of Ta₂O₅ and PCL/MgO-Ag nanofiber coatings on Mg alloys may therefore have potential applications for reducing bone infection as related to orthopedic implants for bone repair.