Carbon-infiltrated carbon nanotube coating effect on bacterial resistance and Ti6Al4V substrate material properties

Carbon-infiltrated carbon nanotube (CI-CNT) coatings have emerged as a promising biomaterial infection prevention strategy due to their inherent topography-driven bacterial resistance. This study examined the impact of CI-CNT manufacturing methods, specifically the use of a hydrogen versus an argon carrier gas environment, on the mechanical properties and bacterial resistance of Ti-6Al-4V (Ti64) coated substrates. Tensile and torsional testing, electron backscatter diffraction (EBSD), and fracture profile analysis were used to characterize variations in substrate yield strength, ultimate tensile strength, elastic moduli, microstructure, and ductility. Hydrogen-based processing induced severe hydrogen embrittlement and degradation of mechanical properties, with reductions of up to 34% in yield strength, 47% in shear yield strength, and indisputable evidence of brittle fracture morphology. Argon-based treatments preserved near-control mechanical properties, with an average reduction of just 2.7% in tensile yield strength and a reduction of 12.0% in shear yield strength compared to an untreated control. Argon processing also maintained coating integrity under elastic operational conditions, and exhibited substantial plastic deformation prior to failure in tensile samples, with torsion samples withstanding failure entirely. Antibacterial efficacy of the CI-CNT coatings was confirmed by 36 h Staphylococcus aureus culture assays. A 2.5-fold reduction in bacterial colonization was observed in both hydrogen and argon-based CI-CNT variants as compared to uncoated Ti64 control surfaces. These findings establish argon-based CI-CNT processing and the resultant coatings as a potential alternative for biomedical and structural applications, while conventional hydrogen processing demonstrated significant material strength reduction and reliability risk.