Mechanical inactivation of Staphylococcus aureus and Pseudomonas aeruginosa by titanium substrata with hierarchical surface structures

Titanium is the material of choice for the manufacture of orthopaedic and dental implants because of excellent corrosion resistance and proven biocompatibility. The occurrence of premature implant failure due to implant-associated infections, however, remains a prominent concern for clinicians. In this work, titanium substrata possessing micron-scale surface architectures were fabricated using a process of mask-less plasma etching of bulk titanium for periods of 5, 10, 20, 30 and 40 minutes. The resultant surfaces were characterised using two-dimensional Fast-Fourier Transforms (2D-FFT), scanning electron microscopy (SEM) and atomic force microscopy (AFM), which highlighted the formation of a two-tier pillared surface topology at the maximum etch period. Each of the substrata were assessed for antibacterial efficiency against two common human pathogens, Pseudomonas aeruginosa and Staphylococcus aureus bacteria, achieving maximum antibacterial efficiencies of 87.2 +/- 2% and 72.5 +/- 13%, respectively. Significantly, the formation of these three-dimensional (3D) hierarchical features was found to minimise the extent of attachment of S. aureus cells, directionally trapping the cells inside the micron size pillars with the second tier of pillars acting to kill the cells. The results of this work shed new light on the development of smart mechano-bactericidal surfaces based on tuning their micron-scale surface topology and suggest that such complex hierarchical surfaces can be particularly effective towards inactivation of cocci bacteria, such as S. aureus.