Dragonfly wings have evolved surface nanoprotrusions that are reported to induce mechanical rupture and lysis of bacteria and fungi upon contact. This unique antimicrobial mechanism has drawn significant research interest, as the physical nature of killing could provide an effective strategy to prevent infections of medical implants and devices, whilst negating the current need to use materials impregnated with antibiotics. To date, no consensus has been reached on the precise mechanism that leads to microbial cell death on nanotextured materials, addressing this fundamental knowledge gap is crucial to facilitate the translation of this technology into clinical applications. In this study, dragonfly mimetic nanotopographies were generated on grade 5 titanium alloy (Ti-6Al-4V) using a simple, low-cost and scalable thermal oxidation technique. Multiple experimental approaches were employed to robustly assess bacterial physiology on dragonfly mimetic nanotopographies, including culture based and microscopic investigations (CFU analysis and LIVE/DEAD staining), biochemical methods (BacTiter-Glo and RealTime-Glo) and quantitative proteomic analysis. Dragonfly mimetic nanotopographies mediated time dependent antibacterial effects toward Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative (Escherichia coli and Klebsiella pneumoniae) bacteria, with enhanced activity against Gram-negative cell types. To obtain a more complete and accurate understanding of the antibacterial mechanism, advanced imaging techniques including SEM, TEM tomography and focused ion beam milling, were used to determine the effect of dragonfly mimetic nanotopographies on Gram-positive and Gram-negative envelope morphology and ultrastructure. Here we show four possible mechanisms via which dragonfly mimetic nanotopographies mediate antibacterial effects: 1) nanowire-induced envelope deformation, 2) nanowire-induced envelope penetration, 3) nanowire-induced cell impedance and 4) nanowire-induced oxidative stress. Of note, nanowire-induced envelope deformation and penetration was most prominent in Gram-negative bacteria, yet this did not result in mechanical rupture and lysis of the cell.
|Date of Award||28 Nov 2019|
- The University of Bristol
|Supervisor||Angela H Nobbs (Supervisor), Bo Su (Supervisor) & Paul Verkade (Supervisor)|