Nanoscale surface structures for antibacterial applications

Antibiotic resistance is poised to become one of the greatest healthcare challenges of our time. With more and more bacteria becoming resistant to common antibiotics there is an unprecedented need for alternative ways to overcome their growth and proliferation. Nanostructured surfaces have been discovered as a promising tool as a way to combat bacterial growth across a variety of materials. The exact mechanism of bacterial cell death remains unknown; however, it is an area of active research. This work seeks to add to the literature by investigating the effects of feature density as well as the impact of a dual-height arrangement of nanoneedles on bacterial activity/proliferation. Using block copolymer micelle lithography, different nanoparticle hard masks were fabricated on silicon substrates using different metal precursors. Each of these masks was evaluated for their ability to produce nanoneedle arrays with a height in the target range of 200-300 nm. Etching of the masked silicon allowed the production of silicon nanoneedle arrays of varying densities. The height and density of features present were tailored by careful choice of the nanoparticle hard masks and the etch time. Low-density (3 ± 1 features/µm2) and high-density (201 ± 12 features/µm2) nanoneedle arrays were tested for their antibacterial activity against Gram-negative bacteria, Pseudomonas fluorescens. The low density nanoneedle arrays were found to be significantly more effective, killing 54 ± 9% of bacteria over 24 hr. Dual height arrays inspired by the dragonfly wing were also investigated but were found not to be significantly different from the flat silicon controls in these experiments. Finally, multi-layered electrospun polysulfone membranes consisting of submicron fibres were fabricated and characterised for their ability to reject various micron scale particles. Initial testing to introduce nanostructures to the surface was attempted but was unsuccessful. However, these membranes show promise both in microfiltration and for use as prefilters for high-selectivity membranes.