Functional hybrid PVD-coated/textured antimicrobial surfaces

Hall, Niall (2023) Functional hybrid PVD-coated/textured antimicrobial surfaces. Masters by Research thesis (MPhil), Manchester Metropolitan University.

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Abstract

Titanium nitride and silver are a combination of materials that have been extensively used for production of antimicrobial coatings via physical vapour deposition (PVD), specifically the pulsed DC magnetron sputtering method. There are also widely reported textured samples, via an inexhaustive list of processes, this research project will focus on the laser induced periodic surface structures (LIPSS) method. Whilst there have been numerous studies that investigate the PVD & LIPSS processes individually, at the time of writing to the authors knowledge there were no studies that investigated the two processes combined. The main goal of this project was to investigate the possibility of synergy between the two well established processes of Physical Vapour Deposition and Laser Texturing, to determine if the combination of the two surface types provided an optimised antimicrobial surface that would be fit for purpose as a coating/texture for an external fixation device or would the two properties be antagonistic to each other. Titanium nitride, and silver were the deposited materials, with 316 stainless-steel chosen as the substrate. The bacteria that were chosen for investigation were Staphylococcus aureus and Pseudomonas aeruginosa, which are both common hospital-acquired infections (HAIs). The antimicrobial effect of titanium nitride and silver is demonstrated throughout, with increases in silver content producing increases in antimicrobial activity. The range of silver in the coatings, measured by atomic weight percentage (at%), was between 15 – 30 at%. Changes in number of retained bacterial cells is demonstrated throughout this thesis, with the texturing patterns having a substantial effect on the number of bacteria that were able to adhere to the substrates. These surface patterns were varied between linear grooves, and the randomly organised structures of LIPSS, which each had a different effect on the adherence of the two bacterial strains. Overall, the combination of the two processes reduced the antimicrobial efficacy and increased the number of bacteria cells adhered to the substrate. Utilising various analytical and microbiological tests, such as scanning electron microscope (SEM), energy dispersive x-ray diffraction (EDX), White Light Profilometry (WLP), X-Ray Diffraction Analysis (XRD), LIVE/DEAD staining, and retention assay the thin films produced were tested and analysed.