| Summary: | A thesis submitted to the Faculty of Engineering and the Built Environment, University of
the Witwatersrand, in fulfillment of the requirements for the degree of Doctor of Philosophy, 2020 === Surface contamination and subsequent microbial transmission is a persistent problem in healthcare
facilities, contributing to the global pervasion of nosocomial infections and the aggressive
prevalence of resistant strains. Touch-contact surfaces, as effective intermediaries for pathogenic
transmission, are priority targets for solution development.
Polymer metallisation of ABS, PEEK and PC polymers with antimicrobially active copper, silver
and zinc metals, via multi-step and multi-material additive manufacturing, for antimicrobial
surface coating production, was investigated. Cold spray and polymer 3D printing technologies
were, for the first time, integrated for the application of self-sanitising surface coatings. Theoretical
modelling, in conjunction with a targeted particle depth-of-penetration model and adapted
Taguchi optimisation method, aided cold spray parameter selection. Successful coatings
were achieved using a novel independent parameter effects and variation decision framework
and a tailored experimental optimisation procedure. Antimicrobial efficacy was evaluated using
two, independent, in vitro assays: a diffusion assay and an adapted time-kill assay simulating
touch-contact pathogenic exposure. Preliminary prototype trials were also conducted, which
included a 3D printed smartphone cover.
Enhanced antimicrobial efficacy under both wet and dry contact conditions was observed. In a
touch-contact environment, cold spray coatings were found to be five times more biocidal than
their respective base metals. A 50% w/w copper-zinc coating on a 3D printed ABS substrate
exhibited synergistic bacteriostatic activity: found to be 43% more effective than the combined
average activity of copper and zinc coatings against Staphylococcus aureus, Pseudomonas aer-uginosa and Klebsiella pneumoniae. Additional test pathogens included Enterococcus faecalis
and Candida albicans. A combination of factors is believed to be responsible for this activity,
including the known mechanisms of action of oligodynamic metals, enhanced diffusion of ions
and surface topography supporting direct microbial contact, made possible by the novel coating
process employed. Antimicrobial activity was not signifi cantly impaired by resistant pathogens:
gentamicin-methicillin-resistant S. aureus, azlocillin-carbenicillin-resistant P. aeruginosa and a
uconazole-resistant C. albicans. Against these resistant pathogens - under dry, touch-contact
conditions - the cold spray coatings achieved complete microbial elimination within 12 min for
a copper coating on 3D printed ABS and within 5 min for a copper coating with a 5 wt% silver
additive on a copper metal substrate. In response to the global need for alternative solutions
to infection control and prevention, these effective antimicrobial surface coatings are proposed === CK2021
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