Development of biocide-containing catheters for control of microbial colonisation

Tang, Demi (2019) Development of biocide-containing catheters for control of microbial colonisation. Masters by Research thesis (MSc), Manchester Metropolitan University.

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Abstract

Catheter-­associated urinary tract infections (CAUTIs) are the most common health-­ care associated infections, which contribute greatly to the morbidity and mortality of critically ill patients. This systematic study investigated metal organic framework (MOF) structures in the forms of Zeolitic Imidazolate Framework-­8 (ZIF-­8) and ZnO@ZIF-­8, regarding the effects of synthesis route on antimicrobial ability and their incorporation into silicone elastomer composites. The conformability (in terms of mechanical properties) of each embedded composite sample was assessed, and comparisons were made against commercial, dermatologically tested maxillofacial silicone. Two ZIF-­8 materials were synthesised in organic and aqueous media, correspondingly, which resulted in crystals of different sizes and morphologies. The ZIF-­8 (MeOH) prepared in methanol medium at room temperature resulted in 60 nm spherical nanoparticles. The ZIF-­8 (TEA) prepared in aqueous medium in the presence of triethylamine (TEA) at room temperature contained ca. 250 nm cubic crystals. The two samples were post-­synthetically treated with silver nitrate to convert into ZnO@ZIF-­8 materials, as a result of the spontaneous growth of ZnO nanorods within ZIF-­8. Antimicrobial ability was established for all samples with average minimum bactericidal concentrations (MBCs) (mg/mL) in the range 0.0228 – 0.0709. The samples were incorporated into composite silicone samples (4 wt.% of biocide). Introduction of ZnO-­nanorods to the structures increased the antimicrobial activity. Investigations into composite mechanical properties showed that ZnO@ZIF-­8 (MeOH) interfered with the curing of silicone polymers most, despite presenting the lowest MBC (mg/mL). With regards to other incorporated ZIFs, mechanical properties of the composite silicones were not detrimentally affected. Successful biocidal action of the MOF-­loaded silicones was demonstrated using the microbiology method BS ISO 22196:2011, against the model bacterium, Escherichia coli. This study highlighted the significant potential of antimicrobial ZIFs in the development of biocide-­containing catheters. Incorporation of ZnO-­nanorods in particular, provided promising evidence for the control of microbial colonisation.