Sehmi, SK;
(2016)
Antibacterial surfaces with nanoparticle incorporation for prevention of hospital-acquired infections.
Doctoral thesis , UCL (University College London).
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Abstract
This thesis describes the incorporation of nanoparticles into polymers as antibacterial surfaces for preventing hospital-acquired infections (HAIs). With a high prevalence of HAIs, the use of antibacterial materials can contribute in reducing bacterial contamination associated with frequently touched surfaces in hospitals (e.g. push plates, bed rails, or keyboards). The combination of nanoparticles and light-activated antibacterial agents demonstrate lethal bactericidal activity when encapsulated into medical grade polymer sheets. Upon white light activation, these polymers exhibit significant photobactericidal activity against a range of Gram-negative and Gram-positive bacteria via the production of reactive oxygen species at the polymer surface, through multi-site mechanistic pathways (Type I and/or Type II). These samples are tested under various light intensities to mimic clinical surroundings, but more significantly, some materials show highly efficacious antibacterial activity in dark conditions. All polymers are prepared using a simple ‘swell-encapsulation-shrink’ method, which impregnates the nanoparticles into the polymer substrate and on the surface. These include copper and zinc oxide nanoparticles synthesised with different capping agents. The antibacterial activity of a commonly used biocide encapsulated into the polymer is also assessed. The photosensitiser (crystal violet) is then coated onto the polymer surface in the case of ZnO nanoparticles and activated by white light (~500 – 6600 lux). The combination of crystal violet and zinc oxide nanoparticles is investigated further by adapting the microbiological protocol to more closely replicate a clinical environment and using a lower intensity of light to carry out the antibacterial testing. In addition, the mechanisms operating within the crystal violet and zinc oxide system are examined using specific inhibitors and singlet oxygen quenchers to determine iv whether Type I, Type II, or both photochemical pathways are responsible for the reduction of bacteria in the light and dark. The samples were tested against a range of hospital pathogens, including Escherichia coli, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa and Clostridium difficile endospores. The novel and highly effective antimicrobial materials detailed in this thesis demonstrate a very strong potential to be used in hospitals for reducing the incidence of HAIs.
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