Noimark, SM;
(2015)
Light-Activated Antimicrobial Polymers For Healthcare Applications.
Doctoral thesis , UCL (University College London).
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Abstract
This thesis details the development of potent light-activated antimicrobial silicone polymers for use in healthcare environments. Upon illumination, these polymers induce the lethal photosensitisation of bacteria through the generation of a range of reactive oxygen species at the polymer surface, initiating a non-site specific attack against bacteria in the vicinity. Activation of the antimicrobial technology developed was achieved using laser illumination (635 nm) and UVA illumination for medical device applications, or white hospital lighting conditions for hospital touch surface applications. Moreover, for the first time, some photobactericidal materials developed also demonstrated strong antimicrobial activity through an additional dark-activated mechanism. Antimicrobial polymers were developed through use of a swell-encapsulation-shrink strategy to incorporate photosensitiser dyes such as methylene blue and crystal violet, in addition to a range of nanoparticles including 2 nm gold nanoparticles, zinc oxide nanoparticles and titania nanoparticles, into medical grade silicone. Specifically, the photobactericidal silicone polymer systems detailed in this thesis are: (i) crystal violet-coated, methylene blue and 2 nm gold nanoparticle-encapsulated silicone for both medical device and hospital touch surface applications, (ii) crystal violet-coated, zinc oxide nanoparticle-encapsulated silicone for hospital touch surface applications and (iii) oleic acid-functionalised titania or gold-doped titania nanoparticle-encapsulated silicone for medical device or hospital touch surface applications (in combination with a suitable light delivery system). The materials were characterised using techniques including: light microscopy, fluorescence microscopy, transmission electron microscopy, UV-Vis absorbance spectroscopy, X-ray photoelectron spectroscopy, time-resolved electron paramagnetic resonance spectroscopy and time-resolved detection of near infrared singlet oxygen phosphorescence (∼ 1270 nm). Functional testing indicated that these materials were suitable for targeted applications and demonstrated strong material photostability and dye-polymer stability under aqueous conditions. The polymers demonstrated strong light-activated antimicrobial activity when tested against key Gram-positive and Gram-negative bacteria associated with hospital-acquired infections including Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli, with > 4 log reductions in viable bacterial numbers observed. Significant antimicrobial activity was also noted under dark conditions. It is anticipated that the potent antimicrobial technology detailed in this thesis could ultimately be used in both medical device and hospital touch surface applications, to reduce bacterial surface colonisation and the associated incidence of hospital-acquired infections.
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