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Title: Effects of 405 nm HINS-light on mammalian cells and potential disinfection applications
Author: McDonald, Richard
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2012
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Hospital acquired infection affects approximately 10% of patients admitted to hospital, and is responsible for over 5000 deaths in the UK annually. The cost to the NHS has been estimated at around £1 bn per year. Infections acquired during invasive procedures have particularly high mortality rates, and the majority of these infections are thought to be caused by airborne bacteria present during procedures. High-intensity narrow-spectrum (HINS) light is a novel light-based disinfection system which may be able to aid in the continuous battle against bacteria. HINS-light has been shown to have bactericidal properties, causing near complete inactivation of a number of medically relevant bacteria. The purpose of this study was to investigate potential patient-based applications of HINS-light, to establish if HINS-light could be used during invasive procedures where exposure of tissue to HINS-light would occur. The effect of HINS-light on wound healing was investigated with a fibroblast populated collagen lattice (FPCL) wound model. High intensities of HINS-light (15 mWcm-2: 1 hour exposure) were found to delay FPCL contraction, inhibit α-smooth muscle actin expression and reduce cell viability. Exposure to intensities at and below 5 mWcm-2 for 1 hour had no significant inhibitory effects on any measured aspect of fibroblast function. Infection is a significant risk in orthopaedic joint replacement procedures. To establish if HINS-light could be employed to reduce the number of bacteria present during these procedures without damaging exposed bone tissue, osteoblast cells were exposed to HINS-light. Cell viability was assessed via alkaline phosphatase assay, osteoblast collagen production, osteocalcin expression, and microscopy techniques. Exposure to 15 mWcm-2 HINS-light for 1 hour was found to have inhibitory effects, while exposure to 5 mWcm-2 and below for 1 hour had no significant effects. Having established that 5 mWcm-2 HINS-light could be applied to mammalian cells for 1 hour without significant detrimental effects, this dose was applied to polyester prosthetic vascular graft materials. This dose of HINS-light had no significant effects on the mechanical properties of the tested materials, and caused no visible damage. Extracts produced after treatment of the materials with HINS-light did not cause cytotoxicity to human aortic smooth muscle cells. The bactericidal effects of 5 mWcm-2 HINS-light were investigated on various clinically relevant bacterial species with variable success. Significant reductions in populations of Staphylococcus epidermidis, Staphylococcus aureus and Methicillin resistant Staph. aureus could be achieved when exposed to HINS-light in liquid suspension, with lesser inactivation of Acinetobacter baumannii and Pseudomonas aeruginosa, and no effect on populations of Escherichia coli. However, reduced inactivation rates for all bacteria were observed when exposing the bacteria on agar surfaces, a situation which closer resembles the wound environment. Despite showing that a bactericidal level HINS-light exposure could be established that would not be detrimental to living tissue, the bactericidal benefits of this dose may not be sufficiently beneficial for medical use in practice. Reduced bacterial inactivation by HINS-light in nutritious environments such as a wound bed, combined with the limited penetration into tissue, suggest that the ability of HINS-light to reduce the number of bacteria in a wound would be limited. It is suggested that medical uses of HINS-light should focus on environmental disinfection, and decontamination of medical devices, rather than direct disinfection of wounds.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available