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Biomaterial-associated infections remain a significant complication of medical implants. Of the different strains of bacteria associated with nosocomial infections, 70% are resistant to at least one of the drugs used for treatment (Bren 2002). In 2000 the Center for Disease Control ranked microbial agents as the 4th leading actual cause of death in the United States of America (Mokdad et al. 2004).In an effort to improve the prevention and treatment of infections, this research has three objectives: the development of an alternative sterilization method for medical devices; assessing a new antimicrobial material for the prevention of infections in situ; and assessing mechanisms of acquired microbial resistance. The biocide being investigated in this body of work is chlorine dioxide gas.While multiple sterilization methods are available, there are limitations to all of these technologies. For example, chemical sterilization can leave residues on the surface of the material. These residuals can be toxic, causing sensitization reactions when the materials are implanted in the body (Dolovich et al. 1984; Marshall et al. 1985; Chapman et al. 1986; Dolovich et al. 1987). Research has shown that materials sterilized with increasing concentrations of the chemical sterilizing agent have increasing quantities of residuals (Lyarskii et al. 1984). The studies presented here will ascertain the environmental parameters required for sterilization of biomaterials with low concentrations of chlorine dioxide gas and assess polymers sterilized using these conditions for the cytotoxicity of possible chemical residuals.Investigations into preventing biomaterial-based infections in situ have focused on changing the biomaterial properties. Materials with altered physicochemical characteristics to prevent bacterial adhesion have been developed, and antibiotics and silver have been incorporated into the biomaterials to inhibit bacterial colonization. Unfortunately, the rapid depletion of incorporated antimicrobial agents, altered bactericidal activity in vivo, and the development of antibiotic resistance, have all limited the effectiveness of current technologies. In these studies a chlorine dioxide generating material was assessed using in vitro and in vivo assays.While assessing the bactericidal efficacy of a selection of chlorine dioxide generating materials, a spontaneous bacterial mutant with a reduced susceptibility to chlorine dioxide was isolated. The final section of this work will investigate a potential mechanism of resistance to chlorine dioxide.

The purpose of this thesis was to investigate certain factors important for the operation of a high repetition rate continuously tunable CO2 laser. The tuning range of specific importance for this research program was the R30 region within the ten micron band, since this frequency is of great importance for the laser isotope separation of uranium. This research program focused on: (i) Lowering the pressure at which viable continuous tunability could be achieved. {ii)Resonator design and analysis. {iii)Investigating the feasibility of using water capacitors in a high repetition rate laser system. A theoretical as well as an experimental investigation was done into the use of CO2 isotopes to lower the pressure at which continuous tunability in the R30, ten micron band could be achieved. A theoretical analysis was done into the use of a three mirror resonator with an etalon and a grating to ensure single longitudinal mode tuning in the R30 region. Such a resonator was designed and experimental results obtained were compared with those predicted by the theoretical analysis. A study was done into the use of water as a dielectric medium in a high repetition rate pulse power supply. A mathematical model, describing the electric breakdown of water,was developed. This was compared with published experimental results. Certain parameters important for the design of a water capacitor were experimentally measured. These include the intrinsic time constant,dielectric constant and resistivity of the water. A design proposal as well as a comparison between a water capacitor and other capacitor technologies are presented. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

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