Although the antomicrobial nature of essential oils and their major constituents, the terpenoids, has been widely investigated the mechanism of their antimicrobial action has not been subject to the same scrutiny. In this study the membrane disruptive nature of the terpenoids has been determined by experiments on the effects of terpenes on both microbial membrane and model lipid bilayer systems. These terpenes exhibited a range of membrane damaging effects. Experiments showed that the terpenoids were able to increase disorder in DPPC bilayers, and that antimicrobially active terpenoids cause increased membrane permeability in living cells. The effect of molecular structure on antimicrobial activity and activity differences between each organism were determined for 60 terpenoids. Terpenoids with a low water solubility were found to be inactive. Hydrogen bond donor capacity and hydrogen bond acceptor capacity were found to be the molecular parameters which most strongly discriminated between activities against individual organisms. Activity against Gram negative Escherichia coli and Pseudomonas aeruginosa was associated also with a molecular size parameter. The protective nature of the outer membrane of P. aeruginosa and E. coli was also investigated. The evidence presented in this thesis has enabled the postulation of a two stage process to explain the overall mode of action of these compounds. / Doctor of Philosophy (PhD)

Thesis (M.S.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed December 5, 2007) Includes bibliographical references (p. 55-60).

A new form of antimicrobial surface was developed, which relies on an optical mechanism rather than chemical inactivation of microorganisms. Through the photoluminescence process of upconversion, low energy photons can be amplified into higher energy photons, and in this case, phosphors capable of converting visible light into germicidal UVC radiation were synthesized. Host crystals were doped with a praseodymium activator ion and shown to emit UVC photons upon excitation by blue or violet light. Surface coatings were prepared and proof-of-concept experiments demonstrated that, under exposure to a household fluorescent lamp, sufficient UVC radiation was emitted from the surfaces to achieve observable inactivation of surface bacterial spores and inhibition of biofilm growth. Material engineering was conducted to achieve higher optical conversion efficiency, wherein lithium codoping and development of alternative oxyfluoride host crystals were found to significantly improve upconversion emission. Implications of polychromatic excitation were investigated by conducting photoluminescence spectroscopy under combined laser beam excitation, while the effects of other application parameters are also discussed. These findings show that upconversion-based antimicrobial materials have strong potential for offering sustainable and effective technology for the prevention of diseases.

Thesis (Ph.D.)--University of Alberta, 2010. / A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Department of Chemical and Materials Engineering, Medical Sciences - Biomedical Engineering. Title from pdf file main screen (viewed on January 30, 2010). Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (M.Sc.)(Botany)--University of Pretoria, 2004. / Summary in English. Includes bibliographical references.

Ph.d.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains vii, 113 p. : ill. (some col.) Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Controlled drug delivery devices provide numerous advantages such as reduced side effects, higher therapeutic efficiency and improved patient compliance. Biodegradable polymer has become the most important material for controlled drug delivery device because of the excellent biocompatibility and tunable physicochemical properties. Biodegradable polymeric drug delivery devices are usually processed into various types of micro-particles due to the ease of fabrication and administration. However, controlling the drug release kinetics of these microparticles is still a challenge. One important reason is that drug release kinetics is significantly influenced by the microstructure of drug delivery devices, which is difficult to control. 　Microfluidic method is a group of technologies involved in the manipulation of fluids using channels in the scale of micrometers. Microfluidic method is particularly useful in controlling the structure of micro-droplets and generating homogeneous droplets. Therefore, microfluidics suggests great potential in controlling microstructures of drug delivery devices and drug release kinetics. 　In this study, biodegradable polymer based controlled drug delivery devices were fabricated using microfluidic method. Various types of microstructures were developed such as microspheres, core-shell microspheres, hollow microspheres and hydrogel microspheres. The results showed that microstructures were well controlled by fluid flow rates and geometries of capillary microfluidic devices. Both hydrophobic and hydrophilic drugs could be delivered by choosing drug delivery devices with suitable microstructures. 　Drug release kinetics of biodegradable polymeric microspheres has been studies a lot, yet complete understanding is still to be achieved. The diameter is an important factor which contributes to the drug release kinetics. However, the influence of diameter has not been systemically studied because monodisperse microspheres are difficult to obtain. Using microfluidic method, monodisperse PLGA microspheres with different diameters were fabricated to study the influence of diameter on drug release kinetics. It was found that diameter only influence the duration of the first phase (lag phase) in drug release process and smaller microspheres exhibited shorter lag phase. The relatively faster expansion of smaller microspheres was found to be responsible for the size effect by monitoring physicochemical changes during drug release. 　Rifampicin, a broad-spectrum antibiotic, was encapsulated by PLGA microspheres and PLGA-alginate core-shell microspheres. The long-term antimicrobial effects of drug loaded microspheres were investigated by drug release test and antimicrobial test against Staphylococcus aureus. The results showed that drug delivery devices could provide antimicrobial effect for more than one month. These drug delivery devices show potential in applications of controlled drug delivery and long-term antimicrobial therapy. 　In conclusion, drug delivery devices with different microstructures were fabricated using microfluidic method. The diameter of PLGA microspheres only influence the first phase of drug release profile (lag phase) and smaller microspheres exhibited shorter lag phase. The size effect is due to the relatively faster expansion rate of smaller microspheres. Rifampicin loaded PLGA microspheres and PLGA-alginate core-shell microspheres could provide sustained release of rifampicin for more than one month. The released rifampicin was able to inhibit the growth of Staphylococcus aureus. The controlled drug delivery devices presented showed great potential in long-term antimicrobial applications. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy