This dissertation, "Drug Delivery Devices Fabricated by Microfluidic Method and Their Applications in Long-term Antimicrobial Therapy" by Jun, Wu, 吴隽, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: 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-alg