Browsing by Author "Berchane, Nader Samir"
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Item Experimental and computational investigations of therapeutic drug release from biodegradable poly(lactide-co-glycolide) (plg) microspheres(2009-05-15) Berchane, Nader SamirThe need to tailor release-rate profiles from polymeric microspheres remains one of the leading challenges in controlled drug delivery. Microsphere size, which has a significant effect on drug release rate, can potentially be varied to design a controlled drug delivery system with desired release profile. In addition, drug release rate from polymeric microspheres is dependent on material properties such as polymer molecular weight. Mathematical modeling provides insight into the fundamental processes that govern the release, and once validated with experimental results, it can be used to tailor a desired controlled drug delivery system. To these ends, PLG microspheres were fabricated using the oil-in-water emulsion technique. A quantitative study that describes the size distribution of poly(lactide-coglycolide) (PLG) microspheres is presented. A fluid mechanics-based correlation that predicts the mean microsphere diameter is formulated based on the theory of emulsification in turbulent flow. The effects of microspheres? mean diameter, polydispersity, and polymer molecular weight on therapeutic drug release rate from poly(lactide-co-glycolide) (PLG) microspheres were investigated experimentally. Based on the experimental results, a suitable mathematical theory has been developed that incorporates the effect of microsphere size distribution and polymer degradation on drug release. In addition, a numerical optimization technique, based on the least squares method, was developed to achieve desired therapeutic drug release profiles by combining individual microsphere populations. The fluid mechanics-based mathematical correlation that predicts microsphere mean diameter provided a close fit to the experimental results. We show from in vitro release experiments that microsphere size has a significant effect on drug release rate. The initial release rate decreased with an increase in microsphere size. In addition, the release profile changed from first order to concave-upward (sigmoidal) as the microsphere size was increased. The mathematical model gave a good fit to the experimental release data. Using the numerical optimization technique, it was possible to achieve desired release profiles, in particular zero-order and pulsatile release, by combining individual microsphere populations at the appropriate proportions. Overall, this work shows that engineering polymeric microsphere populations having predetermined characteristics is an effective means to obtain desired therapeutic drug release patterns, relevant for controlled drug delivery.Item Experimental evaluation of the flow field inside an open faced impeller(Texas A&M University, 2005-02-17) Berchane, Nader SamirThe pressure distributions and forces presented in a thesis by Hossain [1] for a centrifugal pump illustrated a somewhat complex inter-relationship between various geometric and operating parameters of the pump studied. The pump had an open faced impeller of 33.65 cm diameter with 5 blades of backswept design. It was felt that the best way to resolve some of the questions related to Hossain?s results was to determine the fluid velocity field inside the pump. Thus the flow field through the impeller passages was measured using a 1-D Laser Doppler Velocimetry (LDV) system. The LDV was used to measure the radial and tangential velocity components as well as the turbulence intensities over the region accessible through the two optical windows in the front of the pump housing. Five axial planes were investigated by recording measurements along two radial lines at azimuthal angles of 45? and 315? (with respect to the horizontal axis of the pump) for design operating conditions. A once per revolution signal was used to supply the LDV system with a reference for the rotor position. It was found out that a leakage flow existed near the front wall of the impeller at z/h = 0.11, which was generated by the pressure difference between the impeller exit and inlet. It was also concluded that the velocity field was not fully two-dimensional in nature. This was believed to be a result of the 90? turn that the fluid endures as it enters the impeller inlet from the suction pipe.