Fischell Department of Bioengineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/6628
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Item Modeling the Pulmonary Effects of Respiratory Protective Masks During Physical Activity(2001) Coyne, Karen Marie; Johnson, Arthur T.; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Current respirator design involves developing and testing a prototype, making modifications, and then re-testing until a suitable mask is obtained. If the physiological effects of the respirator could be modeled, design could proceed more rapidly. Such a model would be an important design tool that would provide valuable information on the potential physiological and psychological compatibility of a respirator with the wearer. The model would not eliminate the need for human testing, but would decrease the number of prototypes required, saving time and money. A successful model would be very complex because of the many factors to consider. And, because of the variability of human response to exercise, work, and respirator wear, the initial development of the model will include many assumptions that may limit the expected accuracy of the predictions. The goal of this research was to develop a model of the pulmonary effects of respirator wear during physical activity that would form the framework of a larger model that would include other factors as well. Empirical equations were developed that related oxygen consumption to physiological work rate, anaerobic threshold, minute ventilation and tidal volume to oxygen consumption, and exhalation time to respiratory period. Respirator resistance and dead volume effects were quantified. The model was implemented in Visual BASIC. The model predicted oxygen consumption, minute ventilation, and tidal volume well for a limited number of subjects exercising below 70% of maximal oxygen consumption. For three subjects wearing respirators and exercising at 80-85%, the errors in the model parameters were greater than those of the original equations. As model equations were based on average responses, predictions for any one individual may have large errors. Model simulations of a subject exercising at five different work rates with and without a respirator showed that the model made rational predictions of the effects of a respirator on respiratory parameters. More data is needed to completely validate the model. These results showed that the model structure was valid and that overall the model was capable of making rational predictions of the average effects of respirator wear on pulmonary system parameters during physical activity.Item Lipid-Hydrogel Nanoparticles: Synthesis Methods and Characterization(2009) Hong, Jennifer S.; Raghavan, Srinivasa R; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation focuses on the directed self-assembly of nanoscale soft matter particles using methods based on liposome-templating. Nanoscale liposomes, nano-sized hydrogel particles ("nanogels"), and hybrids of the two have enormous potential as carriers in drug delivery and nanotoxicity studies, and as nanovials for enzyme encapsulation and single molecule studies. Our goal is to develop assembly methods that produce stable nanogels or hybrid lipid-polymer nanoparticles, using liposomes as size and shape templates. First we describe a bulk method that employs liposomes to template relatively monodisperse nanogels composed of the biopolymer, alginate, which is a favorable material for nanogel formation because it uses a gentle ionic crosslinking mechanism that is suitable for the encapsulation of cells and biomolecules. Liposomes encapsulating sodium alginate are suspended in aqueous buffer containing calcium chloride, and thermal permeabilization of the lipid membrane facilitates transmembrane diffusion of Ca2+ ions from the surrounding buffer into the intraliposomal space, ionically crosslinking the liposome core. Subsequent lipid removal results in bare calcium alginate nanogels with a size distribution consistent with that of their liposome template. The second part of our study investigates the potential for microfluidic-directed formation of lipid-alginate hybrid nanoparticles by adapting the above bulk self-assembly procedure within a microfluidic device. Specifically we investigated the size control of alginate nanogel self-assembly under different flow conditions and concentrations. Finally, we investigate the microfluidic directed self-assembly of lipid-polymer hybrid nanoparticles, using phospholipids and an N-isopropylacrylamide monomer as the liposome and hydrogel precursors, respectively. Microfluidic hydrodynamic focusing is used to control the convective-diffusive mixing of the two miscible nanoparticle precursor solutions to form nanoscale vesicles with encapsulated hydrogel precursor. The encapsulated hydrogel precursor is polymerized off-chip and the resultant hybrid nanoparticle size distributions are highly monodisperse and precisely controlled across a broad range relevant to the targeted delivery and controlled release of encapsulated therapeutic agents. Given the ability to modify liposome size and surface properties by altering the lipid components and the many polymers of current interest for nanoparticle synthesis, this approach could be adapted for a variety of hybrid nanoparticle systems.Item Automated quantification and classification of human kidney microstructures obtained by optical coherence tomography(2009) Li, Qian; Chen, Yu; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optical coherence tomography (OCT) is a rapidly emerging imaging modality that can non-invasively provide cross-sectional, high-resolution images of tissue morphology such as kidney in situ and in real-time. Because the viability of a donor kidney is closely correlated with its tubular morphology, and a large amount of image datasets are expected when using OCT to scan the entire kidney, it is necessary to develop automated image analysis methods to quantify the spatially-resolved morphometric parameters such as tubular diameter, and to classify various microstructures. In this study, we imaged the human kidney in vitro, quantified the diameters of hollow structures such as blood vessels and uriniferous tubules, and classified those structures automatically. The quantification accuracy was validated. This work can enable studies to determine the clinical utility of OCT for kidney imaging, as well as studies to evaluate kidney morphology as a biomarker for assessing kidney's viability prior to transplantation.Item Design of a Novel Portable Flow Meter for Measurement of Average and Peak Inspiratory Flow(2009) Jamshidi, Shaya; Johnson, Arthur T; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The maximum tolerable physical effort that workers can sustain is of significance across many industrial sectors. These limits can be determined by assessing physiological responses to maximal workloads. Respiratory response is the primary metric to determine energy expenditure in industries that use respirator masks to protect against airborne contaminants. Current studies fail to evaluate endurance under conditions that emulate employee operating environments. Values obtained in artificial laboratory settings may be poor indicators of respiratory performance in actual work environments. To eliminate such discrepancies, equipment that accurately measures peak respiratory flows in situ is needed. This study provides a solution in the form of a novel portable flow meter design that accurately measures average and peak inspiratory flow of a user wearing an M40A1 respirator mask.Item ENZYME INHIBITION IN MICROFLUIDICS FOR RE-ENGINEERING BACTERIAL SYNTHESIS PATHWAYS(2009) LARIOS BERLIN, DEAN EDWARD; RUBLOFF, GARY W; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Enzyme-functionalized biological microfluidic (EF-BioMEMS) systems are an emerging class of lab-on-chip devices that manipulate enzymatic pathways by localizing reaction sites in a microfluidic network. An EF-BioMEM system was fabricated to demonstrate biochemical enzyme inhibition. Further, design optimizations to the EF-BioMEM system have been proposed which improve system sensitivity and performance. The pfs enzyme is part of the quorum-sensing pathway that ultimately produces the bacterial signaling molecule AI-2. An EF-BioMEM system was fabricated to investigate the pfs conversion activity in the presence of a transition state analogue inhibitor. A reduction in enzyme conversion was measured in microfluidics for increasing inhibitor concentration that was comparable to the response expected on a larger scale. This EF-BioMEMS testbed is capable of investigating other compounds that inhibit quorum sensing. Design improvements were demonstrates that improve overall system responsiveness by minimizing unintended reactions from non-specifically bound enzyme. EF-BioMEMS signal-to-background performance increased from 0.72 to 2.43.Item ORBITAL FLOOR REGENERATION USING CYCLIC ACETAL HYDROGELS THROUGH ENHANCED OSTEOGENIC CELL SIGNALING OF MESENCHYMAL STEM CELLS(2009) Betz, Martha Wheaton; Fisher, John P; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Orbital floor fractures are a serious consequence of craniofacial trauma and account for approximately 60-70% of all orbital fractures. Unfortunately, the body's natural response to orbital floor defects generally does not restore proper function and facial aesthetics which is complicated by the thin bone and adjacent sinuses. We propose using a tissue engineering strategy to regenerate orbital floor bone. To this end, a functional biomaterial was investigated to enhance orbital floor regeneration. First, a bone marrow stromal cell population was isolated and differentiation assessed via coculture with chondrocytes and osteogenic media supplements. A cyclic acetal biomaterial composed of the cyclic acetal monomer 5-ethyl-5-(hydroxymethyl)-β,β-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA) was then developed for cell encapsulation. The previously investigated bone marrow stromal cells were then used to determine the effects of the ammonium persulfate/N,N,N',N'-tetramethylethylenediamine initiator system used to crosslink the EH-PEG hydrogels on cell viability, metabolic activity, and osteogenic differentiation. Next, EH-PEG hydrogels were implanted into orbital floor defects with bone morphogenetic protein-2, where tissue response and surrounding bone growth was analyzed. To improve surrounding tissue interaction and cell infiltration, macroporous EH-PEG hydrogels were created using porogen-leaching. These hydrogels were characterized using optical coherence tomography for pore size, porosity, and cell viability. In addition, these macroporous hydrogels were created with varying architecture to analyze the effects on osteogenic signaling and differentiation. This work outlines the potential application of EH-PEG hydrogels for use in orbital floor repair.Item Novel Statistical Pattern Recognition and 3D Machine Vision Technologies for Automated Food Quality Inspection(2008-12-02) Zhu, Bin; Tao, Yang; Fischell Department of Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Machine vision technologies have received a lot of attention for automated food quality inspection. This dissertation describes three techniques developed to improve the quality inspection of apple and poultry products. First, a Gabor feature-based kernel principal component analysis (PCA) method was introduced by combining Gabor wavelet representation of apple images and the kernel PCA method for apple quality inspection using near-infrared (NIR) imaging. Gabor wavelet decomposition was employed to extract appropriate Gabor features of whole apple NIR images. Then, the kernel PCA method with polynomial kernels was applied in the Gabor feature space to handle nonlinear separable features. The experimental results showed the effectiveness of the Gabor-based kernel PCA method. Using the proposed Gabor kernel PCA eliminated the need for local feature segmentation and also resolved the nonlinear separable problem in the Gabor feature space. An overall 90.5% detection rate was achieved. Second, a novel 3D-based apple near-infrared (NIR) data analysis strategy was utilized so that the apple stem-end/calyx could be identified, and hence differentiated from defects and normal tissue according to their different 3D shapes. Two automated 3D data processing approaches were developed in this research: 1) A 3D quadratic facet model fitting, which employed a small concave 3D patch to fit the 3D apple surface and the best fit could be found around stem-end/calyx area; and 2) A 3D shape enhanced transform (SET), which enhanced the apple stem-end/calyx area and made it easily detectable because of the 3D surface gradient difference between the stem-end/calyx and the apple surface. An overall 92.6% accuracy was achieved. Third, high resolution on-line laser 3D imaging was investigated for improving the 3D profile recovery for thickness compensation purposes. Parallel processing and memory management were also considered to improve the processing speed of the detection system. Multiple-lane coverage was fulfilled such that a wider conveyor could be used and overall throughput would be increased. To further improve the detection performance of the dual X-ray and laser imaging system, a dynamic thresholding approach was introduced to suppress the errors and noise involved by the imaging system. Unlike the traditional single threshold method, dynamic thresholding monitored the responses of the region of interest under a set of thresholds to determine the true physical contaminants, making it more tolerant to the noise than the single threshold method. An overall 98.6% detection rate was achieved.Item Controlled liposome formation and solute encapsulation with continuous-flow microfluidic hydrodynamic focusing(2008-12-11) Jahn, Andreas; DeVoe, Don L; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Liposomes enable the compartmentalization of compounds making them interesting as drug delivery systems. A drug delivery system (DDS) is a transport vehicle for a drug for in vivo drug administration. Drugs can be encapsulated, bound, or otherwise tethered to the carrier which can vary in size from tens of nanometers to a few micrometers. Liposomal DDSs have shown their capability to deliver drugs in a new fashion, allowing exclusive sales of encapsulated drugs to be extended beyond the initial compound's patent expiration date. However, existing methods to form liposomes and encapsulate drugs are based on bulk mixing techniques with limited process control and the produced liposomes frequently require post-processing steps. In this dissertation, a new method is demonstrated to control liposome formation and compound encapsulation that pushes beyond existing benchmarks in liposome size homogeneity and adjustable encapsulation. The technology utilizes microfluidics for future pharmacy-on-a-chip applications. The microfluidic system allows for precise control of mixing via molecular diffusion with reproducible and controlled physicochemical conditions compared to traditional bulk-phase preparation techniques (i.e. test tubes and beakers). The laminar flow and facile fluidic control in microchannels enables reproducible self-assembly of lipids into liposomes in a sheathed flow-field. Confining a water-soluble compound to be encapsulated to the immediate vicinity where liposome formation is expected to occur reduces sample consumption without affecting liposome loading. The ability to alter the concentration and control the amount of encapsulated compounds within liposomes in a continuous-flow mode is another interesting feature towards tailored liposomal drug delivery. The liposome formation strategy demonstrated in this dissertation offers potential for point-of-care drug encapsulation, eliminating shelf-life limitations inherent to current liposome preparation techniques.Item Biological Nanofactories: Altering Cellular Response via Localized Synthesis and Delivery(2008-11-19) Fernandes, Rohan; Bentley, William E; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Conventional research in targeted delivery of molecules-of-interest involves either packaging of the molecules-of-interest within a delivery mechanism or pre-synthesis of an inactive prodrug that is converted to the molecule-of-interest in the vicinity of the targeted area. Biological nanofactories provide an alternative approach to targeted delivery by locally synthesizing and delivering the molecules-of-interest at surface of the targeted cells. The machinery for synthesis and delivery is derived from the targeted cells themselves. Biological nanofactories are nano-dimensioned and are comprised of multiple functional modules. At the most basic level, a biological nanofactory consists of a cell targeting module and a synthesis module. When deployed, a biological nanofactory binds to the targeted cell surface and locally synthesizes and delivers molecules-of-interest thus altering the response of the targeted cells. In this dissertation, biological nanofactories for the localized synthesis and delivery of the 'universal' quorum sensing signaling molecule autoinducer-2 are demonstrated. Quorum sensing is process by which bacterial co-ordinate their activities at a population level through the production, release, sensing and uptake of signaling autoinducers and plays a role in diverse bacterial phenomena such as bacterial pathogenicity, biofilm formation and bioluminescence. Two types of biological nanofactories; magnetic nanofactories and antibody nanofactories are presented in this dissertation as demonstrations of the biological nanofactory approach to targeted delivery. Magnetic nanofactories consist of the AI-2 biosynthesis enzymes attached to functionalized chitosan-mag nanoparticles. Assembly of these nanofactories involves synthesis of the chitosan-mag nanoparticles and subsequent assembly of the AI-2 pathway enzymes onto the particles. Antibody nanofactories consist of the AI-2 biosynthesis enzymes self assembled onto the targeting antibody. Assembly of these nanofactories involves creation of a fusion protein that attaches to the targeting antibody. When added to cultures of quorum sensing bacteria, the nanofactories bind to the surface of the targeted cells via the targeting module and locally synthesize and deliver AI-2 there via the synthesis module. The cells sense and uptake the AI-2 and alter their natural response. Prospects of using biological nanofactories to alter the native response of targeted cells to a 'desired' state, especially with respect to down-regulating undesirable co-ordinated bacterial response, are envisioned.Item RNA Interference Mediated Suppression of Tn-Caspase-1 as a means of investigating apoptosis and improving recombinant protein production in Trichoplusia ni cells(2008-11-17) Hebert, Colin G; Bentley, William E; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The baculovirus expression system has proven to be a robust and versatile system for recombinant protein production in insect cells. A wide range of promoters is available for the facile expression of transgenes, and yields of up to 50% of total protein have been reported. However, in many cases production is decreased as a result of proteases and host cell apoptosis. To combat this problem, RNA interference (RNAi) has been used as a metabolic engineering tool to knockdown host genes responsible for decreasing the yield of recombinant protein. A novel caspase (Tn caspase-1) derived from Trichoplusia ni cells has been identified and characterized. Through modulation of caspase levels via either RNAi or through interaction with baculovirus protein p35, the overall level of apoptosis present in cell culture has been decreased. In addition, the use of in vitro RNAi targeted against Tn caspase-1 has increased the production of recombinant green fluorescent protein. To further study the effect of suppressing Tn caspase-1, a stable cell line producing in vivo RNAi was developed, resulting in a nearly 90% decrease in caspase enzymatic activity. This suppression was able to improve culture viability under adverse conditions and increase recombinant protein production levels up to two-fold that of standard cells.