UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Effect of Load History on Ovine Intervertebral Disc Biomechanics(2014) Goodley, Addison; Hsieh, Adam H; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Loading of the intervertebral disc (IVD) alters biomechanical properties by modifying fluid distribution in the nucleus pulposus -changing hydrostatic pressure and tissue response- during force transmission along the spine. This study combines pressure, vertical displacement, and radial bulge measurements to assess biomechanical function during healthy and adverse loading of ovine lumbar motion segments. High compressive loads and simultaneous transient exertions, representative of obesity or other high-load lifestyles, are expected to limit fluid recovery and inhibit IVD biomechanical function compared to low compressive load controls with similar transient exertions. Specifically, the adverse group will (1) lose the ability to generate intradiscal pressures equivalent to control discs at equal loads and (2) exhibit a greater degree of deformation and bulge during comparable loading. This study contributes a greater understanding of the effects of load on IVD health. Findings may inform future efforts to preserve disc biomechanics and reverse IVD loss of function.Item Development of Collagen Thin Films for Intervertebral Dis Cell Culture & Examination of Cell Phenotypes and Interactions(2011) Morschauser, Michael Anthony; Hsieh, Adam H; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intervertebral disc degeneration and the associated low back pain lead to a decrease in the quality of life for many individuals, as well as a substantial burden on the health care system. Current therapies are often aimed at resolving the symptoms of degenerative disc disease, rather than addressing the underlying causes of disc degeneration. Researchers have strived to develop cell-based therapies that will not only manage the associated symptoms of disc degeneration but also reverse the degenerative process. To do so, a thorough understanding of the function of each cell type of the disc, both in a healthy and degenerative state, must be reached. For this project, in vitro cell culture substrates for each disc cell phenotype were developed using collagen thin film technology. Hybrid films were created with both type I and type II collagen fibers, the presence of which were confirmed using fluorescently-labeled antibodies. The hybrid films, along with type I and type II collagen thin films, were used to characterize the annulus fibrosus and nucleus pulposus cell phenotypes by examining morphology and gene expression. Annulus fibrosus cell morphology was observed to be independent of collagen type, but instead on the presence of fibers. Time dependence was also noted. No statistically significant differences were noted for substrate dependent gene expression of either cell type. Various methods for separating the multiple cell types of the nucleus pulposus were evaluated, and filtration was chosen as the most acceptable. By culturing the two cell types together or individually and examining the gene expression trends, it was observed that chondrocyte-like cells and notochordal cells influence each other in vitro. This has significance regarding disc degeneration, as notochordal cells disappear from the disc. This work was able to develop novel substrates for culture of intervertebral disc cells and utilize these substrates to further characterize the distinct phenotypes of the different cell types found in the disc. It also examined the influence of the disappearance of notochordal cells from the disc has on the remaining chondrocyte-like cells' gene expression. This information could aid in the development of future cell-based therapies for intervertebral disc degeneration.Item The Regulation Of Intervertebral Disc Cell Interactions With Their Surrounding Microenvironment(2010) Rastogi, Anshu; Hsieh, Adam H; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intervertebral disc degeneration is the major cause of back pain in the US, which can be both physically debilitating and costly to treat. Current treatments include invasive surgeries, which can be effective in ameliorating pain, but also contain the risk of complications. Additionally, these strategies target clinical manifestations of disc degeneration, rather than examine the cause of degenerative changes. Therefore, current research focuses on finding minimally invasive treatments for disc disease such as gene therapy. Regulating intervertebral disc cell interactions with their immediate environment can be a useful tool in the development of therapeutic strategies. This was explored through environmental changes to assess shifts in cell phenotype as well as genetic modulation to elucidate alterations in cell function. Biochemical, nutritional, and physical factors were examined in immature nucleus pulposus cells to assess changes in gene expression, attachment, and proliferation. It was found that nutritional and physical factors can alter gene expression levels of NP cells, thereby altering cell phenotype. In addition, down-regulation of the proteolytic enzyme MMP-2 was explored through RNAi interference. Five shRNA lentiviral vectors were designed and validated for the sustained gene silencing of MMP-2. Silencing MMP-2 activity resulted in the inability of disc cells to focally degrade gelatin films as well as reduced ability of disc cells to remodel fibers in type I collagen gels, resulting in weakened gel architecture. These functional consequences were further explored in an in vivo study utilizing an annular needle-puncture model of disc degeneration. Injection of the shMMP lentiviral construct lead to decreased expression of MMP-2 in the disc, as well as improved disc height and morphology. Thus, the functional consequences of silencing MMP-2 were examined, elucidating its role in the degradative pathway leading to degenerative disc disease. The results of these studies can lay the foundation for developing therapeutic treatments for intervertebral disc degeneration.Item Miniature Fiber Optic Pressure Sensors for Intervertebral Disc Pressure Measurements in Rodents(2007-08-13) Nesson, Silas Carl; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mechanical stress due to interstitial fluid pressures can play a major role in the development of disc degeneration, a common cause of lower back pain. Pressures generated in the intervertebral disc have previously been measured in humans and animals. However, due to their small size, thus far it has been difficult to experimentally measure pressures in rodents. With the prevalent use of rodent disc models in mechanobiology, it is important to characterize the intradiscal pressures under externally applied stresses. In this thesis research, two different optical systems with novel miniature fiber optic pressure sensors have been developed. These systems are an intensity based solid-tip sensor system and a low coherence Fabry-Perot sensor system. Pressure sensors, which have diameters of only 363 µm, were designed to measure pressures in rat discs without disrupting the structure and altering the intradiscal pressures. For the first time, in vitro intradiscal pressure measurements of rodents have been successfully demonstrated by using these sensors.Item Biomechanics of the Intervertebral Disc: The Effects of Load History on Mechanical Behavior(2007-06-20) Gabai, Adam Shabtai; Hsieh, Adam; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Degenerative disc disease is associated with back pain, and can be a debilitating disorder. In addition to the biological contributions of genetics and aging, mechanical factors have been implicated in accelerating the progression of disc degeneration. Two studies were performed in order to explore the effects of various loading conditions on disc biomechanics. The first study explores the effects of compressive historical loads and disc hydration on subsequent creep loading and recovery. The second study investigates the restorative powers of creep distraction between compressive loading periods. In both cases three commonly applied mathematical models were employed to characterize disc behavior and the effectiveness of each model was validated. The studies confirm that hydration level has a significant impact on disc stiffness and time dependent behavior. Distraction and conditioning phases are shown to have a significant impact on hydration level and thus subsequent mechanical behavior.