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 BPOD: A WIRELESS INTEGRATED SENSOR PLATFORM FOR CONTINUOUS LOCALIZED BIOPROCESS MONITORING(2019) Stine, Justin Matthew; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Process parameter spatial inhomogeneities inside cell culture bioreactors has attracted considerable attention, however, few technologies allow investigation of the impact of these variations on process yield. Commercially available sensing probes sit at fixed locations, failing to capture the spatial distribution of process metrics. The bio-Processing online device (bPod) addresses this problem by performing real-time in situ monitoring of dissolved oxygen (DO) within bioreactor cell cultures. The bPod is an integrated system comprised of a potentiostat analog-front-end, a Bluetooth Low Energy microcontroller, and a Clark-type electrochemical DO sensor. The Clark-type sensor uses chronoamperometry to determine the DO percent saturation within a range relevant for mammalian cell culture. The free-floating capsule is packaged inside a 3D-printed biocompatible shell and wirelessly transmits data to a smartphone while submerged in the reactor. Furthermore, the bPod demonstrated a sensitivity of 37.5 nA/DO%, and can be adapted to multiple sensor types, enabling numerous bioprocess monitoring applications.Item Dual-Chambered Membrane Bioreactor for the Dynamic Co-Culture of Dermal Stratified Tissues(2019) Navarro Rueda, Javier; Fisher, John P; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Every year over 11 million patients suffer severe burns worldwide. Facial burn statistics include victims of violence (warfare, acid attacks, scalding) and trauma (flame, electrical, chemical). Skin is the first barrier against external mechanical and biochemical factors, such as burning agents, and is composed of the epidermis, dermis, and hypodermis layers. When burned, skin cannot regulate temperature or fluid transport, or stop bacterial infection. Due to the importance of the skin barrier, natural healing and grafting treatments aim to quickly close the wounds with fast proliferation of fibroblasts and collagen deposition, a process that results in scarring, loss of function, and disfigurement. Tissue engineering has produced epidermis-dermis skin scaffolds for clinical use and in vitro dermal models. Throughout this work we studied 3D printing and bioreactor strategies for the simultaneous physiologic and topographic reconstruction of burnt facial skin tissues. First, we formulated a keratin-based bioink that can be used for 3D printing on a lithography-based 3D printer. Second, we implemented the keratin bioink in the production of Halofuginone-laden face masks for the improvement of contracture, scarring, and aesthetics in severe skin wound healing in an animal model. Due to lack of collagen organization and microstructural development, we introduced a novel dual-chambered (DCB) bioreactor system to study stratified tissues. For this, crosslinking density of the keratin-based hydrogels was used to fine tune the transport properties of membranes for potential use in guided tissue regeneration applications. Then, we assessed the viability of our novel DCB for co-culturing adjacent cell populations with the inclusion of a regulatory keratin membrane. Last, having studied the DCB with flat interfaces, we assessed its viability for perfusing curved interfaces. The integration of both curvature and cell populations allowed to assess the synergistic development of adjacent dermis fibroblasts and hypodermis stem-cell-derived adipocytes and evaluate whether including topography parameters would alter cell viability in the DCB. The strategies developed here elucidate on tissue stratification and aesthetic reconstruction. Furthermore, the keratin-based bioink, the engineered membranes, and the DCBs can be extended to study other stratified or gradient tissues and to fine-tune communication between cell populations in complex 3D constructs.Item EFFECTS OF 3D PRINTED VASCULAR NETWORKS ON HUMAN MESENCHYMAL STEM CELL VIABILITY IN LARGE BONE TISSUE CONSTRUCTS(2015) Ball, Owen Matthew; Fisher, John P; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)There is a significant clinical need for engineered bone graft substitutes that can quickly, effectively, and safely repair segmental bone defects. One emerging field of interest involves the growth of engineered bone tissue in vitro within bioreactors, the most promising of which, are perfusion bioreactors. Utilizing a tubular perfusion system bioreactor, which allows media to perfuse freely around alginate scaffolds laden with human mesenchymal stem cells, large-scale bone constructs can be created by simply aggregating these beads together in the desired shape. However, these engineered constructs lack inherent vasculature and quickly develop a necrotic core, where no nutrient exchange occurs. Through the use of 3D printed vascular structures, used in conjunction with a TPS bioreactor, cell viability after just one day of aggregation was found to increase by as much as 50 percent in the core of these constructs, with in silico modeling predicting construct viability at steady state.Item TUBULAR PERFUSION SYSTEM BIOREACTOR FOR THE DYNAMIC CULTURE OF HUMAN MESENCHYMAL STEM CELLS(2012) Yeatts, Andrew Bryan; Fisher, John P; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In vitro culture techniques must be improved in order to increase the feasibility of cell based tissue engineering strategies. Limitations of current techniques are largely a result of the slow diffusion of molecules such as oxygen into the interior of three dimensional scaffolds in static culture. In order to enhance nutrient transport we have developed a novel bioreactor, the tubular perfusion system (TPS), to culture human mesenchymal stem cells (hMSCs) in three dimensional scaffolds. In our design, hMSCs are cultured on scaffolds tightly packed in a tubular growth chamber. Media is perfused by a peristaltic pump through the growth chamber and around the tightly packed scaffolds. In the first part of the work hMSCs are encapsulated in alginate scaffolds and results demonstrate bioreactor culture enhances late osteoblastic differentiation of hMSCs. An investigation into shear stress in the system revealed that osteogenic markers increase with increasing shear stress and that the differentiation of hMSCs is dependent on cell radial position within scaffolds. In order to enhance the ability to implant these constructs in vivo, a method to create an aggregated cell containing construct in vitro in a bioreactor system was developed. In this part of the work hMSCs are cultured in individual alginate beads in the TPS bioreactor and the beads are aggregated to form one large construct. Following this the TPS bioreactor was investigated to culture synthetic poly-L-lactic acid scaffolds which were fabricated using supercritical carbon dioxide gel drying. In addition to investigating the effects of perfusion on hMSC growth in these scaffolds, the effect of microporosity was investigated. In the final part of the work, a study was completed to determine how TPS culture influenced in vivo bone regeneration. Here alginate beads as well as synthetic PLGA/PCL constructs were used as scaffolds. Results revealed the efficacy of using the tubular perfusion system for bone tissue engineering and demonstrated increased bone formation as a result of hMSC implantation in both alginate and PLGA/PCL scaffolds. These studies highlighted the need for bioreactor culture in vitro as well as scaffolds to support in vivo tissue interaction.