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.
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Item Engineering Biodegradable Vascular Scaffolds for Congenital Heart Disease(2015) Melchiorri, Anthony John; Fisher, John P; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The most common birth defects worldwide are congenital heart defects. To treat these malformations in a child’s cardiovascular system, synthetic grafts have been used as a primary intervention. However, current grafts suffer from deficiencies such as minimal biological compatibility, inability to grow and adapt, and high failure rates. Additionally, the grafts are not customized to the patient, which may lead to graft failure given that defects may vary significantly from patient to patient. The work presented here aims to adapt tissue engineering paradigms to develop customizable vascular grafts for congenital heart defects using to reduce the long-term risk and the number of surgeries experienced by patients. The first component of this research focuses on solvent-cast vascular grafts. This system of fabrication was used to explore how various strategies and graft modifications affect the graft’s performance in vivo. Grafts were fabricated with the mechanical properties necessary to withstand the stresses of a physiological environment and support neotissue formation. To improve tissue formation, the grafts were modified with bioactive molecules to improve vascular tissue growth. In addition, the grafts were combined with a tissue perfusion bioreactor. The bioreactor applied fluid flow to support cell seeding, differentiation, and growth of endothelial progenitor cells on the grafts, demonstrating a robust strategy for tissue formation prior to implantation. The second component of this research centers on the development of a biomaterial for 3D printing. 3D printing offers unparalleled customizability, as a graft can be designed based on medical images of a patient, tested via computer modeling, and then printed for implantation. A resin was developed consisting to produce grafts that were mechanically compatible with native blood vessels and maintained patency and tissue formation six months after implantation. The library of 3D printed vascular graft materials was also expanded by creating a novel copolymer resins, which varied in mechanical properties and degradation profiles. In addition, the concepts and strategies of biofunctionalization developed in the solvent-cast vascular grafts can be combined with the 3D printed graft strategies. Grafts designed, printed, and modified using these combinatorial approaches can greatly improve the long-term outcomes of treating congenital heart disease.Item Self-assembly of inorganic nanoparticle amphiphiles for biomedical applications(2015) Liu, Yijing; Nie, Zhihong; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ensembles of interacting nanoparticles (NPs) can exhibit novel collective properties ─ arising from the coupling between NPs ─ that can be radically different from individuals. Realizing the enormous potential of NPs in biomedical applications requires the organization of NPs into hierarchically ordered structures. My dissertation is focused on the design of NP amphiphiles (NPAMs) and the use of NPAMs as building blocks to construct polymer-inorganic hybrid materials. The NPAMs are made from NPs surface-grafted with amphiphilic block copolymers (BCPs). In this way, the NPAMs synergistically combine the properties of both inorganic NPs and grafted BCPs, such as optical and magnetic properties of NPs, and flexibility of BCPs. First, we demonstrated that NPAMs with relatively low polymer ligand densities (~0.03 chain/nm2) self-assembled into vesicular nanostructures composed of a single layer of NP chains in the membrane. The decrease in the interparticle distance between NPAMs in the chain vesicles led to strong plasmon coupling of NPs and hence enhanced efficiency in photoacoustic imaging. Second, we fabricated hybrid vesicles with well-defined shapes and surface patterns by co-assembling amphiphilic BCPs and NPAMs, which include Janus-like vesicles (JVs) with different shapes, patchy vesicles, and homogeneous vesicles. Third, we prepared magneto-plasmonic hybrid vesicles with various structures through concurrent self-assembly of NPAMs, free BCPs, and hydrophobic magnetic NPs. The hybrid vesicles were demonstrated for both light-triggered release of payload and magnetic resonance imaging. Particularly, the magnetic manipulation of vesicles to specific location can be used to enhance the photothermal effect of the vesicles in cancer imaging and therapy. Finally, we reported that the use of a microfluidic flow-focusing device for the self-assembly of JVs that can act as vesicular motors. The vesicles can be used to encapsulate active compounds, and the release of this payload can be effected using near-infrared light. This systematic study will help us gain deeper understanding of the self-assembly of NPAMs into controllable nanostructures and control the collective properties of NP ensembles for various applications. This research will also provide new insights into the fundamental questions that must be overcome before the hybrid materials can be utilized in effective cancer imaging and treatment.Item Low and Atmospheric Pressure Plasma Interactions with Biomolecules and Polymers(2015) Bartis, Elliot Andrew James; Oehrlein, Gottlieb S; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cold atmospheric plasma (CAP) sources have emerged as economical and environmentally friendly sources of reactive species with promising industrial and biomedical applications. Many different sources are studied in the literature for advanced applications including surface disinfection, wound healing, and cancer treatment, but the underlying mechanisms for these applications are not well-understood. The overall goals of this dissertation are to 1) identify how plasma treatments induce surface modifications and which plasma species are responsible for those modifications; 2) identify how changes in surface and plasma chemistry contribute to changes in biological activity of biomolecules; and 3) investigate how fluxes of reactive species produced by atmospheric pressure plasma devices can be controlled. As a first step, a well-studied low pressure plasma system was used to isolate the effects of ions, high energy photons, and radicals using Ar and H2 plasma. The finding that plasma-generated radicals can biodeactivate and modify films with negligible etching motivated further study at atmospheric pressure. Two very different CAP sources were used under mild, remote conditions to study the biological deactivation of two immune-stimulating biomolecules: lipopolysaccharide (LPS), found in bacteria such as Escherichia coli, and peptidoglycan, found in bacteria such as Staphylococcus aureus. The surface chemistry was measured to understand which plasma- generated species and surface modifications are important for biological deactivation. To simplify the complex molecular structure of the biomolecules and study specific moieties, model polymer films were studied including polystyrene, poly(methyl methacrylate), polyvinyl alcohol, and polypropylene. The interaction of the plasma plume with the environment was studied as a parameter to tune surface modifications. It was found that increasing ambient N2 concentrations in an N2/Ar ambient decreased surface modifications of LPS, similarly to how adding N2 to the O2/Ar feed gas decreased the plasma-generated O3 density and O atom optical emission. In this work, we first observed the formation of surface-bound NO3 after plasma treatment, which had not been reported in the literature. The plasma-ambient interaction was further studied using polystyrene as a model system. This detailed study demonstrated a competition between surface oxidation and nitridation, the latter of which occurs under very specific conditions. It was found that NO3 formed on all the materials studied in this dissertation after plasma treatment. This NO3 formed after treatment by both sources, but in different concentrations. The surface-bound NO3 correlated better with changes in biological activity than general oxidation, demonstrating its importance. Studying model polymers revealed that this surface moiety preferentially forms on – OH containing surfaces. Since the atmospheric pressure plasma jet (APPJ) operates with low N2/O2 admixtures to Ar and the surface microdischarge (SMD) operates with N2/O2 mixtures, the mechanisms that cause biological deactivation must be different, and are discussed.Item Investigation of a thiolated Polymer In Gene Delivery(2012) Bacalocostantis, Irene; Kofinas, Peter; Muro-Galindo, Silvia; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Thiol-containing bioreducible polymers show significant potential as delivery vectors in gene therapy, a rapidly growing field which seeks to treat genetic-based disorders by delivering functional synthetic genes to diseased cells. Studies have shown that thiolated polymers exhibit improved biodegradability and prolonged in vivo circulation times over non-thiolated polymers. However, the extent to which thiol concentrations impact the carrier's delivery potential has not been well explored. The aim of this dissertation is to investigate how relative concentrations of free thiols and disulfide crosslinks impact a polymeric carriers delivery performance with respect to DNA packaging, complex stability, cargo protection, gene release, internalization efficiency and cytotoxicity. To accomplish this goal, several fluorescent polymers containing varying concentrations of thiol groups were synthesized by conjugating thiol-pendant chains onto the primary amines of cationic poly(allylamine). In vitro delivery assays and characterization techniques were employed to assess the effect of thiols in gene delivery.Item SEQUENCE MODELING OF RAFT POLYMERIZATIONS WITH THE METHOD OF MOMENTS(2008-10-13) Zargar, Amin; Schork, Joseph; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Attempts to model the sequence structure of copolymers consisted of probabilistic functions that were incomplete and inaccurate. A novel technique to track sequence parameters is developed that determines not only copolymer composition, but sequence distribution as well. RAFT polymerizations are simulated with two independent and concurrent models to track MWD, conversion, copolymer composition, and sequence characteristics. Batch polymerizations are simulated with varying reactor conditions as a proof-of-concept to illustrate the power of the sequence model to track the composition of the polymer. Series of CSTR and PFR reactors with varying reactor conditions are then presented as applications to iteratively fine-tune copolymers with predetermined sequence and compositional structure.Item Ethylene Polymerization Using a Zirconium Amidinate Supported Catalyst(2004-05-07) Young, Andrea Elise; Sita, Lawrence; ChemistryA series of W. R. Grace Davison IOLA(TM), methylaluminoxane-silica (MAO/Silica) and MAO/IOLA support materials were used to activate and immobilize a zirconium amidinate single site catalyst of the formula Cp*ZrMe2[tBuNC(Me)NCEt]. Ethylene homo-polymerizations and co-polymerizations with 1-hexene were conducted in heptane and compared. The catalysts activity was investigated under varying condition such as pre-catalyst loading, pressure, temperature, co-monomer incorporation and additives. The catalyst supported on the MAO/IOLA B support material proved to be more active than the IOLA and m-IOLA support activators, and the MAO/Silica and MAO/IOLA A support materials. A difference in activity of as much as 1015 gPE/gcat.h-1 was noted. The catalyst sensitivity to varying ethylene polymerization conditions such as temperature and pressure were investigated for the MAO/IOLA B supported catalyst. Catalyst activities of more than 2100 gPE/gcat.h-1 were achieved. Homo-polymer and co-polymer samples were characterized and compared with respect to their melting temperature, molecular weights and polydispersities.