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Browsing by Subject "Collagen"

Now showing 1 - 6 of 6
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    Advances in nanostructured materials via templated sol-gel structure control and self-assembly
    (2015-04) Rudisill, Stephen Gabriel
    This dissertation describes a body of work focused on understanding and improving morphology control of nanoporous structures via their aqueous chemistry. Synthesis of materials was carried out primarily using the Pechini process with metal nitrates and colloidal crystal templates. CeO2 and CeO2-derived compounds were used for a substantial portion of the dissertation as they are useful for thermochemical cycling experiments. Templated CeO2 shows a tenfold improvement over an untemplated material as well as a nanoparticle powder under lab-scale thermochemical cycling experiments.The Pechini process itself was then investigated as a means to obtain greater structural control over colloidal crystal templated materials. The process was demonstrated to involve phase separation, which allowed for the production of microspheres and bicontinuous networks of templated CeO2-based solids. Microspheres produced were between 1-3 µm in size, with polydispersity less than 15%. Further experimentation demonstrated that this phase separation methodology was generalizable to Fe2O3 and Mn3O4, though higher polydispersities were obtained for these materials.The final research project accomplished in this dissertation involves a method to produce ordered collagen fibrils through the incorporation of nanocrystalline cellulose during fibrillogenesis. Results were verified via scanning electron microscopy and a mechanism was proposed based on infrared spectroscopy results indicating a decrease in collagen-collagen hydrogen bonding.
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    Design of Silica-Collagen Nanocomposite for Corneal Replacement
    (2015-09) DiVito, Michael
    The cornea is the most commonly transplanted tissue in the United States. Globally, corneal diseases are the second leading cause of blindness. Due to strict FDA regulations, lack of eye banking facilities, and other factors which limit the supply of donor tissue, designing an artificial cornea made of readily available materials is of great interest. The synthetic constructs that are currently clinically available in the United States have had moderate success, but biocompatibility issues such as stromal melting and epithelial defects are still common. When considering a potential material for corneal replacement, it must meet the design criteria of the normal functioning cornea. The relevant design criteria can be broken down into three main groups: optical behavior, biomechanical properties, and biocompatibility. The presented work proposes silica-collagen nanocomposites as a viable candidate material to meet these design criteria. A bottom-up approach starting from the molecular level is utilized to modify the surface chemistry and physical properties of collagen fibrils. In doing so, methodologies are presented which allow for fine-tuning of optical, biomechanical, and biodegradation behavior. The first part of this work validates the theory that light scattering of collagen hydrogels is heavily dependent on the change in the material’s index of refraction over length scales comparable to the wavelength of incident light. This work shows that light scattering of collagen hydrogels can be minimized by a rapid neutralization technique, and by the addition of nanocrystalline cellulose. Additionally, collagen hydrogels with embedded magnetic nanowires can be polarized to form an aligned fibril microstructure and show an increase in light transmission. The second part of this thesis characterizes the mechanical and optical behavior, as well as the biocompatibility of silica-collagen nanocomposites. This work shows that a copolymerization method can be used to make implants which have improved biomechanical properties (when compared to pure collagen hydrogels) and can be re-epithelialized in an ex vivo rabbit model. Additionally, an improved two-step process for silica deposition onto collagen fibrils is presented. This new method shows that poly-L-lysine can be used to induce a uniform silica shell around collagen fibrils in the absence of large silica aggregates. This new method increases mechanical stiffness and enzymatic degradation resistance without producing any additional light scattering in the material. Silica-collagen nanocomposites show great potential in the context of corneal replacement. The methods developed and results presented here can be useful for improving any collagen-based corneal replacement, as well as in other applications such as drug delivery and silica nanoparticle templating.
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    LYVE1+ Macrophages Regulate Collagen Content in the Mitral Valve
    (2022-08-03) Peck, Alyssa L; Binstadt, Bryce; Osinski, Victoria; Auger, Jennifer; Farager, Jessica
    Regulation of cardiac extracellular matrix (ECM) is crucial to an organism’s overall health. Valvular ECM composition is important because valves maintain blood pressure and direction of flow. If the mitral valve becomes inflexible, it decreases blood flow in the body. Valvular stability and flexibility necessitate ECM proteins such as collagen, which must be regulated. Without regulation, a buildup of ECM proteins can occur. Many essential cardiovalvular regulatory mechanisms are poorly understood. However, regulation of collagen by specialized resident macrophages has been seen in arteries. Hyaluronan receptors (LYVE1) are present on specialized macrophages that, when bound, release matrix metalloproteinases (MMPs) that proteolyse collagen. To further our understanding on valvular flexibility, we used cross-sections of mitral valves from Lyve1-cre x Csf1r-floxed mouse models to compare mice with LYVE1+ macrophages to mice with depletion of LYVE1+ macrophages. We hypothesized that when LYVE1+ macrophages are depleted, there will be increased collagen content in the mitral valve. We found through picrosirius red staining and analysis that mice with LYVE1+ macrophages contain less collagen in the mitral valve when compared to mice where LYVE1+ macrophages were depleted. This indicates that LYVE1+ macrophages assist in the maintenance of ECM composition.
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    Re-aligning patient prognosis: the role of collagen in establishing an immunosuppressive microenvironment and facilitating cancer cell dissemination in pancreatic ductal adenocarcinoma
    (2021-10) Callaway, Mackenzie
    Pancreatic ductal adenocarcinoma (PDA) is an aggressive cancer with particularly poor clinical outcomes, in part, because of a dramatically altered stromal environment and striking immune dysfunction. Physical properties within tumors— such as aligned fiber architectures—are fundamental to cancer progression and invasion, and negatively correlate with survival in cancers like those of the breast. However, the influence of aligned architectures in PDA remains unexplored. Here, we elucidate the role extracellular matrix alignment has in establishing an immunosuppressive, metastasis-conducive tumor microenvironment in early, preinvasive PDA, as well as in precursory pancreatic inflammation. Using both mouse and human samples, we demonstrate an inextricable link between collagen, alignment, and 1) immunosuppressive macrophage localization, phenotype, and function (Chapter 2); 2) epithelial cell extrusion and subsequent invasion from intact ductal structures (Chapter 3). The contribution of alignment in both driving macrophage polarization and tumor cell dissemination could be attributed to altered focal adhesion dynamics, as targeting FAK in vivo resulted in a concomitant decrease in aligned collagen architectures, disseminated tumor cells, metastatic burden, and elongated, immunosuppressive macrophages. In Chapter 4, we explore the interplay between macrophages, collagen, and cancer cell extrusion using novel 3D microtissue co-cultures and human biopsies to reveal contributions of macrophages to dissemination in vitro and in vivo. Importantly, we show aligned collagen signatures and immunosuppressive macrophages are abundantly prevalent in pancreatitis, a known risk factor for PDA, suggesting that pancreatic precursory disease may create stromal memory that is later conducive to early immunosuppression and dissemination of PDA. This work highlights the opportunity to utilize FAK inhibitors to target stromal immunity and architectures and supports a model in which collagen architecture drives the early involution of an immunosuppressive, malignant microenvironment. Further, this thesis underscores the importance of targeting stromal matrices in precursor inflammation, limit cancer progression, and “reprogram” stromal immunity.
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    Temporal Changes in the Muscle Extracellular Matrix Due to Volumetric Muscle Loss Injury Promote Functional Fibrosis
    (2020-09) Hoffman, Daniel
    Skeletal muscle exhibits a remarkable ability to adapt and recover from a variety of stressors placed upon it. For example, numerous models of muscle injury, such as freeze, crush, and myotoxin, display immediate robust physical damage to the tissue when observed histologically. Yet in all three models the damaged tissue is able to completely regenerate back to pre-injury levels of fiber numbers and function. A complex process of cellular signaling mediates the successful regeneration seen in these models, which is ultimately achieved through satellite cell proliferation and fusion into new and existing myofibers. However, in more severe cases of traumatic injury, such as volumetric muscle loss (VML), there is a degree of damage that cannot be overcome endogenously. Instead of muscle regeneration, VML results in extensive fibrotic deposition and prolonged inflammatory signaling that dramatically reduces muscle function. The persistent fibrotic (TGF-β1, CCN2/CTGF) and inflammatory (IL-6, TNF-α) signaling further limits the ability of current treatment options to make significant improvements in patient outcomes. Moreover, the temporal changes in these processes have not been well documented following VML injury. Therefore, a study design using terminal time points of 3, 7, 14, 21 and 48 days following VML injury was created to evaluate the changes in extracellular proteins leading to fibrosis. Briefly, an initial significant increase in the proportion of collagen III was observed, which was subsequently reduced and overtaken by collagen I after 48 days post-VML. Similarly, histological results indicated an increase in loosely packed collagen through 21 days, before switching to an overwhelmingly dense collagen matrix by 48 days post-VML. Taken together, the window for successful intervention is likely before this shift to densely packed collagen I. Future work will evaluate immediate and delayed CCN2/CTGF inhibition combined with minced muscle graft implantation post-VML injury for effectiveness as interventions. Furthermore, the relationship between impaired neuromuscular junctions and fibrotic signaling will be assessed.
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    Thermobiomechanics of arteries
    (2008-11) Venkatasubramanian, Ramji T.
    Conventional treatments for arterial diseases, such as balloon angioplasty, often result in restenosis or re-narrowing of the arteries. In the last few years, the clinical importance of thermal therapies for atherosclerosis involving both freezing (cryoplasty) and heating (in-stent heating) has increased significantly because of their potential to control or minimize restenosis. An alternative to these therapies includes replacing the diseased artery through preserved arterial grafts which brings with it the need to effectively preserve them. Cryopreservation, i.e. preservation of tissues by freezing to very low temperatures, has therefore become an important problem in medicine. As mechanical properties of arteries play a large role in blood flow, a complete understanding of the biomechanical changes following thermal treatments and the underlying mechanisms is essential for further optimization of these treatments through controlling biomechanical changes. The objective of this dissertation was to quantify the biomechanical changes and investigate the underlying mechanisms post freeze-thaw. In this dissertation, the following specific aims were pursued: 1. Quantification of freeze-thaw induced biomechanical changes in arteries 2. Investigation of underlying mechanisms of thermobiomechanics SA1 involved quantification of freeze-thaw induced mechanical property changes in arteries using both uniaxial tensile tests and indentation. While uniaxial tensile tests were chosen for relatively easy sample preparation and testing, indentation was performed in order to study a more localized biomechanical response while characterizing the diseased artery response. SA2 involved investigation of the mechanisms underlying the biomechanical changes. This primarily involved understanding the changes to the collagen matrix and SMCs following thermal treatments. Changes to collagen matrix stability were assessed by quantifying the changes to the amide-III band using the FTIR spectroscopy. Changes in SMC function were studied from the response of arteries to norepinephrine and acetylcholine. Finally, MD simulations were performed as a tool to further investigate dehydration induced increase in thermal stability of the collagen matrix due to freeze-thaw at the molecular level. The important conclusions of this dissertation research are: 1. Freeze-thaw causes significant stiffening of the arteries. While, significant increase in the physiological elastic modulus (and reduction in toe region) was observed in the uniaxial tensile response, the peak and equilibrium modulus measured from indentation increased significantly following freeze-thaw. 2. Freeze-thaw induces significant changes in the collagen matrix and smooth muscle cells (SMCs) that are arguably the most important components of an artery. While dehydration accompanied by increased thermal stability was observed following freeze-thaw in the collagen matrix, it caused complete destruction of SMCs measured through loss in function. 3. At the molecular level, dehydration due to freeze-thaw (or any osmotic treatments) results in formation of new sidechain-backbone hydrogen bonds that are typically absent under hydrated conditions. These newly formed intra-protein hydrogen bonds in the absence of water molecules increase the thermal stability of the tropocollagen molecule.