<p>Endothelial dysfunction is the predominant pathophysiological state prior to the onset of atherosclerosis. Currently, treatments for endothelial dysfunction are evaluated in vitro using two-dimensional (2D) cell culture assays or in vivo animal models. Microphysiological systems are small-scale three-dimensional (3D) tissue models that recapitulate the native tissue structure and function. An ideal microphysiological system is comprised of human cells embedded within a 3D matrix introduced to physiological fluid perfusion. Immune challenge in the form of cytokines or immune cells further recapitulates the native microenvironment.</p><p>A vascular microphysiological system was developed from a small-diameter tissue engineered blood vessel (TEBV) in a perfusion culture circuit. TEBVs were created from collagen gels embedded with human neonatal dermal fibroblasts and plastically compressed to yield collagen constructs with high fiber densities. TEBVs are rapidly producible and can be directly introduced into perfusion culture immediately after fabrication. Endothelium-independent vasoconstriction in response to phenylephrine and endothelium-dependent vasodilation in response to acetylcholine were used to analyze the health and function of the endothelium non-destructively over time.</p><p>Endothelial dysfunction was induced through introduction of the pro-inflammatory cytokine tumor necrosis factor – α (TNF-α). Late-outgrowth endothelial progenitor cells derived from the peripheral blood of coronary artery disease patients (CAD EPCs) were evaluated as a potential endothelial source for autologous implantation in both a two-dimensional (2D) direct co-culture model as well as a 3D model as an endothelial source for a tissue engineered blood vessel. CAD EPCs demonstrated similar adhesive properties to a confluent, quiescent layer of smooth muscle compared to human aortic endothelial cells. Within the TEBV system, CAD EPCs demonstrated the capacity to elicit endothelium-dependent vasodilation. CAD EPCs were compared to adult EPCs from young, healthy volunteers. Both CAD EPCs and healthy volunteer EPCs demonstrated similar endothelium-dependent vasoactivity in response to acetylcholine; however, in response to TNF-α, CAD EPCs demonstrated a reduced response to phenylephrine at high doses.</p><p>The treatment of TEBVs with statins was explored to model the drug response within the system. TEBVs were treated with lovastatin, atorvastatin, and rosuvastatin for three days prior to exposure to TNF-α. In all three cases, statins prevented TNF-α induced vasoconstriction in response to acetylcholine within the TEBVs, compared to TEBVs not treated with statins. Overall, this work characterizes and validates a novel vascular microphysiological system that can be tested in situ in order to determine the effects of various patient populations and drugs on endothelial health and function under healthy and inflammatory conditions.</p> / Dissertation

<p>Recent technological advances enable us to examine bacterial population dynamics with high temporal resolution with capacity for collecting high throughput data. Precise quantification of bacterial population dynamics can help us to further extend our understanding of how bacteria respond to environmental conditions. Such analysis provides critical information for improving antibiotic treatment protocols and for predictable engineering cellular behavior with synthetic gene circuits. </p><p>A fundamental question in bacterial population dynamics is how fast bacteria are killed in response to antibiotics. Due to their mode of action, β-lactams are more effective against fast-growing bacteria than against slow-growing bacteria. Indeed, it has been recognized that the rate of lysis by β-lactam antibiotics depends on the growth rate of the bacteria, based on previous works. However, past studies examined the growth rate modulation of lysis only during balanced growth and for very limited combinations of bacteria and drugs. Although there is evidence that growth plays key role in determining bacterial response to antibiotics, more comprehensive understanding on how wide range of growth rates affect antibiotic dose response had been overlooked. Instead, bacterial growth has been largely described to be in either growing or non-growing states. </p><p>To examine the general applicability of this growth rate dependence of antibiotic response, I examined how growth rate influences the lysis rate induced by beta-lactams. I found that there is a robust correlation between growth and lysis rates beyond what had been demonstrated in the previous work. Even during unbalanced growth, and regardless of how growth rate was modulated, the robust correlation between growth and lysis rates in bacterial populations were observed. Also, my data suggested a striking versatility of this correlation in different bacterial specie-drug pairs. Thus, my quantification greatly expands previous work by further examining the dependence of lysis rate on growth rate, and extends our understanding of the phenomenon associated with β-lactam antibiotic treatment, and of possible consequences arising from variable lysis rate. My strategy on modulating growth rates and measuring corresponding lysis rates demonstrates a simple and robust method for examining this phenomenon. These results have direct implications in two aspects.</p><p> First, my quantification method allows greater degree of freedom in modulating growth states of bacteria. Indeed, I was able to examine a wide range of growth rates in bacteria that allowed analyses of robust correlation in growth and lysis rates. The simple correlation reported from my work suggests the underlying reasoning for slow or fast lysis of bacterial population that can lead to designing optimal protocols depending on the growth rates of bacterial population. Due to frequent observation of slow-growing cells under conditions such as biofilm of pathogenic bacteria that complicates clinical symptoms and treatments in patients, they have been an important aspect of study for antibiotic tolerance. A quantitative understanding of the robust correlation between growth and lysis rates is critical for designing effective treatment protocols using β-lactams. </p><p> Second, the robust correlation serves as a foundation for predicting dynamics of synthetic gene circuits engineered for practical applications. In my work, I developed a prototype microbial swarmbot, which employs spatial arrangement to control growth dynamics of engineered bacteria. I demonstrated an engineered safeguard strategy to prevent unintended bacterial proliferation with this platform technology. In this work, I adopted several synthetic gene circuits to program collective survival in Escherichia coli: the engineered bacteria could only survive when present at sufficiently high population densities. When encapsulated by permeable membranes, these bacteria can sense the local environment and respond accordingly. The cells inside microbial swarmbots will survive due to their high densities. Those escaping from a capsule, however, will be killed due to a decrease in their densities. In this work, using antibiotics to control growth dynamics of the engineered populations was critical, and optimization of the growth dynamics depended on their environmental conditions that modulated their growth rates.</p><p>Together, my investigation on quantifying and analyzing bacterial growth dynamics demonstrated that understanding of bacterial population dynamics is crucial in addressing antibiotic tolerance in bacteria as well as in using them for engineered functions. By further examining the dependence of lysis rate on growth rate, we extended our understanding of the phenomenon associated with β-lactam antibiotic treatment, and of possible consequences arising from variable lysis rate. This information is important in designing a modular and readily generalizable platform technology as well. Therefore, my work demonstrates quantitative approach towards understanding of bacterial populations, and lays the foundation for engineering integrated and programmable control of hybrid biological-material systems for diverse applications.</p> / Dissertation

No description available.

Articular cartilage represents a primary target for tissue engineering strategies as it does not functionally regenerate within the joint. Many tissue engineering approaches have focused on the in vitro generation of neo-cartilage using chondrocyte-seeded scaffolds. Several studies have reported the morphological appearance of native cartilage, although its functional competence has not been demonstrated. Accordingly, mechanical conditioning has often been introduced to enhance biosynthetic activity of chondrocytes within 3D constructs. However although this strategy has significantly up-regulated proteoglycan synthesis, its effects on the synthesis of the other major solid constituent, type II collagen, has been modest. Analyses of normal joint activities reveal that cartilage is subjected to shear superimposed on uniaxial compression. This complex mechanical state has motivated the design of a biaxial loading system intended for use in vitro to stimulated bovine chondrocytes seeded in agarose constructs. This necessitated the redesign of the construct from cylindrical morphology to accommodate shear loading. The experimental approach was complemented with the development of computational models, which permitted prediction of both cell distortion under biaxial loading regimens and nutrient diffusion within the 3D constructs. An initial study established the profile of proteoglycan and collagen synthesis in free swelling cultures up to day 12. The introduction of dynamic compression (15% strain, 1 Hz for 48 h) enhanced proteoglycan synthesis significantly. In addition, when dynamic shear (10%, 1 Hz) was superimposed on dynamic compression, total collagen synthesis was also up-regulated, within 3 days of culture, without compromising proteoglycan synthesis. Histological analysis revealed marked collagen deposition around individual chondrocytes. However, a significant proportion (50%) of collagen was released into the culture medium, suggesting that it was not fully processed. The overall biosynthetic activity was enhanced more when the biaxial stimulation was applied in a continuous mode as opposed to intermittent loading. The present work offers the potential for a more effective preconditioning of cell-seeded constructs with functional integrity intended for use to resolve defects in joint cartilage.

The rheological behavior analysis of Engineered Cementitious Composites (ECC) is key to understand how the different preparation techniques affect the composite mechanical performance. However, the rheological assessment of reinforced materials becomes more complex since fibers usually cause flow disturbances not found in nonreinforced cementitious materials. Besides that, simple workability measurement techniques are not able to fully understand the composite behavior in the fresh state creating the need for more precise techniques to be employed. The main objectives of this study were to evaluate the ECC rheological behavior using different rheometer devices (Vane system and Ball measuring system) and investigate the influence of mixing processes on the fiber homogenization and rheological behavior. Additionally to this, a link between rheological behavior and mechanical performance was investigated. In the end, the ball measuring system revealed to be more efficient than the vane system when evaluating the composite rheological behavior. In addition, the mixing process influenced the rheological behavior of PVA-ECC especially regarding the moment which fibers are added. Fiber addition after mortar mixture improved fibers homogenization and reduced mixing energy by around 8%. Moreover, a correlation between rheological and mechanical properties showed that a 2-times variation in either yield stress or viscosity can lead to a variation of more than 50% in flexural strength without significantly affecting the composite compressive strength. It was also found that the lower the composite yield stress and viscosity the higher was its ultimate strain. To conclude, all those parameters contributed to understand the composite rheological behavior and globally optimize its performance. / Sem resumo

No description available.

Nanoparticles have gained growing attention of the scientific community over the past few decades due to their high potential to be used in diverse industrial applications. Nanoparticles often possess superior characteristics, such as catalytic activity, photochemical activity, and mechanical strength, compared to their bulk counterparts, making them more desirable in different industrial applications. During the past few decades, the use of the nanoparticles in various industries has been increased. With increasing usage release of nanoparticles into the environment has also increased. There is a growing concern about the nanoparticle toxicity and numerous studies have shown the toxic effects of different nanoparticles on various plants, animals, and microorganisms in the environment. Toxicity of nanoparticles is often attributed to their morphology and their ability to undergo different transformations in the environment. These transformations include aggregation, dissolution, and surface adsorption. Natural organic matter (NOM) are the most abundant natural ligands in the environment which include Humic acid and Fulvic acid. These high molecular weight organic molecules have complex structures and contain many different functional groups such as carboxylic acid groups, hydroxyl, amino and phenolic groups that can interact with the nanoparticle surface. The nature and the intensity of the interaction are dependent on several factors including the size and the surface functionality of nanoparticles and pH of the medium. The smaller the nanoparticle, the higher the adsorption of NOM due to the high surface to volume ratio of smaller particles. Functional groups on the surface dictate the surface charge of the nanoparticles in water depending on the acidity. The higher the acidity, higher the adsorption of NOM due to increased electrostatic attractions between positively charged nanoparticles and the negatively charged NOM molecules. Adsorbed NOM on nanoparticles affect the other transformations such as aggregation and dissolution and can in turn alter the reactivity and toxicity of the nanoparticles. Therefore, effect of NOM is an important factor that should be considered in environmental toxicity related studies of nanoparticles.

Utah State University Division of Environmental Engineering student, under the direction of Ms. Judith L. Sims, has investigated the fate of six pharmaceuticals and personal care products (PPCPs) in conventional and engineered on-site wastewater drain fields. The presence of PPCPs in the environment, especially in aquatic environments, has raised awareness to the effects of PPCPs on aquatic life and the fate of these PPCPs, and has caused regulators to become more involved in setting requirements for the removal of PPCPs from wastewater. This research investigated the fate of caffeine, acetaminophen, carbamazepine, sulfamethoxazole, progesterone, and fluoxetine in laboratory scaled columns that simulate conventional pipe and gravel on-site wastewater drain fields as well as engineered columns similar to the pipe and gravel simulated columns, but with the addition of media below the gravel layer to enhance PPCP removal via sorption and biodegradation. Results from the month long experiment showed that sulfamethoxazole removal in the columns representing conventional systems peaked at 74%. The other PPCPs were non-detectable. Sulfamethoxazole removal increased to 81% in columns engineered with a layer of sphagnum peat moss beneath the gravel layer and below the method detection limit (5.5 ng/mL) in columns engineered with a layer of charred straw beneath the gravel layer. No other PPCPs analyzed from the engineered columns were detected. Batch experiments indicated that sorption is the main mechanism for PPCP removal with the exception of progesterone, where biodegradation is a major mechanism.

Bentonite clay is widely used in barrier systems due to its low hydraulic conductivity and it high swell capacity. Exposure to inorganic solutions can cause significant increases in hydraulic conductivity, due to changes in the surface chemistry and fabric. This phenomenon can be attributed to a reduction in the thickness of the double layer, due to the cation exchange capacity of the clay. The clay can be modified with polymers to render it less susceptible to chemical attack. The treatment process allows the clay to be engineered to enhance specific properties, such as permeability and sorption. In the present study, engineered soils are prepared by sorbing organic polymers to the surface of Na-bentonite. Three classes, cationic, anionic and nonionic polymers are investigated. The sorbents are water-soluble compounds based on the polymerization of acrylamides (PAM). Mixing and sample preparation techniques are developed and discussed. The interaction of the polymeric compounds and the clay mineral surface are evaluated by testing the liquid limit, swell index and specific gravity of the soils. Permeability tests are performed to determine if the polymer treatment enhances the hydraulic performance of the clay when permeated with highly concentrated salt solutions. The effect of permeant, void ratio, initial wetting condition and preparation techniques are found to have a significant affect on the hydraulic conductivity.

Thesis (M.S.) -- Mississippi State University. Department of Forest Products. / Title from title screen. Includes bibliographical references.