Browsing by Subject "fiber"

The development of electronic textiles, which have many potential healthcare and consumer applications, is currently limited by a lack of energy storage that can be effectively incorporated into such devices while having sufficient energy density, power density, and durability to perform well. The overall goal of this work was to improve the energy density and potential for use in electronic textile applications of a nanostructured composite of few-walled carbon nanotubes, manganese oxide, and reduced graphene oxide. Two approaches towards improving the desired properties by controlling the macroscopic structure of the composite were pursued: one, to make fiber or wire-shaped electrodes via wet-spinning in aqueous chitosan solutions (10% acetic acid), and the other, to make composite films with controlled porous structures using nitrocellulose as a sacrificial filler material. Both approaches yielded the desired macroscopic structures. The composite fibers were non-conductive due to the insulating nature of manganese oxide and its positioning on the surface of the fibers. Composite fibers of few-walled carbon nanotubes and reduced graphene oxide made by the same method were found to have good volumetric capacity, rate capability, stability and flexibility. Nonintuitively, electrochemical performance of composite films declined with increasing porosity due to a decrease in conductivity, highlighting the importance of balancing the interplay between properties important to device performance when designing controlled structures of complex materials.

The human gut microbiome is increasingly recognized as having a causal or contributing role in a wide variety of diseases. While mechanisms by which the microbiome contributes to or triggers disease processes are myriad, short-chain fatty acid (SCFA) production has been found to be a powerful regulator of inflammation and gastrointestinal (GI) function, and may be central to the link between host and microbiota. Supplementing the diet with microbially accessible carbohydrates, termed prebiotics, is one mechanism by which SCFA production can be augmented or altered. While prebiotic therapies to increase SCFA in the gut have shown some promise in treating or preventing disease, treatment potential is limited by substantial inter-individual variation in responses to prebiotics. Determining the cause for this variation is necessary to develop treatment approaches that maximize patient responsiveness. Ultimately, tools to predict an individual’s response to a prebiotic and to guide treatment options must be developed. Here, I seek to understand the drivers of inter-individual and intra-individual variation in prebiotic response and to develop strategies to predict this response. In Chapter One, I introduce the human gut microbiome and its roles in maintaining host health and contributing to disease processes. I also present the existing evidence for substantial variation in SCFA productive response to prebiotic supplementation and highlight the need for a more nuanced understanding of the drivers of such variation. In Chapter Two, I explore the contributions of host factors and prebiotic choice to variation in SCFA production. This chapter introduces a novel in vitro fiber fermentation system, which is used throughout this thesis, and shows our methods validation of such. We find not only that host identity and prebiotic choice both impact SCFA production, but that the interaction of these terms is a significant contributor, introducing the possibility of the need for personalization. We then identify multiple host factors, including microbiota community composition and baseline SCFA metabolic state of stool, that explain some portion of inter-individual variation in prebiotic response. In Chapter Three, this relationship is further explored during the first in vivo triple-crossover prebiotic supplementation study. We supply 28 healthy adults with three different prebiotic supplements in a balanced and uniform crossover design, measuring SCFA as the primary outcome. This study makes the major contribution of quantifying the relative contribution of individual identity and prebiotic choice to butyrogenic response, and identifying individual as the vastly stronger predictor. We also identify habitual diet and baseline fecal SCFA concentrations as potential predictors of prebiotic efficacy. As a secondary analysis, we apply co-inertia analysis to draw associations between dietary choices and fecal SCFA metabolism. Together, these works highlight the need for personalization of prebiotic therapy and introduce potential biomarkers of responsiveness. In Chapter Four, we apply the concept of prebiotic therapy to graft-versus-host disease (GVHD) and show efficacy in a murine model. Importantly, we show that efficacy of prebiotics in this model of GVHD is dependent on the starting state of the microbiota, as observed through community composition analysis and functional in vitro fiber fermentation.

This thesis explores the application of nanofibrous and microfibrous materials in the fields of cartilage repair and water electrolysis.

Articular cartilage lesions have a limited intrinsic ability to heal and are associated with joint pain and disability. The current treatment options suffer from high failure rates, prolonged rehabilitation times, and can be very costly. Therefore, an ideal solution is a low cost, mechanically strong, biocompatible replacement material with long lifetime.

To develop a cartilage replacement material, I first developed a two-step method to 3D print double network hydrogels at room temperature with a low-cost ($300) 3D printer. A first network precursor solution was made 3D printable via extrusion from a nozzle by adding a layered silicate to make it shear-thinning. After printing and UV curing, objects were soaked in a second network precursor solution and UV-cured again to create interpenetrating networks of poly(2-acrylamido-2-methylpropanesulfonate) and polyacrylamide. By varying the ratio of polyacrylamide to cross-linker, the trade-off between stiffness and maximum elongation of the gel can be tuned to yield a compression strength and elastic modulus of 61.9 and 0.44 MPa, respectively, values that are greater than those reported for bovine cartilage. The maximum compressive (93.5 MPa) and tensile (1.4 MPa) strengths of the gel are twice that of previous 3D printed gels, and the gel does not deform after it is soaked in water. By 3D printing a synthetic meniscus from an X-ray computed tomography image of an anatomical model, I demonstrate the potential to customize hydrogel implants based on 3D images of a patient’s anatomy.

On the basis of the previous work, I developed the first hydrogel with the strength and modulus of cartilage in both tension and compression, and the first to exhibit cartilage-equivalent tensile fatigue at 100,000 cycles. These properties were achieved by infiltrating a bacterial cellulose nanofiber network with a PVA-PAMPS double network hydrogel. The bacterial cellulose provided tensile strength in a manner analogous to collagen in cartilage, while the PAMPS provided a fixed negative charge and osmotic restoring force similar to the role of aggrecan in cartilage. The hydrogel has the same aggregate modulus and permeability as cartilage, resulting in the same time-dependent deformation under confined compression. The hydrogel is not cytotoxic, has a coefficient of friction 45% lower than cartilage, and is 4.4 times more wear-resistant than a polyvinyl alcohol hydrogel. The properties of this hydrogel make it an excellent candidate material for replacement of damaged cartilage.

In the field of water electrolysis, I studied the effect of fiber dimensions to their performance in water electrolysis. Water electrolysis is a good way to convert excess renewable energy to hydrogen. The generation of renewable electricity is variable, leading to periodic oversupply. Excess power can be converted to hydrogen via water electrolysis, but the conversion cost is currently too high. One way to decrease the cost of electrolysis is to increase the maximum productivity of electrolyzers. I investigated how nano- and microstructured porous electrodes could improve the productivity of hydrogen generation in a zero-gap, flow-through alkaline water electrolyzer. Three nickel electrodes—foam, microfiber felt, and nanowire felt—were studied to examine the tradeoff between surface area and pore structure on the performance of alkaline electrolyzers. Although the nanowire felt with the highest surface area initially provided the highest performance, this performance quickly decreased as gas bubbles were trapped within the electrode. The open structure of the foam facilitated bubble removal, but its small surface area limited its maximum performance. The microfiber felt exhibited the best performance because it balanced high surface area with the ability to remove bubbles. The microfiber felt maintained a maximum current density of 25,000 mA cm-2 over 100 hrs without degradation, which corresponds to a hydrogen production rate 12.5- and 50-times greater than conventional proton-exchange membrane and alkaline electrolyzers, respectively.

The gut microbiome is a complex ecosystem of hundreds of species that is constantly subject to perturbations as a result of day-to-day dietary variation, among other factors. In some cases, disturbances to microbial communities have been associated with lasting impacts on microbiome structure. While much research has been done to uncover sources of inter-individual variation in the gut microbiome, less focus has been given to understanding the ecological mechanisms governing intra¬-individual variation. To address this, we carried out dietary intervention studies in human cohorts and analyzed microbiome composition, metabolism, and physical particulate structure. We also employed in vitro models of the gut microbiome to manipulate variables difficult to modulate in vivo, and to collect samples with a greater temporal resolution. As discussed in more detail in Chapter 2, we found that bacterial communities retain an “ecological memory” of past prebiotic exposures, which is encoded within one day by changes to the abundance and transcriptional state of primary degraders. Chapter 3 details findings from an investigation into fecal particle size, in which we found this metric to correlate with microbiome diversity and to be stable within individuals. Together, the results presented in this dissertation present fundamental new insights into the ecology of the gut microbiome.