Scholarship & Research

Using a magnetic resonance microscopy (MRM) technique, velocity perturbations due to biofouling in capillaries were detected in 3D velocity maps. The velocity images in each of the three square capillary sizes (2, 0.9, and 0.5 mm i.d.) tested indicate secondary flow in both the x- and y-directions for the biofouled capillaries. Similar flow maps generated in a clean square capillary show only an axial component. Investigation of these secondary flows and their geometric and dynamic similarity is the focus of this study. The results showed significant secondary flows present in the 0.9 mm i.d. capillary, on the scale of 20% of the bulk fluid flow. Since this is the “standard 1 mm” size capillary used in confocal microscopy laboratory bioreactors to investigate biofilm properties, it is important to understand how these enhanced flows impact bioreactor transport.

Due to the complicated nature of studying living bacterial communities, Magnetic Resonance Microscopy (MRM) is a necessary tool providing unique data that is complementary to other techniques such as confocal microscopy and microelectrodes. MRM has the ability to probe an opaque system non-invasively and collect velocity measurements, imaging data, diffusion, and relaxation values and is an asset in the quest to learn how biofilms establish, grow, and die. The goal of these studies was to extend current biofilm research using MRM to enhance our understanding of transport phenomena over a hierarchy of scales, from the microscopic diffusion level to the macroscopic bulk flow. Staphylococcus epidermidis was the bacteria chosen for the biopolymer diffusion and the secondary flow studies due to its common identification in opportunistic biofilm infections. This diffusion study was the first Pulse Gradient Spin Echo (PGSE) MRM measurements of the impact of environmental and chemical challenges on the biomacromolecular dynamics in medically relevant S. epidermidis biofilm material demonstrating the ability to characterize molecular dynamics in biofilms, providing a basis for sensors which can indicate the state of the biofilm after thermal or chemical treatment and provide information to further understand the molecular level mechanisms of such treatments. The secondary flow data clearly support the conclusion that reactor size impacts studies of spatially distributed biological activity, and the idea that, scaling of transport models in biofilm impacted devices is possible but requires more study. Additionally, due to the increasing amount of CO 2 in the earth's atmosphere and the need to understand the options of sequestering this CO 2 to combat the impacts of global warming, studies were conducted to understand how biofilms grow in porous media. The resilience of Bacillus mojavensis biofilms to super critical CO 2 is documented, and thus, this bacteria was chosen. Results indicate that by varying exchange times, T 2-T 2 experiments can determine the extent of biofilm growth in an opaque porous media as demonstrated in multiple glass bead pack configurations. Using MRM as a tool to study these biofilm systems over a wide range of environmental conditions is the focus of the research presented in this dissertation.

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