Novel Methods for Rheological Characterization of Polymers and Polymeric Biofilms.

This dissertation reports that environmental conditions significantly impact the bulk mechanical properties of Staphylococcus epidermidis bacterial biofilms. Bacterial biofilms are commonly found as infections of implanted medical devices, which experience large shear forces within the bloodstream. The biofilm’s ability to withstand these forces and host immune responses makes infections difficult to eliminate. We aim to reduce the disease burden of biofilms by understanding the mechanical properties that allow them to survive in the bloodstream. In this dissertation, we will discuss various methods of in situ characterization of these biofilms that allows them to be studied directly in their natural growth environments. Additionally, we present a technique to weaken the biofilm that may allow for easier removal of infections. First, we design an in situ parallel plate bio-rheometer to grow the biofilm while replicating the shear stress (0.1 Pa) and temperature (37°C) environment that Staphylococcus epidermidis would encounter in the bloodstream. We are then able to directly characterize the elastic modulus (G’) and determine how biofilms respond to environmental conditions, such as osmotic stresses and temperature. We notice a non-monotonic dependence of G’ on NaCl concentration and an irreversible decrease in G’ after heating up to 60°C. Additionally, we determine the yield stress (~20 Pa) and fit the linear creep behavior with viscoelastic models to find the relaxation time (~750 s). We then investigate the effects of temperature on biofilm on three different scales: the bacterial cells, the extracellular polymers, and the bulk biofilm. We follow our growth protocol with a one-hour exposure at three temperatures: 37°C, 45°C, and 60°C. We find little difference between the lower temperatures, but significant decrease in cell viability and yield stress following a 60°C treatment. Finally, we examine a technique, cavitation rheometry, to rapidly characterize the elastic modulus of a material, which we believe can be used for in vivo diagnostics of soft biological matter. Through experimentation, simulation, and theoretical analysis, we extend this technique to viscoelastic materials of ~1 microliter volumes, comparable to typical clinical biofilm infections. Collectively, these results facilitate diagnostics of biological soft matter and bacterial biofilm infections based on material elasticity.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110442/1/leopavlo_1.pd

Two‐step continuous production of monodisperse colloidal ellipsoids at rates of one gram per day

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141576/1/aic16009_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141576/2/aic16009.pd

Characterization of a Reverse-Phase Perfluorocarbon Emulsion for the Pulmonary Delivery of Tobramycin

Background: Aerosolized delivery of antibiotics is hindered by poor penetration within distal and plugged airways. Antibacterial perfluorocarbon ventilation (APV) is a proposed solution in which the lungs are partially or totally filled with perfluorocarbon (PFC) containing emulsified antibiotics. The purpose of this study was to evaluate emulsion stability and rheological, antibacterial, and pharmacokinetic characteristics. Methods: This study examined emulsion aqueous droplet diameter and number density over 24?hr and emulsion and neat PFC viscosity and surface tension. Additionally, Pseudomonas aeruginosa biofilm growth was measured after 2-hr exposure to emulsion with variable aqueous volume percentages (0.25, 1, and 2.5%) and aqueous tobramycin concentrations (Ca=0.4, 4, and 40?mg/mL). Lastly, the time course of serum and pulmonary tobramycin concentrations was evaluated following APV and conventional aerosolized delivery of tobramycin in rats. Results: The initial aqueous droplet diameter averaged 1.9±0.2??m with little change over time. Initial aqueous droplet number density averaged 3.5±1.7?109 droplets/mL with a significant (p<0.01) decrease over time. Emulsion and PFC viscosity were not significantly different, averaging 1.22±0.03?10?3 Pa·sec. The surface tensions of PFC and emulsion were 15.0±0.1?10?3 and 14.6±0.6?10?3 N/m, respectively, and the aqueous interfacial tensions were 46.7±0.3?10?3 and 26.9±11.0?10?3 N/m (p<0.01), respectively. Biofilm growth decreased markedly with increasing Ca and, to a lesser extent, aqueous volume percentage. Tobramycin delivered via APV yielded 2.5 and 10 times larger pulmonary concentrations at 1 and 4?hr post delivery, respectively, and significantly (p<0.05) lower serum concentrations compared with aerosolized delivery. Conclusions: The emulsion is bactericidal, retains the rheology necessary for pulmonary delivery, is sufficiently stable for this application, and results in increased pulmonary retention of the antibiotic.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140105/1/jamp.2013.1058.pd

Heritability of a skeletal biomarker of biological aging

Changes in the skeletal system, which include age-related bone and joint remodeling, can potentially be used as a biomarker of biological aging. The aim of the present study was to investigate the extent and mode of inheritance of skeletal biomarker of biological aging—osseographic score (OSS), in a large sample of ethnically homogeneous pedigrees. The investigated cohort comprised 359 Chuvashian families and included 787 men aged 18–89 years (mean 46.9) and 723 women aged 18–90 years (mean 48.5). The TOSS - transformed OSS standardized in 5-year age groups for each sex, was analyzed as a BA index. We evaluated familial correlations and performed segregation analysis. Results of our study suggest the familial aggregations of TOSS variation in the Chuvashian pedigrees. In a segregation analysis we found a significant major gene (MG) effect in the individual’s TOSS with a dominant most parsimonious model (H2 = 0.32). Genetic factors (MG genotypes) explained 47% of the residual OSS variance after age adjustment and after including sex-genotype interaction, they explained 52% of the residual variance. Results of our study also indicated that the inherited difference in the skeletal aging pattern in men lies mostly in the rate of aging, but in women in the age of the onset of the period of visible skeletal changes

Characterization of a reverse-phase perfluorocarbon emulsion for the pulmonary delivery of tobramycin.

<p>BACKGROUND: Aerosolized delivery of antibiotics is hindered by poor penetration within distal and plugged airways. Antibacterial perfluorocarbon ventilation (APV) is a proposed solution in which the lungs are partially or totally filled with perfluorocarbon (PFC) containing emulsified antibiotics. The purpose of this study was to evaluate emulsion stability and rheological, antibacterial, and pharmacokinetic characteristics.</p> <p>METHODS: This study examined emulsion aqueous droplet diameter and number density over 24 hr and emulsion and neat PFC viscosity and surface tension. Additionally, Pseudomonas aeruginosa biofilm growth was measured after 2-hr exposure to emulsion with variable aqueous volume percentages (0.25, 1, and 2.5%) and aqueous tobramycin concentrations (Ca=0.4, 4, and 40 mg/mL). Lastly, the time course of serum and pulmonary tobramycin concentrations was evaluated following APV and conventional aerosolized delivery of tobramycin in rats.</p> <p>RESULTS: The initial aqueous droplet diameter averaged 1.9±0.2 μm with little change over time. Initial aqueous droplet number density averaged 3.5±1.7×10(9) droplets/mL with a significant (p</p> <p>CONCLUSIONS: The emulsion is bactericidal, retains the rheology necessary for pulmonary delivery, is sufficiently stable for this application, and results in increased pulmonary retention of the antibiotic.</p