Non-Specific Interactions Between Cationic Nanoparticle-Polymer Composites and Biomolecules

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Doctor of Philosophy (PhD)
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Materials Science & Engineering
atomic force microsopy
Mechanics of Materials
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This dissertation describes the consequences of non-specific binding between cationic nanoparticles (NPs) and biological materials ranging from persistence length reduction of single actin filaments, to modified kinetics of myosin V motility, and culminating with correlating THP-1 cell metabolic stress to viscoelastic changes. The bulk of the thesis (chapters 3-5), utilizes optically transparent polymer-NP composites with controllable hierarchical roughness to tune the interaction strength between actin filaments and the surface and impact myosin V kinetics. To generate hierarchical roughness, precise control over the thermodynamics and dynamics of NH2-functionalized NPs in polystyrene-ran-acrylic acid (SAA) is demonstrated in chapter 3. In particular, an interplay between aggregation and dispersion of NPs occurs by varying SAA composition, leading to roughness ranging from a few nms to hundreds of nms and tunable wettability with water contact angles ranging from 70° to 170°. Chapter 4 describes the relationship between roughness and actin binding with a model based on the worm-like chain model that weighs the bending energy associated with actin binding to surface features based on their size and density against the electrostatic potential of the surface. The model predicts the experimentally observed weakening of f-actin surface binding with increasing roughness, from immobilized, to side-on wobbly, and eventually end-on. Chapter 5 quantifies how perturbations in actin structure by electrostatic surface attachment effects myosin V kinetics. Myosin V velocity is slowed by backward stepping on NP-decorated surfaces. The Michaelis-Menten relationship of myosin velocity versus [ATP] exhibits a reduction in KM and VMAX explained by a reduced coordination between myosin and f-actin which causes backwards stepping and an increased ADP affinity. Chapter 7 outlines the method of variable indentation-rate rheometric analysis by Laplace transform (VIRRAL) which is developed to utilize basic Hertzian fitting of force curves to measure the viscoelasticity of THP-1 cells. Dextran-lysozyme nanogels loaded with Ag nanoparticles cause mitochondrial damage which metabolically stresses cells decreasing the ATP/ADP. Reduced [ATP] increases f-actin concentration and slows intracellular transport making the cytoplasm stiffer by increasing both low and high-frequency elasticity and the viscosity. Thus, metabolic stress in THP-1 cells is correlated with proportional increases in viscosity and elasticity, while the relaxation time of the cell, τ, remains unchanged.

Russell J. Composto
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