Molecular Transport Across Lipid-Based Nanochannels
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Date
2019
Publication Type
Doctoral Thesis
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Abstract
This doctoral thesis investigates the diffusion mechanism of unstructured polymers across three dimensional periodic networks of lipid-based nanochannels. Molecular transport of macromolecules and several types of molecules with different sizes and structures in confined media has been focus of interest in numerous applied and fundamental research fields. Inverse bicontinucous cubic phases (IBCPs) are a ubiquitous subset of lipidic mesophases with rich and intricate three-dimensional geometrical characteristics. Developing a better insight into diffusion phenomena inside IBCPs along with a better understanding of underlying mechanisms in self-assembly of lipid-water systems will bring the fields of nanotechnology, biology and drug delivery forward.
The first chapter introduces lipid-based mesophases, lyotropic liquid crystalline systems, and their several geometrical and physicochemical properties as well as their wide application in several scientific and technological areas. To this aim, emergence of rich topological structures in lipid-based mesophases at modified environmental conditions are explained. Furthermore, particular geometrical features of IBCPs along with molecular transport inside cubic phases as a function of symmetry or interactions of the diffusing solute with the lipidic matrix is discussed in detail. The chapter finishes with the principal aim of the work.
The second chapter is devoted to exploring the transport mechanism of unfolded polymers. Polyethylene glycol (PEG) is considered as the model polymer diffusing across the cubic phase with double diamond symmetry (Pn3 ̅m). While keeping the radius of water channel at a constant value, PEG of different sizes display altered transport properties. A change in diffusion regimes was observed once the size of the PEG is comparable to the size of the water channel. Due to the analogy of our experimental findings to the principles of polymer diffusion physics in confined media, the experimental observations are explained in the light of scaling arguments coupled with effective medium theory.
The third chapter describes the systematic transport of different molecules as a combined function of geometrical characteristics of the IBCP and the molecular properties of the diffusing solute. In terms of geometrical attributes of different bicontinuous cubic phases, the four-folded symmetry of the Pn3 ̅m phase reveals an enhanced diffusive performance compared to the six-folded Im3 ̅m phase. Additionally, these results point to a more dominant role of the Pn3 ̅m phase in achieving faster diffusion of gold nanoparticles. Furthermore, the results shed light on the influence of electrostatic potentials on the passage profile of the solute. Strikingly, in contrast to point-like molecules or nanoparticles, the unstructured polymers represent accelerated diffusion inside the Im3 ̅m phase. This is explained in the context of potential interactive effects of the polymers’ conformational changes with the bottlenecks ascribed to difference in symmetrical features of cubic phases or altered chemical conditions of the system.
The fourth chapter deals with the influence of the molecular affinity to the lipid-water system and partial equilibration of the model molecule, caffeine in determining its release mechanism from the lipid-based mesophase. The release kinetics strongly depends on the time protocol for pickups in a typical release experiment and such dependency is reflected in the values of effective diffusion coefficient computed using diffusion models. Our results point to remarkable effect of perfect-sink conditions in determining the release kinetics, where a model with more refined conditions, suitable to the release experiments is introduced, making it possible to gain enhanced understanding of the release data.
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Examiner : Mezzenga, Raffaele
Examiner: Isa, Lucio
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ETH Zurich
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Subject
Molecular transport; Inverse Bicontinuous Cubic Phases; Diffusion; Porous media; Lipid-based mesophases; Symmetry; Topology; Drug delivery; Release kinetics; Polymer; colloidal particles
Organisational unit
03857 - Mezzenga, Raffaele / Mezzenga, Raffaele