Abstract
Amphiphilic block copolymers within a range of volume fraction spontaneously form vesicles in aqueous solution, where a water core is enclosed by a polymer bilayer. Thin-film rehydration is a method used to produce vesicles routinely; a thin film is immersed in water, the film swells, and vesicles are formed which bleb off from the film surface. We have studied the early stages of hydration for PEO–PBO block copolymer thin films under controlled water vapor conditions to understand this formation mechanism and so enable more efficient ways to encapsulate molecules using this method. Neutron and X-ray measurements show that the initial film exhibits weakly ordered structure with isotropic parallel and vertical orientation; the films initially swell and maintain the same orientation. At a critical point the layer swells rapidly and makes highly ordered lamellae structure at the same time. The lamellae are almost exclusively oriented parallel to the substrate and swell with increasing water absorption.
Highlights
Lipid molecules were among the first primitive biological containers on the primordial earth; they provided compartments that enabled complexity and specific cellular function in biological systems, all of which are essential for the evolution of life
Polymersomes are vesicles composed of amphiphilic copolymers and have a number of advantages compared to naturally derived biobased liposomes in particular: their diverse chemistry, tunable membrane permeability, stability under high shear, variable adhesion, and ability to store hydrophobic and hydrophilic molecules
The experimental results were complemented by self-consistent field theory calculations, which showed a good agreement after the fast reordering of the lamellae during swelling
Summary
Lipid molecules were among the first primitive biological containers on the primordial earth; they provided compartments that enabled complexity and specific cellular function in biological systems, all of which are essential for the evolution of life. Polymersomes are vesicles composed of amphiphilic copolymers and have a number of advantages compared to naturally derived biobased liposomes in particular: their diverse chemistry, tunable membrane permeability, stability under high shear, variable adhesion, and ability to store hydrophobic and hydrophilic molecules. They can have stealth-like properties, making them able to circulate in the body for a long time. The problem currently is the very low efficiency with which a particular molecule is sequestered inside This is because of the complex structural formation pathway in going from individual isolated amphiphilic molecules into vesicle aggregates. We follow in detail the way an initially disordered thin film orders on exposure to water vapor in situ using an environmental chamber (Figure 1)
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