Encapsulation Processes by Bilayer Vesicles

Encapsulation Processes by Bilayer Vesicles 423 Mean Curvature... 

In this brief review we will describe some important encapsulation processes by vesicular aggregates. Encapsulation will be broadly interpreted. Apart from solubilization in the aqueous pool inside the vesicle, the term will also encompass binding of solubilizates to all binding sites available in the vesicular system. We will not discuss bilayer vesicles formed from amphiphiles further functionalized by receptor molecules, such as amphiphilic cyclodextrins. ... 

Earlier reports [50] showed that vesicles composed of oleic acid can grow and reproduce as oleoyl anhydride spontaneously hydrolyzed in the reaction mixture, thereby adding additional amphiphilic components (oleic acid) to the vesicle membranes. This approach has recently been extended by Hanczyc et al. [51], who prepared myristoleic acid membranes under defined conditions of pH, temperature, and ionic strength. The process by which the vesicles formed from micellar solutions required several hours, apparently with a rate-limiting step related to the assembly of nuclei of bilayer structures. However, if a mineral surface in the form of clay particles was present, the surface in some way catalyzed vesicle formation, reducing the time required from hours to a few minutes. The clay particles were spontaneously encapsulated in the vesicles. The authors further found that RNA bound to the clay was encapsulated as well. 

The permeability of solutes across lipid bilayers is a product of the partition coefficient and the transverse diffusion coefficient [30]. Bilayer polymerization can alter solute diffusion by modifying either or both of these processes. In order to examine the effect of polymerization on bilayer permeability a nonionic solute of moderate permeability, [3H-glucose], was encapsulated in the vesicles prior to polymerization, removed from the exterior after polymerization, and its permeation across the bilayer was measured periodically [31]. Quantitative measurements of the 3H-glucose leakage revealed that the formation of linear polymer chains from methacryloyl lipids reduced the permeability coefficient to 0.3 to 0.5 of that of the unpolymerized lipid vesicles. A larger reduction (two orders of magnitude) was only found when crosslinked polymer networks were formed [31]. 

Vesicles form when a surfactant bilayer encapsulates an aqueous core (Fig. 1). The microstructure resembles that of a biological cell in which the plasma membrane has been replaced by a surfactant bilayer. These structures can form either spontaneously or as a result of shear or other processing of lamellar liquid crys-... 

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