Polymeric vesicles, formation

Battaglia G, Ryan AJ (2006) Pathways of polymeric vesicle formation. J Phys Chem B 110 10272-10279... 

Polymer formation from monomeric butadiene lipid vesicles is demonstrated by the decrease of the monomer absorption at 260 nm as well as by GPC of the residue of a freeze dried polymer vesicle dispersion. The latter method was also used for proving the formation of polymeric vesicles from the methacryloyl lipids. 

On sonication, surfactants (4, 5) form vesicles which are polymerized by an initiator or by UV irradiation across either their bilayers or their head groups depending on the position of the double bond (Fig. 8). The polymeric vesicles are stable for extended periods even in 25 % C2H5OH. Efficient charge separation has been realized in such chemically disymmetrical polymerized vesicles. Photoexcitation of Ru(bpy)2 + placed on the outside of the vesicle resulted in the formation of long-lived reduced viologens on the inside. 

Polymerized-polymeric vesicles 3D 300-10 000 A diameter Polymerization of surfactants prior (polymeric) or subsequent (polymerized) to vesicle formation Months to a year Highly stable systems with controllable morphologies could be generated 55, 71, 72... 

In other reports, solvents immiscible with water were used to form polymeric vesicles. Feijen and coworkers reported on vesicle formation for diblock copolymers of PEO and polyesters or poly(carbonates) with both water-miscible and immiscible solvents [155], In some cases it is very difficult to remove the organic solvent and experiments with vesicles formed in water-immiscible solvents are limited to some extent. 

Polymersomes, self-assembled polymer shells composed of block copolymer amphiphiles. These synthetic amphiphiles with amphiphilicity similar to lipids constitute a new class of drug carriers. They are spontaneously formed in aqueous media, as unilamellar vesicles up to tens of microns in diameter. Amphiphilic block copolymers form a range of self-assembled aggregates including spherical, rod-like, tubular micelles, lamellae, or vesicles, depending on polymer architectnre and preparation conditions. Polymers having low hydrophobicity (less than 50%) favor the formation of micelles, however, intermediate level of hydrophobicity (50%-80%) favors the formation of vesicles. Polymeric vesicles, which have a liposome-like structure with a hydrophobic polymer membrane and hydrophilic inner cavity, are called polymersomes. 

The general approach used to attain such structures has been the synthesis of conventional vesicle-forming amphiphilic materials containing polymerizable functionalities in the molecule, vesicle formation, and subsequent polymerization, preferably by some nonintrusive means such as irradiation. In principle, the polymerizable functionality can be located at the end of the hydrophobic tail, centrally within the tail, or in association with the ionic or polar head group (Fig. 15.14). The choice of a preferred structure will probably be determined by the final needs of the system and the synthetic availability of the desired materials. 

COPI and COPII vesicles mediate anterograde or retrograde traffic between the endoplasmic reticulum and the Golgi apparatus (Lee et al, 2004). Generation of COP vesicles is a multi-event process that starts with the recruitment of small G-proteins and large coat complexes on the Golgi or the endoplasmic reticulum (ER) membrane. At the membrane surface, coat proteins collect transmembrane proteins and polymerize into a curved lattice. The lattice shapes the underlying membrane into a bud, which by membrane fission leads to the formation of an individual transport vesicle. After vesicle formation, the coat depolymerizes and the COP components are recycled in the cytosol for another round. 

Membrane and microfiuidic devices have also been adopted for the precision manufacture of solids from double-emulsion templates. To date, several different types of particles have been successfully produced by incorporating use of various membrane and microfiuidic devices in processes of polymerization, gel formation, crystallization, and molecular or particle self-assembly. Membrane emulsification is more suited to the fabrication of less sophisticated particulates, such as solid lipid micro-Znanoparticles, gel microbeads, coherent polymeric microspheres, and inorganic particles such as silica microparticles. Microfiuidic devices allow more sophisticated particle designs to be created, such as colloidosomes, polymerosomes, 3D colloidal assemblies, asymmetric vesicles, core-shell polymer particles, and bichromal particles. 

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