Membranes of block copolymers

Comparison of Simulations of Lipid Membranes with Membranes of Block Copolymers... 

FIGURE 6. Infrared spectra of unoriented solid membranes of block copolymers and PMLG homopolymer cast from TFE. 

Release of compounds from delivery systems is currently a major field of research,especially in medical applications, for which the release of active compounds is needed at desired locations. Mueller et alP used DLS to assess the successful embedding of a hydrophobic substrate into the hydrophobic membrane of block-copolymer vesicular structures, without affecting the morphology of the self-assembly. Poly(butadiene)-fc-poly(ethylene oxide) self-assembles into unilamellar vesicles in dilute aqueous solution. A constant hydrophobic shell thickness was measured by DLS when the average hydrodynamic radius and size distribution depended on the nature of the encapsulated hydrophobic substrate. 

Daoulas KC, Muller M (2010) Comparison of simulations of lipid membranes with membranes of block copolymers. In Meier WP, Knoll W (eds) Polymer membranes/ biomembranes. Advances in Polymer Science, vol 224. Springer, Berlin Heidelberg, pp 43-85... 

Hammer and coworkers prepared PEG-h-PCL polymersomes entrapping DXR (Fig. 11a). The release of DXR from the polymersomes was in a sustained manner over 14 days at 37 °C in PBS via drug permeation through the PCL membrane, and hydrolytic degradation of the PCL membrane [228]. The release rate of encapsulated molecules from polymersomes can be tuned by blending with another type of block copolymer [229]. Indeed, the release rate of encapsulated DXR from polymersomes prepared from mixtures of PEG- -PLA with PEG- -PBD copolymers increased linearly with the molar ratio of PEG- -PLA in acidic media (Fig. lib). Under acidic conditions, the PLA first underwent hydrolysis and, hours later, pores formed in the membrane followed by final membrane... 

Block copolymers possess unique and novel properties for industrial applications. During the past 20 years, they have sparked much interest, and several of them have been commercialized and are available on the market. The most common uses of block copolymers are as thermoplastic elastomers, toughened thermoplastic resins, membranes, polymer blends, and surfactants. From a chemist s point of view, the most important advantage of block copolymers is the wide variability of their chemical structure. By choice of the repeating unit and the length and structure of both polymer blocks, a whole range of properties can be adjusted. 

In addition to its major use in determining the number-average molecular weight (Ma) of polymers, osmometry has also been used to determine M of block copolymer micelles. The method involves determining the osmotic pressure (77) across a membrane that is permeable to solvent only. Because osmotic pressure is a colligative property, it depends on the number of particles, and hence yields Ma. It also depends on the interactions between particles, and thus... 

The properties of ordered structures in block copolymer melts have yet to be fully exploited, but the structural and rheological anisotropy is likely to lead to applications not all of which can be envisaged yet. The precision self-assembly of block copolymers into ordered structures for thin film and interfacial applications has enormous potential. Other applications such as nanoscale templates, membranes and filters could exploit the self-assembly of block copolymers into domains with periods 10-100 nm. The possibilities are limited only by the molecular engineer s imagination. 

In biological membranes, integral proteins are amphipatic molecules their hydro-phobic moiety is embedded in the lipid bilayer and their hydrophilic moiety protrudes from the surface of the membrane279. So, it was interesting to prepare polymeric models of such amphipatic proteins. For that purpose, two new classes of block copolymers have been synthetized in Orleans, namely copolymers with a polyvinyl block and a polypeptide block and copolymers with a saccharide and a peptide block. We shall give some information concerning the preparation of these copolymers and then describe their structure. 

General Aspects of Block Copolymer Membrane Formation. 117... 

Recently, scientific interest has been concentrated on interactions between amphiphilic block copolymers and lipid mono- and bilayers [196-200], Understanding the nature of such interactions will open a route towards multiple applications in fields as biophysics, biomedicine, and biotechnology. Particular areas of scientific interest are, for instance, elucidation of the mechanism of membrane-sealing capabilities of block copolymers penetrating into lipids [198,201] and how adsorption of amphiphilic block copolymers to liposomes enhances their stability [202,203], Furthermore, the interactions between polymers and biomembranes play a central role in the investigation of polymer-induced flip-flop within lipid membranes [200, 204, 205], and in the triggered generation of synthetic membrane channels and pores in lipid membranes [196],... 

Features such as mechanical stability, tunable properties, responsiveness to environmental stimuli, ability to encapsulate both hydrophilic and hydrophobic compounds, etc. make polymer membranes excellent candidates for use in medical, pharmaceutical, and environmental fields. Hence, polymer membranes have attracted a considerable attention in recent years. In this section, we review the potential applications of block copolymer vesicles. 

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. 

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