Small unilamellar vesicles preparation

Liposomes are formed due to the amphiphilic character of lipids which assemble into bilayers by the force of hydrophobic interaction. Similar assemblies of lipids form microspheres when neutral lipids, such as triglycerides, are dispersed with phospholipids. Liposomes are conventionally classified into three groups by their morphology, i.e., multilamellar vesicle (MLV), small unilamellar vesicle (SUV), and large unilamellar vesicle (LUV). This classification of liposomes is useful when liposomes are used as models for biomembranes. However, when liposomes are used as capsules for drugs, size and homogeneity of the liposomes are more important than the number of lamellars in a liposome. Therefore, "sized" liposomes are preferred. These are prepared by extrusion through a polycarbonate... 

In model systems for bilayers, one typically considers systems which are composed of one type of phospholipid. In these systems, vesicles very often are observed. The size of vesicles may depend on their preparation history, and can vary from approximately 50 nm (small unilamellar vesicles or SUVs) up to many pm (large unilamellar or LUV). Also one may find multilamellar vesicular structures with more, and often many more than, one bilayer separating the inside from the outside. Indeed, usually it is necessary to follow special recipes to obtain unilamellar vesicles. A systematic way to produce such vesicles is to expose the systems to a series of freeze-thaw cycles [20]. In this process, the vesicles are repeatedly broken into fragments when they are deeply frozen to liquid nitrogen temperatures, but reseal to closed vesicles upon thawing. This procedure helps the equilibration process and, because well-defined vesicles form, it is now believed that such vesicles represent (close to) equilibrium structures. If this is the case then we need to understand the physics of thermodynamically stable vesicles. 

Although detailed protocols for preparation of small unilamellar vesicles (SUVs) are published [80-82], their preparation is more time-demanding and complicated. In contrast, bicelles are prepared similarly to micelles with little effort. 

Entrapment of plasmid DNA and/or protein into liposomes entails the preparation of a lipid film from which multilamellar vesicles and, eventually, small unilamellar vesicles (SUVs) are produced. SUVs are then mixed with the plasmid DNA and/or protein destined for entrapment and dehydrated. The dry cake is subsequently broken up and rehydrated to generate multilamellar dehydration-rehydration vesicles (DRV) containing the plasmid DNA and/or protein. On centrifugation, liposome-entrapped vaccines are separated from nonentrapped materials. When required, the DRV are reduced in size by microfluidization in the presence or absence of nonentrapped materials or by employing an alternative method (7) of DRV production, which utilizes sucrose (see below). 

Quantitative entrapment of vaccines into small (up to about 200 nm diameter) liposomes in the absence of microfluidization (which can damage DNA and other labile materials when extensive) can be carried out by a novel one-step method (7) as follows SUVs (e.g., cationic) prepared as in section Preparation of Small Unilamellar Vesicles are mixed with sucrose to give a range of sucrose-to-lipid weight/weight ratio of 1.0 to 5.0 and the appropriate amount of plasmid DNA (e.g., 10-500 pg) and/or protein (e.g., up to 1 mg). The mixture is then rapidly frozen and subjected to dehydration by freeze-drying, followed by rehydration as in section Preparation of Vaccine-Containing Dehydration-Rehydration Vesicles. ... 

One very simple way to prepare small unilamellar vesicles is by the injechon method (as shown in Figure 9.22), i.e., when vesicles are formed by adding a concentrated methanol solution of surfactant into the aqueous solution of the solute to be entrapped (Domazou and Luisi, 2002 Stano et al, 2004). By this method, or by extrusion, vesicles of different average size, say 50 nm and 200 nm can... 

Liposomes used for transfection are either large unilamellar vesicles (LUVs) of 100 to 200 nm in diameter or small unilamellar vesicles (SUVs) of 20 to 100 nm. Liu et al.124 have reported that for a given liposome composition, multilamellar vesicles (MLVs) of 300 to 700 nm in diameter exhibit higher transfection efficiency than SUVs. However, more recent studies on the nature of the liposome-DNA complex (or lipoplex) revealed that lipoplexes from SUVs or MLVs do not differ significantly in size. On the other hand, the composition of the medium, not the type of the liposome used in the preparation of the lipoplex, plays a key role in determining the final size of the complex. And the transfection efficiency is also shown to depend on the final size of the complexes but not the type of the liposome.125... 

Artificial biomembrane mimetic model systems are used to characterize peptide-membrane interactions using a wide range of methods. Herein, we present the use of selected membrane model systems to investigate peptide-membrane interactions. We describe methods for the preparation of various membrane mimetic media. Our applications will focus on small unilamellar vesicles (SUVs) and large unilamellar vesicles (LUVs) as well as on media more suited for nuclear magnetic resonance (NMR) techniques, micelles, and fast-tumbling two-component bilayered micelles (bicelles). 

Ethanol Injection Small unilamellar vesicles (with diameter of 30 nm) can be prepared with the ethanol injection technique [128], Lipids are dissolved in ethanol and injected rapidly in the aqueous solution under stirring (final concentrations up to 7.5% (v/v) ethanol can be applied).The method is very easy, having the advantage of avoiding chemical or physical treatment of lipids. However, there is an extra step to remove ethanol and the concentration of vesicles produced is rather low. Also encapsulation of hydrophilic drugs is also low, due to the high volumes used. 

Liposomes occur in nature, but can also be easily synthesized in the laboratory. Depending on the preparation method used, whioh influenoes their size — in relation to the number of bilayer shells — and physical properties, liposomes are olassified as small unilamellar vesicles (SUVs, 25-50 nm), large unilamellar vesioles (LUVs, 100 nm to 1 pm), giant unilamellar vesicles (GUVs, 1.0-200 pm) multilamellar vesioles (MLVs, 0.1-15 pm), and multi-vesicular vesicles (MWs, 1.6-10.5 pm) the last consists of several small vesicles. Bicelles, which contain surfactant molecules in the lipid bilayer, constitute a special type of liposome. 

This may not be the case when the model system is a small unilamellar vesicle in which the monolayer curvatures are significantly different for the inner and outer monolayer. If these vesicles are prepared from a mixture of lipids, the inner monolayer may be expected preferentially to contain that lipid species that has a more negative spontaneous curvature at the bilayer water interface. 

Small unilamellar vesicles (SUV) were prepared by sonication. Briefly, phospholipids (DPPC, DPPG) and cholesterol (70/20/50 molar ratio) dissolved in chloroform/methanol (9 1, v/v) were mixed in a round-bottom flask. 

Methodology for Liposome Preparation - An informal agreement was reached on the use of a three-letter acronym to designate the type of liposome such as multllamellar vesicles (MLV) or small unilamellar vesicles (SUV) or large unilamellar vesicles (LUV) with the chemical composition in parenthesis after the acronym (Ref. 21, p. 367). The tern liposomes is therefore to be used as a generic name to Include all types of artificial vesicles composed of phospholipids and other amphipathlc lipids. 

Here, planar lipid bilayers are prepared by a modification of the original technique described by McConnell et al. (1). First, small unilamellar vesicles are prepared from phospholipids and then... 

The antiviral activity of the oil obtained from Artemisia arborescens L was also studied by Sinico et al. (2005). They studied the influence of vesicle structure and composition on the antiviral activity, against herpes simplex virus type 1 (HSV-1), of the vesicle-incorporated oil, multilamellar vesicles (MLV), and small unilamellar vesicles (SUV) positively charged liposomes prepared by the film method and sonication. The liposomal incorporation of A. arborescens EO enhanced the in vitro antiherpetic activity mainly when vesicles were made with hydrogenated soy phosphatidylcholine. 

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