Multilamellar vesicles, formation

Faure, C., Derre, A. and Neri, W. (2003) Spontaneous formation of silver nanoparticles in multilamellar vesicles. Journal of Physical Chemistry B, 107, 4738-4746. 

Semple SC, Klimuk SK, Harasym TO, et al. Efficient encapsulation of antisense oligonucleotides in lipid vesicles using ionizable aminolipids formation of novel small multilamellar vesicle structures. Biochim Biophys Acta 2001 1510 152. 

Closed bilayer aggregates, formed from phospholipids (liposomes) or from surfactants (vesicles), represent one of the most sophisticated models of the biological membrane [55-58, 69, 72, 293]. Swelling of thin lipid (or surfactant) films in water results in the formation of onion-like, 1000- to 8000-A-diameter multilamellar vesicles (MLVs). Sonication of MLVs above the temperature at which they are transformed from a gel into a liquid (phase-transition temperature) leads to the formation of fairly uniform, small (300- to 600-A-diameter) unilamellar vesicles (SUVs Fig. 34). Surfactant vesicles can be considered to be spherical bags with diameters of a few hundred A and thickness of about 50 A. Typically, each vesicle contains 80,000-100,000 surfactant molecules. 

Closed, spherical, single-bilayer, 300- to 600-A-diameter surfactant and/or phospholipid aggregates dispersed in aqueous solutions. Ultrasonic dispersal of multilamellar vesicles (MLVs) or employing procedures such as French Press filtration result in SUV formation. 

In conventional film-shaking liposome preparation, lipids (see Note 2) are dissolved in chloroform and the solvent removed by evaporation to leave a lipid film. Insulin-containing citrate buffer (pH 4.0) is added to hydrate the lipid film. Mechanical shaking of the mixture results in the formation of multilamellar vesicles. 

Dried Reconstituted Vesicles (DRV) (see Note 1), were initially developed in 1984 by Kirby and Gregoriadis (1). They are oligo-or multilamellar liposomes with capability of encapsulating high amounts of aqueous soluble molecules. The fact that the DRV technique involves vesicle formation under mild conditions (e.g., conditions that do not cause decomposition or loss of activity of active substances), makes this technique the method of choice for preparation of liposomal formulations of sensitive active substances as peptides, proteins or enzymes. 

Numerous techniques for the preparation of liposomes have been described. Typical procedures involve the hydration of lipid mixtures in buffer, resulting in the formation of large multilamellar vesicles (MLV). These are of limited use in... 

Tong, Q., Kosmeha, S. and Koetz, J. (2006) Formation of rodlike CdS nanoparticles in SDS/decanol based multilamellar Vesicles. Progr. Colloid Polym. Sci., 133, 152-158. 

Despite most of the myelin studies having focused on growth and late timescale behavior the mechanism for their formation is still unknown. Penetration scans using onion phase (lamellar phase is presheared into multilamellar vesicles or onions) have shown that myelin formation can be suppressed (48), This implies that there formation is sensitive to bilayer organization in the lamellar phase. Dissolution of these onion phases also have interesting and exotic behavior (48, 49),... 

Figure 12 exhibits that incorporation of cholesterol to dication artificial amphiphile induced a transformation of the aggregated structure from monolayer lamellae to monomolecular liposome (multilamellar liposome or single-walled vesicles). The vesicles are 100 200 nm in diameter and their membrane thickness is at least 5 20 nm. It is suspected that cholesterol molecules are mostly located in the outer half of the membrane, thus creating curvature suitable for the vesicle formation. 

Fascinating kinetics is observed when the systems are driven out of equilibrium. Typically, this is accomplished by mechanical treatment, by a sudden change of composition, or by a temperature jump. The most intensively studied mechanically induced transition is the formation of multilamellar vesicles ( onions ), which occur on shearing of a lamellar phase [32-36]. A sudden change of composition may lead to the formation of myelins [36-39]. Mechanical pinch-... 

The systems form flat stacked bilayers at rest when the systems have a small charge density, while at higher charge densities multilamellar vesicles are present. Increase of the ionic strength also again leads to the formation of flat bilayers with high amounts of the cationic surfactant. 

---