Liposomes elastic vesicles

Transfersomes are vesicles prepared from lipids and an edge activator that might be a single-chain lipid or surfactant. The edge activator renders the vesicles elastic. As a result of the hydration force in the skin, elastic vesicles can squeeze through SC lipid lamellar regions [47], Transfersomes were much more effective than conventional liposomes when applied nonocclusively with respect to mass flow of lipid across the skin. After 8 h of transfersome application... 

Recently, for the transdermal delivery of drugs using carrier systems, attention has been focused on the development of transformable [284,285] or elastic vesicles [12], These vesicles are liposomes that contain surfactants or in general edge activators in addition to phospholipids in their lipid membranes (Figure 10), a fact that... 

During recent years, the topical delivery of liposomes has been applied to different applications and in different disease models (188). Current efforts in this area concentrate around optimization procedures and new compositions. Recently, highly flexible liposomes called transferosomes that follow the trans-epidermal water activity gradient in the skin have been proposed. Diclofenac in transferosomes was effective when tested in mice, rats and pigs (189). The concept of increased deformability of transdermal liposomes is supported by the results of transdermal delivery of pergolide in liposomes, in which elastic vesicles have been shown to be more efficient (190).The combination of liposomes and iontophoresis for transdermal delivery yielded promising results (191, 192). 

The effect of US on content release is attributed to the rarefaction phase of the sound wave. Thus, when the negative US wave impinges upon the liposomes, the air pocket expands and stresses the bounding monolayers and also those in the adjacent bilayer. If the pressure drop is large enough, then the stress exceeds the elastic limit of the weakest surface and, at some point, either the bilayer or the monolayer rends. When the integrity of the vesicle is lost, some or all contents are released. If the air in the pocket is expanded faster than it is diffused to the external aqueous phase, then, the monolayer... 

This potential force occurs in microstructured fluids like microemulsions, in cubic phases, in vesicle suspensions and in lamellar phases, anywhere where an elastic or fluid boundary exists. Real spontaneous fluctuations in curvature exist, and in liposomes they can be visualised in video-enhtuiced microscopy [59]. Such membrane fluctuations have been invoked as a mechanism to account for the existence of oil- or water-swollen lamellar phases. Depending on the natural mean curvature of the monolayers boimding an oil region - set by a mixture of surfactant and alcohol at zero -these swollen periodic phases can have oil regions up to 5000A thick With large fluctuations the monolayers are supposed to be stabilised by steric hindrance. Such fluctuations and consequent steric hindrance play some role in these systems and in a complete theory of microemulsion formation. 

Although vesicles that occur in nature and in drug delivery applications are much smaller, GUV can give valuable data on the behavior of SUV because most observations are universal and scale invariant (i.e. permeability coefficients, first-order elastic constants, etc. are liposome size independent) or can be scaled down to smaller dimensions (entrapped volume, encapsulation efficiency, surface area). For many applications, however, the large size is preferred due to easier observation. 

The first application of liposome electroformation was in supplying the starting objects (isolated unilamellar vesicles of a particular lipid composition, size and membrane tension) for membrane bending elasticity measurements by image analysis of membrane thermal fluctuations [14,15,23,27], See also Chapter 14 of this book. 

Liposome is a closed vesicle with the lipid-bilayer membrane, which takes a variety of shapes such as biconcave discocytes, cup-shaped stomatocytes and prolate and oblate ellipsoids, depending on the temperature and the osmotic conditions [1]. Among various attempts made to explain these shapes [2,3], Helfrich has discussed the bending elastic energy [4] of fluid membranes formed by lipids as... 

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