Phospholipid-stabilized emulsions vesicles

The chapter has dealt with the stability and stabilisation of colloidal systems and covered topics such as their formation and aggregation. If the particle size of a colloidal particle determines its properties (such as viscosity or fate in the body), then maintenance of that particle size throughout the lifetime of the product is important. The emphasis in the section on stability is understandable. Various forms of emulsions, microemulsions and multiple emulsions have also been discussed, while other chapters deal with other important colloidal systems, such as protein and polymer micro- and nanospheres and phospholipid and surfactant vesicles. 

Colloidal liquid aphrons are a kind of emulsion in which micrometre-size dispersed droplets have an unusually thick stabilizing film and exist clustered together as opposed to either separated, nearly spherical droplets. The stabilizing aqueous film, sometimes called a soapy shell, is thought to have inner and outer surfactant monolayers. Taking this a step further, vesicles are droplets characterized by the presence at their surface of a lipid bimolecular film (bilayer) or series of concentric bilayers. A vesicle can be single or multilamellar and stabilized by natural or synthetic surfactants. Vesicles made from lipid or fat (e.g. phospholipid) bilayers are called liposomes (or, sometimes,/jofyso/wes). 

Emulsions are defined as dispersions of one liquid in another, stabilized by an interfacial film of emulsifiers such as surfactants and lipids. Emulsion formulations include water in od and oil in water emulsions, multiple emulsions, microemulsions, microdroplets, and liposomes. Microdroplets are unilamellar phospholipid vesicles that consist of a spherical lipid layer with an oil phase inside. 

W/O/W emulsions stabilized with soy lecithin-Span 80 mixtures have been used as the basis for the preparation of phospholipid vesicles [158]. A water-in-n-hexane emulsion was first prepared and the bulk of the hexane removed, the concentrate being dispersed in aqueous solution using a low concentration of hydrophilic surfactant which itself could then be removed leaving the phospholipid vesicles. 

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