Liposomes, niosomes and surfactant vesicles

Phospholipids and other surfactants having two hydrophobic chains have CPP values of approximately 1 (see section 6.3.3) and tend to form lamellar phases. When equilibrated with excess water, these lamellar phases may form vesicles that can entrap dmg and these have potential use as dmg carriers. In this section we will consider several types of vesicular stmc-mres Box 6.4 (p. 213) shows some of the amphiphiles that form such stmcmres. 

Surfactants having two alkyl chains can pack in a similar manner to the phospholipids (see Box 6.4 for examples). Vesicle formation by the dialkyldimethylammonium cationic surfactants has been studied extensively. As with liposomes, sonication of the turbid solution formed when the surfactant is dispersed in water leads ultimately to the formation of optically transparent solutions which may contain single-compartment vesicles. For example, sonication of dioctadecyldimethyl-ammonium chloride for 30 s gives a turbid solution containing bilayer vesicles of 250-450 nm diameter, while sonication for 15 min produces a clear solution containing monolayer vesicles of diameter 100-150 nm. The main use of such systems has been as membrane models rather than as drug delivery vehicles because of the toxicity of ionic surfactants. 

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