Chemical penetration enhancers phospholipids

Niosomes In order to circumvent some of the limitations encountered with liposomes, such as their chemical instability, the cost and purity of the natural phospholipids, and oxidative degradation of the phospholipids, niosomes have been developed. Niosomes are nonionic surfactant vesicles which exhibit the same bilay-ered structures as liposomes. Their advantages over liposomes include improved chemical stability and low production costs. Moreover, niosomes are biocompatible, biodegradable, and nonimmunogenic [215], They were also shown to increase the ocular bioavailability of hydrophilic drugs significantly more than liposomes. This is due to the fact that the surfactants in the niosomes act as penetrations enhancers and remove the mucous layer from the ocular surface [209]. 

The chemical composition of liposomes is an important parameter for their transdcrmal penetration. The most common phospholipid used for tlie preparation of topically applied liposomes is egg or soy derived phosphatidylcholine in mixtures with cholesterol. Phosholipids are very-attractive molecules for skin treatment as they combine penetration enhancement with skin hydration properties due to their tendency to bond water molecules. Their low toxicity makes them even more suitable for topical formulations. 

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