Chapter 4 - Elastic liposomes and other vesicles

Abstract

Vesicles are described and evaluated in this chapter. Liposomes are lipid bilayers rolled up into spherical shells with enclosed liquid within shells, separated from the outer (surrounding) liquid solution. On the other hand, elastic liposomes (ELs; Transfersomes) are phospholipid vesicles similar to traditional liposomes, but they are different from the latter because of the presence of edge activators (surfactants) that impart deformability and elasticity. It has been reported that these vesicles can enter the bloodstream through the skin. The claim that ELs can permeate intact skin is still controversial since skin pores can be opened without major impairment to only 20–40 nm. It has been postulated that Transfersomes are transported across the skin via concentration-independent, naturally occurring, and most likely hydration-based, transepidermal gradient(s). The chapter also discusses other vesicles such as other surfactant-based elastic vesicles, niosomes, ethosomes (ESMs), and transethosomes. The elastic vesicles were formulated from the micelle-forming surfactant octaoxyethylene laurate ester (PEG-8-L) and the bilayer-forming surfactant sucrose laurate ester (L-595). When nonionic surface active agents self-assemble, they form vesicles called niosomes. Nonionic surfactants such as polysorbates (Tweens), polyethoxy fatty ethers (Brij), and sorbitan fatty acid esters (Spans) are used for the preparation of niosomes. Compared to liposomes, niosomes have a larger membrane flexibility, a higher chemical stability, and a low cost of production. ESMs refer to lipid vesicles with relatively high ethanol content. These vesicular systems can increase the skin permeation of medications. Most ESMs are prepared from phospholipid, water, and ethanol. ESMs may also contain propylene glycol or isopropyl alcohol along with ethanol. Transethosomes are vesicles formulated by adding penetration enhancers or an edge activator (surfactant) to conventional ESMs. Transethosomes combine the advantages of ESMs and deformable liposomes.