**2.7 Liposomes**

Liposomes are spherical microscopic vesicles containing one or more phospholipid bilayer (**Figure 10**). The inner core of the liposomes consists of hydrophilic parts of the phospholipid, while the lipophilic parts tend to remain in the lipid portion of the phospholipid bilayer. Extensive research has been carried out on the liposome-based delivery system for their application in the delivery of proteins or peptides, mainly via the oral delivery route. The advantage of liposome in oral delivery is mainly protecting the protein or peptide (e.g., insulin) from enzymatic hydrolysis in the GIT [57]. This protection is due to the encapsulation of the protein or peptide in the interior of the liposome, and thus, the protein or peptide is inaccessible to the proteolytic enzymes in the GIT. Liposomes also enhance the absorption of proteins or peptides (e.g., insulin) in the small intestine. The activity of the insulin-containing liposome depends on various factors such as the lipid components of the liposome, the charge on the surface of the liposome, etc. [58].

It is worth mentioning that the bile salts in the GIT can solvate the liposome resulting in their rupture and consequent release of the encapsulated proteins or peptides in the GIT. This solvation of liposomes is a problem with the application of liposomes as the oral delivery system. However, the problem with the *in vivo*

**Figure 10.** *General structure of liposomes.*

stability of liposomes can be improved by adopting strategies like coating the liposome with a polymer or using dehydrated forms of liposomes [31].
