**5. Liposomes**

Liposomes can be defined as spherical vesicles, which involve one or more layers of phospholipids. These drug carriers can be used to load hydrophilic drugs in the inner core and/or lipophilic drugs in the double layer of phospholipids [54].

The main advantages of liposomes are their augmented stability and decreased toxicity of the encapsulated drug, capacity to be fused directly with the target cell membranes (**Figure 5**), biologically inert, non-antigenic, and non-pyrogenic, increased efficacy and therapeutic index of several drugs (actinomycin-D, amphotericin B, Taxol, Daunorubicin), improved stability via encapsulation, nontoxic, flexible, biocompatible, completely biodegradable, and non-immunogenic for systemic and non-systemic administrations, reduce the toxicity of the encapsulated agent, help reduce the exposure of sensitive tissues to toxic drugs, site avoidance effect, flexibility to couple with site-specific ligands to achieve active targeting [55].

On the contrary, the main issues of liposomes are linked to their production; several methods have been developed, but industries prefer to use batch-mode methods, which are characterized by low repeatability. Moreover, raw materials employed are particularly non-economic, low-solubility, with short half-life, sometimes phospholipid undergoes oxidation and hydrolysis-like reaction, leakage and fusion of encapsulated drug/molecules, the production cost is high, and fewer stables [54].

**Figure 5.** *Liposomes as drug carriers.*
