Table 1.

Main lipid-based drug delivery systems and summary of their characteristics.

Type		Core	Lipid lamellarity	Size	Characteristic	Reference
Micelles		- Hydrophobic drug	- Monolayer	- 2 nm to 80 nm	- Lipid micelles are small-sized vesicles for solubilization of various poorly soluble pharmaceuticals.	[22]
Liposomes		- Hydrophilic - Hydrophobic drug (inner membrane space)	- One to twenty bilayers	- 30 nm to 3000 nm	- Liposomes are synthetically constructed phospholipid vesicles can encapsulate both hydrophobic and hydrophilic drug.	[23]
Nanoemulsions		- Hydrophobic drug (O/W) - Hydrophilic drug (W/O)	- Monolayer	- 50 nm to 500 nm	- Nanoemulsions are kinetically stable liquid-in-liquid dispersions with droplet sizes which has high surface area.	[24]
Solid lipid nanoparticles		- Solid lipid core-drug matrix	- Monolayer	- 50 nm to 1000 nm	- Solid lipid core instead of liquid oils may provide stability and controlled drug release as the mobility of the drug in a solid lipid matrix.	[25]
Polymer-lipid hybrids		- Polymeric core-drug (PLGA, gold, silica, iron oxide and etc.)	- Monolayer - Bilayer	- Polymer core (smaller than typically 300 nm) + bilayer (3 nm to 5 nm)	- Hybrid vesicles have an advanced vesicular structure to integrate best characteristics of liposomes and polymer in a new, single vesicle.	[26]
Biomimetics	Exosomes	- Hydrophilic/hydrophilic drug	- Bilayer	- 40 nm to 100 nm	- Exosomes are small intracellular membrane-based vesicles with desirable features such as a long circulating half-life, the intrinsic ability to target tissue and biocompatibility	[27]
	Blood cells (RBC, WBC and platelet)	- Polymeric core-drug - Hydrophilic/hydrophilic drug	- Monolayer - Bilayer	- 100 nm (nanovesicles) to 8 µm (whole cells)	- Blood cell-based vesicles have many unique advantages such as long life-span in circulation (especially erythrocytes), target release capacities (especially platelets), and natural adhesive properties (leukocytes and platelets).	[28]
	Cancer cells	- Polymeric core-drug - Hydrophilic/hydrophilic drug	- Monolayer - Bilayer	- Polymer core (smaller than typically 300 nm) + bilayer (3 nm to 5 nm)	- Cancer cell-derived vesicles carry the full array of cancer cell membrane antigens, and thus offer the inherent homotypic binding phenomenon frequently observed among tumor cells.	[29]