Recent advances in non-ionic surfactant vesicles (niosomes): self-assembly, fabrication, characterization, drug delivery applications and limitations

Figures & data

Figure 1. Locations of entrapped hydrophilic, lipophilic and amphipathic drugs in niosomes.

Figure 2. Major types of niosomes, MLV (multilamellar vesicles), OLV (oligolamellar vesicles) and ULV (unilamellar vesicles). Small circles (o) represent polar head group, sticks (–) represents apolar tails of single-chain surfactant molecules and a bilayer membrane represent a circular double surfactant molecules layer oriented in continuous tails-to-tails and polar heads lining the inner and outer circle.

Figure 3. Schematic of a single-chain surfactant, a_o = hydrophilic head group area, v = hydrophobic chain volume, l_c = hydrophobic chain length.

Table 1. Geometrical characteristic of surfactants and proposed various surfactant aggregates. Bulky head groups’ surfactants form micelles, cone-shaped surfactants form inverted micelles and cylindrical-shaped surfactants form bilayers.

Figure 4. Chemical structure of cholesterol.

Figure 5. Hypothetical positions occupied by DCP (A), Solulan (B) and sodium cholate (C) in the bilayer membrane of Span 60 niosomes stabilised by cholesterol (Abdelkader et al., 2011).

Table 2. Chemical structure, molecular weight, CMC and phase transition temperature of ionic and surfactant additives.

Figure 6. Confocal laser scanning micrographs of discomes (left) and conventional spherical niosomes (right) loaded with carboxyfluorescein (Abdelkader et al., 2012b).

Table 3. Overview of main characterization techniques for niosomes.

Characteristic	Instrumentation	Additional features	References
Bilayer formation	Polarized-light microscopy		(Abdelkader et al., 2010)
Morphology	TEM		(Perrie et al., 2007,  Egelhaaf et al., 2003)
	Cryo-SEM	Lamellarity determination	(Abdelkader et al., 2010,  Abdelkader et al., 2011)
	CLSM	Differentiation between  niosomes and discomes	(Abdelkader et al., 2012b,  Uchegbu et al., 1997)
Size	Dynamic light scattering	Nano-sized niosomes	(Mukherjee et al., 2007)
	Laser diffraction	Micro-sized niosomes	(Abdelkader et al., 2011)
Spreading ability	Goniometer	For better corneal uptake	(Abdelkader et al., 2012b)
Gel/liquid transition temperature	DSC	Fluidity of bilayer membranes	(Abdelkader et al., 2010)
Rigidity	AFM		(Manosroi et al., 2003,  Nakanoa et al., 2008)
Separation/purification	Ultracentrifugation		(Abdelkader et al., 2011)
	Gel-filtration		(Uchegbu & Vyas, 1998)
	Exhaustive dialysis		(Abdelkader et al., 2012b)
Skin/corneal penetration	CLSM		(Touitou et al., 2000)

TEM, Transmission electron microscopy; Cryo-SEM, Cryogenic scanning electron microscopy; CLSM, Confocal laser scanning microscopy; DSC, Diffrential scanning calorimetry; AFM, Atomic force microscopy.