Recent Developments in Lyotropic Liquid Crystals as Drug Delivery Vehicles - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 217

Figure 8.1 Schematic representations of common LLC phases formed by amphiphiles
in water (Gin et al., 2008).
the surfactants, packing parameters, and interfacial curvature energy consid-
erations, LLCs can be formed with aqueous domains ranging from planar
bilayer lamellae to extended, cylindrical channels, to three-dimensional inter-
connected channels and manifolds (Gruner, 1989). These mesophases are
defi ned as lamellar (L α ), hexagonal (H), bicontinuous cubic [Q (or V)], and
discontinuous cubic (I) phases, based on their symmetry (Seddon, 1990). In
addition, most lyotropic mesophases exist as symmetric pairs, a “normal”
(type I) oil-in-water (O/W) system, consisting of lipid aggregates in a continu-
ous water matrix, and a topologically “inverted” (type II) water-in-oil (W/O)
version. The head-groups hydrated by water are arranged within a continuous
nonpolar matrix, which is composed of the fl uid hydrocarbon chains (Seddon,
1990). In addition to its biological signifi cance, inverse lipid phases could
be useful as host systems for incorporation of food additives (Sagalowicz
et al., 2006a,b), the crystallization of membrane proteins for drug delivery
(Cherezov et al., 2006; Sagalowicz et al., 2006b), and for inorganic synthesis
(Boyd et al., 2007).
The lamellar structure does not possess any intrinsic curvature and is con-
sidered as the midpoint of an ideal, symmetrical LLC phase progression (Fig.
8.1) (Gruner, 1989; Seddon, 1990). The current review is mainly focused only
on the inverted (W/O) mesophases (cubic and hexagonal), representing an
important class of nanostructures for potential applications.