Hierarchically Organized Systems Based on Liquid Crystalline Phases - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 159

There are other types of hierarchically ordered forms of LC nanostructures
not directly linked to the current discussion, such as poly (high internal phase
emulsions) (Sergienko et al., 2002), liquid crystalline elastomers (Ohm et al.,
2010), bicontinuous interfacially jammed emulsion gels (Cates and Clegg,
2008), polymerized LC phases (Armitage et al., 1996; Forney and Guymon,
2010; Srisiri et al., 1998; Yang et al., 2002), lipid nanocapsules (Huynh et al.,
2009), and layer-by-layer assemblies involving LC nanostructures. Structured
emulsions, formed primarily from simple monoglycerides, are the focus of the
current contribution.

6.2 ISA SOMES : FORMATION AND CHARACTERIZATION

Dispersing the LC nanostructures in excess water (typically 80-95%) in the
form of submicron-sized (typically 200-400 nm) particles without loss of the
original structure has been a requirement for most industrial applications for
the last two decades. Cubosomes and hexosomes, which consist of cubic and
hexagonal nanostructures, respectively, were originally developed by Gustafs-
son et al. (1996, 1997). Similar systems were later explored for further internal
nanostructures by Yaghmur et al. (2005) who gave them the general term
ISAsomes, from internally self-assembled somes (or particles). Subsequent
developments on ISAsomes have shown that their internal structure is not
only limited to the cubic (Pn3m, Im3m, or Fd3m) and hexagonal but can also
include microemulsion (Yaghmur et al., 2005), lamellar (Yaghmur et al., 2008)
or even sponge phases (Angelov et al., 2011). Due to the tunable nanostruc-
ture of the oil phase, these fascinating superstructures fi nd applications in
various scientifi c, technological, and medical disciplines.
ISAsomes are simply O/W emulsions that have been kinetically stabilized.
The primary components of ISAsomes are lipids, stabilizer, and water. Until
now the lipids monoolein (MO) and monolinolein (ML) have been utilized
directly or in their commercial forms (DU and GMO), although Phytantriol
(PT) has also been used in recent years to target specifi c applications (Lee
et al., 2009; Nguyen et al., 2010; Salonen et al., 2010b). Monoelaidin (ME) has
the same chemical formula as MO but a different molecular orientation, with
a trans rather than cis conformation of MO. ME is currently being investigated
(Yaghmur et al., 2008) as it forms the Im3m cubic phase along with two other
phases, Ia3d and Pn3m (Kulkarni, 2009, 2011; Kulkarni et al., 2007, 2009,
2010c ).
A range of surfactants, polymers, polysaccharides, and food hydrocolloids
are utilized as emulsion stabilizers. In fact, the amphiphilic triblock copolymer,
Pluronic F - 127 (PEO 99 - PPO 67 - PEO 99 ), hereafter simply F-127, has been most
widely used for structured emulsions such as ISAsomes (Guillot et al., 2010;
Gustafsson et al., 1996, 1997); nevertheless, polysaccharide- and polyethylene-
glycol-based stabilizers (Huynh et al., 2009) are also used with varying levels
of success. Emulsions are also known to be stabilized by proteins such as casein
and lactoglobulin (Dickinson, 2009; Salentinig et al., 2011). Solid particles, such