Nonlamellar Lipid Liquid Crystalline Structures at Interfaces - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 287

nanoparticles (LCNP) have great potential as delivery vehicles and can also
be used to functionalize surfaces with nanostructures.
The lipid LCNP recently has gained an increasing interest in the medical
fi eld as a drug delivery vehicle because of its (1) space-dividing nature to allow
incorporation of different substances and (2) sustained drug release from the
crystalline matrix (Drummond and Fong, 1999; Lawrence, 1994). The nonla-
mellar phases can be used for delivery through topical application to the skin,
subcutaneous/intravenous injection, and mucoadhesion. Excellent reviews on
the use of lipid liquid crystalline phases as drug delivery vehicles can be found
(Drummond and Fong, 1999; Larsson et al., 2006; Lawrence, 1994; Malmsten,
2007b; Shah et al., 2001; Spicer, 2005; Yang et al., 2004). Other than the ability
to encapsulate drugs, the nonlamellar phase can also protect peptides from
enzymatic digestion (Drummond and Fong, 1999; Ericsson et al., 1983; Larsson,
2009; Larsson et al., 2006; Razumas et al., 1996a,b; Shah et al., 2001), which
prompts the idea of using LCNP for surface coating. To enable LCNP for
surface coating, it is important to understand the nature of the interaction of
the lipid crystalline structure with the interface. For example, the formation of
nonlamellar crystalline surfaces may be possible through direct deposition or
adsorption with lipid LCNP. In this review, we will focus on recent progress in
the formation of nonlamellar dispersions and its interfacial properties at the
solid-liquid and biologically relevant interfaces such as biological membrane
and mucosa. The effect of surface chemistry, phase structure, and solvent con-
ditions on the LCNP at the solid-liquid interface will be discussed. Key articles
on the interfacial behavior of liquid crystalline particles discussed in this
review are summarized in Table 10.1 .

10.2 BACKGROUND

10.2.1 Lipid Phases

The self-assembly property of lipids is driven by its amphiphilic structure.
Lipids aggregate in the aqueous solution exposing their hydrophilic domains
to water to maximize the polar interactions and cluster the hydrophobic moi-
eties to minimize interaction with the aqueous phase (Evans and Wenner-
ström, 1994). The phase behavior of lipids depends on many different factors,
ranging from the molecular structure, intermolecular forces, to lipid concentra-
tion and temperature (Jonsson, 1998; Kaasgaard and Drummond, 2006). The
so-called geometric packing properties of the amphiphilic molecule can be
used to understand and sometimes even predict the formation of a particular
phase (Israelachvili et al., 1976; Mitchell and Ninham, 1981). This concept is
based on the cross-section area of the polar head group in relation to that of
the acyl chain. This property can be expressed by the so-called packing
parameter ( v / al ), which is defi ned as the ratio between the volume of the
hydrophobic chain ( v ) and the product of the head-group area ( a ) and the