Chemistry Reference
In-Depth Information
10.4
Nonlamellar Liquid Crystalline Surface Layers
298
10.4.1
Solid Interface
298
10.4.2
Model Biological Interface — Implications for Drug Delivery
303
10.5
Formation of Surfaces
307
10.5.1
Adsorption of LCNP
307
10.5.2
Forming from Components
308
10.5.3
Formation by Chemical Reactions (e.g., Lipolysis)
309
10.6
Structural Characteristics
310
10.6.1
Internal Structure of the Layer
310
10.6.2
Phase Transitions at the Interface
311
10.6.3
Effect of Including Guest Molecules
312
10.7
Applications and Future Outlook
313
References
313
10.1
INTRODUCTION
The amphiphilic nature of lipids allows it to self-assemble into many different
structures depending on the lipid shape, mixture composition, and external
conditions such as temperature. This self-association, driven by minimizing the
contact between the hydrophobic regions from the aqueous phase and balance
by head-group (repulsive) interaction and packing constrains of acyl chains,
gives rise to a rich variety of phases (Evans and Wennerström, 1999; Mouritsen,
2005; Seddon, 1990). In particular, the nonlamellar phase-based crystalline
structures have been the focus of great interest and study in the last two
decades. Unlike the micellar and lamellar structures, nonlamellar crystalline
structures, such as cubic, hexagonal, and sponge phases, have extremely high
surface area and may solubilize hydrophobic, hydrophilic, and also amphiphi-
lic molecules (Angelova et al., 2011; Larsson, 2000; Larsson et al., 2006; Larsson
and Tiberg, 2005; Lawrence, 1994; Malmsten, 2007a; Sagalowicz and Leser,
2010; Sagalowicz et al., 2006b). The crystalline phases can be dispersed into
particles with excess water. This was fi rst demonstrated for lamellar phases by
Bangham and colleagues in the 1960s (Bangham and Horne, 1964), and today
vesicles and liposomes are often used for a range of applications in formula-
tions for drug delivery, food, and consumer products as well as models for
biomembranes. (The term
vesicle
is often used for unilamellar aggregate,
whereas
liposome
refers to multilamellar structures.) Nearly 20 years ago,
Larsson and co-workers demonstrated that it was possible to prepare disper-
sions of nonlamellar liquid crystalline lipid phases, fi rst as lipid-aqueous cubic
phase particle, Cubosome (Gustafsson et al., 1996, 1997; Landh, 1994; Larsson,
1989, 2000; Larsson et al., 2006), which with appropriate dispersion stabilizer
could be made monodisperse. The dispersed particles are in equilibrium
with water and retain their internal structure. These lipid liquid crystalline
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