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bilayer coverage (Vandoolaeghe et al., 2009c). The rearrangement within the
surface layer results in interfacial instability that releases particles after a criti-
cal amount of lipids have been exchanged. An SAXS study of the interaction
between unilamellar DOPC vesicles and the CPNP particles demonstrated
that the exchange leads to local phase change as an additional lamellar phase
appears with time (Vandoolaeghe et al., 2009a). In addition, the cubic phase
unit cell dimension decreases with time and the peaks corresponding to the
cubic phase eventually disappear. The exchange between the CPNP and the
supported lipid bilayer is slower, if the bilayer was made up of lipids in the gel
state, for example, dipalmitoylphosphatidylcholine (DPPC) (Vandoolaeghe
et al., 2009a). These studies demonstrated the usefulness of combining several
techniques to reveal the mechanism of interaction. In this case, null ellipsom-
etry revealed the adsorption kinetics, including the appearance of an adsorp-
tion maximum; QCM-D revealed the change in interfacial structure and
proved that indeed intact CPNP particles adsorbed to the bilayer; and NR
revealed the time-dependent change in composition. The SAXS data revealed
the change in composition is associated with a phase transition. The interesting
and controllable interaction of the nanoparticles with model membranes,
where the particles released are triggered by a local phase transition due to
the lipid exchange, suggests an interesting concept for the phase change trig-
gered release that might have potential in drug delivery systems.
10.4.2.2 Mucous Membrane
To use LCNP as an oral and topical delivery
system, it is important to understand the interaction between the mucous gel
layer and the crystalline phases. The mucous membrane is the outermost lining
of many biological systems, for example, the mouth, stomach walls, intestines,
eyes, and genital areas. The mucoadhesion property of GMO has been tested
using a fl ushing system with intestinal surface where the GMO forms liquid
crystals once in contact with the wet mucosa (Nielsen et al., 1998). The study
shows that the cubic phase is mucoadhesive when formed on wet mucosa.
To facilitate the delivery of the highly viscous cubic phase, particulate dis-
persion of the cubic phase has been made as a promising vehicle for mucosal
drug delivery. The interaction between CPNP and mucin, the main constituent
of the mucous layer, was tested using null ellipsometry and particle electro-
phoresis (Svensson et al., 2008b). This work shows a weak interaction between
the particles and mucin that is similar to the interaction between mucin and
PEO chains. This fi nding suggests that the CPNP are covered with the stabiliz-
ing PEO chains from the Pluronic stabilizer where the PEO chains dictate the
adsorption behavior.
To enhance the interaction between CPNP and the mucin surface, CPNPs
were modifi ed with positively charged chitosan (Svensson et al., 2008a).
The chitosan - modifi ed CPNPs show substantially larger adsorption on the
mucin surface compared to the unmodifi ed particles. The result suggests
that the electrostatic attraction between the positively charged chitosan and
negatively charged mucin increased the adsorption. This study demonstrates
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