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Cubic Im3m
FAST RELEASE
pH 7
pH 2
Haxagonal Hu
SLOW RELEASE
pH 7
Cubic Im3m
FAST RELEASE
pH
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Figure 8.17
Schematics of the proposed pH-responsive drug delivery strategy across
the gastrointestinal tract. At pH 7, the drug nanocarrier has a reverse bicontinuous
cubic phase (Im3m) symmetry; at pH 2, in the stomach, the symmetry of the mesophase
changes to reverse hexagonal phase, slowing down diffusion and preventing the pre-
mature release of the drug; and at neutral pH in the intestine, the symmetry reverts to
bicontinuous cubic phase (Im3m), triggering the release of the active ingredients
loaded in the mesophase (Negrini and Mezzenga, 2011).
grade. Second, it offers a general, tunable release and diffusion strategy that
is not specifi c to the particular drug ingredients. Finally, the release can be
controlled in a fully reversible way and makes it suitable for a targeted deliv-
ery to specifi c points (pH) of the gastrointestinal tract.
The lipid (monolinolein), the pH-responsive molecule (linoleic acid), and
the model hydrophilic polyphenol drug (phloroglucinol) were used in this
study, and the main idea behind the strategy proposed is highlighted in Fig.
8.17. Because of the presence of linoleic acid, which can be in either the depro-
tonated or protonated state when changing the pH from neutral to acidic
conditions, respectively, the LLC undergoes a structural change from reverse
bicontinuous cubic phase to reverse columnar hexagonal phase, which is
accompanied by a change in the release rate by a factor of 4, thus preventing
the release in the stomach and making this system an ideal candidate for the
targeted delivery of active ingredients in the basic environment typical of the
intestinal tract.
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