Biomedical Engineering Reference
In-Depth Information
between active Si-OH groups. A water-soluble fl uorescent molecular probe (see Figure 12.3B) was
dissolved in the upper aqueous solution, and its permeation through the monolayer immobilized on
the porous glass plate (average pore diameter of 5 nm) was evaluated through increase of the fl uo-
rescence at 340 nm (excited at 280 nm) in the lower solution phase. Permeation coeffi cients at dif-
ferent temperatures are plotted in the form of an Arrhenius plot (Figure 12.4A). The glass plate with
the immobilized monolayer clearly suppressed the permeability of the water-soluble probe (plot (a))
compared to a bare glass plate (curve (b)). Permeation through the immobilized monolayer exhib-
ited a discontinuous change at around 45°C, which is very close to the phase transition temperature
of polymerized dialkylorganosilane
in aqueous solution, as determined by differential scanning cal-
orimetry (DSC). The obtained result demonstrates that permeability of the water-soluble molecular
probe was successfully regulated by phase transition of a single monolayer. This is the fi rst example
of permeation control using only 2 nm thick monolayer, which is the thinnest lipid fi lm operating as
a permeation valve. This permeation control was accomplished by hybridization of weak monolayer
structure to rigid support of porous glass.
Stabilization of lipid membrane structures through hybridization that inorganic structure was
extended to aqueous vesicle systems, as reported by Katagiri et al. Cerasome, that can form a siloxane
network covalently attached to the bilayer membrane surface, was newly developed (see Figure 12.5)
[14,15]. The term “Cerasome” was named after ceramics and soma. Alkoxysilane-bearing amphiphi-
les (Figure 12.5A) were dispersed in aqueous medium under appropriate conditions, resulting in multi-
lamellar vesicle structures with a bilayer thickness of ca. 4 nm and vesicular diameter of 150 nm,
as seen in transmission electron microscopic (TEM) image (Figure 12.5B). The TEM image of the
vesicular aggregates was also observed in the same specimen (Figure 12.5C). The vesicles retained
their original spherical structure even in their aggregates, implying suppression of the collapse and
fusion of the Cerasome, probably due to the formation of the intra- and intermembrane siloxane
network. Hybridization of vesicle structures with inorganic framework makes it possible to form
stable multicellular mimic.
(A)
(B)
At high temperature
−
6.0
−
6.5
(b)
−
7.0
(a)
−
7.5
2.8
3.0 3.2
Temperature (K
−
1
)
3.4
3.6
At low temperature
FIGURE 12.4
(A) Permeation coeffi cients at different temperatures are plotted in the form of an Arrhenius
plot: (a) monolayer-immobilized porous glass plate and (b) bare porous glass plate. (B) Illustration for control
of material permeation upon temperature changes.
