Biomedical Engineering Reference
In-Depth Information
Figure 8. Schematic picture of: (a) splitting and spreading of a vesicle on a solid-
supported thiolipid monolayer; (b) unrolling and spreading of a vesicle on a solid-
supported hydrophilic spacer.
The kinetics of vesicle fusion, followed by monitoring the po-
sition of the minimum of the SPR reflectivity curves, depends on
the composition and molecular shape of the vesicular lipids and on
the nature of the substrate. As a rule, bilayer formation by vesicle
unrolling onto a hydrophilic surface is faster than monolayer for-
mation by vesicle fusion onto a hydrophobic surface. This is prob-
ably due to the fact that the processes involved in forming a planar
bilayer starting from a vesicular bilayer are considerably less com-
plex than those involved in forming a planar monolayer.
13,14
The pathway of vesicle fusion on hydrophilic surfaces de-
pends on several factors: the nature of the support (its surface
charge, chemical composition and roughness), the nature of the
lipid vesicles (their composition, charge, size and physical state),
and the aqueous environment (its composition, pH and ionic
strength). As a general trend, calcium ions are found to promote
the adsorption and rupture of vesicles and lipid bilayer formation.
15
Effects are particularly strong on mica.
16
It has been suggested that
the initial rapid stage of vesicle adsorption on hydrophilic surfaces
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