Vesicle shape transformation

Vesicle Shape Transformations Induced by Alternating Electric Fieids... 

Peterlin, P., Arrigler, V., Kogej, K., Svetina, S., and Walde, P. (2009) Growth and shape transformations of giant phospholipid vesicles upon interaction with an aqueous oleic acid suspension. Chemistry and Physics of Lipids, 159 (2), 67-76. 

Angelova, M.I. et al.. Shape transformations of giant unilamellar vesicles induced by ethanol and... 

Besides issues related to the accuracy of force fields in spatially inhomogeneous systems comprising many chemically distinct components, the basic restriction related to the chemically detailed models is the rather small length and time scales that they can access. This limitation imposes severe restrictions for considering collective phenomena in amphiphilic vesicles, i.e., processes that involve large particle numbers. Typical examples include vesicle assembly, vesicle fusion, phase separation and shape transformations of multicomponent amphiphilic vesicles. For many of these processes, it is expected that the underlying atomistic details of the molecular constituents can be captured by a small number of relevant characteristics and universality classes, comprised of systems with a rather different atomistic structure, can be identified. These phenomena can be successfully investigated via minimal... 

Shape Transformations of Giant Vesicles Extreme Sensitivity to Bilayer Asymmetry. 

Another report showed that cyclodextrin vesicles (CDVs) (Section 5.3) can be decorated with peptides functionalized with an adamantane anchor. It was found that a (LeuGlu)4 octapeptide can induce a pH-dependent shape transformation of the vesicles at pH 7.4, the peptide merely binds to the vesicle surface, whereas at pH 5.0 it forms a jS-sheet and transforms the vesicles into a nanotube (Figure 7). It was shown that the vesicles release their contents as a result of this shape transformation. It should be emphasized that the pH range of this shape transformation matches the decrease in pH that occurs upon endosomal uptake by cells. Hence, these experiments suggest that the peptide-decorated CDVs may be a useful vehicle for intracellular delivery of drugs or antigens that are encapsulated inside the vesicle or bound on the surface of the vesicle. 

Egelhaaf, S. and Schurtenberger, P. 1994, Shape transformations in the lecithin-bile salt system From cylinders to vesicles. J. Phys. Chem. 98, 8560. 

This difficulty does not seem to affect the main physical properties of giant vesicles, and for several years physical studies on bending elasticity have been analyzed by direct photographic observation also, movements and shape transformations can be recorded in real time. Several reports on this type of physicochemical investigation are given in this book. 

Figure 7.6 Calculated shape transformation of an oblate vesicle in shear flow — yz. The numbers in each frame refer to time in seconds after the shear flow is turned on. They hold for a vesicle with i> = 0.8, shear rate y = 1/s", bending rigidity k— 10 erg, and size R = 10 pm. In each frame, the top picture shows the view onto the (x, z) plane. The bottom one shows the view onto the (x, y) plane. The arrows give the local velocity of the membrane.

Shape transformations of vesicles with intramembrane domains. Physical Review E, 53, 2670-83. 

Julicher, F., Seifert, U. and Lipowsky, R. (1993) Phase diagrams and shape transformations of toroidal vesicles. Journal De Physique II, 3,1681-705. 

Berndl K, Kas J, Lipowsky R, Sackmann E, Seifert U (1990) Shape transformations of giant vesicles extreme sensitivity to bilayer asymmetry. Europhys Lett 13(7) 659-664... 

Deformable vesicles of phospholipids, known as transfersomes, have recently been investigated for buccal delivery of insulin [83]. Transfersomes are morphologically identical to liposomes, but these vesicles can respond to external stresses by rapid shape transformations requiring low energy. This high deformability allows them to deliver therapeutics across buccal barriers. Sodium cholate or sodium deoxycholate is incorporated into the vascular membrane to prepare transfersomes. Pharmacological bio availability of insulin after administration of deformable vesicles is higher relative to subcutaneous insulin and buccal conventional insulin vesicles. 

The deformation of single RBCs and single fluid vesicles in capillary flows were studied theoretically by lubrication theories [214-216] and boundary-integral methods [217-219]. In most of these studies, axisymmetric shapes which are coaxial with the center of the capillary were assumed and cylindrical coordinates were employed. In order to investigate non-axisynunetric shapes as well as flow-induced shape transformations, a fully three-dimensional simulation approach is required. 

Fig. 6 Cryo-TEM micrographs show the shape of the aggregates in the course of the vesicle-to-micelle transformation in the MGO/CTAB mixture. (A) Coexistence of globular micelles, elongated micelles that are probably ribbon-like, and vesicles (lipid mole fraction 0.47). (B) Perforated vesicles (lipid mole fraction 0.64). Reproduced from Ref. [30] with permission of the American Chemical Society.

The basic nanoreactor in particle formation is a reverse micelle in most cases, with a generally accepted spherical shape. The particles generated from these micelles transforming into W/O microemulsions are also often spherical in shape. However, other surfactant architectures may also yield particles. Thus, vesicles have been instrumental in the formation of particles in many cases (not discussed in this book) [98] similarly, cylindrical micelles could also generate elongated nanoparticles with the required manipulations in the system. Unfortunately clear-cut evidence on this offshoot procedure of synthesis, i.e. rodlike particle formation from rod-like micelles is apparently not so extensively available. 

As the vesicular concentration is equivalent to tnoles/volume and V = 4/3nr, so r is proportional to the cubed root of the vesicle content [8,20], Thus, the data for each release event can be replotted as the frequency of release events versus the cubed root of vesicular amount (in moles). A second explanation suggests that a lognormal distribution of vesicular amount will result if multiplicative deviations from the mean occur such as if integral differences in the number of uptake transporters per vesicle result in multiplicative transmitter accumulation rates [21], Thus, release event data can also be plotted as the frequency of release events vs. the log transform of quantal size. When the amperometricaUy recorded data are plotted after either of the aforementioned transformations, a dramatically different histogram with a nearly gaussian distribution results that is said to reflect the vesicular size distribution. Small deviations in the gaussian shape are possibly due to variations in the vesicular concentration, which is assumed to be constant. 

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