Vesicles and vesicle gels - structure and dynamics of formation

Abstract

Vesicles constitute an interesting morphology formed by self-aggregating amphiphilic molecules. They exhibit a rich structural variety and are of interest both from a fundamental point of view (for studying closed bilayer systems) and from a practical point of view (whenever one is interested in the encapsulation of active molecules). In many circumstances vesicular structures have to be formed by external forces, but of great interest are amphiphilic systems, where they form spontaneously. Here the question arises of whether this means that they are also thermodynamically stable structures, which at least in some systems appears to be the case. If such vesicles are well defined in size, it is possible to pack them densely and thereby form vesicle gels that possess highly elastic properties even for relatively low volume fractions of amphiphile. Conditions for the formation and the microstructure of such vesicle gels have been studied in some detail for the case of unilamellar vesicles. Another important and topical issue is the dynamics of vesicle formation/breakdown, as the understanding of the transition process will open the way to a deeper understanding of their stability and also allow controlling of the structures formed, by means of their formation processes. Significant progress in the study of the transformation processes has been achieved, in particular by means of time-resolved scattering experiments.

Physicochemical and toxicological properties of novel amino acid-based amphiphiles and their spontaneously formed catanionic vesicles

“…In addition, results are also presented here for novel catanionic vesicles prepared from 12Lys12/DTAB [24] and 12Lys12/12Ser [25] mixtures. From a colloidal standpoint, catanionic vesicles bear several advantages as compared to conventional liposomes: (i) they form spontaneously upon mixing of individual co-solute micellar solutions, requiring no high-energy methods; (ii) they have long-term stability and in many cases exist as equilibrium structures (thus, indefinitely stable); (iii) they often present chain melting transitions well below room temperature; (iv) they offer the possibility of charge regulation, due to variation of the surfactant mixing ratio [9,[12][13][14][15]26,27].…”

Planar lamellae and onions: a spatially resolved rheo–NMR approach to the shear-induced structural transformations in a surfactant model system

“…Shear-induced MLVs have been found in many L a phases, [25][26][27][28][29] independent of the type of surfactant used. They have been observed in systems containing anionic, [1][2][3][4]19,[30][31][32][33][34][35][36][37][38][39] cationic, [40][41][42][43] nonionic 17,23,[44][45][46][47][48][49] or mixed cationic/anionic surfactants 50 as well as in lamellar phases formed by polymeric surfactants of the block copolymer [51][52][53] or the side-chain polymer type.…”

Pharmaceutical applications for catanionic mixtures

“…However, there are numerous variations in the appearance of the catanionic phase diagram. Gradzielski (2003) notes how the chain lengths of the two different surfactants in a catanionic system affect the symmetry of the phase diagram: the larger the difference in chain length, the more the asymmetry in the phase diagram. The types of structures that are formed mainly depend on the cationic/anionic ratio, but also on the total concentration at a certain ratio.…”

“…Traditionally, several different methods are used for the preparation of vesicles, such as sonication, thin-film hydration or high-pressure extrusion, whereas for other situations it may be sufficient to vortex or just shake a mixture vigorously to accomplish vesicle formation (Gradzielski 2003). Thus, one of the particularly interesting features of catanionic vesicles is their ability to form spontaneously.…”