Curvature-Tuned Preparation of Nanoliposomes

Abstract

Numerous methods have been reported for the preparation of liposomes, many of which, in addition to requiring time-consuming preparative steps and the use of organic solvents, result in heterogeneous liposome populations of incontrollable size. Taking into consideration the phenomenon of spontaneous vesiculation and the theory of curvature, here we present an extremely rapid and simple, solvent-free method for the preparation of monodisperse solutions of highly stable small unilamellar vesicles using both charged and zwitterionic lipids mixed with lyso-palmitoylphosphatidylcholine, exploiting a combination of a rapid pH change followed by a defined period of equilibration. Various experimental parameters and their interactions were evaluated in terms of their effect on resulting liposome size and shape, as well as on liposome stability and size distribution, with transmission electron microscope imaging being used to visualize the formed liposomes, and photon correlation spectroscopy to obtain statistical data on mean diameter and monodispersity of the liposome population. zeta potential measurements also provided information about the interpretation of vesiculation kinetics and liposome stability. The time interval of pH jump, operation temperature, equilibration time, and lipid type were shown to be the determining factors controlling the size, shape, and monodispersity of the liposomes. Buffer type was also found to be important for the long-term storage of the liposomes. Ongoing work is looking at the application of the developed method for encapsulation of bioactive molecules, such as drugs, genetic materials, and enzymes.

pH-Driven Self-Assembly of Acidic Microbial Glycolipids

“…16,21 The giant micelles-to-vesicle transition observed in the G-C18:1 sample is undoubtedly explained by the presence of the less bulky glucose headgroup, with respect to the sophorose disaccharide. The fact that this compound has the same oleic acid moiety as SL-C18:1 is a good hint of the fact that the headgroup plays the most important role in driving the formation of micelles, or vesicles.…”

“…Small Angle X-ray Scattering (SAXS): several publications have shown that the stimuli-driven self-assembly of lipids is a non-equilibrium process; 16,17 for this reason, we have repeated SAXS experiments on three different instruments using both ex-situ and in-situ analyses, one being complementary to the other. In the ex-situ approach, the self-assembled structures are analyzed within a few hours after their preparation.…”

“…16,17,19 The ex-situ SAXS spectra are presented in Figure 6b. First of all, one can recognize the similar scattering profile previously observed in-situ, indicating that the mode of preparation does not have a striking influence on the overall morphology.…”

“…This is shown in These minor discrepancies seem to be coherent with the kinetics-driven self-assembly behaviour expected in pH-jump systems and described earlier for other compounds. 16 …”

“…These factors are known to have an important influence on the self-assembly of most amphiphiles, including glycolipids. It was shown, for instance, that the rate of pH 16 or temperature 17 jump in vesicle-forming ethylene glycol-based amphiphiles, or in phospholipids, influences the size and type of aggregation: slow variation in temperature or in pH induces the formation of larger, or more aggregated, vesicles. In general, it was shown that, even if self-assembly properties of amphiphiles (aggregation number, critical micellar concentration, size and shape of micelles) can be predicted at equilibrium using thermodynamic arguments, 18 kinetics of aggregation and shape evolution should not be disregarded, because of the non-equilibrium phenomena.…”