Characterization of giant vesicles formed by phase transfer processes

Vesicles are of great interest as drug delivery system or models for cell membranes. For many applications, it is necessary to produce vesicles which are unilamellar, monodisperse, easy to adjust in size, and which can be filled with various types of active compounds. In a series of experiments, we produced giant vesicles with dimension of several millimeters by phase transfer processes. This new technique allowed synthesizing defined vesicles with lipid and surfactant membranes. The preparation of these aggregates occurred in two steps. First, we filled some amount of water into a cuvette and covered this liquid with an oil phase. Surfactants or lipids were solved either in the water or the oil phase. In the second step, a water droplet filled with methyl blue and saccharose was formed with a syringe in the oil phase. Due to density difference, the water droplet passed the plane oil/water interface and during this process it was transformed into a vesicle. The giant liposomes, thus formed, showed a high sensitivity against variations of the osmotic pressure, and their stability reached from seconds to hours. Due to the phase transfer process, the vesicle membranes often contained incorporated lenses of oil. If this hydrophobic liquid was released from the membrane, the vesicles decayed into smaller liposomes with a broad particle size distribution.