[Kinetics stability of liposomes]

Liposomes find extensive use as drug carriers. The surface characteristics of vesicles (particle size, charge, composition, hydrophobicity etc.) and also, the kinetic stability of liposomes are all key factors for controlling fundamental carrier properties, such as the encapsulation or adsorption efficiency, the organ distribution of the carrier or the RES clearance etc. Small unilamellar (SUV) vesicles of dimyristoyl-phosphatidylcholine (DMPC) were prepared under standardized conditions. The liposomes were prepared both in the absence and the presence of an uncharged polymer [polyvinyl alcohol (PVA), polyvinyl acetal (PVA1) and polyvinyl pyrrolidone (PVP) respectively] and simultaneously, the long-term (kinetic) stability of the aqueous lipid dispersions were studied. The aggregation behavior of colloidal dispersions of DMPC liposomes were tested in physiological salt solution and polymer solutions, respectively. Particle aggregation, which may take place on storage or when the stability is lowered, are well reflected in the shift of the mean size and the distribution function towards higher values. The particle sizes, the size distribution and their change in time were measured by photon correlation spectroscopy using a Malvern ZETASIZER 4 apparatus (Malvern Instruments, UK).