[Interaction of lipid membranes and neutral polymers by differential scanning calorimetry (DSC)]. / Lipidmembránok és neutrális polimerek kölcsönhatásának differenciál "scanning" kalorimetriás (DSC) vizsgálata.

Polymer-free and polymer-bearing liposomes from dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG) and cholesterol (Ch) 10:1:1 (w/w/w) were prepared. Polymer-bearing liposomes were formed by incorporating an uncharged polymer [poly(vinyl alcohol) (PVA), poly(vinyl alcohol-co-vinylacetal) (PVA-Al), poly(vinyl alcohol-co-vinyl propional) (PVA-Prol) poly(vinyl alcohol-co-vinyl butiral) (PVA-Bul) copolymer, polyvinyl pyrrolidone (PVP) or polyethylene glycol (PEG) respectively]. The effect of some polymers on the phase transition parameter of phospholipids (DMPC and DMPG) has been studied by differential scanning calorimetry (DSC). DSC has become a standard technique for studying the thermally induced transition of phospholipid molecules from an ordered crystalline-like state at low temperature (gel phase) to a liquid crystalline-like state at higher temperature. The interaction between phospholipids and polymers was characterized by the alteration of the phase transition parameters (Tp, Tm, delta T1/2, delta Hp, delta Hm) measured by DSC. It was observed that some phase transition parameters were affected by all polymers but in different extent. PVA-Prol copolymer exhibited a prominent effect in increasing the membrane cooperativity. The influence of PVA-Bul was unique; it decreased the cooperativity of phospholipid molecules. It was also shown that the lipid membranepolymer interaction considerably depends on both the chemical structure and the molecular mass of the polymers.

[Kinetics stability of liposomes]. / Liposzómák kinetikai állandóságának jellemzése.

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).