Stabilization of small unilamellar DMPC-liposomes by uncharged polymers

Abstract

Polymer-free and polymer-bearing small unilamellar (SUV) liposomes from dimyristoyl-phosphatidylcholine (DMPC) were prepared under standardized conditions. Polymer-bearing liposomes were formed by incorporating an uncharged polymer [hydrolyzed 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 or poly(vinyl pyrrolidone) (PVP)] into the membrane bilayer of vesicles. The kinetic (long-term) stability of the liposome dispersions stored in distilled water, in physiological NaCl solution and at various pH values, respectively, were studied. The physical stability of vesicles was tested by measuring the size and the zeta potential of liposomes by means of a Malvern Zetasizer 4 apparatus. It was shown that most of these polymers are effective steric stabilizers for the DMPC-liposomes. Among the polymers, the PVA-Bul and PVA-Prol copolymers and the PVP of high molecular mass exhibited the most efficient stabilizing effect at each pH studied, indicating that the formation of a relatively thick polymer layer around the lipid bilayers ensures an enhanced and prolonged physical stability of liposomes. Also, the butiral or propional side chain in the PVA-based copolymers presumably promotes the anchoring of macromolecules to the vesicles. Using these macromolecules, the colloidal interactions between vesicles can be modified and so the physical stability of liposomes and the kinetic stability of liposome dispersions can also be controlled.