Influence of cyclodextrins on the physical stability of DPPC-liposomes

This paper reports on the physical stability of DPPC-(dipalmitoyl phosphatidyl choline) liposomes in various aqueous dispersions and its control by uncharged polymers. The effect of natural (α-, β-, γ-) cyclodextrins (CDs) on the stability of bare and polymer-bearing liposomes and also, the attachment of the CD molecules and the macromolecules, respectively, to the DPPC-bilayers of small unilamellar vesicles (SUV) were studied. It was found that above a CD/DPPC ratio, each cyclodextrin caused a definite destruction in the phospholipid bilayers. The extent of membrane destabilization due to a cyclodextrin closely related to the amount of the CD molecules bound to the DPPC-bilayers. The polymer-coated liposomes formulated by incorporating a dissolved homopolymer or copolymer into the phospholipid bilayer of the vesicles exhibited higher physical stability. Uncharged polymers effectively hindered the disintegration of the liposomal membranes brought about by the CD molecules. The polymer layers formed around the phospholipid bilayers ensured an enhanced steric stabilization for the DPPC-liposomes. Methylcellulose (MC) with high molecular mass and a polyvinyl alcohol-co-vinyl propional copolymer alike exhibited efficient stabilizing effect.