Liposome—glass interaction. Influence of the lipid bilayer phase state

Abstract

The adsorption of dipalmitoylphosphatidylcholine (DPPC) and palmitic acid from multilamellar lipid dispersions in excess water onto hydrophilic and hydrophobic glass surfaces was studied. Adsorption isotherms at different temperatures were obtained. The adsorbed lipid amount at saturation, Γ ∞, was found to depend strongly on the phase state of the lipid dispersion. For DPPC, a sharp decrease of Γ ∞ was observed at the gel—liquid crystal phase transition at 41 °C (P β′-L α). The DPPC adsorption from the gel phases L β′ and P β′ was significantly greater than that from the low-temperature crystalline L c phase. The L c-isotropic phase transition of palmitic acid was also clearly reflected in the temperature dependence of Γ ∞ for this lipid. Electron microscopy yielded direct evidence for the presence of lipid aggregates and restructured liposomes on the glass surface. In combination with the adsorption data, this shows that fluid liposomes bind less to glass surfaces than solid liposomes.