Interactions between liposomes and hydroxypropylmethylcellulose

The characteristics of the adsorption process of hydroxypropylmethylcellulo se (HPMC) of molecular weight 35 400 Da and nominal viscosity 100 cps onto liposomes prepared with different egg lecithin-cholesterol molar ratios wer e examined. Adsorption isotherms were constructed and analysed to investiga te the mechanisms implicated in the incorporation of the polymer to the int erface. Only the isotherms obtained with cholesterol-free liposomes were fi tted with Langmuir model. When cholesterol is present in the composition th ey present a sigmoidal slope. The mechanism of adsorption depends on liposo me composition being the main force that drives polymer adsorption of hydro phobic nature. The apparent volumes of HPMC indicate that the conformation of the adsorbed macromolecules depends on liposome composition. Hydration e nthalpy values show that adsorbed polymers do not give more hydrophilic sys tems after freeze-drying as expected with the hydrophilic characteristics o f the HPMC. (C) 2000 Elsevier Science B.V. Ail rights reserved.