EFFECT OF THE OSMOTIC CONDITIONS ON THE VALUE OF ZETA-POTENTIAL OF DMPC MULTILAMELLAR LIPOSOMES

The variation of the zeta potential of liposomes as a function of the ionic strength obtained under different osmotic conditions is studied. Dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles have be en selected and the electrolyte used was NaCl. Three different methods were followed for the preparation of the vesicles. (a) In aqueous med ium at different ionic strengths. In this case, the liposomes are unde r iso-osmotic conditions. (b) Lipidic vesicles under hypo-osmotic cond itions are obtained by diluting with water a suspension of liposomes p repared in iso-osmotic conditions as in (a). (c) Lipidic vesicles unde r hyperosmotic conditions are obtained by the addition of NaCl to lipo some samples prepared as in (a). Under iso-osmotic conditions, the res ults allow us to obtain the ionic strength value corresponding to the maximum of the zeta potential through a parabolic fit. The maximum sta bility and the minimum of aggregation occur at that ionic strength val ue; this is a similar behaviour to that expected from DLVO theory. Und er non-iso-osmotic conditions the results do not follow the above beha viour. Under hyperosmotic conditions, the results follow an opposite b ehaviour to the above which could be explained by a reduction of lipos ome size and content. Under hypo-osmotic conditions, a strong decrease of the zeta potential values takes place; therefore the tendency towa rds coalescence and aggregation increases.