KINETICS OF ACCUMULATION OF MOLECULES INTO LIPOSOMES

In previous report (Ceh, B.; Lasic, D. D. Langmuir 1995, 11, 3356), th e accumulation of external molecules into preformed liposomes by the i nfluence of various gradients, a very important feature in recent appl ications of liposomes as drug carriers, was presented. The thermodynam ic model of liposome loading with weak bases/acids used preset permeab ility coefficients that allowed or disallowed penetration of noncharge d and charged species, respectively, across the vesicle membrane. Now in this article we investigate the kinetics of drug loading. Using Fic k's first law, we can calculate kinetics of loading, expressing the di ffusion constant as a permeability coefficient and defining an associa ted now rate. Results of this theoretical approach, which in the limit of long times converge to the result of the thermodynamic model, show the filling of liposomes with particular molecules as a function of t ime, as well as time dependence on pH changes and concentration of any other species in the liposome internal or external environment.