Abstract
Amphiphilic graft copolymers containing both the mPEG and cholesterol side chains were synthesized and successfully incorporated into liposomes via the cholesterol side chains. Excellent colloidal stability of the copolymer-intercalated liposomes was achieved. By contrast, the native liposome lost its colloidal stability rapidly upon aging. Isothermal titration microcalorimetry experiments along with the theoretical calculation of the net potential energy between two vesicles were carried out to study the inter-vesicle interactions. The electrostatic repulsion potential energy was comparable to van der Waals attraction potential energy for the native liposome and the net repulsive potential energy barrier was not high enough to prevent vesicles from coalescence. On the other hand, the steric repulsion force provided by the surface mPEG was the predominant parameter that controlled the colloidal stability of the copolymer-modified liposomes. © 2005 Elsevier B.V. All rights reserved.