Flexible membranes which are in contact with dispersed nanoparticles o
r colloids are theoretically studied. For closed vesicles, the membran
e/particle interactions change the ''spontaneous'' curvature of the me
mbrane provided the surrounding solution contains more than one specie
s of particles. If the membrane/particle interactions are repulsive, t
he membrane curves toward the larger particles. If the membrane/partic
le interactions are attractive, the membrane curves away from the adso
rption layers of small particles but wraps itself around large particl
es which become completely encapsulated.