A pH sensitive carrier is obtained by coating a cyclodextrin vesicle with an adamantane-terminated octapeptide through the formation of an inclusion complex. Upon lowering the pH from 7.4 to 5.0, the formation of peptide B-sheets on the vesicle surface induces a transition of the bilayer from a sphere to a fiber. This transition is fully reversible and repeatable. The vesicles release their cargo upon fiber formation.