A stent 10, for example, is provided with a plurality of frame elements 16 which may have an undulating form. The stent 10 is provided with a plurality of magnetic elements 30 between adjacent stent elements 16. The magnetic elements 30 have the same polarities so as to produce repulsive forces 40 biasing the stent structure into a radially expanded configuration. The magnetic elements 30 provide an alternative opening force on the stent 10, enabling the stent 10 to be made of struts 16 of thinner and weaker material or of a non-sprung material. The magnetic elements 30 also provide a constant opening force in order to retain the stent reliably in position within a vessel. The stent 10 could be made of a biodegradable material.
