An expandable tube for deployment within a blood vessel, comprising: an elongate frame that is reversibly switchable from a radially expanded and longitudinally contracted state to a radially contracted and longitudinally expanded state, wherein: the frame comprises a plurality of longitudinally deformable elements for providing longitudinal expansion and contraction of the frame and a plurality of circumferentially deformable elements for providing radial expansion and contraction of the frame; the longitudinally deformable elements can be expanded or contracted longitudinally substantially without any change in the shape of the circumferentially deformable elements; the plurality of circumferentially deformable elements comprises a plurality of sets of circumferentially deformable elements, each set of circumferentially deformable elements forming a closed ring around an axis of elongation of the frame, each closed ring consisting exclusively of the circumferentially deformable elements; each of one or more of the circumferentially deformable elements on one of the closed rings is aligned in a direction parallel to the axis of elongation of the elongate frame with a corresponding identical one of the circumferentially deformable elements on another of the closed rings when the frame is in the radially expanded and longitudinally contracted state; and at least two of the closed rings occupy overlapping ranges of longitudinal positions when the frame is in the radially expanded and longitudinally contracted state and occupy non-overlapping ranges of longitudinal positions when the frame is in the radially contracted and longitudinally expanded state, characterised in that: the aligned circumferentially deformable elements are separated from each other by at least one closed ring having circumferentially deformable elements that are not aligned. the frame comprises a plurality of longitudinally deformable elements for providing longitudinal expansion and contraction of the frame and a plurality of circumferentially deformable elements for providing radial expansion and contraction of the frame; the longitudinally deformable elements can be expanded or contracted longitudinally substantially without any change in the shape of the circumferentially deformable elements; the plurality of circumferentially deformable elements comprises a plurality of sets of circumferentially deformable elements, each set of circumferentially deformable elements forming a closed ring around an axis of elongation of the frame, each closed ring consisting exclusively of the circumferentially deformable elements; each of one or more of the circumferentially deformable elements on one of the closed rings is aligned in a direction parallel to the axis of elongation of the elongate frame with a corresponding identical one of the circumferentially deformable elements on another of the closed rings when the frame is in the radially expanded and longitudinally contracted state; and at least two of the closed rings occupy overlapping ranges of longitudinal positions when the frame is in the radially expanded and longitudinally contracted state and occupy non-overlapping ranges of longitudinal positions when the frame is in the radially contracted and longitudinally expanded state, characterised in that: the aligned circumferentially deformable elements are separated from each other by at least one closed ring having circumferentially deformable elements that are not aligned.