Helical stent
A stent for insertion in a fluid conduit of a human or animal body when the stent is in a collapsed condition and for expansion to an expanded condition, includes an outer wall for engagement with the conduit. The outer wall has a helical portion which in the expanded condition extends longitudinally and circumferentially, and which, upon expansion of the stent from the collapsed condition to the expanded condition, resists extension.
1. A stent for insertion in a fluid conduit of a human or animal body when the stent is in a collapsed condition and for expansion to an expanded condition, the stent comprising:
an outer wall for engagement with the fluid conduit, the outer wall defining an internal diameter of the stent, wherein in the expanded condition the stent has a center line which follows a substantially helical path, so as to promote a swirl flow effect within the fluid conduit supported by the stent, and wherein the stent when expanded ex vivo has a helix angle less than or equal to 65° and a helical center line having an amplitude less than or equal to 0.7 of the internal diameter of the stent;
wherein the stent, in the expanded condition, is substantially free of ribs which would project into a flow lumen of the conduit; and
wherein the helix angle and/or amplitude of the helical center line varies along the length of the stent so as to introduce a swirl flow effect at an upstream end of the stent and to increase the swirl flow effect in a downstream direction.
2. A stent as claimed in claim 1 , being a self-expanding stent.
3. A stent as claimed in claim 1 , being a balloon expandable stent.
4. A stent as claimed in claim 1 , wherein the amplitude of the helical centre line of the stent divided by the internal diameter of the stent is at least 0.05.
5. A stent as claimed in claim 1 , wherein the helix angle is less than or equal to 15°.
6. A stent as claimed in claim 1 , wherein the flow lumen of the conduit supported by the stent is of substantially circular cross-section.
7. A stent as claimed in claim 1 , wherein the helical centre line of the conduit supported by the stent extends over just part of the overall length of the stent.
8. A stent as claimed in claim 1 , wherein the helical centre line of the conduit supported by the stent extends over substantially the entire length of the stent.
9. A stent as claimed in claim 1 , wherein the centre line of the stent follows a substantially helical path about an axis which is curved.
10. A stent as claimed in claim 1 , further comprising a pharmaceutical coating.
11. A stent as claimed in claim 1 wherein the amplitude of the helical center line of the stent divided by the internal diameter of the stent is at least 0.1.
12. A stent as claimed in claim 1 wherein the stent undergoes at least one turn of the substantially helical path.
13. A stent as claimed in claim 1 wherein a helical portion of the stent has the same number of turns both when the stent is collapsed and when it is expanded.
14. A stent as claimed in claim 1 , wherein the amplitude and the pitch of the helical center line vary along the length of the stent.