Tubular conduit
A tubular conduit is disclosed. The tubular conduit comprises a tubular portion made from a flexible material and an axially extending external helical formation located around the outside of the tubular portion. The external helical formation is for supporting the tubular portion. Optionally the tubular portion also comprises an axially extending internal helical protrusion, which imparts a helical flow to a fluid passing through the tubular portion. It is preferred that the tubular conduit is a vascular graft.
1. A method of making a tubular conduit for fluid flow therethrough comprising the steps of:
(a) providing a solid tubular portion comprising a first end and a second end and a lumen therebetween and made from a flexible material;
(b) flowing a moulding liquid in an axially extending, helical form around the exterior of the tubular portion; and
(c) solidifying the moulding liquid.
2. The method according to claim 1 wherein step (b) comprises the step of flowing a moulding liquid in two axially extending helical forms around the exterior of the tubular portion.
3. The method according to claim 2 wherein the two helical forms each has a different helix angle.
4. The method according to claim 1 wherein step (b) comprises: (i) deforming the tubular portion so as to provide an internal helical protrusion on the inside of the tubular portion and a corresponding external helical groove; and (ii) flowing the moulding liquid into the external helical groove to form an axially extending helical form.
5. The method according to claim 4 , wherein step (b) comprises the step of flowing a moulding liquid into two axially extending helical forms around the exterior of the tubular portion; and wherein the two helical forms each has a different helix angle; and wherein the helix angle of the moulding liquid flowed into the external helical groove is less than the helix angle of the other axially extending helical form.
6. The method according to claim 4 wherein the helix angle of the moulding liquid flowed into the external helical groove is between 8° and 20°.
7. The method according to claim 1 wherein step (b) comprises locating the tubular portion over a mandrel; and encasing the tubular portion within a mould such that the tubular portion is sandwiched between the mandrel and the mould.
8. The method according to claim 4 , wherein step (b) comprises locating the tubular portion over a mandrel; and encasing the tubular portion within a mould such that the tubular portion is sandwiched between the mandrel and the mould, the mandrel having an axially extending helical channel on its surface and wherein step (i) further comprises the step of introducing the moulding liquid between the tubular portion and the mould such that the moulding liquid deforms the tubular portion by pressing the tubular portion into the helical channel on the mandrel to provide the internal helical protrusion.
9. The method according to claim 8 further comprising, between the steps of locating of the tubular portion over the mandrel and encasing the tubular portion within the mould, the step of: pushing the tubular portion at least partially into the, helical channel on the mandrel.
10. The method according to claim 8 , wherein the step of introducing the moulding liquid comprises injecting the moulding liquid into the mould above the helical channel in the mandrel.
11. The method according to claim 7 wherein the mould has an axially extending helical channel about its inside surface and wherein step (b) further comprises the step of introducing the moulding liquid between the tubular portion and the mould such that the moulding liquid flows into the helical channel in the mould.
12. The method according to claim 11 , wherein the helix angle of the helical channel in the mould is greater than 50°.
13. The method according to claim 12 wherein the helix angle of the helical channel in the mould is between 65° and 80°.
14. The method according to claim 1 further comprising, between steps (b) and (c), the step of sintering the moulding liquid onto the flexible material of the tubular portion.
15. The method according to claim 1 wherein step (b) is carried out between 600 and 800 kPa and between 170 and 210° C.
16. The method according to claim 15 wherein step (b) is carried out at 689 kPa and 190° C.
17. The method according to claim 1 further comprising the step of coating the inner surface of the tubular portion with carbon.
18. The method according to claim 1 wherein the moulding liquid is polyurethane.
19. The method according to claim 1 wherein the flexible material is ePTFE.