Elastic stent graft
A stent graft including a stent having a wall having at least one opening, an outer surface, and an inner surface and a covering of a composite material having a least one expanded fluoropolymer membrane and an elastomer is provided. The cover can be used to cover the outer and/or the inner surface of the stent. The expanded fluoropolymer membrane contains serpentine fibrils. In exemplary embodiments, the fluoropolymer is polytetrafluoroethylene. The composite material may be axially and/or circumferentially wrapped around the stent. The composite material is fold-free throughout its operating diameter range and exhibits a sharp increase in stiffness at a predetermined diameter. The stent graft can be designed to have a stop point in either a radial or axial direction. The stent graft can advantageously be implanted undersized with respect to a nominal diameter without having material infolding.
1. A method of manufacturing a stent graft comprising:
positioning a cover comprising a composite material under tension sufficient to overcome a retraction force of said composite material on at least one surface of a stent at an expanded diameter of said stent to form a stent graft; and
bonding said cover to said stent,
wherein said composite material comprises at least one expanded fluoropolymer membrane and an elastomer, and
wherein said expanded fluoropolymer membrane comprises serpentine fibrils, wherein each serpentine fibril curves or turns generally one way and then generally in another way.
2. The method of claim 1 , wherein each serpentine fibril of said serpentine fibrils has a width of about 1.0 micron or less.
3. The method of claim 2 , wherein each said serpentine fibril has a width of about 0.5 micron or less.
4. The method of claim 1 , wherein said cover is wrinkle-free before loading and after deployment.
5. The method of claim 1 , wherein said the at least one surface of the stent is at least one of an outer surface and an inner surface of said stent.
6. The method of claim 1 , wherein said at least one expanded fluoropolymer membrane comprises a plurality of pores and said elastomer is present in a substantial amount of said pores.
7. The method of claim 1 , further comprising applying an adhesive to said stent prior to positioning said cover on said at least one surface of said stent.
8. The method of claim 1 , wherein the expanded fluoropolymer membrane comprises a microstructure of substantially only serpentine fibrils.
9. The method of claim 1 , wherein the fluoropolymer membrane comprises polytetrafluoroethylene.
10. The method of claim 1 , wherein the fluoropolymer membrane comprises a microstructure of substantially only fibrils.
11. The method of claim 1 , wherein when said cover is wrinkle-free when expanded to about 80% of a nominal diameter.
12. The method of claim 1 , wherein said cover has a diameter substantially larger than a nominal diameter of said stent.
13. The method of claim 1 , wherein said bonding step occurs substantially at room temperature.
14. The method of claim 1 , wherein said cover in a relaxed state has a diameter substantially smaller than said expanded diameter of said stent.