Compressed tissue for heart valve leaflets

• US 20030212454A1
• Filed: 05/08/2002
• Published: 11/13/2003
• Est. Priority Date: 05/08/2002
• Status: Active Grant

• Current Assignee: Edwards Lifesciences Corporation
• Original Assignee: Edwards Lifesciences Corporation
• Inventors: Scott, Michael J., Khanna, Rajesh A.
• Granted Patent: US 7,141,064 B2
• Time in Patent Office: Days
• US Class Current: 623/2.14
• CPC Class Codes: A61F 2/2412 with soft flexible valve members, e.g. tissue valves shaped like natural valves check valves with flexible valve members in general F16K15/14
• CPC Class Codes: A61F 2/2415 Manufacturing methods
• CPC Class Codes: A61F 2/2418 Scaffolds therefor, e.g. support stents
• CPC Class Codes: A61F 2/2475 Venous valves
• CPC Class Codes: A61F 2/92 Stents in the form of a rolled-up sheet expanding after insertion into the vessel , e.g. with a spiral shape in cross-section
• CPC Class Codes: A61F 2220/0075 sutured, ligatured or stitched, retained or tied with a rope, string, thread, wire or cable
• CPC Class Codes: Y10S 623/918 Heart

Abstract

A process and system for compressing bioprosthetic tissue for use in medical implants. The process involves placing the tissue between two compressive surfaces and applying a force to reduce any nonuniformity of thickness in the tissue, while at the same time reduce the overall thickness. One particularly useful application is the compression of bioprosthetic sheet during the preparation of heart valve leaflets. Bovine pericardium may be compressed to reduce its thickness by about 50%, and then formed into heart valve leaflets. The thinned leaflets have substantially the same absolute strength as those made from uncompressed tissue, and are particular desirable for use in minimally invasive valves which must be compressed into a small profile. The thin tissue enables a reduction in the overall size of the minimally invasive heart valve for delivery. For instance, rolled MIS valves may be reduced in size to as small as 20 mm in diameter. Desirably, a cross-linking step is combined with the compression step to fix the reduced thickness of the tissue. One apparatus may include porous compression substrates through which a cross-linking solution may diffuse so as to perform the fixation and compression simultaneously.

Claims

1. A method of making a heart valve, comprising:

providing a sheet material having a first thickness;

compressing the sheet material into a modified sheet having a second thickness less than the first thickness but with substantially the same absolute tensile strength as the sheet material having the first thickness;

forming heart valve leaflets from the modified sheet.

2. The method of claim 1, wherein the leaflets are affixed to a support structure such that the leaflets form a one-way valve.

3. The method of claim 1, wherein the sheet material is bioprosthetic tissue.

4. The method of claim 3, further including cross-linking the sheet material during or just after the step of compressing.

5. The method of claim 4, wherein the step of compressing comprises providing two substrates on either side of and in contact with the sheet material and applying pressure to the sheet material with the substrates, and wherein the step of cross-linking comprises contacting the sheet material with a chemical solution.

6. The method of claim 5, wherein the step of contacting the sheet material with a chemical solution comprises flowing the solution through at least one of the substrates.

7. The method of claim 5, further including limiting the spacing between the two substrates to determine the second thickness.

8. The method of claim 4, wherein the step of cross-linking is done for a sufficient period of time such that the modified sheet retains its compressed configuration.

9. The method of claim 8, further including, between the step of simultaneously compressing and cross-linking the sheet material and the step of forming the heart valve leaflet, the step of:

immersing the modified sheet in a cross-linking solution for a sufficient quarantine time to render the bioprosthetic tissue safe for implant and fully cross-link the bioprosthetic tissue.

10. The method of claim 1, wherein the second thickness is less than about 0.23 mm (0.009 in).

11. The method of claim 1, wherein the second thickness is less than about 90% of the first thickness.

12. The method of claim 11, wherein the second thickness is between about 50-60% of the first thickness.

13. A method of preparing bioprosthetic tissue for implantation, comprising:

providing a sheet of bioprosthetic tissue having a first thickness;

compressing the sheet of bioprosthetic tissue into a modified sheet having a second thickness; and

cross-linking the sheet of bioprosthetic tissue during or shortly after the step of compressing.

14. The method of claim 13, wherein the second thickness is less than about 0.23 mm (0.009 in).

15. The method of claim 13, wherein the second thickness is less than about 90% of the first thickness.

16. The method of claim 15, wherein the second thickness is between about 50-60% of the first thickness.

17. The method of claim 13, wherein the step of cross-linking is done for a sufficient period of time such that the modified sheet retains its shape.

18. The method of claim 13, wherein the bioprosthetic tissue is mammalian pericardium and the step of cross-linking comprises contacting the mammalian pericardium with glutaraldehyde.

19. The method of claim 13, wherein the step of compressing comprises:

sandwiching the sheet of bioprosthetic tissue between two substrates and applying pressure to the sheet of bioprosthetic tissue with the substrates.

20. The method of claim 19, wherein the two substrates are solid.

21. The method of claim 20, further including limiting the spacing between the two substrates to determine the second thickness.

22. The method of claim 19, wherein the two substrates are flexible.

23. The method of claim 19, wherein the step of cross-linking comprises flowing a chemical solution through at least one of the substrates.

24. The method of claim 23, wherein the chemical solution is pressurized and causes said at least one of the substrates to apply pressure to the sheet of bioprosthetic tissue.

25. The method of claim 23, wherein the two substrates are semi-permeable and the chemical solution flows through both substrates.

26. The method of claim 25, wherein the chemical solution flows through both substrates in the same direction.

27. The method of claim 25, wherein a pressure gradient is created across the substrates.

28. A system for preparing a sheet of material for implantation in a human body, comprising:

a pair of semi-permeable substrates having cooperating surfaces configured to receive a sheet material therebetween, the cooperating surfaces having similar shapes so that the surfaces sandwich the sheet material therebetween;

means for compressing the sheet material between the cooperating surfaces to form a modified sheet of reduced thickness;

a source of cross-linking solution; and

means for contacting the modified sheet with the cross-linking solution.

29. The system of claim 28, wherein the semi-permeable substrates are solid.

30. The system of claim 29, further including shims interposed between the two substrates to control the reduced thickness.

31. The system of claim 29, wherein the means for compressing the sheet material between the cooperating surfaces comprises applying mechanical pressure to at least one of the substrates.

32. The system of claim 28, wherein the means for compressing the sheet material between the cooperating surfaces comprises means for applying fluid pressure to at least one of the substrates.

33. The system of claim 32, wherein the means for contacting the modified sheet with the cross-linking solution is the same as the means for applying fluid pressure to at least one of the substrates.

34. The system of claim 33, wherein the semi-permeable substrates are flexible, and the system further includes a hollow chamber which receives the sandwiched pair of substrates and sheet material, and wherein the means for applying fluid pressure comprises means for pressurizing the hollow chamber with the cross-linking solution.

35. A heart valve comprising:

a structural component; and

a plurality of cross-linked bioprosthetic tissue leaflets attached to the structural component, the leaflets having been compressed during or just before cross-linking to reduce their thickness.

36. The heart valve of claim 35, wherein bioprosthetic tissue is mammalian pericardium.

37. The heart valve of claim 36, wherein the leaflets have a reduced thickness of less than about 0.23 mm (0.009 in).

38. The heart valve of claim 35, wherein the thickness of the leaflets has been reduced by more than about 10% by compression during fixation.

39. The heart valve of claim 38, wherein the thickness of the leaflets has been reduced to between about 50-60% of its original thickness by compression during fixation.

40. The heart valve of claim 35, wherein the structural component is a tubular stent that has cutouts, the edges to which the leaflets attach.

41. The heart valve of claim 40, wherein the tubular stent is a sheet-like member bent into a tube and having two sides parallel to the tube axis that are joined together, the stent being configured to be delivered in a rolled up spiral with one of the two sides being on the inside of the spiral and the other of the two sides being on the outside of the spiral.

42. The heart valve of claim 41, wherein the rolled up spiral configuration of the tubular stent has a diameter of less than about 20 mm.