Continuous heart valve support frame and method of manufacture

• US 20040078950A1
• Filed: 04/24/2003
• Published: 04/29/2004
• Est. Priority Date: 09/20/2002
• Status: Active Grant

• Current Assignee: Edwards Lifesciences Corporation
• Original Assignee: Edwards Lifesciences Corporation
• Inventors: Schreck, Stefan
• Granted Patent: US 7,137,184 B2
• Time in Patent Office: Days
• US Class Current: 29/447
• 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 2220/0075 sutured, ligatured or stitched, retained or tied with a rope, string, thread, wire or cable
• CPC Class Codes: Y10T 29/49405 Valve or choke making
• CPC Class Codes: Y10T 29/49865 by temperature differential [e.g., shrink fit]
• CPC Class Codes: Y10T 29/49885 with coating before or during assembling
• CPC Class Codes: Y10T 29/49895 Associating parts by use of aligning means [e.g., use of a drift pin or a "fixture"]
• CPC Class Codes: Y10T 29/49904 Assembling a subassembly, then assembling with a second subassembly
• CPC Class Codes: Y10T 29/49906 Metal deforming with nonmetallic bonding
• CPC Class Codes: Y10T 29/49995 Shaping one-piece blank by removing material

Abstract

Methods for forming a support frame for flexible leaflet heart valves from a starting blank include converting a two-dimensional starting blank into the three-dimensional support frame. The material may be superelastic, such as NITINOL, and the method may include bending the 2-D blank into the 3-D form and shape setting it. A merely elastic material such as ELGILOY may be used and plastically deformed in stages, possibly accompanied by annealing, to obtain the 3-D shape. Alternatively, a tubular blank could be formed to define a non-tubular shape, typically conical. A method for calculating the precise 2-D blank shape is also disclosed. A mandrel assembly includes a mandrel and ring elements for pressing the blank against the external surface of the mandrel prior to shape setting.

Claims

1. A method of forming an elastic material into a heart valve support frame, comprising:

providing a two-dimensional blank of a continuous support frame in the elastic material;

forming the two-dimensional blank into a continuous three-dimensional heart valve support frame.

2. The method of claim 1, further comprising:

providing a flat sheet of the elastic material; and

separating the two-dimensional blank from the flat sheet.

3. The method of claim 2, wherein the step of separating comprises cutting the elastic material along the perimeter of the two-dimensional blank.

4. The method of claim 1, wherein the elastic material is a metal.

5. The method of claim 1, wherein the elastic material is superelastic.

6. The method of claim 5, wherein the superelastic material is NITINOL.

7. The method of claim 6, wherein the step of forming includes heat-setting the NITINOL into the three-dimensional heart valve support frame.

8. The method of claim 1, wherein the elastic material is a metal and the step of forming includes plastically deforming and then annealing the metal.

9. The method of claim 1, wherein the step of forming further includes:

providing a mandrel;

conforming the two-dimensional blank over the mandrel so that it assumes a three-dimensional shape matching the exterior shape of the mandrel; and

altering the properties of the elastic material while on the mandrel such that when it is removed from the mandrel it remains substantially in the three-dimensional shape corresponding to the heart valve support frame.

10. The method of claim 9, wherein the heart valve support frame includes three cusps and three commissures and the two-dimensional blank accordingly has three cusp regions and three commissure regions, and wherein the step of conforming the two-dimensional blank over the mandrel further includes:

orienting the two-dimensional blank over the mandrel by registering the cusp regions and commissure regions with a series of pins provided on the mandrel; and

pressing the two-dimensional blank flat against the exterior shape of the mandrel using at least one ring element.

11. The method of claim 1, further including the step of surface treating the three-dimensional heart valve support frame to reduce features of high stress concentration.

12. The method of claim 11, wherein the step of surface treating comprises electropolishing.

13. A method of calculating the shape of and making a heart valve support frame, comprising:

entering the desired shape of a heart valve support frame into a finite element program to obtain a three-dimensional support frame model;

simulating forces on the support frame model to cause it to assume a two-dimensional pattern; and

using the shape of the two-dimensional pattern to form a two-dimensional blank from a sheet of elastic material.

14. The method of claim 13, further including forming the two-dimensional blank into a three-dimensional heart valve support frame.

15. The method of claim 14, further including:

providing a mandrel;

conforming the two-dimensional blank over the mandrel so that it assumes a three-dimensional shape matching the exterior shape of the mandrel.

16. The method of claim 15, wherein the elastic material is a superelastic material, and the method further includes:

altering the material properties of the blank while on the mandrel such that when it is removed from the mandrel it remains substantially in the three-dimensional shape of the mandrel.

17. The method of claim 13, wherein the support frame model comprises three arcuate cusps separated by three generally axially oriented commissures, and wherein the step of simulating forces comprises simulating the application of generally axially oriented forces on the model such that the commissures rotate inward and the two-dimensional pattern appears substantially like a three-leaf clover.

18. The method of claim 13, wherein prior to forming the two-dimensional blank, the two-dimensional pattern is formed into a three-dimensional virtual support frame shape within the finite element program and is compared with the desired shape of the heart valve support frame.

19. The method of claim 18, further including adjusting the two-dimensional pattern if the virtual support frame shape does not match the desired shape of the heart valve support frame.

20. A method of manufacturing a heart valve, comprising:

providing a heart valve support frame blank made of superelastic material;

forcing the support frame blank into substantially the final shape of a heart valve support frame;

maintaining the support frame blank in its substantially heart valve support frame shape;

altering the internal structure of the superelastic material while maintaining the support frame blank in its heart valve support frame shape so that it assumes that shape and forms the support frame; and

assembling the heart valve by coupling a bioprosthetic valve or flexible leaflets to the support frame.

21. The method of claim 20, further comprising:

providing a tube of the superelastic material;

wherein the step of providing a heart valve support frame blank comprises separating a continuous support frame blank from the tube;

wherein the step of forcing comprises forcing the support frame blank from its tubular configuration to other than a tubular configuration and then performing the step of altering the internal structure of the superelastic material.

22. The method of claim 21, wherein the other than tubular configuration is conical.

23. The method of claim 20, further comprising:

providing a flat sheet of the superelastic material;

wherein the step of providing a heart valve support frame blank comprises separating a two-dimensional blank of a continuous support frame from the flat sheet; and

wherein step of forcing comprises forcing the two-dimensional blank over a mandrel so that it assumes a three-dimensional shape matching the exterior shape of the mandrel.

24. The method of claim 20, wherein:

the step of providing comprises providing a slender wire of the superelastic material; and

the step of forcing comprises bending the slender wire over a mandrel so that it assumes a three-dimensional shape matching the exterior shape of the mandrel.

25. The method claim 20, wherein the superelastic material is NITINOL and the step of altering comprises heat setting the NITINOL.

26. An intermediate apparatus in the formation of a prosthetic tissue-type heart valve, comprising:

a two-dimensional continuous heart valve support frame blank.

27. The apparatus of claim 26, wherein the support frame blank is NITINOL.

28. The apparatus of claim 26, wherein support frame blank has a square cross-section.

29. The apparatus of claim 26, wherein the tissue-type heart valve is the type having three leaflets, wherein the two-dimensional continuous support frame blank includes three arcuate cusps and three commissures therebetween in a pattern that resembles a three-leaf clover.

30. The apparatus of claim 29, wherein the commissures each have widened tips to increase their radius of curvature relative to commissures tips that have not been widened.

31. A method of forming a heart valve support frame, comprising:

providing a heart valve support frame; and

electropolishing the heart valve support frame.

32. The method of claim 31, wherein the heart valve support frame is metallic and has a rectilinear cross-section.

33. The method of claim 32, wherein the heart valve support frame is made of NITINOL.

34. The method of claim 31, further including:

prior to electropolishing, first removing oxidation from the outer surface of the heart valve support frame.

35. The method of claim 34, wherein the step of removing oxidation comprises microblasting the outer surface of the heart valve support frame.

36. The method of claim 31, wherein the step of electropolishing comprises:

submerging the heart valve support frame into a conductive fluid bath;

providing an anode and a cathode; and

flowing a current between the anode and the cathode to electropolish the heart valve support frame.

37. The method of claim 36, wherein the step of providing an anode comprises positioning plate anodes within the conductive fluid bath around the heart valve support frame.

38. The method of claim 36, wherein the conductive fluid bath comprises nitric acid and methanol.

39. The method of claim 36, wherein the conductive fluid bath is maintained at a temperature of between about −

28-32°

C.

40. The method of claim 36, wherein the conductive fluid bath is maintained at a conductivity level of between about 140-190 μ

s at 23°

C.

41. The method of claim 36, wherein the current flows at a voltage of between about 9-10 V.

42. The method of claim 36, wherein the heart valve support frame has an undulating shape with three cusps and three commissures, the method further comprising:

within the conductive fluid bath, holding the heart valve support frame at three points around the undulating shape; and

periodically repositioning the heart valve support frame during the electropolishing process.

43. The method of claim 42, wherein the step of periodically repositioning comprises twice rotating the heart valve support frame 120°

from an initial position.