Reducing Crimping Damage to Polymer Scaffold

• US 20120042501A1
• Filed: 08/23/2010
• Published: 02/23/2012
• Est. Priority Date: 08/23/2010
• Status: Active Grant

• Current Assignee: Abbott Cardiovascular Systems Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Abbott Cardiovascular Systems Incorporated (Abbott Laboratories Incorporated)
• Inventors: Wang, Yunbing, Vazquez, Luis, Nguyen, Hung T., Mueller, Scott H., Yan, Kathleen
• Granted Patent: US 8,539,663 B2
• Time in Patent Office: Days
• US Class Current: 29/505
• CPC Class Codes: A61F 2/82 Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents stent-grafts for tubular structures of the body other than blood vessels A61F2/04; stent-grafts for blood vessels A61F2/07; instruments specially adapted for placement or removal of stents or stent-grafts A61F2/95; for closing wounds, or holding wounds closed A61B17/04 - A61B17/115; dilators A61M29/00
• CPC Class Codes: A61F 2/95 Instruments specially adapted for placement or removal of stents or stent-grafts
• CPC Class Codes: A61F 2/9522 Means for mounting a stent or stent-graft onto or into a placement instrument
• CPC Class Codes: A61F 2/9524 Iris-type crimpers
• CPC Class Codes: A61F 2/958 Inflatable balloons for placing stents or stent-grafts
• CPC Class Codes: A61F 2002/91566 connected trough to trough
• CPC Class Codes: A61F 2250/0067 Means for introducing or releasing pharmaceutical products into the body
• CPC Class Codes: B29C 53/30 of tubes by blow-moulding B29C49/00
• CPC Class Codes: B29C 67/0014 for shaping tubes or blown tubular films
• CPC Class Codes: B29D 23/00 Producing tubular articles B29D24/00 takes precedence
• CPC Class Codes: B29D 23/001 Pipes; Pipe joints pleated hoses B29D23/18
• CPC Class Codes: Y10T 29/49908 Joining by deforming
• CPC Class Codes: Y10T 29/49925 Inward deformation of aperture or hollow body wall
• CPC Class Codes: Y10T 29/49927 Hollow body is axially joined cup or tube
• CPC Class Codes: Y10T 29/4994 Radially expanding internal tube
• CPC Class Codes: Y10T 29/49945 by driven force fit
• CPC Class Codes: Y10T 29/53996 by deforming

Abstract

A medical device includes a polymer scaffold crimped to a catheter having an expansion balloon. The scaffold is crimped to the catheter by a multi-step process for increasing scaffold-catheter yield following a crimping sequence. Damage reduction during a crimping sequence includes modifying blades of a crimper, adopting a multi-step crimping sequence, and inflating a supporting balloon to support the scaffold during crimping.

Claims

1. A method for crimping a polymer scaffold to a balloon, comprising:

providing a crimping assembly for crimping the scaffold from a first diameter to a reduced second diameter, the crimping assembly including a plurality of movable blades, each blade having a hardness, a first side and a second side converging to form a tip, the tips being arranged to collectively form an iris about a rotational axis thereof, the iris defining a crimp aperture about which the movable blades are disposed;

disposing a polymer material between an edge of the blade tips and the scaffold surface to reduce the hardness in the blade edges;

supporting the scaffold while the scaffold is disposed within the iris including inflating a balloon within the scaffold to provide interior support to the scaffold, whereby adjacent struts of the scaffold twisted irregularly by a crimper blade are supported by the balloon surface to deter one of the struts from overlapping or twisting irregularly relative to the other strut; and

displacing the plurality of movable wedges from the first diameter to the reduced second diameter to reduce the diameter of the scaffold from the first scaffold diameter to a second scaffold diameter, respectively.

2. The method of claim 1, wherein the polymer material is a coating disposed on a leading edge of the blade

3. The method of claim 2, wherein the coating has a uniform thickness

4. The method of claim 2, wherein the coating has a coating thickness that tapers away from the leading edge of a blade and along a side that contacts the scaffold surface when the scaffold has the first scaffold diameter.

5. The method of claim 1, wherein the polymer scaffolding has ring structures forming a tubular body having a distal end, a proximal end, and an intermediate segment between the distal and proximal ends, the ring structures connected to each other by linear link struts that are oriented axially, the ring structures and link struts forming W-shape closed cells, and

wherein the inflating step includes maintaining a position of a first ring structure relative to an adjacent, second ring structure by the balloon one of being inflated during diameter reduction or after diameter reduction so as to reduce the possibility of the one ring structure from overlapping the second ring structure, or one twisting relative to the other.

6. The method of claim 1, wherein the polymer scaffolding has ring elements forming a plurality of closed cells or zigzag annular bands connected by horizontal linking elements, and

wherein the inflating step includes one of

maintaining a position of a first annular band relative to an adjacent, second annular band by the balloon one of being inflated during diameter reduction or after diameter reduction so as to reduce the possibility of the one annular band from overlapping the second annular band, or one twisting relative to the other, and

maintaining a position of a first ring element relative to an adjacent, second ring elements by the balloon one of being inflated during diameter reduction or after diameter reduction so as to reduce the possibility of the one ring elements from overlapping the second ring elements, or one twisting relative to the other.

7. The method of claim 6, wherein the scaffold has zigzag annular bands connected by horizontal linking elements, and wherein the first scaffold diameter is about 2.5 to 3 times larger than a final crimped diameter for the scaffold.

8. The method of claim 7, wherein the scaffold has zigzag annular bands connected by horizontal linking elements, and wherein the balloon has a constant pressure when the scaffold is reduced in diameter

9. The method of claim 1, wherein the balloon pressure is increased after reducing the scaffold in diameter.

10. The method of claim 6, wherein the scaffold has zigzag annular bands connected by horizontal linking elements, and wherein the balloon is a disposable support balloon used to support the scaffold when the scaffold has the first diameter, wherein the scaffold is reduced in diameter by about 30-40% when reduced in diameter from the first diameter to the second diameter, and

further including the step of reducing the scaffold from the second diameter to a third diameter, including placing the scaffold on the scaffold delivery balloon before reducing the diameter to the third diameter.

11. The method of claim 1, wherein the inflating the balloon step occurs after a partial crimping of the scaffold, wherein the inflated balloon pushes a deformed strut into position following the partial crimping.

31. The method of claim 1, wherein the balloon is inflated and sealed during the displacing the plurality of wedges step such that that the internal balloon pressure increases as the diameter is reduced.

32. The method of claim 1, wherein the balloon is inflated and allowed to purge when the diameter is reduced from the first diameter to the second diameter.

33. The method of claim 1, wherein the first diameter is about 2.5 to 3.0 times the second diameter.

35. The method of claim 1, wherein the polymer is a polymer disposed on the blades, further including the step of

providing a thickness of the polymer coating over the blade wherein the thickness is selected to reduce indentations, cutting or gouging of the scaffold by the edge of a blade bearing down on a scaffold.

36. The method of claim 35, further including the step of heating the blades so as to raise the temperature of the scaffold during crimping, and selecting a thickness for the polymer such that heat may be effectively conducted and radiated from the blade edge to raise the scaffold temperature to a crimping temperature without additional heating sources being used.

37. The method of claim 36, wherein the crimping temperature is at the polymer glass transition temperature or 5-10 degrees below the glass transition temperature.

38. The method of claim 37, wherein the polymer is PLLA and the temperature is between about 45 and 54 degrees Celsius.

12. A method for crimping a polymer scaffold to a balloon, comprising:

providing a crimping assembly for crimping the scaffold from a first diameter to a reduced second diameter, the crimping assembly including a plurality of movable blades, each blade having a first side and a second side converging to form a tip, the tips being arranged to collectively form an iris about a rotational axis thereof, the iris defining a crimp aperture about which the movable blades are disposed;

providing a polymer coating on the blade tips to soften a leading edge of the tip;

supporting the scaffold during crimping by an inflated balloon within the scaffold wherein the balloon applies a radially outward pressure to provide a stabilizing pressure to a strut displacing out of plane or twisting due to uneven crimping forces being applied to the strut or near the strut; and

displacing the plurality of movable blades from the first diameter to the reduced second diameter to reduce the diameter of the scaffold;

wherein the balloon pressure is adjusted as the scaffold diameter is reduced by the tip including the leading edge such that the radially directed outward force applied on the scaffold by the balloon supports the scaffold to avoid or compensate for irregular bending or twisting of scaffold structure.

13. The method of claim 12 wherein the scaffold is brought to a crimping temperature by heat convection and radiation from metal blades, and wherein the polymer coating is applied such that heat convection and/or radiation from a metal blade to the scaffold is not substantially impaired by the presence of the applied coating between the scaffold and metal blade.

14. The method of claim 12 wherein the tip portion has a first thickness at the leading edge and a second thickness adjacent the leading edge, the first thickness being greater than the second thickness.

15. The method of claim 13 wherein a polymer coating is applied only near the leading edge of a blade.

16. The method of claim 12 wherein the leading edge has a radius of curvature with the center of the circle being offset from a line bisecting the converging surfaces of a wedge shape describing the general shape of the blade.

17. A method for crimping a polymer scaffold to a balloon using a crimping device of type that has a plurality of movable blades formed from a metal having a first hardness, each blade having a respective first side and a second side converging to form a tip, the tips arranged to collectively form an iris about a rotational axis thereof, the iris defining a crimp aperture about which the movable blades are disposed, a first and second sheet of polymer film extending between a first and second pair of blades such that a portion of the first and second sheets extends across an aperture formed by the iris, the method including the steps of:

placing the scaffold on a balloon;

disposing the scaffold and balloon in the aperture such that the scaffold and balloon are located between the first and second sheet portions;

inflating the balloon; and

displacing the plurality of movable blades from about the first diameter to about the second diameter;

wherein the balloon pressure is adjusted as the scaffold diameter is reduced by the blades such that the balloon'"'"'s radially directed outward pressure applied on the scaffold by the balloon supports the scaffold to avoid or compensate for irregular bending or twisting of scaffold structure caused by the polymer sheets.

18. The method of claim 17, further including the step of deionizing the polymer sheet portions before the displacing step.

19. The method of claim 18, further including the step of increasing the balloon pressure after the diameter reduction.

20. The method of claim 19, further including the step of increasing the balloon pressure both before and after the diameter reduction.

34. The method of claim 17, wherein after the scaffold is reduced in diameter, the scaffold is rotated through an angle relative to the position of the first and second sheets to compensate for twisting of the scaffold induced by the sheets being brought into contact with the scaffold when the crimper blades engage the scaffold surface.

21. A method for crimping a polymer scaffold to a balloon, comprising:

placing a scaffold having a first diameter on a support balloon;

inflating the support balloon to a pressure for supporting and stabilizing the scaffold at the first diameter while the scaffold is being crimped;

crimping the scaffold from the first diameter to a second diameter while the first balloon is supported by the support balloon;

replacing the support balloon with a balloon catheter after the scaffold is reduced to the second diameter; and

crimping the scaffold to a third diameter, less than the second diameter while the scaffold is supported on the balloon catheter.

22. The method of claim 21, wherein the support balloon is a compliant balloon and the catheter balloon is a non-compliant balloon.

23. The method of claim 21, wherein the scaffold first diameter is greater than the fully deployed diameter of the catheter balloon.

24. The method of claim 21, wherein the scaffold is disposed between polymer sheets when crimped.

25. The method of claim 21, wherein the scaffold is heated and contacted by crimper blades coated with a polymer for softening the crimper blades.

26. The method of claim 21, further including the step of rotating the scaffold about the support balloon following a first crimping using the support balloon, reducing the diameter of the scaffold, then replacing the support balloon with the balloon catheter so as to produce a more uniform crimping of the scaffold about the circumference of the scaffold.

27. A crimping assembly for crimping a polymer scaffold to a balloon, comprising:

a plurality of movable blades, each blade having a hardness, a first side and a second side converging to form an edge, the edges arranged to collectively form an iris about a rotational axis thereof, the iris defining a crimp aperture about which the movable blades are disposed;

wherein the blade edge is one or both of a polymer coated to reduce the hardness of the blade, or formed as a blunted edge wherein the blunted edge is non-symmetrically disposed about a bisecting line defining a line of action of the blade when the crimping mechanism adjusts the iris from a first to a second diameter.

28. The assembly of claim 27, wherein the blunted edge includes a radius of curvature with the center of the circle being offset from a line bisecting the converging surfaces of a wedge shape describing the general shape of the blade.

29. The assembly of claim 27, wherein a polymer coating is formed over the blunted edge.

30. The assembly of claim 27, wherein a polymer coating is formed over the blunted edge and surfaces leading to the blunted edge and contacting the scaffold, wherein the edge contacts the scaffold when the scaffold has a first diameter, and the surface leading to the edge contacts the scaffold at a second diameter, the first diameter being less than the second diameter.