Methods for Crimping a Polymeric Scaffold to a Delivery Balloon and Achieving Stable Mechanical Properties in the Scaffold After Crimping

• US 20120285609A1
• Filed: 05/13/2011
• Published: 11/15/2012
• Est. Priority Date: 05/13/2011
• Status: Active Grant

• Current Assignee: Abbott Cardiovascular Systems Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Abbott Cardiovascular Systems Incorporated (Abbott Laboratories Incorporated)
• Inventors: Wang, Yunbing
• Granted Patent: US 8,752,265 B2
• Time in Patent Office: Days
• US Class Current: 156/156
• 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 2240/001 Designing or manufacturing processes
• CPC Class Codes: A61L 31/06 obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds A61L31/041 takes precedence
• CPC Class Codes: A61L 31/16 Biologically active materials, e.g. therapeutic substances A61L31/047 takes precedence
• CPC Class Codes: A61M 25/1034 Joining of shaft and balloon
• CPC Class Codes: B23P 11/025 by using heat or cold
• CPC Class Codes: B29D 23/00 Producing tubular articles B29D24/00 takes precedence
• CPC Class Codes: B29K 2067/043 PGA, i.e. polyglycolic acid or polyglycolide
• CPC Class Codes: B29K 2067/046 PLA, i.e. polylactic acid or polylactide
• CPC Class Codes: B29K 2995/0082 Flexural strength; Flexion stiffness
• CPC Class Codes: C08L 67/04 Polyesters derived from hydroxycarboxylic acids, e.g. lactones C08L67/06 takes precedence
• CPC Class Codes: Y10T 29/49865 by temperature differential [e.g., shrink fit]
• CPC Class Codes: Y10T 29/49913 by constricting outer annulus
• 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 29/49929 Joined to rod

Abstract

A medical device-includes a polymer scaffold crimped to a catheter having an expansion balloon. The scaffold is crimped to the balloon by a process that includes inflating the delivery balloon during a diameter reduction to improve scaffold retention. A crimping temperature is maintained at about the onset of glass transition of the polymer material to facilitate more rapid stabilization of mechanical properties in the scaffold following crimping.

Claims

1. A method for crimping a balloon-expanded scaffold to a balloon, comprising the steps of:

providing a tube comprising PLLA characterized by a glass transition temperature range having a lower limit of about TG-low;

radially expanding the tube to increase its radial stiffness;

forming the scaffold from the radially-expanded tube; and

crimping the scaffold to the balloon while the scaffold has a crimping temperature of between about TG-low to about 5 degrees Celsius above TG-low including maintaining a pressure in the balloon as the scaffold diameter is being reduced in size.

2. The method of claim 1, wherein the crimping step includes a first crimping step, a final alignment step, then a final crimping step, wherein the balloon pressure is maintained during the final crimping step and the first crimping step.

3. The method of claim 1, wherein the balloon pressure is allowed to decrease from a first to second pressure during the first crimping step and maintained at a constant pressure during the final crimping step.

4. The method of claim 2, wherein the scaffold diameter is reduced in diameter by about 50% for the first crimping step and by about 30% for the final crimping step.

5. The method of claim 3, wherein the crimping temperature is about 58°

C.

6. The method of claim 2, wherein following the first crimping step the balloon is inflated and the scaffold maintained at a first diameter for a first dwell period, followed by a third crimping step, wherein the balloon is inflated during the first dwell period to a pressure of about twice the balloon pressure for the final crimping step.

7. A method for securing a scaffold to a balloon, comprising the steps of:

crimping the scaffold to the balloon while the scaffold has a temperature of between about TG-low to about 5 degrees Celsius above TG-low, the scaffold being made from a polymer comprising PLLA or PLGA, the crimping step including the steps of

(a) reducing the scaffold diameter from a starting size to a first size while the balloon has a first pressure,

(b) maintaining the first size for a first dwell period to allow for stress relaxation in the polymer while the balloon has the first pressure,

(c) reducing the scaffold diameter from the first size to a second size while the balloon has the first pressure,

(d) maintaining the second size for a second dwell period to allow for stress relaxation in the polymer while the balloon has the first pressure, and

(e) reducing the scaffold diameter from the second size to a third size,

wherein the balloon has a second pressure while the scaffold diameter is being reduced from the second size to the third size.

8. The method of claim 7, wherein the polymer comprises PLLA or PLGA.

9. The method of claim 8, wherein the polymer comprises PLGA, the temperature range is about 50-60 degrees centigrade and the GA content of PLGA is 15%.

10. The method of claim 7, wherein the scaffold has a circumferential series of closed cells having a W-shape and linear link struts connecting the W-shape cells.

11. The method of claim 7, wherein the scaffold diameter is reduced in size by about 30% in step (e).

12. The method of claim 7, wherein the scaffold diameter is reduced in size by about 50% from steps (a) to (d).

13. The method of claim 7, wherein the scaffold is crimped in a crimper mechanism, further including removing the scaffold from the crimper mechanism after the scaffold diameter is reduced to the second size,

wherein the scaffold is removed from the crimper after its diameter is reduced by 50%, and

wherein the scaffold diameter is reduced in diameter by an additional about 30% when it attains the third size.

14. The method of claim 13, wherein the first pressure is about twice the second pressure.

15. A method of making a balloon-expanded scaffold, comprising the steps of:

forming the scaffold from a polymer;

crimping the scaffold to the balloon, including

selecting a crimping temperature of between about a TG-low for the polymer and about 5 degrees centigrade above TG-low to accelerate stress relaxation throughout the crimped scaffold and thereby reduce the period of time it takes for radial strength, recoil and other important scaffold properties to stabilize.

16. The method of claim 15, wherein the scaffold is made from a polymer comprising PLLA or PLGA and the scaffold has a circumferential series of closed cells having a W-shape and linear link struts connecting the W-shape cells.

17. The method of claim 15, further including the steps of providing a precursor tube made from the polymer, radially expanding the tube to increase its radial stiffness and forming the scaffold from the radially-expanded tube.

18. The method of claim 15, wherein the crimping step reduces the scaffold diameter by a factor of at least 2.5.

19. The method of claim 18, wherein the crimping includes a dwell period after each of a first and second reduction in diameter of the scaffold in a crimper, followed by a final diameter reduction, followed by a final dwell period to allow stress relaxation to occur to thereby reduce recoil and stabilize the radial strength.

20. The method of claim 19, wherein the final dwell period is at least 10 times longer than the dwell period following the first and second diameter reductions.

21. The method of claim 20, wherein the first and second diameter reductions occur over the span of less than about 3 seconds, the dwell periods following the first and second diameter reductions are less than about 20 seconds and the final dwell period is about 200 seconds for a scaffold comprising PLLA or PLGA.