Methods for Increasing a Retention Force Between a Polymeric Scaffold and a Delivery Balloon

• US 20120261858A1
• Filed: 04/18/2011
• Published: 10/18/2012
• Est. Priority Date: 04/18/2011
• Status: Active Grant

• Current Assignee: Abbott Cardiovascular Systems Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Abbott Cardiovascular Systems Incorporated (Abbott Laboratories Incorporated)
• Inventors: Yan, Kathleen, Knott, Boyd V., Roberts, Lily Ayo, McNiven, Sean A., Beer, Jeremy B., Johnson, Mark C.
• Granted Patent: US 8,961,848 B2
• Time in Patent Office: Days
• US Class Current: 264/249
• CPC Class Codes: A61F 2/2436 Deployment by retracting a sheath
• CPC Class Codes: A61F 2/915 with bands having a meander structure, adjacent bands being connected to each other
• 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 2002/9583 Means for holding the stent on the balloon, e.g. using protrusions, adhesives or an outer sleeve
• CPC Class Codes: A61F 2250/0067 Means for introducing or releasing pharmaceutical products into the body
• CPC Class Codes: A61L 31/00 Materials for other surgical articles , e.g. stents, stent-grafts, shunts, surgical drapes, guide wires, materials for adhesion prevention, occluding devices, surgical gloves, tissue fixation devices shape or structure of stent-grafts A61F2/07, of stents A61F2/82, of surgical gloves A61B42/00, of surgical drapes A61B46/00, of occluding devices A61B17/12022
• CPC Class Codes: B29B 11/04 by assembling preformed material
• CPC Class Codes: B29C 2793/0009 Cutting out
• CPC Class Codes: B29C 55/24 radial
• CPC Class Codes: B29C 65/66 by liberation of internal stresses, e.g. shrinking of one of the parts to be joined
• CPC Class Codes: B29C 65/7817 in the form of positioning marks
• CPC Class Codes: B29C 66/532 Joining single elements to the wall of tubular articles, hollow articles or bars
• CPC Class Codes: B29C 66/63 Internally supporting the article during joining B29C66/49 takes precedence
• CPC Class Codes: B29C 66/71 characterised by the composition of the plastics material of the parts to be joined welding bar compositions B29C65/125
• CPC Class Codes: B29C 66/73117 Tg, i.e. glass transition temperature
• CPC Class Codes: B29C 66/73791 biodegradable
• CPC Class Codes: B29C 66/91411 of the parts to be joined, e.g. the joining process taking the temperature of the parts to be joined into account
• CPC Class Codes: B29C 66/91421 of the joining tools
• CPC Class Codes: B29C 66/91945 : lower than said glass transition temperature
• CPC Class Codes: B29C 66/92445 : by steps
• CPC Class Codes: B29C 66/9292 : in explicit relation to another variable, e.g. pressure diagrams
• CPC Class Codes: B29C 66/92921 : in specific relation to time, e.g. pressure-time diagrams
• CPC Class Codes: B29C 66/949 : characterised by specific time values or ranges
• CPC Class Codes: B29C 67/0014 : for shaping tubes or blown tubular films
• 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 2101/00 : Use of unspecified macromolecular compounds as moulding material use of unspecified rubbers B29K2021/00
• CPC Class Codes: B29L 2028/00 : Nets or the like
• CPC Class Codes: B29L 2031/7534 : Cardiovascular protheses
• CPC Class Codes: B29L 2031/7543 : Balloon catheters

Abstract

A medical device-includes a 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 and maintaining an inflated balloon during the diameter reduction and prior and subsequent dwell periods.

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 5 to 15 degrees below 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 only during the final crimping step.

3. 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.

4. The method of claim 3, wherein the crimping temperature is about 48°

C.

5. 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.

6. The method of claim 1, wherein a final crimped diameter for the scaffold has a retention force that is greater than 1.0 lbs, the scaffold has a length of no more than 18 mm and the final crimped diameter is at least 2.5 times less than the scaffold diameter before crimping.

15. The method of claim 1, wherein the scaffold has a starting diameter, intermediate diameter, and final diameter and the crimping step uses a crimping mechanism, the crimping step further including:

reducing the scaffold diameter to the intermediate diameter, and

removing the scaffold from the crimping mechanism to adjust, if necessary, the position of the scaffold on the balloon before reducing the scaffold to the final diameter,

placing the scaffold back into the crimping mechanism, and

reducing the scaffold to the final diameter;

wherein the ratio of the final diameter to the intermediate diameter is greater than the ratio of the intermediate diameter to the final diameter.

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 and 15 degrees below TG, 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,

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

(c) reducing the scaffold diameter from the first size to a second size,

(d) maintaining the second size for a second dwell period to allow for stress relaxation in the polymer while the balloon has a 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 43 to 54 degrees centigrade and the GA content of PLGA is between about 15% to 0%.

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.