Method for extending shelf-life of constructs of semi-crystallizable polymers

• US 20070032634A1
• Filed: 08/02/2005
• Published: 02/08/2007
• Est. Priority Date: 08/02/2005
• Status: Active Grant

• Current Assignee: Advanced Cardiovascular Systems Incorporated
• Original Assignee: Advanced Cardiovascular Systems Incorporated
• Inventors: Hossainy, Syed, Kleine, Klaus, Gale, David, Huang, Bin
• Granted Patent: US 7,297,758 B2
• Time in Patent Office: Days
• US Class Current: 528/480
• 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 31/148 Materials at least partially resorbable by the body
• CPC Class Codes: C08J 2367/04 Polyesters derived from hydroxy carboxylic acids, e.g. lactones C08J2367/06 takes precedence
• CPC Class Codes: C08J 3/005 Processes for mixing polymers
• CPC Class Codes: C08L 2666/02 Organic macromolecular compounds, natural resins, waxes or and bituminous materials
• CPC Class Codes: C08L 67/04 Polyesters derived from hydroxycarboxylic acids, e.g. lactones C08L67/06 takes precedence

Abstract

This invention relates to a method of extending the shelf-life of constructs, in particular bioabsorbable stents, comprising semi-crystalline polymers by increasing the crystallinity of the polymers.

Claims

1. A method of extending the shelf-life of constructs comprising a semi-crystalline polymers or an immiscible blend of two or more polymers of which at least one is a semi-crystalline polymer, by reducing embrittlement in the polymers by slowing the rate, and/or reducing the amount, of physical aging of the polymers comprising:

determining a glass transition temperature (T_g) of each polymer;

determining a melting temperature (T_m) of each polymer;

heating the polymer, immiscible blend of polymers or construct of such polymer or blend of polymers to a temperature between T_g and T_m of the polymer or one or more of the polymers of the immiscible blend of polymers;

holding the polymer, immiscible blend of polymers or construct of such polymer or blend of polymers at the temperature until one or more of the polymers independently is above about 25% crystalline and,

removing the polymer, immiscible blend of polymers or construct of such polymer of blend of polymers from the source of heat.

2. The method of claim 1, wherein the temperature is from about T_g+0.05(T_m−

T_g) to about T_g+0.4(T_m−

T_g).

3. The method of claim 2, wherein the temperature is from about T_g+0.17(T_m−

T_g) to about T_g+0.21(T_m−

T_g).

4. The method of claim 1, wherein the polymer, immiscible blend of polymers or construct of which polymer or polymer blend is held at the temperature until the polymer or at least one of the immiscible blend of polymers or at least one of the polymers comprising the construct is from about 40% to about 60% crystalline.

5. The method of claim 1, wherein the polymer, immiscible blend of polymers or construct of which polymer or polymer blend is held at the temperature until the polymer or at least one of the immiscible blend of polymers or at least one of the polymers comprising the construct is from about 45% to about 55% crystalline.

6. The method of claim 1, wherein the polymer or a polymer of the blend of polymers is poly(lactic acid).

7. The method of claim 6, wherein the poly(lactic acid) is heated at from about 70°

C. to about 100°

C.

8. The method of claim 7, wherein the poly(lactic acid) is heated at from about 75°

C. to about 95°

C.

9. The method of claim 8, wherein the poly(lactic acid) is held at the selected temperature from about 5 minutes to about 15 minutes.

10. The method of claim 9, wherein the poly(lactic acid) is held at the selected temperature from about 4 to about 7 minutes.

11. The method of either claim 9 or claim 10, wherein the poly(L-lactic acid) is from about 40% to about 45% crystalline after heating at a selected temperature for a selected time.

12. The method of claim 1, wherein the construct is a medical device.

13. The method of claim 12, wherein the medical device is an implantable medical device.

14. The method of claim 13, wherein the implantable medical device is a stent.

15. The method of claim 13, wherein the implantable medical device comprises a layer of poly(lactic acid).

16. The method of claim 14, wherein the stent comprises a layer of poly(lactic acid).

17. The method of claim 1, wherein crystallinity is determined by differential scanning calorimetry.