Crosslinked polymers including one or more antioxidants, methods for making same and methods for selecting antioxidants

Patent metadata

Field	Value
Publication number	US-9370602-B2
Application number	US-201113991719-A
Country	US
Kind code	B2
Filing date	Dec 5, 2011
Priority date	Dec 6, 2010
Publication date	Jun 21, 2016
Grant date	Jun 21, 2016

Abstract

The present disclosure is directed to polymer compositions having one or more antioxidants providing high crosslink density and improved oxidation resistance to the polymer composition and methods for making same. Such polymer compositions can be advantageously used to make orthopedic implants. The disclosure also provides methods for selecting antioxidants providing desirable properties to the polymer composition. In one embodiment, a measure of OIT can be used to select the antioxidant and antioxidant blend. In another embodiment, measurements of OIT and OI-rate can be used to select the one or more antioxidants. In an other embodiment, the product of OIT and crosslink density can be calculated to predict wear resistance and oxidation resistance of a polymer composition including one or more antioxidants.

First claim

The invention claimed is:

1. An orthopedic implant comprising:
a homogeneous consolidated and crosslinked UHMWPE blend comprising UHMWPE resin,
a first antioxidant that is a primary antioxidant chosen from lauryl gallate, octyl gallate, propyl gallate, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, vitamin E, gamma-tocopherol, 2,2,5,7,8-penta-methyl-6-chromanol, and gallic acid, and
a second antioxidant that is bis(2,4-dicumylphenyl)pentaerythritol diphosphite;

wherein a combined concentration of the first and second antioxidants prior to crosslinking is about 0.05% to about 5% by weight of the UHMWPE blend.

2. The orthopedic implant of claim 1 , wherein the consolidated and crosslinked UHMWPE blend has a crosslink density, an oxidation index rate, and an oxidation induction time measured by the offset method, and the product of the crosslink density and oxidation induction time is greater than 1.5.

3. The orthopedic implant of claim 1 , wherein the product of the crosslink density and the inverse of the oxidation index rate of the consolidated and crosslinked UHMWPE blend is greater than 2500.

4. The orthopedic implant of claim 1 , wherein the consolidated and crosslinked UHMWPE blend has an oxidation induction time as measured by the offset method of greater than 15 minutes.

5. The orthopedic implant of claim 1 , wherein the consolidated and crosslinked UHMWPE blend has an oxidation index rate of less than 0.006 OI/week.

6. The orthopedic implant of claim 1 , wherein the primary antioxidant is sufficient to react directly with free peroxy radicals (—OO.) at a higher rate than directly with hydroperoxides (—OOH).

7. The orthopedic implant of claim 1 , wherein the secondary antioxidant is sufficient to react directly with hydroperoxides (—OOH) at a higher rate than directly with free peroxy radicals (—OO.).

8. The orthopedic implant of claim 1 , wherein the combined concentration of the first and second antioxidants prior to cross linking the UHMWPE blend is about 0.05% to about 2% by weight of UHMWPE blend.

9. The orthopedic implant of claim 1 , wherein the concentration ratio of the first antioxidant to the second antioxidant is about 10:1 to about 1:10.

10. The orthopedic implant of claim 1 , wherein at least one of:
the first antioxidant is lauryl gallate, and
the first antioxidant is vitamin E.

11. The orthopedic implant of claim 1 , wherein the first antioxidant comprises vitamin E and the UHMWPE blend further comprises 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid.

12. A method of making the implant of claim 1 , the method comprising:
a. mixing UHMWPE resin with the first antioxidant and the second antioxidant to obtain a homogeneous blend, wherein the combined concentration of the first and second antioxidants prior to crosslinking the UHMWPE blend is about 0.05% to about 1% by weight of the UHMWPE blend;
b. consolidating the blend; and
c. irradiating the consolidated blend to crosslink the consolidated blend.

13. The method of claim 12 , wherein the mixing comprises at least one of:
mixing the UHMWPE resin with lauryl gallate and bis(2,4-dicumylphenyl)pentaerythritol diphosphite, and
mixing the UHMWPE resin with vitamin E and bis(2,4-dicumylphenyl)pentaerythritol diphosphite.

14. The method of claim 12 , wherein the step of irradiating the consolidated blend to crosslink the consolidated blend comprises irradiating the consolidated blend with at least one of electron beam radiation, gamma radiation, and x-ray radiation.

15. The method of claim 14 , wherein a total crosslinking irradiation dose is substantially between about 50 kGy and about 1000 kGy.

16. The method of claim 12 , wherein the irradiation treatment is provided by e-beam radiation at a dose rate of at least 1 MegaGrey per hour.

17. The method of claim 12 , wherein the method further includes preheating the consolidated blend to a preheat temperature below the melting point of the consolidated blend.

Assignees

• Thomas Brian H
• Acker Dean M
• Gsell Ray
• Stark Norman
• Zimmer Inc

Inventors

• Thomas Brian H
• Acker Dean M
• Gsell Ray
• Stark Norman

Classifications

• A61L2/16

  using chemical substances · CPC title

• A61L27/16 Primary

  obtained by reactions only involving carbon-to-carbon unsaturated bonds · CPC title

• C08L23/06

  Polyethylene · CPC title

• A61L27/505

  Stabilizers · CPC title

• A61L27/50

  Materials characterised by their function or physical properties {, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials} · CPC title