# US 2014/0194548 A1 · Sequentially cross-linked polyethylene

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- Number: US 2014/0194548 A1
- Document ID: US20140194548A1
- Status: Published application
- Kind: A1
- Application number: 14/174,035
- Filed: 2014-02-06
- Published: 2014-07-10
- Earliest claimed: 2002-06-06
- Assignees: Howmedica Osteonics Corp.
- Applicants: Howmedica Osteonics Corp.
- Inventors: Aiguo Wang; John H. Dumbleton; Aaron Essner; Shi-Shen Yau
- Web page: https://patentgrep.com/patent/US20140194548A1

## CPC

- C08J 3/28: Treatment by wave energy or particle radiation
- A61L 27/16: obtained by reactions only involving carbon-to-carbon unsaturated bonds
- C08J 3/247: {Heating methods}
- C08L 23/06: Polyethylene
- C08L 2312/06: by radiation
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- A61L: METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES (preservation of bodies or disinfecting characterised by the agents employed A01N; preserving, e.g. sterilising, food or foodstuffs A23; preparations for medical, dental or toiletry purposes A61K)
- C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06)

## Abstract

A method of producing an improved polyethylene, especially an ultra-high molecular weight polyethylene utilizes a sequential irradiation and annealing process to form a highly cross-linked polyethylene material. The use of sequential irradiation followed by sequential annealing after each irradiation allows each dose of irradiation in the series of doses to be relatively low while achieving a total dose which is sufficiently high to cross-link the material. The process may either be applied to a preformed material such as a rod or bar or sheet made from polyethylene resin or may be applied to a finished polyethylene part.

## Claims

### Claim 1

A method for increasing the wear resistance of an ultra high molecular weight polyethylene (UHMWPE) medical implant comprising:
a) heating a preformed UHMWPE in a solid state to a temperature between about 110° C. and about 135° C. but below the melting point;
b) thereafter irradiating the preformed UHMWPE at an incremental radiation dose and maintaining the temperature for at least about 4 hours and then allowing the UHMWPE to cool to room temperature;
repeating steps a) and b) at least two more times until a total radiation dose of 5 to 10 Mrad is achieved.

### Claim 2 (depends on 1)

The method for increasing the wear resistance as set forth in claim 1, wherein the total radiation dose is 9 Mrad.

### Claim 3 (depends on 2)

The method for increasing the wear resistance as set forth in claim 2, wherein an incremental dose for each irradiation is 3 Mrad.

### Claim 4 (depends on 1)

The method for increasing the wear resistance as set forth in claim 1, wherein the weight average molecular weight of the UHMWPE is 106 to 107 grams per mole prior to cross-linking with irradiation.

### Claim 5 (depends on 1)

The method as set forth in claim 1 further including the step of machining the preformed UHMWPE into a medical implant.

### Claim 6 (depends on 5)

The method as set forth in claim 5 wherein the irradiating and heating is performed on the preformed polyethylene prior to forming the medical implant to a final implantable shape.

### Claim 7 (depends on 1)

The method as set forth in claim 1 wherein after the last irradiation and cooling the preformed UHMWPE has a free radical content of 12±1×1014 spins per gram.

### Claim 8 (depends on 1)

The method as set forth in claim 1 wherein after the last irradiation and heating step the preformed UHMWPE has a tensile strength of 54.8±1.2 Mpa.

### Claim 9 (depends on 1)

The method as set forth in claim 1 wherein after the last irradiation and heating step the preformed UHMWPE has a crystallinity of 58±0.9%.

### Claim 10

A method of making an ultrahigh molecular weight polyethylene (UHMWPE) medical implant comprising heating a preformed UHMWPE to a temperature between about 110° C. and about 135° C. but lower than the melting point, thereafter irradiating the preformed UHMWPE at least three times to a total dose of 5 to 10 Mrad maintaining the temperature for about 8 hours after each irradiation followed by cooling to room temperature after each heating and thereafter forming the medical implant.

### Claim 11 (depends on 10)

The method as set forth in claim 10, wherein the UHMWPE is cross-linked by a total radiation dose is about 9 Mrad.

### Claim 12 (depends on 11)

The method for increasing the wear resistance as set forth in claim 11, wherein an incremental dose for each irradiation is 3 Mrad.

### Claim 13 (depends on 10)

The method for increasing the wear resistance as set forth in claim 10, wherein the weight average molecular weight of the UHMWPE is 106 to 107 grams per mole prior to cross-linking with irradiation.

### Claim 14 (depends on 10)

The method as set forth in claim 10 further including the step of machining the preformed UHMWPE into a medical implant.

### Claim 15 (depends on 10)

The method as set forth in claim 10 wherein after the last irradiation and cooling the preformed UHMWPE has a free radical content of 12±1×1014 spins per gram.

### Claim 16 (depends on 10)

The method as set forth in claim 10 wherein after the last irradiation and heating step the preformed UHMWPE has a tensile strength of 54.8±1.2 Mpa.

### Claim 17 (depends on 10)

The method as set forth in claim 10 wherein after the last irradiation and heating step the preformed UHMWPE has a crystallinity of 58±0.9%.

### Claim 18

A method for increasing the wear resistance of an ultrahigh molecular weight polyethylene (UHMWPE) medical implant comprising: irradiating a preformed ultra-high molecular weight polyethylene in a solid state at least three times to a desired total radiation dose of 5 to 10 MRad; and heating the preformed UHMWPE after each irradiation for at least about 8 hours at a temperature from about 110° C. to about 135° C. but below the melting point followed by cooling to room temperature after each heating.

### Claim 19 (depends on 18)

The method for increasing the wear resistance as set forth in claim 18, wherein the total radiation dose is 9 MRad.

### Claim 20 (depends on 19)

The method for increasing the wear resistance as set forth in claim 19, wherein an incremental dose for each irradiation is 3 MRad.

### Claim 21 (depends on 18)

The method for increasing the wear resistance as set forth in claim 18, wherein the weight average molecular weight of the UHMWPE is 106 to 107 grams per mole prior to cross-linking with irradiation.

### Claim 22 (depends on 18)

The method as set forth in claim 18 further including the step of machining the preformed UHMWPE into a medical implant.

### Claim 23 (depends on 18)

The method as set forth in claim 18 where the irradiating and heating are performed on the preformed polyethylene prior to forming the medical implant to a final implantable shape.

### Claim 24

A method of making an ultrahigh molecular weight polyethylene (UHMWPE) medical implant comprising irradiating the UHMWPE at least three times to a total dose of 5 to 10 MRad and heating for at least about 8 hours at a temperature from 110° C. to 135° C. but lower than the melting point of the UHMWPE after each irradiation followed by cooling to room temperature after each heating.

### Claim 25 (depends on 24)

The method as set forth in claim 24, wherein the UHMWPE is cross-linked by a total radiation dose is about 9 MRad.

### Claim 26 (depends on 24)

The method as set forth in claim 24 where the irradiating and heating are performed on the UHMWPE prior to forming the medical implant to a final implantable shape.

### Claim 27

A method of making an ultrahigh molecular weight polyethylene (UHMWPE) medical implant comprising heating a preformed UHMWPE to a temperature between about 110° C. and about 135° C. but lower than the melting point, thereafter irradiating the preformed UHMWPE at least three times to a total dose of 5 to 10 Mrad maintaining the temperature for about 8 hours after the irradiation followed by cooling to room temperature after heating and thereafter forming the medical implant.