JPH09122222A - Manufacture of sliding member for prosthetic joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sliding member for an prothetic joint having a small creep deformation factor and no deterioration of a surface layer and excellent in sliding characteristic and abrasion resistance by irradiating a prescribed quantity of γ-rays to ultrahigh-molecular weight polyethylene as the absorbed dose, heat-treating it at the prescribed temperature, then molding it into the desired shape by cut machining. SOLUTION: γ-rays 500-10,000kGy are irradiated to ultrahigh-molecular weight polyethylene as the absorbed dose, it is heat-treated at 80-200 deg.C, then it is cut- machined into the desired shape to manufacture a sliding member for an prothetic joint. When γ-ray irradiation and heat treatment are combined, the creep deformation is suppressed to less than 1%, and the creep resistance and abrasion resistance can be remarkably improved. The sliding member is molded into the desired shape by cut machining after γ-ray irradiation and heat treatment, the deteriorated raw material surface of the ultrahigh-molecular weight polyethylene is removed, and the sliding characteristic and abrasion resistance of the sliding face can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sliding member used in an artificial joint for prosthesis of a human joint.

[0002]

2. Description of the Related Art Conventionally, in artificial joints, for example, in artificial hip joints, artificial bone heads made of metal or ceramics and artificial acetabulum (socket) made of plastic (mainly ultra-high molecular weight polyethylene [UHMWPE] excellent in wear characteristics).
Was used to construct the joint.

However, the artificial acetabulum made of ultra-high molecular weight polyethylene is deformed and abraded due to long-term use in a living body, loosens between itself and a living bone, and causes various problems such as an inflammatory reaction of a living tissue due to abrasion powder. Is waking up. (Reference "In vivo we
ar of polyegthylen acetabular components '', THE JO
URNAL OF BONE AND JOINT SURGERY, VOL 75-B, NO.2, MA
RCH 1993) Regarding modification of ultra high molecular weight polyethylene as a sliding member for artificial joints, polyethylene is added to USP 5037928 by heating at about 200 ° C. for about 1 hour or more and at least 280 MPa (about 2800 atm). Improves creep deformation resistance by thermal crosslinking,
A method of improving wear resistance is disclosed, and it is described that such a method can reduce the creep deformation rate to about 0.5% based on the AMST standard.

In addition, a report by Shikita et al. ("Conversion of artificial joint material from metallic material to non-metallic material", Medical Vol. 32, No. 4)
1978.4), in the molded polyethylene, γ
Attempts to crosslink ultra high molecular weight polyethylene by irradiation have been described.

According to a report by Onishi and Shikita, one of the inventors of the present invention (“Artificial Hip Joint with Excellent Wear Resistance”, Supplementary Orthopedic Surgery No. 18 P216-221, 1990), it was fixed to ultrahigh molecular weight polyethylene. Amount of γ-ray irradiation (10 ⁵ to 10 ⁶ r
ad and 5 × 10 ⁷ to 10 ⁸ rad, 1 Mrad =
10 kGy) is effective in reducing the wear of the sliding member made of ultra high molecular weight polyethylene.

[0006]

However, the above-mentioned prior art has the following problems. That is, about 200
280 MPa (about 28 hours) while heating to ℃
In the method of thermally cross-linking polyethylene by applying a pressure of not less than 00 atm), the creep deformation rate is
It is possible to provide ultra-high molecular weight polyethylene with low wear resistance that can be reduced to about 0.5% based on the standard, but the above heat treatment must be performed under high pressure, and large-scale equipment and a large amount of equipment are required. There was a problem that cost was required.

On the other hand, in the method for irradiating γ rays to crosslink ultrahigh molecular weight polyethylene, it is possible to crosslink ultrahigh molecular weight polyethylene with a relatively simple and inexpensive device. The irradiation dose is 5 × 10 ⁷ to 10 ⁸ ra
Therefore, there is a problem that the initial wear is large due to the surface deterioration of the ultra high molecular weight polyethylene.

[0008]

SUMMARY OF THE INVENTION In view of the problems of the prior art as described above, the present invention is made of ultra-high molecular weight polyethylene having a low creep deformation rate and no deterioration of the surface layer, and thus excellent in sliding characteristics and wear resistance. To provide a novel manufacturing method capable of preparing a sliding member for an artificial joint with a relatively simple and inexpensive device and at a low running cost, and to provide an ultrahigh molecular weight polyethylene having a further improved creep deformation rate than ever before. It is an object of the present invention to provide a method for manufacturing a sliding member for artificial joints made of steel.

[0009]

In order to solve the above-mentioned problems of the prior art, the present invention provides ultra high molecular weight polyethylene as a raw material with a large amount of γ rays (absorption heat dose of 500 kGy to 1,
000 kGy), heat treatment at 80 ° C. to 200 ° C. for about 30 minutes to 12 hours, and thereafter, cutting into a desired shape to form a desired shape, producing a sliding member for an artificial joint. Provide a way.

[0010]

In the production method of the present invention, a large amount of γ-rays (absorption heat dose of 5) is added to the ultra-high molecular weight polyethylene as a raw material.
Irradiate with 00kGy to 1,000kGy), and
Creep deformation of less than 1% due to the combination of both heat treatment at ℃ to 200 ℃ (Material test based on ASTM D621 Loading condition: 1000 psi ・ 24h
r), and the cleave resistance and wear resistance can be significantly improved.

Further, after the γ-ray irradiation and the heat treatment, the material surface of the deteriorated ultra-high molecular weight polyethylene is removed by forming it into a desired shape by cutting, so that the sliding characteristics and wear resistance of the sliding surface are improved. Excuse me.

For γ-ray irradiation, the equipment used for sterilization of feed and medical equipment can be used as it is, and a commercially available vacuum heat treatment equipment can be used for heat treatment. Therefore, the equipment cost and the running cost of manufacturing can be compared. Can be kept low. Further, since the surface layer deteriorated by γ-rays can be removed by cutting after irradiation, it is not necessary to use a special vacuum container or the like during the irradiation of γ-rays.

The surface of the material is deteriorated by γ-rays because the bond (oxidation reaction) between polyethylene and oxygen is accelerated by the γ-rays. Although it is possible to reduce the amount of oxygen and suppress oxidation by using a vacuum container,
Oxygen cannot be completely turned to O. Therefore, some degree of oxidative deterioration of the polyethylene surface due to a large amount of γ-ray irradiation is unavoidable.

Therefore, the cutting process in the present invention is an essential step for removing the surface deterioration layer. Although it is virtually impossible to completely separate the material from the active gas such as oxygen during the γ-ray irradiation, the deterioration layer is removed by cutting to obtain stable physical properties.

The absorbed dose is 500 as the γ-ray irradiation dose.
If it is less than kGy, a sufficient effect cannot be obtained even if heat treatment is performed. On the other hand, the absorbed dose is 10,000 as the γ-ray dose.
If it is larger than kGy, the brittleness of the material becomes too high,
There is a possibility of breaking during processing or use.

The heating temperature does not need to be strictly controlled, but if it is 80 ° C. or lower, it is not processed in a practical time, and if it is 200 ° C. or higher, the polyethylene may be severely deformed and deteriorated.

The heating time is from 30 minutes to 12 minutes.
Time is preferred. If the heating time is 30 minutes or less, sufficient characteristics cannot be obtained, and if the heating time is 12 hours or more, the deformation and deterioration of polyethylene become large even at a relatively low temperature.
In addition, there is a risk of cost disadvantage.

In the present invention, the more preferable range of the absorbed dose as the above γ-ray dose and the heating temperature is as follows.
The absorbed dose is 1,000 to 9,000 kGy and the heating temperature is 80 to 200 ° C. The heating temperature is more preferably 100 ° C. to 150 ° C., and temporal control is easy.

Further, according to such a manufacturing method, the creep deformation rate of the artificial joint sliding member made of ultra-high molecular weight polyethylene can be made 0.3% or less based on the AMST standard.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

[0021]

Embodiments of the present invention will be described below.

Example 1 Ultrahigh molecular weight polyethylene having an average molecular weight of 7,300,000 is used as a material. A cylindrical material having a diameter of about 10 cm and a height of about 10 cm was put into a γ-ray treatment device using cobalt 60 as a radiation source, and the absorbed dose was 500,10.
Irradiation with gamma rays of 00, 1500 and 2000 kGy was performed. After that, heat treatment was performed at 110 ° C. for 2 hours in a pressure of 10 torr or less using a vacuum heat treatment device, and then naturally cooled to room temperature. From the treated material, the following test pieces for mechanical property test were prepared by cutting. In addition,
During the processing, a portion of about 1 mm from the surface was completely removed.

For tensile test: JIS K7113 No. 2 (1/2) type [total length 60 mm, thickness 2 mm] For creep test: ASTM D621 [cube of 1.25 mm square] Measured values of mechanical properties of this test piece It shows in Table 1.

[0024]

[Table 1]

Example 2 Ultrahigh molecular weight polyethylene having an average molecular weight of 4.4 million is used as a material. A 2 × 2 × 10 cm square material was used, and the material was placed in a γ-ray processing device using cobalt 60 as a radiation source and irradiated with γ-rays having an absorbed dose of 1000,2400 kGy. Then, using a vacuum heat treatment device, 10t
The mixture was heat-treated at 110 ° C. for 2 hours under atmospheric pressure of orr or lower and naturally cooled to room temperature. A test piece for a mechanical property test was produced from this treated material by cutting. When processing,
A part of about 1 mm from the surface was completely removed.

Table 1 shows measured values of mechanical properties of this test piece.

Further, as a comparative example, a test piece not irradiated with γ-ray was similarly prepared, and the mechanical property of this test piece was measured by the same method.

Example 3 Ultra high molecular weight polyethylene having an average molecular weight of 4.4 million is used as a material. Place a 2 x 2 x 10 cm square material in a hard glass vacuum container and seal the tube.
It was put into a γ-ray processing apparatus using cobalt 60 as a radiation source and irradiated with γ-rays of 5000 kGy as an absorbed dose.

The vacuum container was broken at the end of irradiation due to the influence of strength deterioration due to γ-rays.

Thereafter, only the raw material was heat-treated at 110 ° C. for 2 hours at a pressure of 10 torr or less using a vacuum heat treatment device, and then naturally cooled to room temperature. A test piece for a mechanical property test was produced from this treated material by cutting. During the processing, a portion of about 1 mm from the surface was completely removed.

Table 1 shows the measured values of the mechanical properties of this test piece.

Further, as comparative examples, test pieces which were not irradiated with γ-rays and test pieces which were irradiated with 500 kGy but not heat-treated were prepared in the same manner, and the mechanical properties of these test pieces were measured by the same method.

As is clear from the results shown in Table 1, the ultra-high molecular weight polyethylene material used as the sliding member was irradiated with γ-rays having an absorbed dose of 500 kGy or more, and then at 1
By subjecting it to heat treatment for at least the time and then forming it into a desired shape by cutting, creep deformation was suppressed to less than 1%, and wear resistance was improved.

In particular, with respect to the creep deformation rate, except for one example, all showed extremely excellent results of 0.3% or less, and all of them had an extremely small amount of wear in the experiment. When such ultra-high molecular weight polyethylene is used as a sliding member for an artificial joint, even if it is used for many years, the abrasion powder of the polyethylene is hardly generated, and therefore it is safe for the living body.

On the other hand, in the above comparative example in which neither γ-ray irradiation nor heat treatment was applied, the creep deformation rate was 1% or more, and the wear amount was relatively large.

By the way, according to the above-mentioned embodiment, since the apparatus used for sterilizing feed and medical equipment can be used as it is for γ-ray irradiation, and a commercially available vacuum heat treatment apparatus can be used for the heat treatment, The costs and running costs for manufacturing can be kept relatively low. Further, since the surface layer deteriorated by γ-rays can be removed by cutting after irradiation, it is not necessary to use a special vacuum container or the like during the irradiation of γ-rays.

The absorbed dose is 500 as the γ-ray irradiation dose.
If it is less than kGy, a sufficient effect cannot be obtained even if heat treatment is performed. On the other hand, the absorbed dose is 10,000 as the γ-ray dose.
If it is larger than kGy, the brittleness of the material may be too high, causing breakage during processing or use.

The heating temperature does not need to be strictly controlled, but if it is 80 ° C. or lower, it is not processed in a practical time, while if it is 200 ° C. or higher, the polyethylene may be severely deformed and deteriorated.

In the present invention, the more preferable range of the absorbed dose as the above γ-ray irradiation amount and the heating temperature is as follows.
The absorbed dose is 1,000 to 9,000 kGy and the heating temperature is 80 to 200 ° C. The heating temperature is more preferably 100 ° C. to 150 ° C., and temporal control is easy.

[0040]

As described above, according to the method for manufacturing a sliding member for an artificial joint of the present invention, a large amount of γ-rays is irradiated to the ultra-high molecular weight polyethylene as a raw material, and this is heat-treated. Therefore, the creep deformation rate of the ultra high molecular weight polyethylene that constitutes the above sliding member is very small, and the creep deformation rate is AM.
It is also possible to reduce it to 0.3% or less based on the ST standard. Therefore, the slidable member for artificial joints manufactured in this manner has an extremely small amount of wear in the living body, and thus has an excellent effect that it is safe for living bodies and can be used safely for a long period of time.

According to the production method of the present invention, the above γ
Since the member is formed into a desired shape by cutting after the irradiation of rays and the heat treatment and the deteriorated surface layer is removed, a large-scale device or device is not required, which is very advantageous in terms of cost.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shingo Masuda 1 at 10 Kawai, Gamo-cho, Gamo-gun, Shiga Prefecture Kyocera Corporation Shiga factory

Claims (1)

[Claims] 1. Ultra-high molecular weight polyethylene is irradiated with γ-rays as an absorbed dose of 500 kGy to 10,000 kGy and then heat-treated at 80 ° C. to 200 ° C., which is then cut into a desired shape. A method for manufacturing a sliding member for an artificial joint.