JPH11239611A - Sliding member for artificial joint and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a sliding member for an artificial joint excellent in oxidation, abrasion and fatigue resistances. SOLUTION: A polyethylene composition containing Vitamin E and polyethylene having a limiting viscosity number [η] >=1 dl/g measured in o- dichlorobenzene at 135 deg.C is prepared. Radioactive rays are irradiated on a sliding member for an artificial joint molded from this composition. The polyethylene composition may contain <=10 wt.% α-olefin resin other than polyethylene having a limiting viscosity number [η] >=1 dl/g measured in o-dichlorobenzene at 135 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding member for an artificial joint made of polyethylene used for a medical artificial joint and a method of manufacturing the sliding member.

[0002]

2. Description of the Related Art In general, polyolefin is a synthetic resin having excellent safety for living bodies among synthetic resins, and is therefore widely used as various medical materials including artificial joints. Artificial joints have been used in recent years as the most effective therapeutic members for joints that have failed to function sufficiently due to rheumatoid arthritis or osteoarthritis, such as knee joints, hip joints, elbow joints, and finger joints. The effect has been recognized.

An artificial joint generally comprises a sliding member made of polyolefin and a stem made of a material having a relatively high elastic modulus such as various alloys and ceramic materials. Such artificial joint sliding members are used by being implanted in the body for a long period of time, and in addition to sliding and abrasion with the stem part as well as receiving shock due to various operations of the human body, sliding for artificial joints is performed. As a raw material for members, high-density polyethylene, which is particularly chemically stable among polyolefins and is excellent in slidability, abrasion resistance and impact resistance, is generally widely used.

[0004] Such artificial joints are medical materials,
Sufficient sterilization must be performed before use for use in vivo. Generally, radiation such as gamma ray or electron beam is applied for sterilization. However, irradiation with gamma rays generates free radicals in polyethylene, which reacts with oxygen remaining in and between polyethylene particles to cause oxidation. This oxidation lowers the wear resistance and fatigue resistance of polyethylene. In particular, destruction due to early wear of polyethylene sliding members due to reduced fatigue resistance is a phenomenon that was not expected at the time when the artificial joint was developed, and surgery for replacing the members was performed again for this destruction. Has become a major problem in recent years.

Various studies have been conducted to elucidate the mechanism of these fractures, and it has been elucidated that the fracture proceeds along the polyethylene grain boundaries. Preventing such destruction is an issue for prolonged use of the artificial joint. As a solution, for example, US Pat.
No. 49 describes a method in which polyethylene is placed in an inert gas and then sterilized by gamma irradiation to prevent oxidation caused by generation of free radicals. However, it is difficult to completely remove oxygen from the polyolefin even if it is put in an inert gas, and it is not possible to completely prevent oxidation. Further, as a method of preventing oxidation by extinguishing free radicals in a short time, performing annealing after gamma ray irradiation has been proposed. However, since oxidation during gamma ray irradiation cannot be suppressed, the effect is not certain. Under such circumstances, in order to use the artificial joint stably for a longer period of time, there is an urgent need to develop a sliding member for an artificial joint having excellent oxidation resistance, wear resistance, and fatigue resistance.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a sliding member for an artificial joint having excellent oxidation resistance, wear resistance and fatigue resistance, and a method for producing the same.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the manufacturing prescription in order to improve the drawbacks of conventional polyethylene sliding members and improve fatigue resistance. The present inventors have found that fatigue resistance can be remarkably improved by irradiating a molded article with gamma rays using vitamin Es having a high effect on the living body and having a low effect on the living body.

That is, the present invention relates to the following sliding member for an artificial joint and a method of manufacturing the same. (1) A sliding member for an artificial joint obtained by molding a polyethylene composition containing a polyethylene having an intrinsic viscosity [η] of 1 dl / g or more in o-dichlorobenzene at 135 ° C. and vitamin Es. (2) The sliding member for an artificial joint according to the above (1), wherein the content of vitamin Es in the polyethylene composition is 0.001 to 10% by weight. (3) 10% by weight of an α-olefin resin other than polyethylene having an intrinsic viscosity [η] of 1 dl / g or more measured in o-dichlorobenzene at 135 ° C.
The sliding member for an artificial joint according to the above (1) or (2), which is a composition containing the following. (4) A method for producing a sliding member for an artificial joint, which comprises molding a polyethylene composition containing a polyethylene having an intrinsic viscosity [η] of 1 dl / g or more in o-dichlorobenzene at 135 ° C. and vitamin Es. (5) The method according to (4), wherein the polyethylene or the polyethylene composition is brought into contact with an inert gas before molding. (6) The method according to (4) or (5) above, wherein the radiation is applied during or after molding.

The polyethylene used in the present invention is 135
Intrinsic viscosity [η] measured in o-dichlorobenzene at ℃
Is 1 dl / g or more, preferably 3 to 40 dl / g, more preferably 5 to 35 dl / g.
Such a polyethylene is mainly composed of ethylene as a monomer component. For example, a homopolymer of ethylene, a copolymer of ethylene with a small amount, for example, 10% by weight or less, preferably 3% by weight or less of a monomer other than ethylene is used. Polymers. The monomer copolymerized with ethylene is not particularly limited as long as it is a monomer copolymerizable with ethylene, and has, for example, 3 to 20 carbon atoms, preferably 3 to 1 carbon atoms.
Α-olefin of No. 5 and the like.

The above α-olefin copolymerized with ethylene includes, for example, propylene, 1-butene, isobutene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, Methyl-1-pentene, 4-methyl-1-pentene, 1-heptene, 1-
Octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-icosene and the like can be mentioned. These are copolymerized by one kind or two or more kinds.

As such polyethylene, commercially available products can be used. In addition, as long as it has the above-mentioned physical properties, a known polyethylene used as a raw material of a conventional sliding member for an artificial joint can be used.

The vitamin E used in the present invention includes:
Vitamin E or compounds having vitamin E activity can be used. These can be used natural and synthetic products. Specific examples include d-α-tocophenol, d-β
-Tocophenol, d-γ-tocophenol, d-δ-
Tocophenol, dl-α-tocophenol, d-α-
Tocotrienol, d-β-tocotrienol, d-γ
-Tocotrienol, d-δ-tocotrienol, d-
α-Tocopheryl acetate, isomers and derivatives thereof, and mixtures thereof can be used. Commercially available products can also be used as the vitamin Es. Vitamin E is a compound that is also used as a food additive or the like, and is safe to use as a component of a sliding member for an artificial joint.

The sliding member for an artificial joint according to the present invention is formed from the polyethylene composition containing the polyethylene and vitamin Es. The polyethylene content in this polyethylene composition is 90 to 99.999% by weight, preferably 95 to 99.99% by weight, and the content of vitamin Es is 0.001 to 10% by weight, preferably 0.0
Desirably, it is 1 to 5% by weight.

The polyethylene composition as a raw material may contain, in addition to the polyethylene and vitamins E, resins and additives that can be used in a living body. Examples of such a resin include α-olefin resins other than the above-mentioned polyethylene, and the content in the polyethylene composition is usually 10% by weight or less, preferably 0.1 to 10% by weight.
5% by weight can be blended. Also, as an additive,
Examples include stearates.

The sliding member for an artificial joint according to the present invention can be manufactured by molding the polyethylene composition. The polyethylene composition used for the production can be prepared by mixing the polyethylene, vitamin Es and other components to be blended if necessary using a mixer such as a Henschel type mixer. It is preferred that the vitamin Es are dispersed as uniformly as possible in the polyethylene composition.

In preparing the polyethylene composition, polyethylene may be used in any shape, for example, powder, pellet or tablet. Vitamin Es can also be used in any shape, for example, powder or pellets, but can be easily and uniformly dispersed when mixed with polyethylene. preferable. In the case of other shapes, it is preferable to use it after crushing.

The preparation of the polyethylene composition and the molding of the sliding member for artificial joints can be performed continuously, or the preparation of the polyethylene composition and its temporary storage can be followed by molding of the sliding member for artificial joints. it can. In any case, the raw material polyethylene and polyethylene composition (hereinafter collectively referred to as raw materials before molding) can be used as it is for molding the sliding member for artificial joints.
It is preferable that the oxygen contained in the polyethylene or the polyethylene composition is replaced with the inert gas to reduce the oxygen concentration before the molding is brought into contact with the inert gas before molding.
By reducing the oxygen concentration, it is possible to prevent oxidation occurring inside due to oxygen enclosed between the particles during or after molding, thereby obtaining a sliding member for an artificial joint having better oxidation resistance. Can be.

As a method of contacting the raw material before molding with the inert gas, for example, a method of temporarily storing the raw material before molding in a closed container filled with an inert gas; After the pressure is reduced, the inert gas is introduced, and the inert gas is forcibly replaced with the inert gas; after the raw material before molding is placed in a closed container, the inert gas is allowed to flow and natural replacement is performed. And the like. As the inert gas, any gas can be used as long as it does not react with polyethylene and the molding material, and examples thereof include nitrogen, helium, neon, and argon.

The molding method for producing the sliding member for an artificial joint of the present invention is not particularly limited, and a known molding method such as extrusion molding, compression molding, or injection molding can be employed. Also,
The molded product molded by these molding methods can be used as it is as the sliding member for artificial joints of the present invention, or it can be used as the sliding member for artificial joints of the present invention after further cutting after molding. Can also. For example, a method of forming a rod by a ram extruder and then forming a sliding member by a cutting process;
A method of forming a sliding member by cutting and the like can be given.

Since the artificial joint sliding member is used for medical purposes, it must be sterilized. Sterilization can be performed during or after molding. The sterilization method is a known sterilization method used for sterilization of medical supplies, and is not particularly limited as long as it can be applied to polyethylene, vitamin Es and other raw materials to be blended as desired. For example, a radiation sterilization method, a dry heat method, a gas sterilization method, or the like can be employed. Among these, a radiation sterilization method that can easily, completely, and completely sterilize, and can crosslink polyethylene is preferable.

The radiation sterilization method is broadly classified into a method of irradiating electromagnetic radiation such as gamma rays and a method of irradiating particle radiation such as an electron beam. Either method may be used. The irradiation dose of radiation is not particularly limited as long as it can be sterilized, but it is preferable that the irradiation dose be such that polyethylene causes a sufficient crosslinking reaction. Usually 0.1Mr
Irradiation of ad or more can sterilize and crosslink polyethylene, so the irradiation amount is 0.1 Mra.
d or more, preferably 0.5 to 5 Mrad. By cross-linking the polyethylene, the wear resistance of the sliding member for an artificial joint can be further improved.
When an α-olefin resin other than polyethylene is blended, the α-olefin is also crosslinked.

In the dry heat method, the sliding member for an artificial joint is
Sterilization can be achieved by drying at 40 to 200 ° C. In the gas sterilization method, the artificial joint sliding member can be sterilized by contacting the sliding member with an ethylene oxide gas or a propylene oxide gas. In this case, care must be taken in the operation because the gas adsorbs and remains on the sterilized material or the gas is toxic.

Sterilization may be performed in air, in an inert gas, or in a vacuum, but is preferably performed in an oxygen-free inert gas or in a vacuum in order to minimize oxidation. Examples of the inert gas include helium, nitrogen, argon, neon and the like. Further, in the case of performing in a vacuum, it is preferable to first perform gas replacement in an inert gas atmosphere and then to perform vacuum in order to avoid remaining of oxygen.

The sliding member for an artificial joint according to the present invention thus obtained is excellent in oxidation resistance and hardly causes oxidation deterioration as compared with the conventional sliding member. Furthermore, since the fatigue resistance, which is considered to be caused by oxidation, is improved and the material is not destroyed even when used for a long period of time, the ideal sliding that meets the demands for artificial joint applications at a high level It is a member.

As described above, the sliding member for an artificial joint of the present invention can be stably used for an artificial joint for a long period of time, and is a very useful product in the medical field.

[0026]

Since the sliding member for an artificial joint of the present invention is formed from a polyethylene composition containing polyethylene and vitamin E, it is excellent in oxidation resistance and hardly undergoes oxidation deterioration. For this reason, the abrasion resistance and fatigue resistance, which are considered to be caused by oxidation, are improved, and even when used for a long time, no destruction of the material is observed.

In the method for manufacturing a sliding member for an artificial joint according to the present invention, since the polyethylene composition containing polyethylene and vitamin E is molded, the sliding member for an artificial joint can be efficiently and simply manufactured. Can be. In addition, by contacting the polyethylene or the polyethylene composition with an inert gas in advance before molding, a sliding member for an artificial joint having more excellent oxidation resistance can be easily manufactured. Further, by performing radiation irradiation during or after molding, the polyethylene can be cross-linked together with sterilization, whereby a sliding member for an artificial joint having more excellent wear resistance can be easily manufactured.

[0028]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 3 Ultra high molecular weight polyethylene (HIZEX Million 240S manufactured by Mitsui Chemicals, Inc., trademark, molecular weight 2,000,000, 135)
Intrinsic viscosity [η] measured in o-dichlorobenzene at ℃
13.5 dl / g), weigh 500 g,
A predetermined amount (manufactured by Wako Pure Chemical Industries, Ltd.) was weighed and added.
Then, with a blend mixer, stir for 3 minutes,
A polyethylene composition for molding was obtained. The polyethylene composition powder was filled in a glass tube having a diameter of 3 cm, and glass wool was used as a filter to prevent scattering of the composition powder at both ends, and then both ends were sealed with a rubber stopper with a glass tube.

Next, for the replacement of nitrogen, 600 ml to 700 ml of nitrogen was supplied from one glass tube connected to a nitrogen cylinder.
The flow was adjusted to a flow rate of / min. After injecting nitrogen for 5 minutes, the polyethylene composition powder
50g was put. Mold (inner size 35mm × 125mm × 12
5 mm) was previously covered with a polyethylene film, and a tube was inserted into the tube from one position, and nitrogen gas was introduced to make a nitrogen atmosphere.

After pressing at room temperature at a pressure of 51 kg / cm ² , degassing was performed once for 5 minutes, the temperature was raised to 185 ° C., the press was continued for 5 minutes, and after the heating was completed, the press was continued and naturally cooled for 6 minutes. . Thereafter, the mold was cooled with water and pressed for 10 minutes to complete the molding. After completion of molding, under a nitrogen gas atmosphere, gamma irradiation treatment at a predetermined amount of a ⁶⁰ Co radiation source was conducted.

5 mm × 5 mm × 20 m from the molding plate
m sample was prepared and heated in an air at 200 ° C. for a predetermined time using an oven. After the heating was completed, IR analysis was performed to examine the absorption of a ketone group and a carbonyl group. The results are summarized in Table 1.

Further, the distance from the forming plate is 60 mm × 60 m.
An mx 10 mm sample was prepared and subjected to a fatigue test using a convex contact fatigue tester. In the test, a wear test was performed by applying a maximum pressure of 3 kg / mm ² with a titanium alloy rod having a spherical head having a radius of curvature of 3 mm in distilled water at 37 ° C. The cracks inside the test piece caused by abrasion are detected by an ultrasonic exploration imager (AT5500, manufactured by Hitachi Construction Machinery, trademark).
Observed using. The occurrence of flaking was confirmed visually and by a stereoscopic microscope. As for the crack area ratio, a portion having an ultrasonic reflection intensity of 0.4 V or more was regarded as a crack area, and the ratio of the crack area to the observation area was determined. Table 1 summarizes the results.

Comparative Examples 1 to 3 Press molding was performed in the same manner as in Example 1 except that vitamin E was not added and nitrogen substitution before molding was not performed. Table 1 summarizes the results of tests performed on the same samples as in Example 1.

[0035]

[Table 1]

Claims (6)

[Claims] 1. A sliding for artificial joint obtained by molding a polyethylene composition containing a polyethylene having an intrinsic viscosity [η] of 1 dl / g or more in o-dichlorobenzene at 135 ° C. and vitamin Es. Element. 2. The sliding member for an artificial joint according to claim 1, wherein the content of vitamin E in the polyethylene composition is 0.001 to 10% by weight. 3. The method of claim 1, wherein the polyethylene composition has an o-
The intrinsic viscosity [η] measured in dichlorobenzene is 1 dl
/ G of α-olefin resin other than polyethylene
The sliding member for an artificial joint according to claim 1 or 2, which is a composition containing 0% by weight or less. 4. Manufacture of a sliding member for an artificial joint for molding a polyethylene composition containing a polyethylene having an intrinsic viscosity [η] of 1 dl / g or more in o-dichlorobenzene at 135 ° C. and vitamin Es. Method. 5. The method according to claim 4, wherein the polyethylene or the polyethylene composition is brought into contact with an inert gas before molding. 6. The method according to claim 4, wherein radiation is applied during or after molding.