KR101040567B1 - Method for manufacturing UHMWPE liner of artificial hip joint prosthesis - Google Patents

Abstract

The present invention relates to a method for manufacturing an ultra-high molecular weight polyethylene liner for artificial joints, which comprises cutting a material made of ultra high molecular weight polyethylene, and putting the cut material into a polyvinyl pack and filling the polyvinyl pack with nitrogen to seal it. And, causing crosslinking of the material made of ultra-high molecular weight polyethylene by gamma irradiation, heat-treating the material to cause recrystallization, processing the shape of the artificial joint liner on the material, and a completed liner Including the step of sterilization using plasma sterilization in a breathable pack, improves wear resistance and provides a sterilized ultra-high molecular weight polyethylene liner without changing the mechanical properties ultimately has the effect of extending the life of the artificial joint.

Description

Method for manufacturing ultra high molecular weight polyethylene liner for artificial joints {Method for manufacturing UHMWPE liner of artificial hip joint prosthesis}

The present invention relates generally to a liner for artificial joints, and more particularly, to a manufacturing method for improving wear resistance of an ultrahigh molecular weight polyethylene liner for artificial joints.

Ultra high molecular weight polyethylene (UHMWPE) has been used as a substitute for cartilage in artificial joints for the past 30 years. The ultra high molecular weight polyethylene has low friction, good biocompatibility and wear resistance, and good mechanical properties. It is considered as the best material in the field of artificial joints.

1 is a view schematically showing an example of a state in which an artificial joint is performed. Referring to the structure of the artificial joint 1, an acetabular cup 10 fixed to the pelvis 8 and the acetabular cup 10 may be described. Acetabular Liner (20) accommodated in the inner space of the), the stem 40 fixed to the femur (9), and the acetabular liner (20) in a state coupled to one end of the stem (40) It is inserted into the inner space of the rotatable head 30 is provided.

The aspheric liner 20 has a flat shape with its opening end face flat and an elevated shape with its opening end face inclined at an angle, which is selectively employed according to the characteristics and preferences of the patient. The only difference is that they can be housed in the same acetabular cup 10, in which the head 30 is freely rotatably inserted in the same configuration.

In addition, when there is little damage to the joint surface of the patient, a bipolar cup may be used instead of the acetabular cup, and after the bipolar liner and the head are assembled, the bipolar liner is inserted into the bipolar cup and is firmly fixed. In charge of joint movement. Here, the acetabular liner and the bipolar liner are made of ultra high molecular weight polyethylene.

Such a member made of ultra high molecular weight polyethylene should be sterilized before being implanted in a patient, and its sterilization currently uses a method of exposing the member to ionizing radiation such as gamma rays, X-rays, electron beam radiation, and the like. Among these, gamma-ray sterilization is commonly used. The problem with gamma-ray sterilization is that gamma-rays can cause chemical reactions that can affect the structure and shape and some mechanical properties of polymer materials such as ultrahigh molecular weight polyethylene. will be.

During irradiation of gamma rays, for example, ions, excited molecules, oxidation products, free radicals are produced in the polymer material. Once free radicals are formed in the polymeric material, the oxygen present in the surroundings of the polymeric material reacts with the free radicals to produce compounds with carbonyl functional groups that affect the oxidative reactions leading to chain breakage and the generation of new free radicals. Can be. Oxidation can reduce the molecular weight of the polymer material and degrade the mechanical properties.

Sterilization of ultrahigh molecular weight polyethylene members by gamma irradiation in air is thought to result in a decrease in wear resistance due in part to oxidation, for example, sterilization of ultrahigh molecular weight polyethylene members in an environment of inert gas such as argon, helium, nitrogen To minimize the oxidation effect has been proposed. Alternatively, vacuum techniques have been used to help purify the oxygen environment prior to performing sterilization with gamma irradiation.

Abrasion resistance is an important mechanical property of ultra high molecular weight polyethylene used in artificial joints. Debris fine particles (wear particles in the absence of ultra high molecular weight polyethylene) caused by excessive friction during the replacement of the artificial joints in the human body can be displaced within the joints, thus preventing the proper mechanical action of the joints. Can cause serious problems. In other words, the joints are loose, cause inflammation and pain, or granulation tissue abnormal growth, and eventually a large number of patients need to be retreated.

In addition, the fine particles of ultra-high molecular weight polyethylene having a size of a few micrometers may cause bone resorption, osteolysis, osteomalacia, etc. by the immune function of the human body. When osteochondralization and the like are expressed in artificial joints, there is usually a discomfort to surgically remove the diseased tissue and correct the artificial joints.

The wear of the ultra high molecular weight polyethylene member is affected by various factors such as the design of the artificial joint and the problem in the procedure, but since the wear resistance of the ultra high molecular weight polyethylene is the most important matter, the wear resistance is improved and sterilization is performed without changing the mechanical properties. There has been a need to provide ultra-high molecular weight polyethylene members to extend the life of artificial joints.

Accordingly, the present invention has been made to solve the above problems, to remove the free radicals to prevent oxidation of ultra-high molecular weight polyethylene, and to obtain excellent wear resistance that can be used in artificial joints, ultra-high molecular weight It is an object of the present invention to provide a method for producing an artificial joint ultra high molecular weight polyethylene liner that can be sterilized without changing the mechanical properties of polyethylene.

According to the present invention, there is provided a method of manufacturing an ultra-high molecular weight polyethylene liner for artificial joint, which comprises cutting a material made of ultra-high molecular weight polyethylene, and putting the cut material into a polyvinyl pack and nitrogen-containing the polyvinyl pack. Sealing by filling with a film, causing crosslinking of the ultra-high molecular weight polyethylene material by gamma irradiation, heat-treating the material to cause recrystallization, and processing the shape of an artificial joint liner in the material. And a step of putting the completed liner into a breathable pack and sterilizing using plasma sterilization.

As described above, according to the present invention, by irradiating gamma rays in a nitrogen-filled environment and heat-treating at a temperature above the melting point, free radicals can be removed to prevent oxidation of ultra high molecular weight polyethylene, and excellent wear resistance can be obtained for artificial joints. In addition, it can be sterilized without changing the mechanical properties of the ultra high molecular weight polyethylene by placing it in a breathable pack and using plasma sterilization, thereby improving wear resistance and ultimately providing a sterilized ultra high molecular weight polyethylene liner without changing the mechanical properties. It is effective to prolong the life of the artificial joint.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even if displayed on different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unclear.

Crosslinked ultra high molecular weight polyethylene and members made from the same are useful as prostheses to replace various parts, such as elements of joints in the human body. For example, in the hip joint, it may be an acetabular cup (as described above) or an insert, liner, or bearing element of the cup. In addition, it may be made of members for knee joints, cuff joints, elbow joints, shoulder joints, spine, temple-mandibular joints (chin), finger joints, and the like.

In the present specification, but mainly described for the liner for artificial joint used in the hip joint, but this is for illustrative purposes and does not mean to be limited thereto.

Figure 2 is a block diagram schematically showing a method of manufacturing an ultra-high molecular weight polyethylene liner for artificial joints according to the present invention. As shown in the drawing, a method of manufacturing an ultra-high molecular weight polyethylene liner for an artificial joint according to the present invention includes the steps of cutting a material made of ultra high molecular weight polyethylene, and putting the cut material into a polyvinyl pack, and converting the polyvinyl pack into nitrogen. Filling and sealing, causing crosslinking of the material of ultra-high molecular weight polyethylene by gamma irradiation, heat-treating the material to cause recrystallization, and processing the shape of an artificial joint liner in the material And placing the finished liner in a breathable pack and sterilizing using plasma sterilization.

Raw materials made of ultra high molecular weight polyethylene are usually extruded into bars or rods. Accordingly, it is preferable to cut the material made of ultra high molecular weight polyethylene into a predetermined length.

The material thus cut is put in a polyvinyl pack, and the polyvinyl pack is filled with nitrogen and sealed. Preferably, the material is put into the polyvinyl pack using a gas exchanger equipped with a vacuum device to reach a vacuum state, and then nitrogen is injected through the inlet of the polyvinyl pack so that nitrogen is substituted, and then the inlet is thermally compressed and sealed. do.

Materials placed in a nitrogen environment in a sealed polyvinyl pack are irradiated with a gamma irradiation device. One of the main features of the present invention is that irradiation of gamma rays, which are usually used for sterilization, is used to cause crosslinking. The dosage is about 100 to 125 kGy. In this way, when irradiated with gamma rays on the material, if the nitrogen is filled so that it does not come into contact with oxygen, less free radicals are generated. As described above, the free radicals promote the oxidation of the ultra high molecular weight polyethylene, which causes the mechanical properties to be inhibited.

Subsequently, after removing the material of ultra high molecular weight polyethylene from the polyvinyl pack, the material is recrystallized by heat treatment at about 140 to 160 ° C., most preferably at about 150 ° C. for about 2 hours using a heat treatment machine. It is known that the melting point of the ultrahigh molecular weight polyethylene is about 135 ° C. Therefore, when the heat treatment is performed at a temperature higher than the melting point, recrystallization occurs and free radicals are completely removed to prevent oxidation of the ultrahigh molecular weight polyethylene. In addition, it is possible to obtain satisfactory excellent mechanical properties for artificial joints, that is, tensile strength of 55 MPa or more, elongation of 234%, hardness of 65 or more, and Izod impact strength of 57.2 kJ / m ² or more. .

The shape of the artificial joint liner is processed on the heat treated material. For example, as described above, it may be machined to have a shape such as an acetabular liner or a bipolar liner as needed, and in the case of an acetabular liner, one of a flat type and an elevated type may be selected for processing. Done.

Once the liner is finished by machining, it is placed in a breathable pack and sterilized using a plasma sterilizer. The breathable pack is made of sterile paper or sterile cloth having some sort of filter performance, such as passing gas but not bacteria. On the other hand, since the sterilization in the medical field applying the plasma is already widely known, a detailed description thereof will be omitted. Would like to emphasize that the mechanical properties of ultrahigh molecular weight polyethylene liners do not change during sterilization.

Additionally, sterilization in a breathable pack may be followed by packaging the ultrahigh molecular weight polyethylene liner in a breathable pack.

The ultra high molecular weight polyethylene liner for artificial joint manufactured by the manufacturing method according to the present invention was subjected to abrasion test using a simulator, and showed better wearability than the conventional liner. Hereinafter, the simulator wear test will be described.

Simulator wear test reproduces the wear mechanism in vivo, and wear resistance can be defined and measured by measuring the weight loss of ultra high molecular weight polyethylene components at defined intervals of the test period. The weight loss can be known by checking the weight change before and after the test. Weight wear is defined as milligrams per million cycles of the simulator. This is the total mass measurement of debris fines generated from the wear surface.

The simulator used is a hip simulator. Ultra high molecular weight polyethylene liners were tested against a 28 mm diameter thigh head made of CoCrMo alloy. Naturally, the liners used herein are those manufactured through the manufacturing method according to the present invention.

Tested under physiological loading and exercise conditions on a servohydraulic 6-station hip simulator (ISO 14242-1), the test period was 5 million cycles at a cycle frequency of 1 Hz and observed at 500,000 cycles, or weight loss. . The test solution was calf serum, and the temperature was 37 ° C ± 2 ° C. Test serum was replaced approximately every 500,000 cycles. Force was applied to the cup and the maximum force applied was 3.0 kN. The direction of the force vector is constant with respect to the cup but with respect to the head. All three angular displacements were implemented: -18 ° to + 25 ° bending and extension, -4 ° to + 7 ° abduction and adduction, and -10 ° to + 2 ° rotation. It became.

The abrasion test results for the four aspheric liner specimens and the four bipolar liner specimens are shown in FIGS. 3 and 4, respectively. One of each of these two groups of specimens (eg, 1-4 specimens of FIG. 3 and 2-4 specimens of FIG. 4) was relatively inferred by measuring the weight increase of the test solution, ie, serum, without measuring the weight wear. .

Through this test, the wear resistance of the crosslinked ultra high molecular weight polyethylene non-guarliner and the wear resistance of the crosslinked ultra high molecular weight polyethylene bipolar liner were measured for a 28 mm diameter thigh head made of CoCrMo alloy. The average wear of the abyss liner prepared according to the invention was 0.18 mg per million cycles, and the average wear of the bipolar liner prepared according to the invention was 1.05 mg per million cycles.

Under the same conditions as the abrasion test described above (ISO 14242-1), the average wear of the liner according to the prior art is known to be 3.30 mg per million cycles and the minimum wear is 2.05 mg per million cycles. Meanwhile, as another representative example, a study by McKelup et al. ("Effect of Femoral Head Size, Material, Surface Roughness and Serum Concentration on the Wear of 5 Mrad Crosslinked- Remelted UHMWPE Acetabular Cups" of H. McKellop, YS. Liao, FW) Shen, W. McGarry; 52nd Annual Meeting of the Orthopaedic Research Society, ORS 2006, paper No. 0638) had an average wear rate of 4.65 mg per million cycles. The same load profile was used.

As a result, the simulator wear test proved that the ultra-high molecular weight polyethylene liner for artificial joint manufactured according to the present invention had much better wear resistance than conventional liners.

Accordingly, the present invention improves wear resistance and provides a sterilized ultra high molecular weight polyethylene liner without changing mechanical properties, thereby ultimately obtaining an effect of extending the life of artificial joints.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a view schematically showing an example of a state in which an artificial joint is performed.

Figure 2 is a block diagram schematically showing a method of manufacturing an ultra-high molecular weight polyethylene liner for artificial joints according to the present invention.

3 and 4 are graphs showing the relationship between the cycle and wear as showing the results of the simulator wear test.

Claims (4)

Cutting the material of ultra high molecular weight polyethylene, Inserting the cut material into a polyvinyl pack and filling the polyvinyl pack with nitrogen to seal it; Causing crosslinking of the material of the ultrahigh molecular weight polyethylene by gamma irradiation; Heat treating the material to cause recrystallization; Processing the shape of the artificial joint liner on the material; Putting the finished liner in a breathable pack sterilized by using plasma sterilization method of manufacturing an ultra-high molecular weight polyethylene liner for articulated joints. According to claim 1, wherein the step of causing the cross-linking of the material of the ultra-high molecular weight polyethylene by the gamma irradiation, irradiating gamma rays using a gamma ray irradiation apparatus, the irradiation amount is artificial joint, characterized in that 100 to 125 kGy Method for producing ultra high molecular weight polyethylene liner for use. The method of claim 1, wherein the recrystallization by heat treatment of the material comprises heat treatment at 140 to 160 ° C. for 2 hours using a heat treatment machine. The method of claim 1, wherein after the sterilization step, the ultra-high molecular weight polyethylene liner for packaging the ultra-high molecular weight polyethylene liner in a state of being put in the breathable pack further comprises.

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