Near-net forming method of high-crosslinking ultra-high molecular weight polyethylene artificial joint friction liner

Abstract

The invention relates to the technical field of medical polymer material forming, in particular to a near-net-shape forming method of a high-crosslinking ultra-high molecular weight polyethylene artificial joint friction liner, which combines near-net-shape forming with high-energy radiation and annealing treatment lower than a melting point. The prepared high-crosslinking ultra-high molecular weight polyethylene artificial joint friction liner has extremely high friction surface smoothness (Ralt; 0.10), high wear resistance, high oxidation resistance and high strength, so that the history that a near-net-shaped artificial joint friction pad cannot use high-crosslinking ultra-high molecular weight polyethylene is overcome, the advantages of a high-crosslinking material and the advantages of near-net forming are perfectly combined, the high smoothness of the friction surface of the pad is kept, and the wear resistance and the oxidation resistance of the friction pad are improved. And the gasket is endowed with high crosslinking degree and long-term wear resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical polymer material forming, in particular to a near-net forming method of high crosslinking ultra-high molecular weight polyethylene artificial joint friction liner. BACKGROUND

[0002] The long-term safety and effectiveness of artificial joints depend largely on the wear resistance, aging resistance and mechanical strength of the ultra-high molecular weight polyethylene of its friction pair. Since the late 1990s, high crosslinking ultra-high molecular weight polyethylene has been widely used in the field of artificial joints, especially in the field of artificial joints, due to its excellent wear resistance. High crosslinking ultra-high molecular weight polyethylene has been widely used due to its excellent wear resistance, which is usually prepared by irradiating ordinary non-crosslinked ultra-high molecular weight polyethylene profiles and heat treatment.

[0003] Artificial joint friction liners can also be directly near-net molded by molding ultra-high molecular weight polyethylene powder. The mold for molding has an inner cavity similar in shape and size to the friction liner, especially the shape and size of the liner friction surface for molding and the final liner friction surface are highly consistent, in addition, the inner cavity surface of the mold has a mirror-polished finish, and the liner after near-net molding has extremely high finish (Ra<0.10), thus having high initial wear resistance.

[0004] However, the long-term wear resistance of artificial joints mainly depends on the crosslinking degree of ultra-high molecular weight polyethylene, and the friction liner after near-net molding will seriously damage the finish of the friction surface after high-energy radiation and remelting treatment, therefore this method is not suitable for near-net molding of the liner. Therefore, a near-net forming method of high crosslinking ultra-high molecular weight polyethylene artificial joint friction liner is proposed. SUMMARY

[0005] The purpose of the present application is to provide a near-net forming method of high crosslinking ultra-high molecular weight polyethylene artificial joint friction liner to solve the problems raised in the background art.

[0006] In order to solve the above technical problems, the present application provides the following technical scheme: In a first aspect, the present application provides a near-net forming method of high crosslinking ultra-high molecular weight polyethylene artificial joint friction liner, comprising the following steps: S1, molding: using medical grade ultra-high molecular weight polyethylene powder as raw material, molding in a mold to obtain a near-net forming semi-finished product with a mirror-finished friction surface; S2, oxygen barrier sealing: placing the semi-finished product in a high-temperature resistant double-layer oxygen barrier packaging bag for sealing, the oxygen content in each layer of the double-layer oxygen barrier packaging bag is not more than 1%; S3, radiation and annealing: the semi-finished product sealed in the double-layer oxygen barrier packaging bag is subjected to high-energy radiation and annealing below the melting point of the material in sequence, annealing is kept, and the semi-finished product is taken out from the annealing furnace after being cooled to below 40°C; the radiation dose is greater than 40 kGy; S4, machining: the processed semi-finished product is taken out and subjected to machining to obtain a final product, and the surface integrity of the friction surface is kept.

[0007] Preferably, the step S1 comprises: The ultra-high molecular weight polyethylene powder is placed in a mold, and cold pressing is performed at room temperature with a pressure of 1-10 MPa; Then, the mold is heated to 135-250°C while a pressure of 5-30 MPa is applied for hot pressing, and the pressure is kept for at least 1 hour; Finally, the mold is cooled to below 40°C in the pressure-keeping state, and the semi-finished product is taken out.

[0008] More preferably, the pressure for the cold pressing is 3-6 MPa; the heating temperature for the hot pressing is 150-250°C, the pressure is 5-20 MPa, and the pressure-keeping time is 2-5 hours.

[0009] More preferably, when the cold pressing is performed, the mold is in air or a non-oxidizing protective atmosphere.

[0010] Preferably, the annealing temperature is 110-130°C, and the annealing keeping time is 3-10 hours.

[0011] Preferably, the radiation dose is 40-100 kGy.

[0012] Preferably, the ultra-high molecular weight polyethylene powder optionally contains an antioxidant.

[0013] In the second aspect, the application provides a high-crosslinking ultra-high molecular weight polyethylene artificial joint friction liner prepared by the above method; the friction liner is an artificial hip joint cup friction liner, an artificial knee joint tibial friction liner, or an artificial shoulder joint friction liner.

[0014] Compared with the prior art, the application has the following beneficial effects: the high-crosslinking ultra-high molecular weight polyethylene artificial joint friction liner prepared by combining near-net forming with high-energy radiation and annealing below the melting point has the advantages of extremely high friction surface smoothness (Ra<0.10), high wear resistance, high oxidation resistance, and high strength, thereby overcoming the history that the near-net formed artificial joint friction liner cannot use high-crosslinking ultra-high molecular weight polyethylene, perfectly combining the advantages of high-crosslinking materials and near-net forming, keeping the high smoothness of the liner friction surface, and endowing the liner with high-crosslinking degree and long-term wear resistance. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification, illustrate embodiments of the application, and together with the description serve to explain the principles of the application. In the drawings: Figure 1 is a schematic diagram of the combination of the ultra-high molecular weight polyethylene powder and the mold.

[0016] Figure 2 is a schematic diagram of the near-net compression molding process.

[0017] Figure 3 is a schematic diagram of the semi-finished product after near-net molding.

[0018] Figure 4 is a schematic diagram of the semi-finished product being double-sealed and packaged.

[0019] Figure 5 is a schematic diagram of the semi-finished product after sealing and packaging being subjected to high-energy radiation.

[0020] Figure 6 is a schematic diagram of the packaged product after radiation being subjected to annealing heat treatment.

[0021] Figure 7 is a schematic diagram of the semi-finished product after annealing being machined into a final product. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0023] Please refer to Figures 1-7 The application provides a technical solution: a near-net molding method for a high-crosslinking ultra-high molecular weight polyethylene artificial joint friction liner, comprising the following steps: S1, compression molding: using medical-grade ultra-high molecular weight polyethylene powder as raw material, the ultra-high molecular weight polyethylene powder optionally contains an antioxidant such as vitamin E, the powder is placed in a mold according to the designed weight, the inner cavity of the mold contains a semispherical mirror surface high polishing surface and a cylindrical inner surface, the inner diameter and depth of the cylinder are both greater than the designed size of the final friction liner product; The assembled mold is placed in a compression molding machine, cold pressing is performed at room temperature, the pressure is 1-10 MPa, generally between 3-6 MPa, the mold can be in air or in a protective atmosphere of non-oxidizing gas; The mold is slowly heated to above the melting point of the UHMWPE material, generally between 135-250°C, preferably between 150-250°C, while the pressure is increased to between 5-30 MPa, generally between 5-20 MPa, for at least 1 hour, generally between 2-5 hours; After the holding time, the mold is slowly cooled to room temperature (below 40°C), while the pressure is maintained between 5-30 MPa, generally between 5-20 MPa, and the cooling time is generally between 1-5 hours, preferably between 1-3 hours; After cooling, the near-net shaped semi-finished product with mirror-finished friction surface is obtained by demolding; S2, oxygen barrier sealing: the semi-finished product is placed in a high-temperature resistant double-layer oxygen barrier packaging bag, which is sealed, vacuumed or filled with non-oxidizing gas such as nitrogen or argon, and the oxygen content in each layer of the double-layer oxygen barrier packaging bag is not more than 1%; S3, radiation and annealing: the semi-finished product sealed in the double-layer oxygen barrier packaging bag is subjected to high-energy ray radiation, such as gamma ray, X-ray or electron beam ray, and the radiation dose is greater than 40 kGy, generally between 40 and 100 kGy; The irradiated double-layer oxygen barrier packaging bag is placed in a heat treatment furnace for annealing treatment at a temperature below the melting point, generally between 110-130°C, and the annealing holding time is generally between 3-10 hours. After the holding time ends, it is cooled to room temperature (<40°C) and then taken out of the annealing furnace; S4, machining: the treated semi-finished product is taken out of the double-layer oxygen barrier packaging bag, and the final product is obtained by machining, and the surface integrity of the friction surface is maintained without damaging the mirror-polished finish of the friction surface.

[0024] The semi-finished product and the finished product of the high-crosslinking UHMWPE artificial joint friction liner prepared by the above method are artificial hip joint cup friction liners, artificial knee joint tibial friction liners or artificial shoulder joint friction liners.

[0025] Examples A medical-grade UHMWPE resin powder (DSM Biomedical B.V., MG001 UHMWPE) is used as the raw material, and the powder is placed in a mold according to the designed weight. The inner cavity of the mold contains a semispherical mirror-finished high-polished surface and a cylindrical inner surface, and the inner diameter and depth of the cylinder are both greater than the designed size of the final friction liner product; The assembled mold is placed in a molding machine and cold-pressed at room temperature; Heat the mold to the set temperature, generally between 135-250°C, preferably between 150-250°C, while maintaining the pressure between 5-20MPa, and the heat and pressure holding time between 1-5 hours; After the heat preservation and pressure holding stage is completed, the mold is cooled to room temperature (below 40°C) under pressure, with a pressure between 5-20MPa and a cooling time between 1-5 hours; Remove the molded semi-finished product from the mold; The shaped semi-finished product is placed in a high-temperature resistant packaging bag, vacuumed or filled with a non-oxidizing gas such as nitrogen or argon, and the packaging bag is sealed. The oxygen content in the bag does not exceed 1%. Place the sealed packaging bag inside a second high-temperature resistant packaging bag, evacuate the air or fill it with a non-oxidizing gas such as nitrogen or argon, and then seal the packaging bag. The oxygen content in the bag should not exceed 1%. High-energy electron beam irradiation was applied to near-net-shape ultra-high molecular weight polyethylene semi-finished products sealed in double-layered packaging bags, with a radiation dose of 75 kGy. The irradiated sealed bags were placed in a heat treatment furnace and annealed at a temperature below the melting point. The annealing temperature was 130°C and the annealing holding time was 6 hours. After the holding time was completed, the bags were cooled to room temperature (<40°C) and then removed from the annealing furnace. After radiation and annealing, the ultra-high molecular weight polyethylene (UHMWPE) liner semi-finished product is removed from the double-layer packaging bag and machined into the final artificial hip joint acetabular cup friction liner. The mirror polish of the friction surface must not be damaged during the processing.

[0026] The highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad prepared by the above technical solution has the advantages of extremely high friction surface smoothness (Ra<0.10), high wear resistance (high degree of cross-linking), high oxidation resistance, and high strength. This overcomes the historical limitation that highly cross-linked ultra-high molecular weight polyethylene cannot be used in near-net-shape artificial joint friction pads, and perfectly combines the advantages of highly cross-linked materials with the advantages of near-net-shape forming.

[0027] Using conventionally machined high-crosslinked ultra-high molecular weight polyethylene acetabular liner as a control, the relevant test results of this embodiment are described in detail below, including the surface finish of the friction surface, the oxidation index of the friction surface, the oxidation index after accelerated oxidation, the degree of crosslinking (swelling degree), and the impact strength.

[0028] 1. Surface smoothness of friction surfaces

[0029] Table 1. Surface roughness (smoothness) test results of the friction surface of the acetabular cup liner. Table 1 shows the test results of the surface finish of the friction surface of the acetabular cup friction pad in this embodiment. The surface finish of the friction surface of the pad in this embodiment is much better than that of the friction surface of the conventionally machined pad.

[0030] 2. Antioxidant properties

[0031] Table 2. Detection results of the maximum oxidation index of the rear liner friction surface before accelerated oxidation. The oxidation resistance of highly cross-linked ultra-high molecular weight polyethylene was tested according to ASTM F2102 and ASTM F2003-02 methods. The oxidation index results of the friction surface before and after accelerated oxidation are shown in Table 2. The lower the oxidation index, the stronger the oxidation resistance. The maximum oxidation index of the friction surface of the pad prepared in the embodiment of the present invention is 0 before and after accelerated oxidation, which is comparable to that of traditional remelted materials.

[0032] 3. Degree of cross-linking (swelling degree)

[0033] Table 3. Results of Swelling Degree Test The degree of crosslinking of ultra-high molecular weight polyethylene (UHMWPE) is generally determined by measuring its swelling degree. A higher degree of crosslinking results in a lower swelling degree. The swelling degree was measured according to the method in ASTM F2214-16. The results are shown in Table 3. The swelling degree of the material in this embodiment is 2.96, which is comparable to that of conventional machined gaskets (2.84).

[0034] 4. Impact strength

[0035] Table 4 Impact Strength Test Results Impact strength was tested according to the method indicated in ASTM F648-21, and the test results are shown in Table 4. The impact strength of the gasket material in this embodiment is approximately 10% higher than that of conventional machined gasket materials.

[0036] The above test results verify that the surface finish of the friction surface of the near-net-shape high-crosslinked ultra-high molecular weight polyethylene artificial joint friction pad of the present invention is at least 20 times better than that of the friction surface of the traditional machined high-crosslinked polyethylene friction pad. In addition, the impact strength of the near-net-shape high-crosslinked ultra-high molecular weight polyethylene artificial joint friction pad material of the present invention is better than that of the traditional machined high-crosslinked polyethylene friction pad, and its oxidation resistance and degree of crosslinking (swelling degree) are the same as those of the traditional machined high-crosslinked polyethylene friction pad.

[0037] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A near-net-shape molding method for a highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad, characterized in that, Includes the following steps: S1. Compression molding: Using medical-grade ultra-high molecular weight polyethylene powder as raw material, compression molding is performed in a mold to obtain a near-net-shape semi-finished product with a mirror-like smooth friction surface. S2. Oxygen barrier sealing: The semi-finished product is placed in a high-temperature resistant double-layer oxygen barrier packaging bag and sealed, wherein the oxygen content in each layer of the double-layer oxygen barrier packaging bag does not exceed 1%; S3. Radiation and Annealing: The semi-finished product sealed in the double-layer oxygen barrier packaging bag is subjected to high-energy radiation and annealing treatment below the melting point of the material in sequence. After annealing and holding at a certain temperature, it is taken out from the annealing furnace after cooling to below 40°C. The radiation dose is greater than 40 kGy. S4. Machining: Take out the processed semi-finished product and machine it to obtain the final finished product, while maintaining the surface integrity of the friction surface.

2. The near-net-shape molding method for a highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad according to claim 1, characterized in that, Step S1 includes: The ultra-high molecular weight polyethylene powder is placed in a mold and cold-pressed at room temperature at a pressure of 1-10 MPa. The mold is then heated to 135-250°C, and a pressure of 5-30 MPa is applied for hot pressing. The heat and pressure are then maintained for at least 1 hour. Finally, the product is cooled to below 40°C under pressure and then demolded to obtain the semi-finished product.

3. The near-net-shape molding method for a highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad according to claim 2, characterized in that, The cold pressing pressure is 3-6 MPa; the hot pressing heating temperature is 150-250°C, the pressure is 5-20 MPa, and the heat and pressure holding time is 2-5 hours.

4. The near-net-shape molding method for a highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad according to claim 2, characterized in that, During the cold pressing process, the mold is in air or a non-oxidizing protective atmosphere.

5. The near-net-shape molding method for a highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad according to claim 1, characterized in that, The annealing temperature is 110-130°C, and the annealing holding time is 3-10 hours.

6. The near-net-shape molding method for a highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad according to claim 1, characterized in that, The radiation dose is 40-100 kGy.

7. The near-net-shape molding method for a highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad according to claim 1, characterized in that, The ultra-high molecular weight polyethylene powder may optionally contain antioxidants.

8. A highly cross-linked ultra-high molecular weight polyethylene artificial joint friction pad, characterized in that, The friction pad is prepared by any one of claims 1 to 7; the friction pad is an artificial hip joint acetabular cup friction pad, an artificial knee joint tibial friction pad, or an artificial shoulder joint friction pad.

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