JP2014124502A - Method for manufacturing sliding member of artificial joint and sliding member of artificial joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a sliding member of an artificial joint by which a sliding member of an artificial joint, having a prolonged durable period can be manufacture, and to provided the sliding member of an artificial joint.SOLUTION: In a molding step of a step A1, an ultrahigh molecular weight polyethylene material containing an antioxidant is molded to obtain a base material of a predetermined shape. In a polymer film forming step of a step A2, the obtained base material is irradiated with ultraviolet light while being immersed in a treatment aqueous solution containing a compound having a phosphorylcholine group, thereby a polymer film containing a polymer chain formed by polymerization of the compound having the phosphorylcholine group is formed on a surface of the base material.

Description

  The present invention relates to a manufacturing method for manufacturing a sliding member suitable for an artificial joint, and a sliding member for an artificial joint manufactured by the manufacturing method.

  A treatment method has been established in which a joint that has lost its original function due to an accidental fracture or osteoarthritis is replaced with a so-called artificial joint, which is an artificial product having an equivalent function. Since an artificial joint is embedded in a living body, there is little adverse effect on the living body, and it is required to maintain a certain function for a long time. If the prosthetic joint used has a short service life and needs to be replaced with a new prosthetic joint, the burden on the patient becomes extremely large and must be avoided.

  The artificial joint is roughly composed of two members, each of which is attached to the end portion of the bone, and when trying to move the joint, the two members move relative to each other and slide. In the case of an artificial hip joint and an artificial knee joint, sliding is repeated every time the user walks.

  Materials used for artificial joints include metal materials such as cobalt chromium alloy and titanium alloy, ceramic materials such as alumina and zirconia, and polymer materials such as polyethylene. In an artificial hip joint, for example, a cobalt-chromium alloy head ball on the femoral side member and a polyethylene cup on the pelvis side member slide, and polyethylene abrasion powder is generated from the cup as the sliding is repeated. Since the generated wear powder is recognized as a foreign substance in the living body, the living immune system functions in order to eliminate it. At this time, multinucleated cells called osteoclasts are activated, and osteolysis occurs in which bone around the artificial joint is absorbed.

  When osteolysis occurs around the artificial joint due to the activation of osteoclasts, a gap is formed between the bone and the artificial joint, resulting in loosening of the artificial joint.

  Since sliding is inevitable as long as it is an artificial joint, it is necessary to use a sliding material excellent in wear resistance that does not generate such abrasion powder.

  Patent Document 1 discloses a sliding member coated with a polymer film formed by grafting a phosphorylcholine group-containing polymer chain onto a sliding surface of a substrate molded from ultrahigh molecular weight polyethylene. Yes.

  It is known that the cartilage surface of living joints is covered with phospholipids, contributing to cartilage protection and high lubrication. When a sliding member having a phosphorylcholine group-containing polymer chain having a structure close to that of phospholipid and covering the surface of a base material is applied to an artificial joint, an artificial joint having a low friction coefficient and almost no wear can be realized.

  In some cases, polymer materials such as polyethylene are irradiated with high energy rays such as gamma rays in order to improve wear resistance and sterilization due to advanced crosslinking. By irradiation with this high energy beam, free radicals are generated in the polymer material. The generated free radical reacts with oxygen in the living body to cause the main chain of the polyethylene to be cleaved, thereby reducing the mechanical properties and wear resistance.

  In Patent Document 2, an antioxidant such as vitamin A, vitamin C, or vitamin E is added to polyethylene in order to improve antioxidant properties.

JP 2008-148850 A Special table 2003-530957 gazette

  The sliding member described in Patent Document 1 can dramatically improve the wear resistance by using a polymer film composed of a phosphorylcholine group-containing polymer chain. The in vivo oxidative action caused by free radicals does not drastically reduce the wear resistance of the polymer material, but if it also has antioxidant properties, the durability of the sliding member described in Patent Document 1 The number of years will be further extended.

  For example, it is conceivable to cover the surface of a polyethylene material containing an antioxidant such as vitamin E with a polymer film composed of a phosphorylcholine group-containing polymer chain, but radical graft polymerization of the phosphorylcholine group-containing polymer chain is performed. In this case, the polymerization reaction is inhibited by the radical scavenging effect of vitamin E, which is an antioxidant, and a polymer film cannot be formed sufficiently.

  The objective of this invention is providing the manufacturing method of the sliding member for artificial joints, and the sliding member for artificial joints which can manufacture the sliding member for artificial joints whose service life further improved.

The present invention is a method for manufacturing a sliding member for an artificial joint,
A base material forming step for obtaining a base material by molding an ultrahigh molecular weight polyethylene material containing an antioxidant;
Ultraviolet rays are irradiated in an aqueous solution containing a compound having a phosphorylcholine group while the substrate is immersed, and a polymer film containing a polymer chain in which a compound having a phosphorylcholine group is polymerized is formed on the surface of the substrate. And a molecular film forming step. A method for producing a sliding member for an artificial joint, comprising:

  Further, the present invention is characterized in that a base material is obtained by performing a crosslinking treatment before the polymer film forming step.

  Further, the present invention is characterized in that in the base material forming step, a base material is obtained by performing a crosslinking treatment by irradiation with 100 to 150 kGy of gamma rays after molding.

  Moreover, this invention is characterized by the density | concentration of the process aqueous solution containing the compound which has a phosphorylcholine group being a density | concentration of 0.25-0.50 mol / L.

  In the present invention, the concentration of the treatment aqueous solution containing the compound having a phosphorylcholine group is preferably a concentration of 0.33 to 0.50 mol / L.

  The present invention is also characterized in that the antioxidant is vitamin E.

  Further, the present invention is characterized by further comprising a cleaning step of cleaning the surface of the substrate by immersing the substrate in a cleaning liquid containing a surfactant after the substrate forming step and before the polymer film forming step. To do.

  Further, the present invention is characterized in that the surfactant is a nonionic surfactant having a polyoxyethylene chain.

  Further, the present invention is characterized in that sterilization treatment by gamma ray irradiation is performed in the polymer film forming step.

  Moreover, this invention is the sliding member for artificial joints manufactured by said manufacturing method of the sliding member for artificial joints.

  According to the present invention, in addition to the wear resistance due to the polymer film containing a phosphorylcholine group, by having oxidation resistance due to an antioxidant, a sliding member for an artificial joint having a further improved service life is manufactured, Can be provided.

It is process drawing which shows the manufacturing method of the sliding member for artificial joints which is 1st Embodiment of this invention. It is process drawing which shows the manufacturing method of the sliding member for artificial joints which is 2nd Embodiment of this invention. It is process drawing which shows the manufacturing method of the sliding member for artificial joints which is 3rd Embodiment of this invention. It is a schematic diagram of the artificial hip joint 1 which is a kind of artificial joint. 1 is a schematic diagram of a acetabular cup 10. FIG. It is a graph which shows the change of the polymer film characteristic with respect to MPC density | concentration.

FIG. 1 is a process diagram showing a method for manufacturing a sliding member for an artificial joint according to a first embodiment of the present invention.
The manufacturing method of the first embodiment is as follows:
(Step A1) The molding step (Step A2) comprises two steps of a polymer film forming step.

  In the molding step of step A1, an ultrahigh molecular weight polyethylene material containing an antioxidant is molded to obtain a substrate having a predetermined shape. In the present embodiment, the base material forming step includes the molding step of step A1.

In the present invention, an ultra-high molecular weight polyethylene (UHMWPE) material is used as the resin material constituting the substrate. UHMWPE is excellent in mechanical properties such as wear resistance, impact resistance, and deformation resistance, and is suitable as a resin material used for artificial joints. The abrasion resistance is higher as the molecular weight is higher, and the molecular weight is preferably 1 million or more, more preferably 1 million or more and 7 million or less, and more preferably 3 million or more and 4 million or less. Here, the molecular weight of UHMWPE constituting the substrate was determined by the following formula (1) by measuring the viscosity of a decahydronaphthalene (decalin) solution at 135 ° C.

  Vitamins such as vitamin A, vitamin C, and vitamin E can be used as the antioxidant contained in the base material. Phenols and fragrances that are general antioxidants that prevent or suppress oxidation of polymers Amine amines, aldehydes, amines having ketones, aminophenol salts and condensates, and thio compounds can also be used.

  Among these compounds, vitamins are preferable, and vitamin E is more preferable. Examples of vitamin E include tocopherol and tocotrienol and derivatives thereof, such as α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol and α-tocotrienol, β-tocotrienol, γ-tocotrienol, δ-tocotrienol and the like. Can be mentioned. It is preferable to use tocotrienol in that it has an excellent antioxidant effect. These vitamin Es may be used alone or in combination.

  The base material can be obtained by putting a mixture of UHMWPE in a powder form, granular form or pellet form into which an antioxidant is mixed, and then compressing or extruding the mixture. UHMWPE is a thermoplastic resin, but its fluidity is low even at a melting temperature or higher. Therefore, it is preferable to put solid UHMWPE into a mold and mold it under high heat and high pressure conditions.

  The antioxidant may be added to solid UHMWPE, and the antioxidant and UHMWPE may be uniformly mixed in advance and put into the mold. The content of the antioxidant contained in the substrate is 0.01 to 5% by weight with respect to UHMWPE, preferably 0.05 to 0.7% by weight, more preferably 0.05 to 0%. 15% by weight.

  The compression molding includes, for example, a normal temperature compression stage, a pressure drop temperature increase stage, a high temperature and high pressure maintenance stage, and a cooling stage.

  In the room temperature compression stage, raw material powder made of a mixture of UHMWPE and an antioxidant is put into a molding die and compressed (pressed) at a pressure of 200 to 250 MPa and a temperature of 25 ° C. (room temperature) for 1 to 10 minutes.

  In the pressure drop temperature rise stage, the pressure is lowered from the value set in the room temperature compression stage to 20 to 35 MPa, the temperature is raised from 25 ° C. to 140 to 275 ° C., and held for 10 to 40 minutes.

  In the high temperature and high pressure maintenance stage, the pressure is raised from the value set in the pressure drop temperature rise stage to 100 to 180 MPa while the temperature is kept at the high temperature set in the pressure drop temperature rise stage and held for 1 to 10 minutes. To do.

  In the cooling stage, the temperature is gradually cooled from the value set in the high temperature and high pressure maintaining stage to 25 ° C. (room temperature) over a period of 10 to 50 minutes while maintaining the pressure at the value set in the high temperature and high pressure maintaining stage. .

  Finally, the pressure is released and the mold is removed from the mold to obtain the substrate of the present invention. The base material obtained here contains an antioxidant such as vitamin E.

  The substrate obtained by compression molding or extrusion molding may be used as it is for the next polymer film forming step, or may be used for the polymer film forming step after its shape is adjusted by cutting.

  Next, in the polymer film forming step of Step A2, the obtained base material is irradiated with ultraviolet rays in a state where it is immersed in an aqueous solution containing a polymerizable monomer which is a compound having a phosphorylcholine group (PC compound). A polymer film including a polymer chain obtained by polymerizing a PC compound is formed on the surface of the material.

  Since the polymer film is formed to reduce the friction coefficient of the sliding surface of the base material, it may be formed at least on the surface portion corresponding to the sliding surface of the base material. For example, when manufacturing an acetabular cup in an artificial hip joint, at least a polymer film may be formed on the inner spherical surface of the cup on which the head ball slides.

  Formation of the polymer film on the surface of the base material is performed by graft polymerization of the polymer chain polymerized with the PC compound onto the surface corresponding to the sliding surface of the base material made of UHMWPE.

  The polymer chain of the OLE_LINK1PCOLE_LINK1 compound can be stably immobilized on the surface of the substrate by graft polymerization. Furthermore, a large amount of phosphorylcholine groups can be formed on the sliding surface of the base material to increase the density of the polymer film.

  For the formation of the polymer film, a polymerizable monomer that is a PC compound is used. In particular, by selecting a polymerizable monomer having a phosphorylcholine group at one end and a functional group capable of graft polymerization with UHMWPE at the other end, A polymer film can be grafted to the sliding surface of the substrate.

  Examples of the polymerizable monomer used in the present invention include 2-methacryloyloxyethyl phosphorylcholine, 2-acryloyloxyethyl phosphorylcholine, 4-methacryloyloxybutylphosphorylcholine, 6-methacryloyloxyhexylphosphorylcholine, ω-methacryloyloxyethylene phosphorylcholine, 4-styryl. Examples include oxybutyl phosphorylcholine. Among these, 2-methacryloyloxyethyl phosphorylcholine (hereinafter referred to as “MPC”) is particularly preferable.

  MPC has a chemical structure as shown in the following structural formula, and is a polymerizable monomer having a phosphorylcholine group and a polymerizable methacrylic acid unit. MPC can be easily polymerized by radical polymerization to form a high molecular weight homopolymer (Ishihara et al .: Polymer Journal, Vol. 22, 355 (1990)). Therefore, when the polymer film is formed as an assembly of polymer chains obtained by polymerizing MPC, graft bonding between the MPC polymer chain and the base material sliding surface can be performed under relatively mild conditions. A high-density polymer film can be formed, and a large amount of phosphorylcholine groups can be formed on the substrate sliding surface.

  The polymer film of the present invention includes not only a homopolymer composed of a single polymerizable monomer having a phosphorylcholine group, but also a copolymer composed of a polymerizable monomer having a phosphorylcholine group and, for example, another vinyl compound monomer. Can also be formed. Thereby, functions such as improvement of mechanical strength can be added to the polymer film depending on the type of other vinyl compound used.

  Below, the formation method of a polymer film is demonstrated in detail. In order to graft-bond the polymer film to the sliding surface of the base material, a photopolymerization initiator is applied to the sliding surface of the base material, and the base material is immersed in an aqueous solution of a PC compound that is a polymerizable monomer. In this state, the sliding surface of the substrate is irradiated with ultraviolet rays (for example, a wavelength of 300 to 400 nm). When the sliding surface of the substrate is irradiated with ultraviolet rays, the PC compound in the vicinity of the sliding surface is polymerized to generate a polymer chain, and the generated polymer chain is grafted to UHMWPE on the sliding surface. The polymer chain is graft-bonded to the sliding surface with a high density, so that a polymer film covering the substrate sliding surface as a whole is formed.

  As the ultraviolet light source, for example, a high-pressure mercury lamp (UVL-400HA manufactured by Riko Kagaku Sangyo Co., Ltd.), LED (MeV365-P601JMM manufactured by YE buoy Co., Ltd.) or the like can be used.

  In this embodiment, it is a graft bond using a photopolymerization initiator, a photopolymerization initiator radical is generated by irradiation with ultraviolet rays, and the generated photopolymerization initiator radical forms a polymerization initiation point on the surface of the substrate, thereby polymerizing. The end of the polymer chain of the PC compound, which is a monomer, reacts with the polymerization initiation point, resulting in branch polymer bonding and subsequent branch polymer growth.

  As described above, in this embodiment, since the base material made of UHMWPE contains an antioxidant such as vitamin E, the photopolymerization initiator radicals generated by the irradiation with ultraviolet rays are oxidized on the surface of the base material. The radicals disappear. When the radical disappears, a polymerization initiation point is not formed on the surface of the base material, so that the polymer chain of the PC compound cannot be bonded to the base material surface. That is, the antioxidant added in anticipation of the in vivo antioxidant action acts as an inhibitor of the radical graft polymerization reaction in the production process. However, since the content of the antioxidant contained in the base material is a relatively small amount of 0.01 to 5% by weight, not all radicals disappear, and if the reaction conditions are set appropriately, Even a base material containing an antioxidant can form a polymer film by graft polymerization.

  This embodiment pays attention to the concentration of the PC compound in the treatment aqueous solution in which the substrate is immersed, and the concentration range of the PC compound that is a polymerizable monomer is set to 0.25 to 0.50 mol / L. The sliding surface of the base material containing the antioxidant can be sufficiently covered with the polymer film by polymerization. Moreover, the more preferable concentration range of PC compound concentration is 0.33-0.50 mol / L.

  Since the number of polymerization initiation points formed on the sliding surface of the substrate decreases due to the disappearance of radicals, the grafting reaction is caused by ensuring the opportunity to contact the polymerization initiation point by sufficiently containing the PC compound in the treatment liquid. Can do.

  When the concentration of the PC compound in the treatment liquid is lower than 0.25 mol / L, a sufficient polymer film is not formed on the sliding surface of the substrate, and when it exceeds 0.50 mol / L, the polymer film and the substrate A void is generated at the interface with the material surface.

  When the PC compound concentration is low, the polymer film is not formed because the PC compound or the polymer chain polymerized by the PC compound cannot be bonded to the surface of the substrate. When the PC compound concentration is high, the degree of polymerization of the PC compound increases, and the polymer chain extends, resulting in steric hindrance, and the PC compound that is an unreacted monomer is not sufficiently supplied to the polymerization starting point. Chains are less likely to bind to the substrate surface. If it does so, the part of the base-material surface to which the polymer chain is not couple | bonded will become remarkable, and the part will remain as a space | gap.

The ultraviolet irradiation conditions in the polymer film forming step may be set as appropriate. For example, the irradiation intensity is 5 mW / cm ² and the irradiation time is 90 minutes. Moreover, it is preferable to perform sterilization treatment by gamma ray irradiation after the polymer film forming step.

  As described above, a sliding member for an artificial joint whose base material surface is coated with a polymer film is obtained.

FIG. 2 is a process diagram showing a method for manufacturing an artificial joint sliding member according to a second embodiment of the present invention.
The manufacturing method of the second embodiment is as follows:
(Process B1) Molding process (Process B2) Cross-linking process (High energy ray irradiation process)
(Process B3) Cross-linking process (heat treatment process)
(Process B4) The process consists of four processes, a polymer film formation process. In the present embodiment, the base material forming step includes a molding step in Step B1, a cross-linking step in Step B2, and a heat treatment step in Step B3.

  The molding process of the process B1 is the same as the molding process of the process A1 in the first embodiment, and the polymer film forming process of the process B4 is the same as the polymer film forming process of the process A2 in the first embodiment. In the present embodiment, detailed description is omitted.

  In the cross-linking step (high energy ray irradiation step) of step B2, UHMWPE is generated by irradiating a substrate made of UHMWPE with high energy rays such as X-ray irradiation, gamma ray irradiation or electron beam irradiation to generate free radicals. To form UHMWPE having a network structure (crosslink, CL). By creating a crosslinked structure in the molecule, mechanical properties such as wear resistance and impact resistance are improved.

  The cross-linking reaction can also be performed by adding a cross-linking agent, but the unreacted cross-linking agent cannot be completely removed. Is preferred.

  Similar to the graft polymerization, the crosslinking reaction can be inhibited by the antioxidant, and therefore, in this embodiment, the progress of the crosslinking reaction is slow. In order to sufficiently advance the cross-linking reaction, it is preferable to irradiate high energy rays at a relatively high dose. A preferable dose is 75 to 200 kGy, and a more preferable dose is 100 to 150 kGy.

  As the high energy ray source, for example, a gamma ray source may be a radiation device using Co (cobalt) 60 as a radiation source, an accelerator that emits an electron beam, or the like.

  In the cross-linking step (heat treatment step) of step B3, free radicals generated by high energy ray irradiation in step B2 are more efficiently consumed by the cross-linking reaction to promote intramolecular cross-linking. The temperature range for the heat treatment is preferably 110 to 130 ° C., and the treatment time for the heat treatment is preferably in the range of 2 to 12 hours.

  In the second embodiment, a cross-linked structure is generated in the molecule by the cross-linking step, and a base material with further improved mechanical properties such as wear resistance and impact resistance is obtained.

The obtained substrate is subjected to radical graft polymerization under the same reaction conditions as in the first embodiment, and the sliding surface of the substrate is covered with a polymer film.
As described above, a sliding member for an artificial joint having further improved characteristics can be obtained.

FIG. 3 is a process diagram showing a method for manufacturing an artificial joint sliding member according to a third embodiment of the present invention.
The manufacturing method of the third embodiment is as follows:
(Process C1) Molding process (Process C2) Cross-linking process (High energy ray irradiation process)
(Process C3) Cross-linking process (heat treatment process)
(Step C4) The cleaning step (Step C5) comprises five steps of a polymer film forming step. In the present embodiment, the base material forming step includes a molding step in step C1, a cross-linking step in step C2, and a heat treatment step in step C3.

  The molding step of step C1 is the same as the molding step of step A1 in the first embodiment, and the polymer film formation step of step C5 is the same as the polymer film formation step of step A2 in the first embodiment, The cross-linking step (high energy ray irradiation step) of step C2 is the same as the cross-linking step (high energy ray irradiation step) of step B2 in the second embodiment, and the cross-linking step (heat treatment step) of step C3 is the second embodiment. Since it is the same as the cross-linking step (heat treatment step) of step B3 in the embodiment, detailed description is omitted in this embodiment.

  In the cleaning step of step C4, the substrate surface is cleaned by immersing the substrate in a cleaning liquid containing a surfactant.

  As described in the first embodiment, the antioxidant present on the surface of the base material inhibits the radical graft polymerization reaction in the polymer film forming step. Therefore, in this cleaning step, the surface of the base material, particularly the polymer film. Clean the sliding surface covered with.

  The cleaning liquid used in the cleaning process needs to clean the antioxidant and not to denature the UHMWPE constituting the base material. Therefore, an aqueous solution containing a cleaning component is preferable, and a surfactant is used as the cleaning component. What is contained is preferable.

  Since vitamin E used as an antioxidant is fat-soluble, it is easily removed by an aqueous solution of a surfactant.

  The surfactant that is a cleaning component may be appropriately selected according to the antioxidant to be removed, and is any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant. These surfactants can also be used. When vitamin E is used as an antioxidant, a nonionic surfactant is preferred.

  As the nonionic surfactant, a nonionic surfactant having a polyoxyethylene chain is more preferable, and polyoxyethylene alkyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan mono Laurate or the like can be used. Since polyoxyethylene sorbitan monolaurate is a kind of food additive, it is preferable as a cleaning component for cleaning a sliding member of an artificial joint, and is commercially available under a trade name such as Tween (registered trademark) 20.

  The concentration of the surfactant in the cleaning solution may be a concentration that can remove the antioxidant on the surface of the substrate, and is, for example, 0.01 to 10.0% by weight, preferably 0.1 to 5.0% by weight. More preferably, it is 0.1 to 1.0% by weight, and particularly preferably 0.3 to 1.0% by weight.

  The base material obtained after washing is subjected to graft polymerization under the same reaction conditions as in the first embodiment, and the sliding surface of the base material is covered with a polymer film. Since the polymer film is more firmly fixed to the surface of the base material, a sliding member for an artificial joint with further improved wear resistance can be obtained.

  FIG. 4 is a schematic diagram of an artificial hip joint 1 which is one of artificial joints, and FIG. 5 is a schematic diagram of an acetabular cup 10. The artificial hip joint 1 includes a acetabular cup 10 fixed to the acetabulum 94 of the hipbone 93 and a femoral stem 20 fixed to the proximal end of the femur 91. The acetabular cup 10 includes a cup base 12 having a substantially hemispherical acetabular fixation surface 14 and a sliding surface 16 that is recessed in a substantially hemispherical shape, and a polymer film 30 that covers the sliding surface 16. Yes. By fitting and sliding the head 22 of the femoral stem 20 into the recess in which the polymer film 30 of the acetabular cup 10 is formed, it functions as a hip joint.

  The acetabular cup 10 is made of a sliding member manufactured according to the first to third embodiments. As shown in FIGS. 4 and 5, in the acetabular cup 10 according to the embodiment of the present invention, the sliding surface 16 of the cup base 12 is covered with a polymer film 30, and the polymer film 30 has a phosphorylcholine group. It is obtained by graft polymerization of the polymer chain having the polymer chain onto the sliding surface 16.

  The polymer film 30 is similar to the structure of the biological membrane, has a high affinity with the lubricating liquid in the joint, and can hold the lubricating liquid inside the film. Therefore, the sliding surface 16 of the conventional acetabular cup 10 is used. Compared with, the friction coefficient can be lowered.

  Thereby, the acetabular cup 10 is obtained as a member having improved sliding characteristics and improved wear resistance.

  Below, the relationship between the PC compound density | concentration which is a polymerizable monomer in the process aqueous solution which immerses a base material, and the characteristic of the polymer film formed on the base-material surface is examined.

  The properties of the formed polymer film were evaluated by (a) water contact angle, (b) phosphoric acid index, (c) film thickness, and (d) surface phosphorus atom concentration.

(A) Contact angle of water When the hydrophilicity of the polymer film 30 covering the sliding surface 16 of the acetabular cup 10 is high, it is considered that the polymer film 30 becomes compatible with the lubricating liquid in the living body. The polymer film 30 sufficiently wetted by the lubricating liquid is expected to impart high lubricity to the acetabular cup 10 and improve the abrasion resistance of the acetabular cup 10. The hydrophilicity of the polymer film 30 was evaluated by measuring the contact angle when water was dropped on the surface of the polymer film 30.

  The contact angle of water was evaluated by a droplet method using a surface contact angle measuring device (DM300 manufactured by Kyowa Interface Science Co., Ltd.). The measurement of the static surface contact angle by the droplet method was performed at 60 seconds after dropping pure water having a droplet amount of 1 μL on the sample surface in accordance with the ISO 15989 standard.

(B) Phosphoric Acid Index The polymer film 30 is formed by bonding a polymer chain obtained by polymerizing a PC compound to the sliding surface 16 of the cup base 12, and the “density” of the polymer film 30 is It is considered that the higher the affinity for the lubricating liquid, the higher the characteristics such as wear resistance.

  Strictly speaking, the “density” of the polymer film is the amount of the polymer chain of the PC compound existing per unit area, but when the film thickness is sufficiently thin, the polymer compound per unit area is polymerized. It can be used as an index indicating the density of molecular chains. Therefore, it can be considered that the higher the density, the denser the polymer chains in which the PC compounds are polymerized on the sliding surface 16 of the acetabular cup 10.

  In the present invention, the “phosphoric acid index” is introduced as an index of the density of the polymer film 30, and the degree of congestion of the PC compound is quantitatively evaluated.

Here, the "phosphoric acid index", in the spectrum of the Fourier transform infrared spectroscopy (FT-IR) analysis, of 1080 cm ^-1 is the absorption of the phosphate group to the peak intensity I _methylene 1460 cm ^-1 is the absorption of the methylene group the intensity ratio of the peak intensity I _phosphate, i.e. defined by I _phosphate / I _methylene.

When a polymer film 30 containing a PC compound is formed on a cup base material 12 made of UHMWPE containing a methylene group and FT-IR measurement is performed as in the present invention, the peak of the methylene group caused by the cup base material 12 And a phosphate group peak due to the polymer film 30 are observed. At this time, if the composition of the cup base 12 is constant and the film thickness of the polymer film 30 does not change drastically (for example, if the film thickness difference is within 1 · 壕), the methylene group is absorbed. The phosphoric acid index calculated from the peak intensity and the peak intensity due to the absorption of phosphate groups is substantially proportional to the number of phosphate groups present per unit area of the cup base 12.
The FT-IR measurement was performed using a FT-IR apparatus (FT / IR-6300 type A manufactured by JASCO Corporation) with a resolution of 4 cm ⁻¹ and a total number of times of 64.

(C) Film thickness If the polymer film 30 has a uniform thickness and can cover the entire surface of the base material in close contact with the base material, the wear resistance of the mortar cup 10 is improved.

  The film thickness of the polymer film 30 was determined by embedding a sample used for measurement in an epoxy resin, staining with ruthenium tetrachloride, cutting out an ultrathin section using an ultramicrotome, and accelerating voltage 100 kV (see FIG. This was measured by observation of a cut surface using JEM-1010 manufactured by JEOL Ltd.). For one image of the obtained electron microscope image, the film thickness at the cut surface was measured at 10 points, and the arithmetic average value was calculated to obtain the film thickness.

(D) Surface Phosphorus Atom Concentration The polymer film 30 is formed by bonding a polymer chain obtained by polymerizing a PC compound to the sliding surface 16 of the cup base 12. Is closer to 5.3 atom%, which is the theoretical value of MPC, and the affinity with the lubricating liquid is higher, and it is considered that characteristics such as wear resistance are improved.

  The surface phosphorus atom concentration of the polymer film 30 was measured using an XPS analyzer (AXIS-HSi165 manufactured by Shimadzu / KRATOS) with an X-ray source of Mg-Kα ray, an applied voltage of 15 kV, and a photoelectron emission angle of 90 °. .

A sample for measuring the characteristics of the polymer film was prepared by the following procedure.
-Molding process In the molding process, UHMWPE powder having a molecular weight of about 3.5 million was made to contain 0.1 wt% of vitamin E (α-tocopherol) as an antioxidant, and then UHMWPE plate material was obtained by compression molding.

・ Crosslinking process (high energy beam irradiation process, heat treatment process)
In the cross-linking step, a UHMWPE bar obtained by machining a UHMWPE plate was irradiated with gamma rays at a dose of 100 kGy and then heat-treated at 123 ° C. for 12 hours to cross-link the UHMWPE into a UHMWPE having a network structure.

  The cross-linked UHMWPE bar was machined to obtain a cup base material.

In the cleaning step, the cup base material was immersed in a cleaning liquid (surfactant concentration: 1% by weight) containing Tween (registered trademark) 20 as a surfactant and washed at a liquid temperature of 70 ° C. for 12 hours.

-Polymer film formation step In the polymer film formation step, the substrate is immersed in a treatment solution containing 0 to 1.0 mol / L of MPC as a PC compound, and ultraviolet light having a wavelength of 300 to 400 nm is applied to the sliding surface of the substrate. Irradiation was performed at 5 mW / cm ² and an irradiation time of 90 minutes to form a polymer film.
Thus, a acetabular cup as a sample was obtained.

FIG. 6 is a graph showing changes in polymer film characteristics with respect to MPC concentration. FIG. 6A is a graph showing changes in the contact angle of water, the horizontal axis indicates the MPC concentration (mol / L), and the vertical axis indicates the contact angle of water (°). FIG. 6B is a graph showing changes in the phosphate index, the horizontal axis indicates MPC concentration (mol / L), and the vertical axis indicates phosphate index I _phosphate / I _methylene (−). FIG. 6C is a graph showing changes in film thickness, the horizontal axis indicates MPC concentration (mol / L), and the vertical axis indicates film thickness (nm). FIG. 6D is a graph showing changes in the surface phosphorus atom concentration, the horizontal axis indicates the MPC concentration (mol / L), and the vertical axis indicates the surface phosphorus atom concentration (atom%).

  As shown in the graph of FIG. 6A, the contact angle once decreased (hydrophilized) when the MPC concentration increased, and further increased when the MPC concentration increased. The contact angle represents the hydrophilicity of the polymer film surface of the acetabular cup, and it is more preferable that the contact angle is smaller as a characteristic. From the graph of FIG. 6A, it can be seen that the MPC concentration is preferable in the concentration range of 0.25 to 0.50 mol / L with a small contact angle.

  As shown in the graph of FIG. 6B, when the concentration is up to 1.0 mol / L, the phosphoric acid index increases as the MPC concentration increases, that is, the density of MPC in the polymer membrane is proportional to the MPC concentration. It can be seen that the degree increases.

  It is known that the phosphoric acid index is preferably 0.32 or more, and when the MPC concentration is in the range of 0.25 to 0.50 mol / L, the phosphoric acid index is 0.32 or more. It can be seen that the degree of congestion is sufficient.

  OLE_LINK2 As shown in the graph of FIG. 6C, it can be seen that if the concentration is up to 1.0 mol / L, the film thickness increases as the MPC concentration increases. OLE_LINK2

  It has been found that the film thickness is preferably 10 to 200 nm, and when the MPC concentration is in the range of 0.25 to 0.50 mol / L, the film thickness is 10 to 200 nm. As it turns out to be sufficient.

  As shown in the graph of FIG. 6 (d), the surface phosphorus atom concentration tended to increase once the MPC concentration increased and further decreased as the MPC concentration increased.

  The surface phosphorus atom concentration is preferably 4.7 atom% or more, and the closer to the theoretical value of 5.3 atom%, the higher the affinity with the lubricating liquid, and the more preferable. Therefore, the graph shown in FIG. Thus, it can be seen that the MPC concentration in the range of 0.33 to 0.50 mol / L is preferable as the surface phosphorus atom concentration.

DESCRIPTION OF SYMBOLS 1 Artificial hip joint 2 Resin part 10 Acetabular cup 12 Cup base material 14 Acetabular fixation surface 16 Sliding surface 20 Femoral stem 22 Bone head 30 Polymer membrane 91 Femur 93 Hipbone 94 Acetabulum

Claims (9)

A method for manufacturing a sliding member for an artificial joint,
A base material forming step for obtaining a base material by molding an ultrahigh molecular weight polyethylene material containing an antioxidant;
A treatment solution containing a compound having a phosphorylcholine group is irradiated with ultraviolet rays in a state where the substrate is immersed, and a polymer film containing a polymer chain in which a compound having a phosphorylcholine group is polymerized is formed on the surface of the substrate. A method of manufacturing a sliding member for an artificial joint, comprising: a polymer film forming step.   The method for producing a sliding member for an artificial joint according to claim 1, wherein the base material is obtained by performing a crosslinking treatment before the polymer film forming step.   The method for producing a sliding member for an artificial joint according to claim 1 or 2, wherein the concentration of the treatment aqueous solution containing the compound having a phosphorylcholine group is 0.25 to 0.50 mol / L.   The concentration of the treatment aqueous solution containing a compound having a phosphorylcholine group is preferably 0.33 to 0.50 mol / L, The production of a sliding member for an artificial joint according to claim 1 or 2, Method.   The method for producing a sliding member for an artificial joint according to any one of claims 1 to 4, wherein the antioxidant is vitamin E.   The substrate further comprising a cleaning step of immersing the substrate in a cleaning liquid containing a surfactant and cleaning the surface of the substrate before the polymer film forming step after the substrate forming step. 6. A method for manufacturing a sliding member for an artificial joint according to any one of 5 above.   The method for producing a sliding member for an artificial joint according to claim 6, wherein the surfactant is a nonionic surfactant having a polyoxyethylene chain.   The method for producing a sliding member for an artificial joint according to any one of claims 1 to 7, wherein a sterilization treatment by gamma ray irradiation is performed after the polymer film forming step.   The sliding member for artificial joints manufactured by the manufacturing method of the sliding member for artificial joints as described in any one of Claims 1-8.

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