Ultra high molecular weight polyethylene molded article for artificial joints and method of preparing the same

Abstract

An ultra high molecular weight polyethylene molded article for artificial joints has molecular orientation or crystal orientation in the molded article, and is low in friction and is superior in abrasion resistance, and therefore is available as components for artificial joints. Further, the ultra high molecular weight polyethylene molded article for artificial joints can be used as a component for artificial hip joints (artificial acetabular cup), a component for artificial knee joints (artificial tibial insert) and the socket for artificial elbow joints, and in addition to the medical use, it can be applied as materials for various industries by utilizing the characteristics such as low friction and superior abrasion resistance.

What is claimed is: 
     
       1. An ultra high molecular weight polyethylene molded block having a molecular weight not less than 5 million, having been crosslinked slightly and having been compression-deformed in a direction perpendicular to a compression plane, cooled and solidified in a compression-deformed state under pressure so as to have orientation of crystal planes in a direction parallel to the compression plane, and a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane. 
     
     
       2. The molded block of  claim 1 , wherein a melting temperature of the ultra high molecular weight polyethylene is in a range of 135 to 155° C. 
     
     
       3. A method for producing an ultra high molecular weight polyethylene molded block having orientation of crystal planes in a direction parallel to a compression plane, comprising slightly crosslinking an ultra high molecular weight polyethylene molded block having a molecular weight not less than 5 million by irradiating the block with a high energy ray and thereby introducing a very small amount of crosslinking points into molecular chains of the block, then heating the crosslinked ultra high molecular weight polyethylene molded block up to a compression deformable temperature, compression-deforming the block by compressing the block in a direction perpendicular to the compression plane so as to deform the block, and then cooling the block while keeping the block in a deformed state under pressure, said block after cooling having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane. 
     
     
       4. The method of  claim 3 , where the high energy ray is a radioactive ray and a dose of the irradiation is in the range of 0.01 to 5.0 MR. 
     
     
       5. The method of  claim 3  or  4 , wherein the compression-deformable temperature is in a range of 50° C. lower than a melting temperature of the crosslinked ultra high molecular weight polyethylene to 80° C. higher than the melting temperature. 
     
     
       6. The method of  claim 3 ,  4  or  5  wherein a weight-average molecular weight of the ultra high molecular weight polyethylene before irradiation is in a range of 2 to 8 million. 
     
     
       7. An ultra molecular weight polyethylene molded block having orientation of crystal planes in a direction parallel to a compression plane, said block produced by slightly crosslinking an ultra high molecular weight polyethylene block having a molecular weight of not less than 5 million by irradiating the block with a high energy ray and thereby introducing a very small amount of crosslinking points into molecular chains of the block, then heating the crosslinked block up to a compression deformable temperature, compression-deforming the block by compressing the block in a direction perpendicular to the compression plane so as to deform the block, and then cooling and solidifying the block while keeping the block in a deformed state under pressure, said block after cooling and solidifying having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane. 
     
     
       8. Artificial joint for implantation in a joint of an animal, the joint comprising a joint component formed from an ultra high molecular weight polyethylene molded block having a molecular weight of not less than 5 million, having been crosslinked slightly and having been compression-deformed in a direction perpendicular to a compression plane, cooled and solidified in a compression-deformed state under pressure so as to have orientation of crystal planes in a direction parallel to the compression plane, said block having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane. 
     
     
       9. Artificial joint according to  claim 8 , the joint for implantation in a joint of a human being. 
     
     
       10. Artificial joint for implantation in a joint of an animal, the joint comprising a joint component formed from an ultra high molecular weight polyethylene molded block having a molecular weight of not less than 5 million, having been crosslinked slightly and having been compression-deformed in a direction perpendicular to a compression plane so as to have orientation of crystal planes in a direction parallel to the compression plane, wherein said block having a thickness range of 5 to 10 mm in a direction perpendicular to the compression plane and the melting temperature of the molded block is in a range of 135 to 155° C. 
     
     
       11. Artificial joint according to  claim 10 , the joint for implantation in a joint of a human being. 
     
     
       12. A method for producing an ultra high molecular weight polyethylene (UHMWPE) artificial hip component, UHMWPE artificial knee component, UHMWPE artificial elbow component, UHMWPE artificial finger component, or UHMWPE artificial shoulder component having improved abrasion resistance, comprising:
 (a) crosslinking an ultra high molecular weight polyethylene block having a molecular weight not less than 5 million by irradiating the block with a high energy radiation at a level of at least 1 MR;   (b) heating said crosslinked block up to a compression deformable temperature below the melting point of the UHMWPE;   (c) subjecting said heated block to pressure; then   (d) cooling said block; and   (e) processing said cooled block to form said component.   
     
     
       13. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said irradiation is gamma irradiation at a level of from 1 MR to 5 MR. 
     
     
       14. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said heating is in a range of from 50° C. lower than the melting temperature of the crosslinked ultra high molecular weight polyethylene to the melting temperature. 
     
     
       15. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said pressure is applied so as to deform the block. 
     
     
       16. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 15, wherein said deformation is in a direction perpendicular to the plane of compression. 
     
     
       17. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 16, wherein said block is cooled in a compression-deformed state under pressure. 
     
     
       18. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 17, wherein said block has an orientation of crystal planes in a direction parallel to the compression plane. 
     
     
       19. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 16, wherein said block has a thickness, after compression, of at least 5 mm in a direction perpendicular to the compression plane. 
     
     
       20. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 16, wherein said block, prior to compression, has a thickness of at least 3 cm. 
     
     
       21. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 18, wherein said cooled block has a melting point of from 135° C. to 155° C. 
     
     
       22. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said irradiation is conducted in the presence of oxygen. 
     
     
       23. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein said irradiation is conducted under a vacuum or in an inert atmosphere. 
     
     
       24. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, additionally comprising processing said block, after cooling, by a process comprising cutting said block to form said component. 
     
     
       25. A method of producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein after said subjecting to pressure step, said block is subjected to isothermal crystallization. 
     
     
       26. A method for producing an ultra high molecular weight polyethylene artificial joint component according to claim 12, wherein after said subjecting to pressure step, said block is subjected to isothermal treatment at a temperature of from around 100° C. to 130° C. for a period of from 1 hour to 20 hours. 
     
     
       27. A method of making an artificial joint component having improved abrasion resistance, the artificial joint component being obtained by fabrication from a crosslinked ultra high molecular weight polyethylene (UHMWPE) which is prepared by the method comprising:
 a) providing raw UHMWPE in the form of a rod;   b) crosslinking the rod with gamma-irradiation at a dose of at least 1 MR;   c) heating the crosslinked rod to a compression deformable temperature below the melting point of the UHMWPE;   d) subjecting the heated rod to pressure; and   e) cooling and solidifying the rod.   
     
     
       28. A method according to claim 27, wherein the dose of gamma-irradiation is 1 MR to 5 MR. 
     
     
       29. A method according to claim 27, wherein the compression deformable temperature is greater than the melting point minus 50° C. 
     
     
       30. A method according to claim 28, wherein pressure is applied in step d) to deform the rod. 
     
     
       31. A method according to claim 30, wherein the deformed rod is cooled in a compression deformed state. 
     
     
       32. A method of producing a UHMWPE artificial joint component comprising making a crosslinked UHMWPE according to claim 27 and processing the rod after solidification to form the joint component. 
     
     
       33. A method according to claim 32, wherein the joint component is selected from hip, knee, elbow, finger, and shoulder. 
     
     
       34. A method according to claim 32, wherein the joint component is a hip component or a knee component.