Chemically crosslinked ultrahigh molecular weight polyethylene for artificial human joints

Abstract

The present invention discloses a method for enhancing the wear-resistance of polymers by crosslinking them, especially before irradiation sterilization. In particular, this invention presents the use of chemically crosslinked ultrahigh molecular weight polyethylene in in vivo implants.

1 . A medical implant for use within a body, said implant being formed of a crosslinked ultrahigh molecular weight polyethylene having a polymeric structure of 51% crystallinity or less, so as to increase wear resistance of said implant within the body. 
   
   
       2 . In a medical implant having at least a first member and a bearing component providing a bearing contact surface for the first member, the bearing component made of crosslinked ultrahigh molecular weight polyethylene and wherein said crosslinked ultrahigh molecular weight polyethylene is characterized by a polymeric structure of at least 97.5% gel content, as determined by using boiling p-xylene. 
   
   
       3 . The medical implant of  claim 2 , wherein crosslinking is achieved according to the method selected from the group consisting of: chemically crosslinking a polyethylene, irradiation crosslinking a polyethylene, and photocrosslinking a polyethylene. 
   
   
       4 . The medical implant of  claim 3 , wherein said implant is further irradiated in the solid state for sterilization. 
   
   
       5 . The medical implant of  claim 4 , wherein said implant is irradiated in air at a sterilization dose. 
   
   
       6 . The medical implant of  claim 3 , wherein said crosslinked ultrahigh molecular weight polyethylene is further characterized by its lack of shrinkage. 
   
   
       7 . The medical implant of  claim 2 , wherein the implant is a hip prosthesis, said first member is a femoral component and said bearing component is an acetabular component. 
   
   
       8 . The medical implant of  claim 2 , wherein the medical implant is a prosthesis selected from the group consisting of: hip, knee, ankle, elbow, jaw, shoulder, finger and spine prostheses. 
   
   
       9 . A medical implant bearing component with improved wear resistance for use within a joint prosthesis within a body, said implant bearing component is made of a crosslinked ultrahigh molecular weight polyethylene having a polymeric structure of at least 97.5% gel content, as determined by using boiling p-xylene, so as to increase wear resistance of said implant within the body. 
   
   
       10 . The medical implant bearing component of  claim 9 , wherein said crosslinked ultrahigh molecular weight polyethylene is characterized by a polymeric structure of about 3.4 degree of swelling or less, as determined by using boiling p-xylene. 
   
   
       11 . The medical implant bearing component of  claim 9 , wherein the joint prosthesis is a hip prosthesis and said implant is an acetabular component which cooperates with a femoral component. 
   
   
       12 . The medical implant bearing component of  claim 9 , wherein the joint prosthesis is selected from the group consisting of hip, knee, ankle, elbow, jaw, shoulder, finger and spine prostheses. 
   
   
       13 . The medical implant bearing component of  claim 9 , wherein said ultrahigh molecular weight polyethylene is further characterized by a smooth fracture surface, decreased tensile strength at break point, and decreased Young's modulus compared to a corresponding uncrosslinked ultrahigh molecular weight polyethylene. 
   
   
       14 . The medical implant bearing component of  claim 9 , wherein crosslinking is achieved according to the method selected from the group consisting of chemically crosslinking a polyethylene, irradiation crosslinking a polyethylene, and photocrosslinking a polyethylene. 
   
   
       15 . The medical implant bearing component of  claim 14 , wherein the medical implant is further irradiated in air at a sterilization dose in its solid state. 
   
   
       16 . The medical implant bearing component of  claim 15 , wherein said ultrahigh molecular weight polyethylene has about 45% crystallinity or less, as determined by differential scanning calorimetry. 
   
   
       17 . The medical implant bearing component of  claim 16 , wherein the crosslinked ultrahigh molecular weight polyethylene is further characterized by a lack of shrinkage. 
   
   
       18 . The medical implant bearing component of  claim 17 , wherein said implant is an orthopaedic bearing component for use in hip or knee joint replacement. 
   
   
       19 - 143 . (canceled)