Bearing material of medical implant and methods for making it

Abstract

Disclosed is a bearing material of a medical implant, which is an ultrahigh molecular weight polyethylene (UHMWPE) composite. The composite comprises, for example, UHMWPE and a polyethylene copolymer having a polymer backbone and pendant hydrophilic groups or pendant surface active agents that are attached to the polymer backbone. Also disclosed are methods for preparing bearing materials. The bearing material has one or more advantageous properties including reduced immune response, reduced wear, and/or increased lubrication.

1 . A bearing material of a medical implant comprising a composite of an ultrahigh molecular weight polyethylene (UHMWPE) and a polyethylene copolymer having a polymer backbone and pendant hydrophilic groups that are attached to the polymer backbone, wherein the bearing material is adopted for articulating against a hard counterface of the medical implant. 
   
   
       2 . (canceled) 
   
   
       3 . The bearing material of  claim 1 , wherein the pendant hydrophilic groups comprise one or more free nonionic groups. 
   
   
       4 . The bearing material of  claim 3 , wherein the nonionic groups are hydroxyl groups. 
   
   
       5 . The bearing material of  claim 1 , wherein the pendant hydrophilic groups are attached to the polymer backbone by a linking group selected from the group consisting of carboxy alkyl, carboxy hydroxyalkyl, carboxy hydroxyalkoxy, carboxy alkoxy, and carboxy alkoxyalkyl. 
   
   
       6 . The bearing material of  claim 2 , wherein the pendant hydrophilic groups are attached to the polymer backbone without a linking group. 
   
   
       7 . The bearing material of  claim 1 , wherein the UHMWPE is crosslinked. 
   
   
       8 . (canceled) 
   
   
       9 . A process for producing a bearing material of a medical implant according to  claim 1  comprising a composite of an ultrahigh molecular weight polyethylene (UHMWPE) and a polyethylene copolymer having a polymer backbone and pendant hydrophilic groups that are attached to the polymer backbone, the process comprising:
 (i) compression molding a mixture comprising an ultrahigh molecular weight polyethylene (UHMWPE), a polyethylene copolymer having a reactive group capable of reacting with a hydrophilic group, and a polyol to obtain a molded product; and   (ii) machining the molded product to obtain the bearing material.   
   
   
       10 . The process of  claim 9 , wherein the reactive group of the polyethylene copolymer is selected from the group consisting of carboxyl, glycidyl, and carboxy anhydride, and the hydrophilic group is hydroxyl. 
   
   
       11 . The process of  claim 9 , wherein the polyethylene copolymer is poly(ethylene-co-glycidyl methacrylate), poly(ethylene-g-maleic anhydride) or poly(ethylene-co-acrylic acid). 
   
   
       12 . The process of  claim 9 , wherein the polyol is selected from the group consisting of ethylene glycol, propanediols, butanediols, glycerol, pentaerythritol, trimethylolpropane, sorbitol, mannitol, diglycerol, triglycerol, and polyglycerol. 
   
   
       13 . The process of  claim 9 , wherein the polyol is a polyether polyol. 
   
   
       14 . The process of  claim 13 , wherein the polyether polyol is a block copolymer of ethylene oxide and propylene oxide, said block copolymer having hydroxyl chain ends. 
   
   
       15 . The process of  claim 9 , further comprising crosslinking the UHMWPE. 
   
   
       16 . The process of  claim 9 , which includes optionally sterilizing the bearing material. 
   
   
       17 . The process of  claim 9 , which includes optionally melt-annealing the molded product prior to machining. 
   
   
       18 . A bearing material produced by the process of  claim 9 . 
   
   
       19 . A process for producing a bearing material of a medical implant comprising a composite of an ultrahigh molecular weight polyethylene (UHMWPE) and a block copolymer having a polymer backbone and pendant hydrophilic groups attached to the polymer backbone, the process comprising:
 (i) compression molding a mixture comprising an ultrahigh molecular weight polyethylene (UHMWPE) and a block copolymer comprising polyethylene segments and hydrophilic segments having hydrophilic pendant groups to obtain a molded product; and   (ii) optionally machining the molded product to obtain the bearing material.   
   
   
       20 . The process of  claim 19 , wherein the hydrophilic segments comprise one or more hydroxy groups. 
   
   
       21 . The process of  claim 20 , wherein the block copolymer is poly(ethylene-co-ethylene glycol). 
   
   
       22 . A bearing material produced by the process of  claim 19 . 
   
   
       23 . A process for producing a bearing material of a medical implant according to  claim 1  comprising a composite of an ultrahigh molecular weight polyethylene (UHMWPE) and a polyethylene copolymer having a polymer backbone and pendant hydrophilic groups that are attached to the polymer backbone, the process comprising:
 (i) compression molding an ultrahigh molecular weight polyethylene (UHMWPE) powder to obtain a consolidated UHMWPE material;   (ii) compressing, in contact with the consolidated UHMWPE material, a mixture comprising a polyethylene copolymer having a reactive group capable of reacting with a hydroxy group, and a polyol to obtain a composite; and   (iii) optionally machining the compression molded product to obtain the bearing material.   
   
   
       24 . A process for producing a bearing material of a medical implant according to  claim 1  comprising a composite of an ultrahigh molecular weight polyethylene (UHMWPE) and a polyethylene copolymer having a polymer backbone and pendant hydrophilic groups that are attached to the polymer backbone, the process comprising:
 (i) providing a consolidated UHMWPE material; and   (ii) compression molding a polyethylene copolymer having a reactive group capable of reacting with hydroxy group, and a polyol in contact with the consolidated UHMWPE material to obtain a composite; and   (iii) optionally machining the compression molded product to obtain the bearing material.   
   
   
       25 . A process for producing a bearing material of a medical implant comprising a composite of an ultrahigh molecular weight polyethylene (UHMWPE) and a block copolymer having a polymer backbone and pendant hydrophilic groups attached to the polymer backbone, the process comprising:
 (i) compression molding an ultrahigh molecular weight polyethylene (UHMWPE) powder to obtain a consolidated UHMWPE material;   (ii) compressing, in contact with the consolidated UHMWPE material, a block copolymer comprising polyethylene segments and hydrophilic segments having reactive hydrophilic pendant groups to obtain a molded product; and   (iii) optionally machining the compression molded product to obtain the bearing material.   
   
   
       26 . A process for producing a bearing material of a medical implant comprising a composite of an ultrahigh molecular weight polyethylene (UHMWPE) and a block copolymer having a polymer backbone and pendant hydrophilic groups attached to the polymer backbone, the process comprising:
 (i) providing a consolidated UHMWPE material; and   (ii) compressing, in contact with the consolidated UHMWPE material, a block copolymer comprising polyethylene segments and hydrophilic segments having reactive hydrophilic pendant groups to obtain a molded product; and   (iii) optionally machining the compression molded product to obtain the bearing material.