Oriented, cross-linked UHMWPE molding for orthopaedic applications

Abstract

A process for forming an oriented orthopaedic implant prosthesis bearing, net-shape bearing, or near net-shape bearing includes the step of placing an irradiated UHMWPE preform or puck of a volume sufficient to accommodate the bearing in a compression mold and compression molding the irradiated preform. The molding is accomplished by applying heat and pressure to form the preform into a desired shape. The compression molding induces biaxial orientation in the formed bearing.

1 . An orthopaedic prosthesis, comprising: 
 a bearing, the bearing being prepared by a process comprising the steps of (i) placing an irradiated polyethylene preform into a compression molding press, and (ii) compression molding the preform to form the bearing by compressive forces effective to create a biaxial orientation of the polyethylene in a plane which is transverse to the direction of compression.    
     
     
         2 . The prosthesis of  claim 1 , wherein the irradiated polyethylene preform is an irradiated ultrahigh molecular weight polyethylene preform.  
     
     
         3 . The prosthesis of  claim 1 , wherein the biaxial orientation is a biaxial molecular orientation.  
     
     
         4 . The prosthesis of  claim 1 , wherein the biaxial orientation is a radially-disposed molecular orientation.  
     
     
         5 . The prosthesis of  claim 1 , wherein the process further comprises the step of cooling the bearing while maintaining the bearing under pressure.  
     
     
         6 . The prosthesis of  claim 1 , wherein the process further comprises the step of preheating the preform prior to the placing step.  
     
     
         7 . The prosthesis of  claim 1 , wherein the process further comprises the steps of: 
 heating the preform, and    soaking the preform for a period of time at a soak pressure which is less than the pressure generated by the compressive forces, wherein the soaking step is performed after the heating step.    
     
     
         8 . The prosthesis of  claim 1 , wherein the process further comprises the steps of: 
 heating the preform, and    exerting an initial pressure on the preform prior to the heating step, wherein the initial pressure is less than the pressure generated by the compressive forces.    
     
     
         9 . The prosthesis of  claim 1 , wherein the process further comprises the steps of: 
 heating the preform, and    exerting an intermediate pressure, which is less than the pressure generated by the compressive forces, on the preform subsequent to the heating step.    
     
     
         10 . The prosthesis of  claim 1 , wherein the process further comprises the step of soaking the bearing for a period of time, after the compression molding step, at a temperature which is greater than ambient temperature, wherein the bearing is maintained under pressure during the soaking step.  
     
     
         11 . The prosthesis of  claim 1 , wherein the process further comprises the step of quenching the preform prior to the compression molding step.