Radiation and melt treated ultra high molecular weight polyethylene prosthetic devices

Abstract

A medical prosthesis for use within the body which is formed of radiation treated ultra high molecular weight polyethylene having substantially no detectable free radicals, is described. Preferred prostheses exhibit reduced production of particles from the prosthesis during wear of the prosthesis, and are substantially oxidation resistant. Methods of manufacture of such devices and material used therein are also provided.

1 - 123 . (Canceled).  
     
     
         124 . A method for increasing the wear resistance of a preformed polyethylene comprising the steps of: 
 (a) crosslinking the polyethylene by irradiating it in a solid state; and    (b) subjecting the crosslinked polyethylene to melting.    
     
     
         125 . A method for increasing the wear resistance of a preformed polymer, comprising the steps of: 
 (a) crosslinking the preformed polymer by irradiating it in a solid state;    (b) subjecting the crosslinked preformed polymer to melting; and    (c) removing the oxidized surface of the thermally treated crosslinked preformed polymer wherein said polymer is selected from the group consisting of polyethylene and polypropylene.    
     
     
         126 . A method for increasing the wear resistance of a preformed polymer, comprising the steps of: 
 (a) crosslinking the preformed polymer by irradiating it in its solid state; and    (b) melting the crosslinked polymer, said polymer being selected from the group consisting of polyethylene and polypropylene.    
     
     
         127 . A method for determining an optimal radiation dose and thermal treatment for treating a polymer to increase its wear resistance, when made into a desired product, while maintaining its desirable physical and/or chemical properties, the method comprises the steps of: 
 (a) irradiating the polymer in the solid state over a range of radiation doses likely to produce the desirable wear resistance and physical and/or chemical properties;    (b) remelting the polymer;    (c) correlating the radiation doses with the wear rate of the desired product made from the irradiated remelted polymer using actual or simulated wear conditions for the desired product;    (d) correlating the radiation doses with each of the physical and/or chemical properties of the desired product made from the irradiated remelted polymer using actual or simulated wear conditions for the desired product;    (e) comparing the correlations in steps (c) and (d) to determine the optimal radiation dose which will produce a desirable wear rate while maintaining the desirable physical and/or chemical properties, if such a radiation dose is arrived at, use this optimal radiation dose for future treatment of the polymer;    (f) if the optimal radiation dose cannot be arrived at in step (e), then determining a dose that would produce a desirable wear rate based on the correlation of step (c) and annealing instead of remelting the polymer which has been irradiated to said dose;    (g) correlating the physical and/or chemical properties of the desired product made from the irradiated and annealed polymer, using actual or simulated wear conditions for the desired product, with different annealing times and temperatures;    (h) determining an annealing temperature and time which will provide the desirable wear rate and physical and/or chemical properties, if this is possible, then use the radiation dose and annealing conditions determined at this step for future treatment of the polymer;    (i) if stop (h) does not provide the desirable wear rate and physical and/or chemical properties, then apply a lower radiation dose and repeat steps (c) to (i) or (h) until the optimal radiation dose and annealing conditions are determined or the steps confirm that no optimal radiation dose and annealing conditions can be obtained for the desired wear rate and physical and/or chemical properties.    
     
     
         128 . A method of increasing the wear resistance of a polymer article, wherein the polymer is selected from the group consisting of polyethylene and polypropylene, wherein the method comprises: (a) crosslinking polymer article by irradiation; and (b) heating the article to a temperature at or above the melting point of the polymer.  
     
     
         129 . The method according to  claim 128 , wherein the polymer is polyethylene.  
     
     
         130 . The method according to  claim 129 , wherein oxidized polymer is removed by machining.  
     
     
         131 . The method according to  claim 129 , wherein the polyethylene is ultrahigh molecular weight polyethylene.  
     
     
         132 . The method according to  claim 128 , wherein the heating and crosslinking are undertaken at the same time.  
     
     
         133 . The method according to  claim 128 , wherein the heating and crosslinking are not undertaken at the same time.