Methods of stabilizing molecular weight of polymer stents after sterilization

Abstract

Methods of stabilizing the molecular weight of polymer stents scaffolds after E-beam sterilization are disclosed. The molecular weight of the polymer of the irradiated scaffolds is stabilized through exposure to gas containing oxygen.

1 - 3 . (canceled) 
     
     
         4 . A method of making a stent, comprising:
 providing a polymeric stent scaffolding comprising a polymer;   selecting a final number average molecular weight (Mn) of the polymer of the scaffolding;   irradiating the scaffolding with E-beam radiation for sterilization in an inert gas environment, wherein the polymer of the scaffolding has an initial Mn after the irradiation;   allowing the Mn of the irradiated scaffolding to increase from the initial Mn to the final Mn in the inert gas environment; and   exposing the scaffolding to an oxygen-containing gas to stabilize the Mn of the scaffolding at the final Mn.   
     
     
         5 . The method of  claim 4 , further comprising storing the stabilized scaffolding in an inert gas environment. 
     
     
         6 . The method of  claim 4 , wherein the oxygen-containing gas is air. 
     
     
         7 . The method of  claim 4 , wherein the scaffolding polymer is poly(L-lactide) (PLLA). 
     
     
         8 . The method of  claim 4 , wherein the scaffolding polymer is a lactide-based polymer. 
     
     
         9 . The method of  claim 4 , wherein the initial Mn is 70 to 80 kDa and the final Mn is 80 to 130 kDa. 
     
     
         10 . The method of  claim 4 , wherein a free radical concentration decays to less than 5×10 7  DI/mg after stabilizing the Mn of the scaffolding. 
     
     
         11 . The method of  claim 10 , wherein the free radical concentration decays to less than 5×10 7  DI/mg in less than 2 days after exposing the scaffolding to the oxygen-containing gas. 
     
     
         12 . The method of  claim 4 , wherein an oxygen content of the oxygen-containing gas is 5 to 10%. 
     
     
         13 . The method of  claim 4 , wherein an oxygen content of the oxygen-containing gas is 10 to 20%. 
     
     
         14 . A method of making a stent comprising:
 providing a polymeric stent scaffolding comprising a polymer;   sterilizing the scaffolding with radiation;   allowing the molecular weight of the sterilized scaffold to increase for a period of time after sterilization; and   stopping the molecular weight increase through exposure of the scaffolding to an oxygen-containing gas to stabilize the polymer at a desired number average molecular weight (Mn).   
     
     
         15 . The method of  claim 14 , further comprising storing the stabilized scaffolding in an inert gas environment. 
     
     
         16 . The method of  claim 14 , wherein the oxygen-containing gas is air. 
     
     
         17 . The method of  claim 14 , wherein the scaffolding polymer is a lactide-based polymer. 
     
     
         18 . The method of  claim 14 , wherein the molecular weight is allowed to increase from an initial Mn of 70 to 80 kDa to a stabilized Mn of 80 to 130 kDa. 
     
     
         19 . The method of  claim 14 , wherein a free radical concentration decays to less than 5×10 7  DI/mg after stabilizing the Mn of the scaffolding. 
     
     
         20 . The method of  claim 19 , wherein the free radical concentration decays to less than 5×10 7  DI/mg in less than 2 days after exposing the scaffolding to the oxygen-containing gas.