Method of mass removal and electropolishing of stent alloys containing noble elements

Abstract

A process for electrochemical mass removal and/or electropolishing a stent formed from a cobalt-chromium-tungsten-platinum alloy. The alloy may also comprise nickel (e.g., at about 10% by weight), where no other elements are present in an amount over 3% by weight. The process includes positioning the stent in an electrolyte solution in an electropolishing cell, wherein the electrolyte includes each of H 2 SO 4 , HCl, and H 3 PO 4 , e.g., in a volumetric ratio (as prepared) of about 6:1:1, wherein the electrolyte further comprises ethylene glycol. The metallic body is electrochemically processed in the electrolyte solution in the electropolishing cell, wherein the mass removal and electropolishing includes application of an alternating current with a forward:reverse current ratio of at least 3:1 (e.g., from 3:1 to 5:1). Voltage may be allowed to float, e.g., within a range of 1 to 6 volts. Superficially similar processes using DC, other AC settings, or without ethylene glycol were ineffective.

1 . A process for electrochemical mass removal and/or electropolishing a metallic body formed from a cobalt-chromium-tungsten-platinum alloy, the process comprising:
 positioning the metallic body in an electrolyte solution in an electropolishing cell, wherein the electrolyte solution includes each of H 2 SO 4 , HCl, and H 3 PO 4 , in a volumetric ratio where at least 5 times more H 2 SO 4  is provided, relative to HCl and/or relative to H 3 PO 4 , wherein the electropolishing electrolyte further comprises ethylene glycol; and   electrochemically removing mass and/or electropolishing the metallic body in the electrolyte solution in the electropolishing cell, wherein the electrochemical mass removal and/or electropolishing includes an alternating current with a forward:reverse current ratio of at least 3:1.   
     
     
         2 . The process of  claim 1 , wherein the volumetric ratio of H 2 SO 4 , HCl, and H 3 PO 4 , of the as prepared electrolyte is about 6:1:1, and the ethylene glycol comprises about 25% to 75% by volume of the electrolyte solution. 
     
     
         3 . The process of  claim 1 , wherein forward and reverse phases of the applied alternating current each having a duration in a range of about 3 ms to about 10 ms during an electropolishing portion of the process, and/or in a range of about 10 ms to 50 ms during an electrochemical mass removal portion of the process. 
     
     
         4 . The process of  claim 1 , wherein the metallic body comprises at least a portion of at least one of a stent, a guidewire, an embolic protection filter, or a closure element. 
     
     
         5 . The process of  claim 1 , wherein the alloy comprises no greater than 30% platinum by weight. 
     
     
         6 . The process of  claim 1 , wherein the alloy comprises cobalt, chromium, tungsten, platinum and nickel. 
     
     
         7 . The process of  claim 6 , wherein the alloy comprises cobalt in an amount from about 20% to about 40% by weight. 
     
     
         8 . The process of  claim 6 , wherein the alloy comprises chromium in an amount of about 20% by weight. 
     
     
         9 . The process of  claim 6 , wherein the alloy comprises nickel in an amount of about 10% by weight. 
     
     
         10 . The process of  claim 6 , wherein the alloy is substantially or entirely free of molybdenum. 
     
     
         11 . The process of  claim 6 , wherein the alloy is substantially or entirely free of carbon. 
     
     
         12 . The process of  claim 6 , wherein the alloy comprises no more than 1% of each of silicon, phosphorus, and sulfur by weight. 
     
     
         13 . The process of  claim 6 , wherein the alloy further comprises manganese in a amount of up to 5% by weight. 
     
     
         14 . The process of  claim 6 , wherein the alloy further comprises iron in an amount of up to 5% by weight. 
     
     
         15 . The process of  claim 6 , wherein the alloy further comprises both manganese and iron in a concentration of up to about 3% each, by weight. 
     
     
         16 . The process of  claim 6 , wherein a sum of cobalt and platinum comprises from 45% to about 60% by weight of the alloy. 
     
     
         17 . The process of  claim 1 , wherein said alloy includes precipitate inclusions, wherein the precipitate inclusions comprise tungsten (e.g., Co 3 W). 
     
     
         18 . The process of  claim 1 , wherein the alloy comprises:
 about 20-37% cobalt;   about 20-30% platinum;   about 19-21% chromium;   about 14-16% tungsten;   about 9-11% nickel; and   about 1-2% manganese.   
     
     
         19 . The process of  claim 18 , wherein the alloy comprises one or more trace elements as follows:
 0-3% iron;   0-0.03% sulfur;   0-0.04% phosphorus   0-0.04% silicon; or   0.05-0.15% carbon.   
     
     
         20 . A process for electrochemical mass removal and electropolishing a stent formed from a cobalt-chromium-tungsten-platinum-nickel alloy, the alloy including no other elements in an amount over 3% by weight, the process comprising:
 positioning the stent in an electrolyte solution in an electropolishing cell, wherein the electrolyte solution includes each of H 2 SO 4 , HCl, and H 3 PO 4 , in a volumetric ratio of about 6:1:1, wherein the electropolishing electrolyte further comprises ethylene glycol; and   electrochemically removing mass and/or electropolishing the metallic body in the electrolyte solution in the electropolishing cell, wherein the electrochemical mass removal and/or electropolishing includes application of an alternating current with a forward:reverse current ratio of 3:1 to 5:1, wherein voltage is within a range of 1 to 6 volts.