Implantable medical Devices Composed of a Radiopaque Alloy and Method of Making the Alloy

Abstract

Implantable medical devices made from a single beta phase Tantalum alloy utilizing Titanium as an alloying agent that are biocompatible, radiopaque and visible under x-ray and fluoroscopy, the alloy having mechanical properties that allow it to be machined by conventional, machining methods for forming the devices, and a method for making the alloy. The alloy is between approximately 10 percent and 25 percent Ti by weight and preferably has a density of 12 g/cm 3 or greater.

1 . An implantable medical device comprising a body composed of an alloy of tantalum and an alloying agent, said alloy having a mass energy absorption coefficient sufficient such that said medical device is visible under x-ray and fluoroscopy. 
   
   
       2 . The device of  claim 1  wherein the mass energy absorption coefficient of said Ta alloy is at least 75% that of platinum. 
   
   
       3 . The device of  claim 1  wherein said alloying agent is chosen from a group consisting of titanium, niobium, cobalt, molybdenum or zirconium. 
   
   
       4 . The device of  claim 1  wherein said alloying agent is titanium. 
   
   
       5 . The device of  claim 2  wherein said alloy is a homogeneous solid solution of tantalum and titanium. 
   
   
       6 . The device of  claim 3  wherein said alloy is in a single beta phase. 
   
   
       7 . The device of  claim 4  wherein said alloy exhibits an ultimate tensile strength between 550 Mpa and 1380 Mpa. 
   
   
       8 . The device of  claim 7  wherein said alloy exhibits an ultimate tensile strength between 690 Mpa and 1040 Mpa. 
   
   
       9 . The device of  claim 4  wherein said alloy exhibits a yield strength between 550 Mpa and 1030 Mpa. 
   
   
       10 . The device of  claim 4  wherein said alloy exhibits an elongation at break between 2% and 15%. 
   
   
       11 . The device of  claim 8  wherein said alloy exhibits an elongation at break between 6% and 14%. 
   
   
       12 . The device of  claim 4  where said alloy is between 10 and 25 percent titanium by weight. 
   
   
       13 . An alloy of tantalum and titanium comprising:
 a. said alloy being between 10 and 25 percent titanium by weight;   b. said alloy having being homogeneous and in a single beta phase; and   c. said alloy having a mass energy absorption coefficient of at least 75% that of platinum.   
   
   
       14 . The alloy of  claim 13  further comprising:
 a. said alloy having an ultimate tensile strength between 550 Mpa and 1380 Mpa;   b. said alloy having a yield strength between 550 Mpa and 1030 Mpa.; and   c. said alloy exhibiting an elongation at break between 2% and 15%.   
   
   
       15 . An implantable medical device composed of the alloy of  claim 13  further comprising said implantable medical device being formed from a sample of said alloy that has been plastically deformed and annealed. 
   
   
       16 . The device of  claim 15 , wherein said device is selected from a group consisting of a stimulation electrode, a sensing electrode a connector and a marker. 
   
   
       17 . the device of  claim 15 , wherein said device is in the shape of a helix. 
   
   
       18 . A method of producing an alloy of Ta and Ti comprising the steps of:
 a. inserting nuggets of Ta and Ti in a vacuum arc furnace, wherein the Ti is between 10% and 25% of the total weight of said Ta and Ti;   b. dropping the pressure in said vacuum arc furnace to 0.75 atm or less;   c. applying an electric arc to said Ta and Ti nuggets to raise them to their respective melting points;   d. allowing said melted Ta and Ti to mix, forming a homogeneous mixture; and   e. drawing said mixture out of said furnace and allowing said mixture to cool rapidly to form a single beta phase alloy.   
   
   
       19 . The method of  claim 18  wherein said pressure is dropped to at least 10 −3  Torr. 
   
   
       20 . The method of  claim 19  further comprising the step of placing getters into said furnace and applying an electric arc to said getters to raise them to their melting points, to remove any trace oxygen from said furnace. 
   
   
       21 . The method of  claim 20  wherein said getters are nuggets of a material selected form a group consisting of Ti and Zr. 
   
   
       22 . The method of  claim 19  further comprising the step of introducing argon into said furnace at a constant rate to raise the pressure to between 150 Torr and 300 Torr. 
   
   
       23 . The method of  claim 22  wherein said argon is not less then 99% pure. 
   
   
       24 . The method of  claim 22  wherein said Ta and Ti are situated such that the electric arc contacts said Ta, thereby allowing said Ta to melt and further wherein said Ti is melted by the heat from said molten Ta. 
   
   
       25 . The method of  claim 24  further comprising the steps of:
 a. melting a percentage of the total volume of Ta and Ti   b. stopping the melting by reducing the power of the arc   c. repeatedly increasing and decreasing the power of the arc until all of the Ti and Ta has been melted; and   d. allowing said melted Ta and Ti to mix, forming a homogeneous mixture.   
   
   
       26 . The method of  claim 24  further comprising the steps of
 a. applying an arc to said Ta and Ti until said Ti starts to evaporate;   b. removing said arc and allowing the mixture of molten Ta and Ti to solidify;   c. reapplying said arc until the solidified alloy is re-melted; and   d. repeating steps a, b, and c until the desired degree of homogeneity is achieved.   
   
   
       27 . The method of  claim 26  further comprising flipping said solidified mixture after step b prior to re-establishing the arc. 
   
   
       28 . The method of  claim 24  further comprising the steps of:
 a. providing two or more cascading receptacles;   b. melting the alloy in a first receptacle and allowing the molten mixture to flow from the first receptacle to the next receptacle in the cascade and solidify;   c. repeating step b until the desired degree of homogeneity is achieved.   
   
   
       29 . The method of  claim 24  wherein said arc is establish by applying 40V at 1000 A -1500 A and thereafter reducing the current to approximately 700-900 A. 
   
   
       30 . The method of  claim 25  further comprising the step of removing the alloy from the furnace and allowing it to cool quickly such that a single beta phase material is formed. 
   
   
       31 . The method of  claim 30  said cooling step further comprises the step of placing the alloy in a water cooled crystallizer. 
   
   
       32 . A method of preparing the alloy of  claim 13  for use in a medical device to achieve a two-staged plastic deformation of the alloy with a total degree of deformation of 70% or greater comprising the steps of:
 a. mechanically treating ingots of said alloy to shape said ingots for subsequent deformation;   b. fractionally deforming the ingots into rods with a total degree of deformation of 40% or greater at first step;   c. interannealing the deformed ingots; and   d. fractionally deforming the ingots into rods with a total degree of deformation of 40% or greater at second step.   
   
   
       33 . The method of  claim 32  wherein said interannealing step further comprises the step of heating the alloy to between 1100° C. and 1300° C. for 30 to 90 minutes. 
   
   
       34 . The method of  claim 32  further comprising repeating steps c and d until a total deformation of 70% or greater is achieved. 
   
   
       35 . The method of  claim 34  wherein said deformed ingots are annealed at a temperature between 1100° C. and 1300° C. for 30-90 minutes to increase percent elongation at break. 
   
   
       36 . The method of  claim 34  further comprising the steps of
 a. drawing said rod-shaped ingot of alloy through dies with the maximum step size of 0.05 mm; and   b. repeating step a until a wire of the desired diameter is achieved