Superelastic guiding member

Abstract

An improved guiding member for use within a body lumen having a unique combination of superelastic characteristics. The superelastic alloy material has a composition consisting of about 30% to about 52% (atomic) titanium, and about 38% to 52% nickel and may have one or more elements selected from the group consisting of iron, cobalt, platinum, palladium, vanadium, copper, zirconium, hafnium and niobium. The alloy material is subjected to thermomechanical processing which includes a final cold working of about 10 to about 75% and then a heat treatment at a temperature between about 450° and about 600° C. and preferably about 475° to about 550° C. Before the heat treatment the cold worked alloy material is preferably subjected to mechanical straightening. The alloy material is preferably subjected to stresses equal to about 5 to about 50% of the room temperature ultimate yield stress of the material during the thermal treatment. The guiding member using such improved material exhibits a stress-induced austenite-to-martensite phase transformation at an exceptionally high constant yield strength of over 90 ksi for solid members and over 70 ksi for tubular members with a broad recoverable strain of at least about 4% during the phase transformation. An essentially whip free product is obtained.

What is claimed is:  
     
         1 . An intravascular guidewire comprising 
 a) an elongated member having a proximal portion and a distal portion and being formed at least in part of a superelastic alloy consisting essentially of about 30 to about 52% titanium, about 38 to about 52% nickel and up to 20% additional alloying elements selected from the group consisting of iron, cobalt, platinum, palladium, copper and vanadium, said alloy part having an austenite phase which has a final transformation temperature below about 45° C., which transforms to a martensite phase upon the application of stress and which has been thermomechanically formed in a procedure which includes a final cold working followed by a heat treatment at a temperature between about 450° to about 600° C. while applying tension to the cold worked elongated member; and    b) torquing means on the proximal end of the elongated member.    
     
     
         2 . The guidewire of  claim 1  wherein the alloy contains one or more additional alloying elements selected from the group consisting of iron, cobalt, platinum and palladium in amounts of up to about 3%.  
     
     
         3 . The guidewire of  claim 1  wherein the alloy contains one or more additional alloying elements selected from the group consisting of copper in amounts of up to 12% and vanadium in amounts of up to about 10%.  
     
     
         4 . The guidewire of  claim 1  wherein the temperature of the heat treatment is between about 475° and about 550° C.  
     
     
         5 . The guidewire of  claim 1  wherein the superelastic portion has a straight memory at a temperature less than about 450° C.  
     
     
         6 . The guidewire of  claim 1  wherein the final cold worked alloy part is mechanically straightened before the heat treatment.  
     
     
         7 . A superelastic alloy body having an austenite phase which is stable at a desired operating temperature and which will transform to martensite phase upon the application thereto of stress, exhibiting a recoverable strain of at least about 4% upon the stress induced transformation of the austenite phase to martensite phase and having been formed by thermomechanical processing which includes a final cold working about 10 to about 75% and a memory imparting heat treatment at a temperature between about 475° and about 600° C.  
     
     
         8 . The body of  claim 7  wherein the strain of the body during the stress induced transformation of the austenite phase to the martensite phase is within the range of about 2% to about 8%.  
     
     
         9 . The body of  claim 7  wherein the austenite-to-martensite transformation occurs at a relatively constant stress above about 50 ksi.  
     
     
         10 . The body of  claim 7  wherein the austenite-to-martensite transformation occurs at a relatively constant stress above about 70 ksi.  
     
     
         11 . The body of  claim 7  wherein a distal portion thereof has a plurality of sections which have progressively smaller cross-sections in the distal direction.  
     
     
         12 . The body of  claim 7  further comprising a flexible member disposed about the superelastic distal portion thereof.  
     
     
         13 . The body of  claim 12  wherein the flexible member is a helical coil with a rounded plug on the distal end thereof.  
     
     
         14 . The body of  claim 6  wherein tension is applied to the elongated body while being subjected to the memory imparting heat treatment.  
     
     
         15 . The body of  claim 6  wherein the body is subjected to mechanical straightening between the cold working and heat treating steps.  
     
     
         16 . A fixed-wire balloon angioplasty catheter comprising: 
 a) an elongated catheter body with an inner lumen extending therein;    b) an inflatable balloon on the distal extremity of the catheter body and having an interior in fluid communication with the inner lumen of the catheter body; and    c) a guiding member which is disposed at least in part within the interior of the inflatable balloon and which is formed at least in part of a superelastic alloy body having an austenite phase which is stable at a desired operating temperature and which will transform to martensite phase upon the application thereto of stress, exhibiting a recoverable strain of at least about 4% upon the stress induced transformation of the austenite phase to martensite phase and having been formed by a thermomechanical processing which includes a final cold working of about 10 to about 75% and then a memory imparting heat treatment at a temperature between about 450° and about 600° C. while tension is applied thereto.    
     
     
         17 . The fixed wire balloon angioplasty catheter of  claim 17  wherein the thermomechanical processing includes a mechanical straightening between the cold working and heat treating.  
     
     
         18 . A method of forming a superelastic elongated member being in an austenite phase which is stable at temperatures less than about 45° C.: 
 providing an elongated member formed of an alloy consisting essentially of about 30 to about 52% titanium, about 38 to about 52% nickel and up to a total of about 20% of one or more additional alloying elements selected from the group consisting of iron, cobalt, chromium, platinum, palladium, copper, vanadium, zirconium, hafnium and niobium;  
 subjecting the elongated member to thermomechanical processing which includes a final cold working of about 10 to about 75% and a heat treatment at a temperature between about 450° and about 600° C. while subjecting the elongated member to a tension of up to about 50% of the room temperature tensile strength.  
 
     
     
         19 . The method of  claim 18  wherein the elongated member is subjected to mechanical straightening after the final cold working but before the heat treatment.  
     
     
         20 . The method of  claim 18  wherein the heat treating temperature is between about 475° and about 550° C.  
     
     
         21 . The method of  claim 18  wherein the final cold-worked number is heat treated for about 0.5 to about 60 minutes.  
     
     
         22 . An elongated tubular body suitable for use within a human body which has a cylindrical wall defining an inner lumen therein, which is formed of a superelastic alloy consisting essentially of about 30 to about 52% titanium, about 38 to 52% nickel, and to about 20% of one or more elements selected from the group consisting of iron, cobalt, chromium, platinum, palladium, copper, vanadium, zirconium, hafnium and niobium in a stable austenite phase which will transform to martensite phase upon the application of stress, which will exhibit a recoverable strain of at least about 4% from the application of stress which transforms the austenite phase to the martensite phase and which has been fabricated by a thermomechanical processing which includes a final cold working of about 10 to about 75% and then a memory imparting heat treatment at a temperature of about 450° to about 600° C.  
     
     
         23 . The tubular body of  claim 22  wherein the stress level at which the austenite phase transforms to the martensite phase is above 50 ksi.  
     
     
         24 . The tubular body of  claim 22  wherein the austenite-to-martensite transformation occurs at a relatively constant yield stress above about 70 ksi.  
     
     
         25 . The tubular body of  claim 22  wherein the alloy contains at least one element selected from the group consisting of up to about 20% copper and up to about 10% vanadium.  
     
     
         26 . The tubular body of  claim 22  wherein the alloy contains at least one element selected from the group consisting of iron, cobalt, palladium and platinum in amounts up to about 3%.  
     
     
         27 . The tubular body of  claim 24  having an outer diameter of about 0.006 to about 0.05 inch and a wall thickness of about 0.001 to about 0.004 inch.  
     
     
         28 . A method of forming a superelastic elongated member having a straight memory comprising subjecting an elongated member having a composition consisting of a predominant amount of NiTi intermetallic constituent to thermomechanical processing which includes a final cold working of about 10 to about 75% and a heat treatment at a temperature between about 450° and about 600° C. while subjecting the cold worked elongated member to sufficient tension to ensure a straight memory.  
     
     
         29 . The method of  claim 28  wherein the elongated member is formed of an alloy consisting essentially of about 30 to about 52% titanium, abut 38 to about 52% nickel and up to a total of about 10% of one or more additional alloying elements selected from the group consisting of iron, cobalt, chromium, platinum, palladium, coppers vanadium, zirconium, hafnium and niobium.  
     
     
         30 . The method of  claim 29  wherein the elongated member is in the austenite phase.  
     
     
         31 . The method of  claim 29  wherein the heat treatment is at a temperature between about 475° to about 550° C.  
     
     
         32 . The method of  claim 29  wherein the elongated member is mechanically straightened after the final cold working and before the heat treating.