Abstract:
Alternative designs and materials suitable for connecting different guidewire sections together. More particularly, connecting two portions of a guidewire having different material compositions with a connector having a third composition which is readily weldable to each of the dissimilar portions of the guidewire. A transition area may be designed to provide a region of desired flexibility characteristics.

Description:
FIELD OF THE INVENTION 
     The present invention generally pertains to intravascular guidewires. 
     BACKGROUND OF THE INVENTION 
     Intravascular guidewires are commonly used in conjunction with intravascular devices such as balloon catheters to facilitate navigation through the vasculature of a patient. Because the vasculature of a human being may be very tortuous, guidewires often have a stiff proximal portion for pushability and torqueability, and a flexible distal portion for trackability. 
     SUMMARY OF THE INVENTION 
     To provide for a relatively stiff proximal portion and a relatively flexible distal portion, the proximal and distal portions of the guidewire may be formed of different materials. The present invention provides several alternative designs, materials and manufacturing methods for connecting different guidewire sections together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is cross sectional fragmentary view of a guidewire (pre-grinding), including a connection utilizing an overlapping tapered joint and a tubular connector for joining a proximal section and a distal section of the guidewire; 
         FIG. 2  is a cross sectional fragmentary view of the guidewire (post grinding) of  FIG. 1 ; 
         FIG. 3  is a cross sectional fragmentary view of an alternative guidewire (post grinding), including a connection utilizing an overlapping joint (without a tubular connector) for joining a proximal section and a distal section of the guidewire; 
         FIG. 4  is a cross sectional fragmentary view of an alternative guidewire (post grinding), including a connection utilizing a butt joint and a tubular connector for joining a proximal section and a distal section of the guide wire; 
         FIG. 5  is a cross sectional fragmentary view of an alternative guidewire (post grinding), including a connection utilizing an overlapping joint and a tubular connector for joining a proximal section and a distal section of the guide wire; and 
         FIGS. 6A-6C  are cross sectional fragmentary views of various end portions for use with the guidewire embodiment of FIG.  5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The detailed description and drawings illustrate examples of various embodiments of the claimed invention, and are not intended to be limiting. 
     Refer now to  FIGS. 1-5  which illustrate cross sectional views of a portion of a guidewire  10  including a connection  20  joining a proximal guidewire section  14  and a distal guidewire section  16 .  FIG. 1  illustrates the guidewire  10  and the connection  20  before a final grinding step, and  FIG. 2  illustrates the guidewire  10  and the connection  20  after the final grinding step, which provides a smooth outer profile. The embodiment of  FIGS. 1 and 2  utilizes an overlapping tapered joint  12  and a tubular connector  18 . 
     The embodiment of  FIG. 3  is similar to the embodiment of  FIGS. 1 and 2 , except that the connection  20  between the proximal guidewire section  14  and the distal guidewire section  16  does not utilize a connector tube  18 , but rather utilizes a connector material  19 . The embodiment of  FIG. 4  is similar to the embodiment of FIGS.  1  and  2 , except that the connection  20  between the proximal guidewire section  14  and the distal guidewire section  16  does not utilize an overlapping joint  12 , but rather uses a butt joint  13 . The embodiment of  FIG. 5  is also similar to the embodiment of  FIGS. 1 and 2 , except that the connection  20  between the proximal guidewire section  14  and the distal guidewire section  16  utilizes an overlapping joint  12  that is not tapered. 
     The proximal and distal guidewire sections  14 / 16  may have a solid cross-section as shown, or a hollow cross-section, and may be formed of metals or metal alloys suitable for metal joining techniques such as welding, soldering, brazing, crimping, friction fitting, adhesive bonding, etc. As used herein, the proximal section  14  and the distal section  16  may generically refer to any two adjacent guidewire sections along any portion of the guidewire. Furthermore, although discussed with specific reference to guidewires, the present invention may be applicable to almost any intravascular device having two adjacent metallic shaft sections. For example, the present invention may be applicable to metallic hypotube shafts for intravascular catheters (e.g., rapid exchange balloon catheters, stent delivery catheters, etc.) or metallic drive shafts for intravascular rotational devices (atherectomy catheters, IVUS catheters, etc.). 
     The proximal guidewire section  14  may be formed of relatively stiff material such as straightened 304v stainless steel wire. Alternatively, proximal portion  14  may be comprised of a metal or metal alloy such as a nickel-titanium alloy, nickel-chromium alloy, nickel-chromium-iron alloy, cobalt alloy, or other suitable material. In general, the material used to construct proximal portion  14  may be selected to be relatively stiff for pushability and torqueability. 
     The distal guidewire section  16  may be formed of a relatively flexible material such as a straightened super elastic or linear elastic alloy (e.g., nickel-titanium) wire. Alternatively, distal portion  16  may be comprised of a metal or metal alloy such as stainless steel, nickel-chromium alloy, nickel-chromium-iron alloy, cobalt alloy, or other suitable material. In general, the material used to construct distal portion  16  may be selected to be relatively flexible for trackability. 
     The distal end  24  of the proximal portion  14  and the proximal end  26  of distal portion  16  (i.e., the joined ends) may form an overlapping tapered joint  12  as shown in  FIGS. 1-3 . Alternatively, the joined ends  24 / 26  may form a butt joint  13  as shown in FIG.  4 . As a further alternative, the joined ends  24 / 26  may form an overlapping joint  12  that is not tapered as shown in FIG.  5 . The non-tapered end portions  24 / 26  may have a uniform profile (diameter)  23  as shown in  FIG. 6A , a bulbous portion  25  for purposes of mechanical interlocking as shown in  FIG. 6B , or a helical form  27  for purposes of mechanical interlocking as shown in FIG.  6 C. In each of the embodiments illustrated in  FIGS. 1-3  and  5 , the end portions  24 / 26  overlap to form an overlapping joint  12 . The overlapping joint  12  blends the stiffness of proximal portion  14  and distal portion  16  by combining the properties of each end section  24 / 26  making up the cross section of the overlapping joint  12 . Thus, the joint  12  forms a flexibility transition region that has a relative flexibility that is between the flexibility of the proximal portion  14  and the flexibility of the distal portion  16 . 
     In the tapered embodiments illustrated in  FIGS. 1-3 , the ends  24 / 26  may be tapered or otherwise formed to have a mating geometry, wherein the cross-sectional area of each end section  24 / 26  gradually decreases toward the middle of the connection  20 . The tapered overlapping portion  12  may define a uniform or a non-uniform transition of the sections  24 / 26 , depending on the transition characteristics desired. For example, the end sections  24 / 26  may be linearly tapered as shown, tapered in a curvilinear fashion, or tapered in a step-wise fashion. If tapered linearly as shown, the angle of the taper may vary. Using the longitudinal center axis of the guidewire  10  as a reference, as measured from the extreme ends of the end sections  24 / 26 , the angle of the taper is acute (i.e., less than 90 degrees), and may be in the range of 5 degrees to 45 degrees, for example. Varying the angle of the tapered ends  24 / 26  also varies the length of the overlapping joint  12  in accordance with geometric principles. The length of the overlapping joint  12  may be selected to obtain a more (longer length) or less (shorter length) gradual transition in stiffness. 
     As mentioned previously, the proximal guidewire section  14  and the distal guidewire section  16  may be formed of different materials (i.e., materials having different moduli of elasticity) resulting in a difference in flexibility. For example, the proximal guidewire section  14  may be formed of stainless steel wire and the distal guidewire section  16  may be formed of nickel-titanium alloy wire, both having the same dimensions, resulting in a 3:1 difference in elastic modulus. Such a difference in elastic modulus (i.e., flexibility) may result in a stress concentration point during flexure and/or torsion that may have a tendency to kink. By virtue of the gradual transition in stiffness provided by the overlapping portion  12 , stress is distributed along the entire length of the connection  20  thereby decreasing the probability that guidewire  10  may kink at the junction. 
     A gradual transition in stiffness may also allow the connection  20  to be located further distally. According to this embodiment, the distal portion  16  may be manufactured to be shorter than proximal portion  14 . Including a relatively long proximal section  14  may advantageously increase the torquability and pushability of the guidewire  10 . Although only one connection  20  is shown, additional connections  20  may be used to connect other guidewire sections of varying stiffness. 
     The connector  18  may comprise a tubular structure such as a hypotube as shown or a coiled wire. The connector  18  may have an inside diameter sized appropriately to receive the ends  24 / 26  of the proximal portion  14  and the distal portion  16 , and an outside diameter sufficient to accommodate a final grinding procedure. The final diameter of the guidewire  10  and the connector  18  may be in the range of 0.010 to 0.018 inches, for example. By way of example, not limitation, the connector  18  may have a length of about 1.0 to 3.0 inches for an overlapping portion  12  of about 0.75 to 2.5 inches. 
     The connector  18  may be comprised of a metal or metal alloy, and may include radiopaque materials. Suitable metals and metal alloys include stainless steels, nickel-titanium alloys (e.g., nitinol), nickel-chromium alloys, nickel-chromium-iron alloys, cobalt alloys, nickel, or other suitable materials. Alternatively, connector  18  may be comprised of a polymer or a metal-polymer composite, including a radiopaque filler. 
     The word nitinol was coined by a group of researchers at the United States Naval Ordinance Laboratory (NOL) who were the first to observe the shape memory behavior of this material. The word nitinol is an acronym including the chemical symbol for nickel (Ni), the chemical symbol for titanium (Ti), and an acronym identifying the Naval Ordinance Laboratory (NOL). 
     Some types of alloys are particularly suitable for connector  18  for purposes of connecting a stainless steel proximal section  14  and a nickel titanium alloy distal section  16 , or visa-versa. An example is a nickel-chromium-iron alloy available under the trade name INCONEL 625, which advantageously welds to both stainless steels and nickel-titanium alloys. INCONEL 625 may be obtained from California Fine Wire Company of Grover Beach, Calif., and has the following composition: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Symbol 
                 % by wat 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Aluminum 
                 Al 
                 0.140 
               
               
                   
                 Carbon 
                 C 
                 0.070 
               
               
                   
                 Chromium 
                 Cr 
                 21.900 
               
               
                   
                 Cobalt 
                 Co 
                 0.010 
               
               
                   
                 Copper 
                 Cu 
                 0.030 
               
               
                   
                 Iron 
                 Fe 
                 2.790 
               
               
                   
                 Manganese 
                 Mn 
                 0.030 
               
               
                   
                 Molybdenum 
                 Mo 
                 9.150 
               
               
                   
                 Nickel 
                 Ni 
                 62.000 
               
               
                   
                 Niobium 
                 Nb 
                 3.540 
               
               
                   
                 Phosphorus 
                 P 
                 0.005 
               
               
                   
                 Silicon 
                 Si 
                 0.230 
               
               
                   
                 Sulfur 
                 S 
                 0.009 
               
               
                   
                 Titanium 
                 Ti 
                 0.250 
               
               
                   
                 Tantalum 
                 Ta 
                 0.010 
               
               
                   
                   
               
             
          
         
       
     
     Another example of a suitable alloy which welds to both stainless steels and nickel-titanium alloys is available under the trade name ALLOY C276 from Fort Wayne Metals Research Products Corporation of Fort Wayne, Ind., which has the following composition: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Symbol 
                 % by wat 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Carbon 
                 C 
                 0.003 
               
               
                   
                 Chromium 
                 Cr 
                 15.810 
               
               
                   
                 Cobalt 
                 Co 
                 1.310 
               
               
                   
                 Copper 
                 Cu 
                 0.100 
               
               
                   
                 Iron 
                 Fe 
                 5.730 
               
               
                   
                 Manganese 
                 Mn 
                 0.520 
               
               
                   
                 Molybdenum 
                 Mo 
                 16.010 
               
               
                   
                 Nickel 
                 Ni 
                 57.000 
               
               
                   
                 Phosphorus 
                 P 
                 0.008 
               
               
                   
                 Silicon 
                 Si 
                 0.020 
               
               
                   
                 Sulfur 
                 S 
                 0.005 
               
               
                   
                 Tungsten 
                 W 
                 3.570 
               
               
                   
                 Vanadium 
                 V 
                 0.160 
               
               
                   
                   
               
             
          
         
       
     
     Another example of a suitable alloy which welds to both stainless steels and nickel-titanium alloys is available under the trade name ALLOY B2 from Fort Wayne Metals Research Products Corporation of Fort Wayne, Ind., which has the following composition: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Material 
                 Symbol 
                 % by wat 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Carbon 
                 C 
                 0.005 
               
               
                   
                 Chromium 
                 Cr 
                 0.450 
               
               
                   
                 Cobalt 
                 Co 
                 0.110 
               
               
                   
                 Copper 
                 Cu 
                 0.030 
               
               
                   
                 Iron 
                 Fe 
                 1.410 
               
               
                   
                 Manganese 
                 Mn 
                 0.150 
               
               
                   
                 Molybdenum 
                 Mo 
                 27.720 
               
               
                   
                 Nickel 
                 Ni 
                 70.000 
               
               
                   
                 Phosphorus 
                 P 
                 0.004 
               
               
                   
                 Silicon 
                 Si 
                 0.020 
               
               
                   
                 Sulfur 
                 S 
                 0.002 
               
               
                   
                 Tungsten 
                 W 
                 0.140 
               
               
                   
                   
               
             
          
         
       
     
     To manufacture the connection  20  of the guidewire  10 , the ends  24 / 26  of the proximal and distal guidewire sections  14 / 16  may be ground to form the desired shape (e.g., uniform diameter  23 , bulbous portion  25 , helix  27 , or taper) to accommodate the overlapping joint  12 . If a butt joint  13  is to be used, such a shape need not be ground. A recess step may be ground into the proximal and distal guidewire sections  14 / 16  to accommodate the connector tube  18 . If a connector tube  18  is not to be used, such a recess step need not be ground. 
     For the embodiments utilizing a connector tube  18 , the connector tube  18  is positioned over one of the ends  24 / 26  of the proximal and distal guidewire sections  14 / 16 . The distal end  24  of the proximal portion  14  and proximal end  26  of the distal portion  16  are then positioned adjacent one another in an overlapping  12  or an end-to-end  13  arrangement. The proximal and distal guidewire sections  14 / 16  and the connector tube  18  may be bonded, welded (e.g., resistance or laser welded), soldered, brazed, or otherwise connected by a suitable technique depending on the material selected for each component. Alternatively, the ends  24 / 26  and the connector tube  18  may be crimped together or may be sized to establish a friction fit therebetween. If a connector tube  18  is not used, the ends  24 / 26  may be bonded, welded (e.g., resistance or laser welded), soldered, brazed, or otherwise connected, using a connector material  19 . Connector material  19  may be the same as or similar to the material of the connector  18 . In all cases, because the connection  20  may reside within a catheter lumen during use, it is preferred that a permanent connection (as opposed to a releasable connection) be used. 
     It is to be appreciated that various welding processes may be utilized without deviating from the spirit and scope of the present invention. Examples of welding processes which may be suitable in some applications include LASER welding, resistance welding, TIG welding, microplasma welding, electron beam, and friction or inertia welding. LASER welding equipment which may be suitable in some applications is commercially available from Unitek Miyachi of Monrovia, Calif. and Rofin-Sinar Incorporated of Plymouth, Mich. Resistance welding equipment which may be suitable in some applications is commercially available from Palomar Products Incorporated of Carlsbad, Calif. and Polaris Electronics of Olathe, Kans. TIG welding equipment which may be suitable in some applications is commercially available from Weldlogic Incorporated of Newbury Park, Calif. Microplasma welding equipment which may be suitable in some applications is commercially available from Process Welding Systems Incorporated of Smyrna, Tenn. 
     Once connected, the connector tube  18  and the proximal and distal guidewire sections  14 / 16  are centerless ground to provide a smooth and uniform profile across the connection  20 , and to straighten out small misalignments between the proximal and distal guidewire sections  14 / 16 . Other portions of the guidewire  10  may be ground as well to provide the desired tapers and changes in diameter. Once finally ground, a flexible coil tip and/or a polymer jacket (optionally covering connection  20 ) may be placed on the guidewire  10 , and a lubricious coating (e.g., hydrophylic) may be applied. 
     The centerless grinding technique may utilize an indexing system employing sensors (e.g., optical/reflective, magnetic) to avoid excessive grinding of the connection  20 . In addition, the centerless grinding technique may utilize a CBN or diamond abrasive grinding wheel that is well shaped and dressed to avoid grabbing the connector  20  during the grinding process. 
     It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.