Abstract:
A method of forming a wire includes providing a first wire segment and a second wire segment. The first and second wire segments are inserted into opposite ends of a coupling segment. The coupling segment is laser welded such that the laser creates an indent in the coupling segment that penetrates into at least one of the first and second wire segments.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/644,818, entitled “JOINED DISSIMILAR MATERIALS,” having a filing date of Dec. 22, 2009, and is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to joined dissimilar materials. In one embodiment, the joined materials form a guide wire configured for intravascular use. For example, intravascular guidewires are used in conjunction with intravascular devices such as catheters to facilitate navigation through the vasculature of a patient. Such guidewires are typically very small in diameter. In some applications, a guidewire can have multiple sections that are joined together in order to form a single wire. Joining sections of such a wire having a small diameter can be challenging, particularly where the sections being joined are configured of different materials. Because there are limitations to many present approaches, there is a need for the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  illustrates a perspective view of a guidewire in accordance with one example. 
           [0004]      FIG. 2  illustrates a cross sectional view of joined dissimilar materials in accordance with one embodiment. 
           [0005]      FIG. 3  illustrates a cross sectional view of joined dissimilar materials with indents in accordance with one embodiment. 
           [0006]      FIG. 4  illustrates a cross sectional view of joined dissimilar materials with a recess in accordance with one embodiment. 
           [0007]      FIG. 5  illustrates a cross sectional view of joined dissimilar materials with indents in accordance with one embodiment. 
           [0008]      FIG. 6  illustrates a cross sectional view of two dissimilar materials in accordance with one embodiment. 
           [0009]      FIG. 7  illustrates a cross sectional view of joined dissimilar materials with indents in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
         [0011]      FIG. 1  illustrates a perspective view of a guidewire  10  in accordance with one embodiment. In one embodiment, guidewire  10  has a proximal section  12  and a distal section  14 . In one case, proximal and distal sections  12  and  14  are configured of separate wire segments that are joined together at joint  16 . In some embodiments, proximal and distal sections  12  and  14  are adapted with differing diameter regions, are adapted and configured to obtain a transition in stiffness, and provide a desired flexibility characteristic. In  FIG. 1 , guidewire  10  is illustrated with a truncation in its ends, as its length may vary in accordance with particular applications. 
         [0012]    As used herein, the proximal section  12  and the distal section  14  can generically refer to any two adjacent wire sections along any portion of guidewire  10 . Furthermore, although discussed with specific reference to guidewires, the wire segments can be applicable to almost any intravascular device. For example, they are applicable to hypotube shafts for intravascular catheters (e.g., rapid exchange balloon catheters, stent delivery catheters, etc.) or drive shafts for intravascular rotational devices (atherectomy catheters, IVUS catheters, etc.). 
         [0013]    In one example, proximal section  12  can be configured of a relatively stiff material, such as stainless steel wire. Alternatively, proximal section  12  can 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 section  12  can be selected to be relatively stiff for pushability and torqueability. 
         [0014]    Also, in some embodiments, distal section  14  can be configured of a relatively flexible material, such as a super elastic or linear elastic alloy) wire, such as linear elastic nickel-titanium (NiTi), or alternatively, a polymer material, such as a high performance polymer. Alternatively, distal section  14  can be configured 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 configure distal section  14  can be selected to be relatively flexible for trackability. 
         [0015]      FIG. 2  illustrates a cross-sectional view of guide wire  30  in accordance with one embodiment. In one embodiment, guidewire  30  includes first wire section  40 , second wire section  50  and coupler  60 . In one example, guidewire  30  is configured for use in conjunction with intravascular devices, such that first wire section  40  has relatively stiff characteristics for pushability and torqueability, and such that second wire section  50  has relatively flexible characteristics for trackability. 
         [0016]    In one embodiment, first and second sections  40  and  50  are formed of different wire segments and joined together using coupler  60 . In one example, a first end  42  of first wire section  40  is placed inside a first end  62  of coupler  60  and a first end  52  of second wire section  50  is placed inside a second end  64  of coupler  60 . In one case, first ends  42  and  52  are pushed together inside coupler  60  such that they are immediately adjacent, for example, so that they touch. Coupler  60  can help facilitate the joining of first and second wire sections  40  and  50 . 
         [0017]    In one embodiment, the joining of first and second wire sections  40  and  50  includes the use of a laser  35 , such as a YAG laser or a fiber laser. In one embodiment, a laser beam from laser  35  is applied directly to coupler  60  in a target area  37  of coupler  60 . When the laser  35  is energized such that the beam is directed to coupler  60 , area  37  is melted. In turn, the melted material in area  37  of coupler  60  will partially melt portions of first and second wire sections  40  and  50  that are immediately adjacent area  37  of coupler  60 . In one embodiment, laser  35  is configured to apply a beam to coupler  60  that is perpendicular to guidewire  30 . In operation, guidewire  30  is pushed and pulled along its axis, such that laser  35  is applied perpendicular to these applied loads. This perpendicular application results in a strong hold between first and second wire sections  40  and  50  and coupler  60 , as explained below. 
         [0018]      FIG. 3  illustrates guidewire  30  with first wire section  40  and second wire section  50  within coupler  60 . In the illustration, first wire section  40  has an outer diameter OD 40  and second wire section  50  has an outer diameter OD 50 . In  FIG. 3 , a plurality of indents  65  are formed. In the embodiment, each of indents  65  penetrate into either first or second wire sections  40  or  50  to a penetration depth PD 65 . 
         [0019]    In one embodiment, after coupler  60  is fitted over first and second wire sections  40  and  50 , laser  35  ( FIG. 2 ) is used to melt areas of coupler  60  such that indents  65  are created from coupler  60 . Indents  65  penetrate down into first and second wire sections  40  and  50 . When the laser beam of laser  35  is applied to coupler  60 , areas ( 37  in  FIG. 2 ) of the material of coupler  60  impacted by the laser  35  are melted. In turn, these melted areas of coupler  60  partially melt the first and second wire sections  40  and  50  adjacent that melted areas of coupler  60 , illustrated in  FIG. 3  as indents  65 . The resulting indents  65 , in conjunction with coupler  60 , provide a secure mechanical connection between first and second wire sections  40  and  50 . 
         [0020]    In one embodiment, there are small spaces between the outer diameters of first and second wire sections  40  and  50  and the inner diameter of coupler  60 . In one embodiment, as material in these areas turns molten with the application of a laser beam, the molten material will tend to fill this space. In such cases, indent  65  can have a slightly “saddle” shape as the molten material flows down the sides of the cylindrical wire sections  40  and  50 . 
         [0021]    In one example, first wire section  40  is a segment of stainless steel wire, second wire section  50  is a segment of linear elastic nickel-titanium (NiTi) alloy, such as nickel-titanium wire, and coupler  60  is a stainless steel hypotube. As such, in that case, indents  65  are also stainless steel from coupler  60  that is forced down into first and second wire sections  40  and  50  upon welding. A guidewire  30  configured in this way allows first wire section  40  to have a relatively stiff characteristics for pushability and torqueability, and allows second wire section  50  to have a relatively flexible characteristics for trackability. 
         [0022]    In one embodiment, because coupler  60  has a snug fit over first and second wire sections  40  and  50  while laser  35  is used to melt areas of coupler  60 , first and second wire sections  40  and  50  are well secured linearly such that they are prevented from relative movement during welding. Much of the shear forces or bending moments between first and second wire sections  40  and  50  are eliminated while they are stabilized by the tight fitting coupler  60 . Shear or bending forces between first and second wire sections  40  and  50  during a weld will tend to degrade the weld. Coupler  60  can help limit or avoid such shear and bending forces. As such, indents  65  generated via these welds tend to be more secure than would welds made where there is even slight movement between first and second wire sections  40  and  50 . 
         [0023]    Also in one embodiment, the beam of laser  35  is applied directly to coupler  60 , and not directly to either first or second wire sections  40  or  50 . In the case where coupler  60  is a segment of stainless steel wire and second wire section  50  is a segment of linear elastic nickel-titanium (NiTi) alloy, the beam of laser  35  will directly impact only the stainless steel and will not directly impact the nickel-titanium. The nickel-titanium will only be indirectly impacted from the melting of adjacent stainless steel in coupler  60  (which receives the direct laser beam). In some embodiments, weaknesses within the nickel-titanium are avoided by avoiding welding with the beam of laser  35  directly on the nickel-titanium material. 
         [0024]    In one embodiment, power levels of laser  35  are controlled such that the penetration depth PD 65  of indents  65  is limited. If indents  65  are allowed to penetrate too deep into first and second wire sections  40  and  50  upon welding, weakness can be introduced into the sections adjacent indent  65 . In one case, the penetration depth PD 65  of indents  65  is limited to less the 50% of the outer diameters OD 40  and OD 50  of first and second wire sections  40  and  50 . In yet another embodiment, penetration depth PD 65  of indents  65  is limited to less the 20% of the outer diameters OD 40  and OD 50  of first and second wire sections  40  and  50  to even further limit any weakness introduced into the sections. 
         [0025]    The illustrated guidewire  30  can be configured in a variety of sizes in accordance with various embodiments. In one example, diameters OD 40  and OD 50  of first and second wire sections  40  and  50  can range from about 0.005 to about 0.02 inches. In one example, indents  65  are produced with the application of laser welds, where the penetration depth PD 65  of indents  65  is limited in the range of about 0.0025 to about 0.01 inches. In another example, indents  65  are produced with the application of laser welds, where the penetration depth PD 65  of indents  65  is limited in the range of about 0.001 to about 0.004 inches. 
         [0026]    Fusion welding of nickel alloy and titanium alloy has challenges, for example, issues of solidification and cracking due to intermetallic formation. Limiting the depth of indents  65  in accordance with embodiments also limits the amount of mixture that occurs between the materials that make up coupler  60  and first and second wire sections  40  and  50 , thereby limiting intermetallic formation. 
         [0027]    For example, when coupler  60  is stainless steel and second wire section  50  is nickel-titanium wire, excessive mixture of these materials in molten states will create brittle intermetallic phases from the combination of stainless steel and nickel-titanium. Examples of such brittle intermetallic phases include: Fe 2 Ti, FeTi, FeTi 2 , FeTiO 4 , and TiC. Creation of excessive amounts of brittle intermetallic phases will weaken wire sections  40  and  50  in these areas where they are created. 
         [0028]    In one embodiment, although indents  65  represent some amount of mixing of the materials that make up coupler  60  and either first or second wire sections  40  or  50 , controlling and limiting the power used for laser  35  limits the penetration depth PD 65  of indents  65  and also minimizes the brittle intermetallic phases created in the area. In this way, this tends to maximize the strength of first and second wire sections  40  and  50 . 
         [0029]    In one example, coupler  60  is stainless steel and second wire section  50  is nickel-titanium. The power used for laser  35  is controlled and limited during the formation of indents  65  such that mixture molten stainless steel and molten nickel-titanium is minimized, as is the creation of brittle intermetallic phases. As such, brittle intermetallic phases, such as Fe 2 Ti, FeTi, FeTi 2 , FeTiO 4 , and TiC, are less than 30 percent of the total material in indent  65 . 
         [0030]    Although  FIG. 3  illustrates one indent  65  in each of first and second wire sections  40  and  50 , in some embodiments, two indents  65  are formed in each of first and second wire sections  40  and  50 , and in yet other embodiments more than two indents  65  are in each section. In one embodiment, coupler  60  is welded in a spiral pattern such that indents  65  are likewise distributed in a spiral pattern about first and second wire sections  40  and  50 . This produces a secure mechanical hold between the wire sections  40  and  50 . Other patterns and distributions for indents  65  are also possible. 
         [0031]    In one embodiment, after coupler  60  is welded to produce indents  65 , guidewire  30  and especially coupler  60  can be ground to decrease the outer diameter of guidewire  30  in the area of coupler  60 . In one example, guidewire  30  can be ground such that substantially no portion of coupler  60  extends beyond the outer diameter of guidewire  30 . 
         [0032]      FIG. 4  illustrates a cross-sectional view of guidewire  80  in accordance with one embodiment. In one embodiment, guidewire  80  includes first wire section  90  and second wire section  100  with respective ends  92  and  102 . First wire section  90  includes recess  94  adjacent end  92  and second wire section  100  includes recess  104  adjacent end  102 . In areas outside of recess  94 , first wire section  90  has an outer diameter OD 90 . Recess  94  is recessed relative to the outer diameter OD 90  of first wire section  90 . Similarly, in areas outside of recess  104 , second wire section  100  has an outer diameter OD 100 . Recess  104  is recessed relative to the outer diameter OD 100  of second wire section  100 . 
         [0033]    When first and first ends  92  and  102  are placed immediately adjacent, recesses  94  and  104  align. In one embodiment, coupler  110  fits over the aligned recesses  94  and  104 , as illustrated in  FIG. 5 . In one embodiment, the thickness of coupler  110  is matched with the depth of recesses  94  and  104  such that the outer diameters OD 90  and OD 100  of first and second wire sections  90  and  100  are equal to the outer diameter OD 110  of coupler  110 . In this way, the overall outer diameter of guidewire  80  is constant, in one embodiment. 
         [0034]    Although the transitions from recesses  94  and  104  to the outer diameters OD 90  and OD 100  are illustrated as sharp, such that the transitions are essentially vertical, other transitions are also possible in accordance with other embodiments. For example, in another embodiment the transitions from recesses  94  and  104  to the outer diameters OD 90  and OD 100  are gradual such that the transitions appear more as a ramp, rather than vertical. In that case, coupler  110  is also gradually tapered at its ends to match the gradual transitions from recesses  94  and  104  to the outer diameters OD 90  and OD 100 . 
         [0035]    With coupler  110  placed in recesses  94  and  104 , a plurality of indents  115  are formed with a laser, such as described above with laser  35 . In the embodiment, each of indents  115  penetrate into either first or second wire sections  90  or  100 . In one embodiment, after coupler  110  is fitted over first and second wire sections  90  and  100 , a laser is directed at areas of coupler  110  such that indents  115  are created from coupler  110  and penetrate down into first and second wire sections  90  and  100 . 
         [0036]    Coupler  110  and indents  115  can help facilitate the joining of first and second wire sections  90  and  100 . In one example, first wire section  90  is a segment of stainless steel wire, second wire section  100  is a segment of linear elastic nickel-titanium (NiTi) alloy, and coupler  110  is a stainless steel hypotube. As such, in that example, indents  115  represent some amount of mixing of the stainless steel of coupler  110  and the nickel-titanium of either first or second wire sections  90  or  100  upon welding. In one embodiment, the power used for laser welding is controlled to limits the penetration depth of indents  115  and minimizes the brittle intermetallic phases created in the area, as discussed above in conjunction with guidewire  30 . 
         [0037]    Also similar to guidewire  30  above, the penetration depth of indents  115  is limited to less the 50% of the outer diameters OD 90  and OD 100  of first and second wire sections  90  and  100 . In yet another embodiment, the penetration depth of indents  115  is limited to less the 20% of the outer diameters OD 90  and OD 100  of first and second wire sections  90  and  100  to even further limit any weakness introduced into the sections. 
         [0038]    In one embodiment, guidewire  80  is configured for use in conjunction with intravascular devices, such that first wire section  90  has relatively stiff characteristics for pushability and torqueability, and such that second wire section  100  has relatively flexible characteristics for trackability. 
         [0039]      FIG. 6  illustrates a cross-sectional view of first and second wire sections  140  and  150 . First wire section  140  includes extension  143  and second wire section  150  includes notch  153 . Guidewire  130  is then formed when extension  143  is placed in notch  153  thereby joining first and second wire sections  140  and  150  as illustrated in  FIG. 7 . 
         [0040]    Also illustrated in  FIG. 7  are indents  155  formed in guidewire  130 . In one embodiment, each of indents  155  penetrates from second wire section  150  into first wire section  140 , and specifically, penetrates into extension  143  of first wire section  140 . In one embodiment, after extension  143  is placed in notch  153 , a laser is used to weld into second wire section  150  adjacent extension  143  such that indents  155  are created from second wire section  150  and penetrate down into first wire section  140 . 
         [0041]    In the embodiment illustrated in  FIG. 7 , no coupling device separate from first and second wire sections  140  and  150  is used. Instead, the portions of second wire section  150  that extend beyond notch  153  function as the couplers  60  ( FIG. 3) and 110  ( FIG. 5 ) did in the above-described embodiments. In this way, indents  155 , along with the fit of extension  143  within notch  153 , can help facilitate the secure joining of first and second wire sections  140  and  150 . 
         [0042]    In one embodiment, first wire section  140  is a segment of linear elastic nickel-titanium (NiTi) alloy, and second wire section  150  is a segment of stainless steel wire. In one embodiment, the laser used to generate indents  155  is applied directly to second wire segment  150 , and not directly to first wire section  140 . In this embodiment where second wire segment  150  is a segment of stainless steel wire and first wire section  140  is a segment of linear elastic nickel-titanium (NiTi) alloy, the laser beam will directly impact only the stainless steel and will not directly impact the nickel-titanium, thereby avoiding weakness within associated with direct welding of the nickel-titanium, as described above. 
         [0043]    As with the prior-described embodiments, power to the laser used to create indents  155  is controlled to limit the penetration depth of the indents and to limit the amount of mixture between the stainless steel of second wire segment  150  and the nickel-titanium of first wire section  140 , thereby limiting brittle intermetallic phases created. In one embodiment, the penetration depth of indents  115  is limited to less than 50% of the outer diameters of first and second wire sections  140  and  150 , and in another limited to 20%. In one embodiment, no more than 30 percent of the material of indents  155  is brittle intermetallic phases. 
         [0044]    In one embodiment, guidewire  130  is configured for use in conjunction with intravascular devices, such that second wire section  150  has relatively stiff characteristics for pushability and torqueability, and such that first wire section  140  has relatively flexible characteristics for trackability. 
         [0045]    Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.