# Patent

## Title
Method of joining dissimilar materials

## 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.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
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
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
FIG. 1 illustrates a perspective view of a guidewire in accordance with one example.
FIG. 2 illustrates a cross sectional view of joined dissimilar materials in accordance with one embodiment.
FIG. 3 illustrates a cross sectional view of joined dissimilar materials with indents in accordance with one embodiment.
FIG. 4 illustrates a cross sectional view of joined dissimilar materials with a recess in accordance with one embodiment.
FIG. 5 illustrates a cross sectional view of joined dissimilar materials with indents in accordance with one embodiment.
FIG. 6 illustrates a cross sectional view of two dissimilar materials in accordance with one embodiment.
FIG. 7 illustrates a cross sectional view of joined dissimilar materials with indents in accordance with one embodiment.



DETAILED DESCRIPTION
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.
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.
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.).
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.
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.
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.
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.
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.
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 OD40 and second wire section 50 has an outer diameter OD50. 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 PD65.
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.
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.
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.
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.
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.
In one embodiment, power levels of laser 35 are controlled such that the penetration depth PD65 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 PD65 of indents 65 is limited to less the 50% of the outer diameters OD40 and OD50 of first and second wire sections 40 and 50. In yet another embodiment, penetration depth PD65 of indents 65 is limited to less the 20% of the outer diameters OD40 and OD50 of first and second wire sections 40 and 50 to even further limit any weakness introduced into the sections.
The illustrated guidewire 30 can be configured in a variety of sizes in accordance with various embodiments. In one example, diameters OD40 and OD50 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 PD65 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 PD65 of indents 65 is limited in the range of about 0.001 to about 0.004 inches.
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.
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: Fe2Ti, FeTi, FeTi2, FeTiO4, and TiC. Creation of excessive amounts of brittle intermetallic phases will weaken wire sections 40 and 50 in these areas where they are created.
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 PD65 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.
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 Fe2Ti, FeTi, FeTi2, FeTiO4, and TiC, are less than 30 percent of the total material in indent 65.
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.
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.
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 OD90. Recess 94 is recessed relative to the outer diameter OD90 of first wire section 90. Similarly, in areas outside of recess 104, second wire section 100 has an outer diameter OD100. Recess 104 is recessed relative to the outer diameter OD100 of second wire section 100.
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 OD90 and OD100 of first and second wire sections 90 and 100 are equal to the outer diameter OD110 of coupler 110. In this way, the overall outer diameter of guidewire 80 is constant, in one embodiment.
Although the transitions from recesses 94 and 104 to the outer diameters OD90 and OD100 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 OD90 and OD100 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 OD90 and OD100.
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.
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.
Also similar to guidewire 30 above, the penetration depth of indents 115 is limited to less the 50% of the outer diameters OD90 and OD100 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 OD90 and OD100 of first and second wire sections 90 and 100 to even further limit any weakness introduced into the sections.
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.
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.
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.
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.
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.
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.
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.
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.

## Claims

1. A method of forming a wire comprising:
providing a first wire segment;
providing a second wire segment;
inserting the first and second wire segments into opposite ends of a coupling segment; and
laser welding the coupling segment such that the laser creates an indent in the coupling segment that penetrates into at least one of the first and second wire segments, wherein the laser welding is controlled such that the indent penetrates into one of the first and second wire segments a distance that is no more than fifty percent of the wire outer diameter.

2. The method of claim 1 further comprising laser welding the coupling segment such that a plurality of indents are created penetrating into each of the first and second wire segments from the coupling segment.

3. The method of claim 1, wherein the laser welding comprises applying a laser beam directly to the coupling segment and not applied the laser beam directly to either the first or second wire segments.

4. The method of claim 1 further comprising controlling the power level of the laser in order to minimize the brittle intermetallic phases created in the generation of the indent such that no more than 30 percent of the materials in the indents are brittle intermetallic phases.

5. The method of claim 1 further comprising applying the laser beam to the coupling segment in a direction that is transverse to the axial length of the wire.

6. A method of forming a wire comprising:
providing a first wire segment having an end portion;
providing a second wire segment having an end portion, one of the first and second wire segments comprising a first material;
providing a coupling segment adjacent the end portions of the first and second wire segments, the coupling segment comprising a second material; and
heating the coupling segment such that at least one indent from the coupling segment penetrates into at least one of the first and second wire segments, wherein the indent comprises a mixture of the first material from the first or second wire segment and the second material from the coupling segment, wherein the mixture of the first material from the first or second wire segment and the second material from the coupling segment is such that no more than 30 percent of the materials in the indents are brittle intermetallic phases.

7. The method of claim 6, wherein heating the coupling segment comprises laser welding the coupling segment such that a plurality of indents are created penetrating into each of the first and second wire segments from the coupling segment.

8. The method of claim 6, wherein the coupling segment is laser welded along a spiral path around at least one of the first and second segments.

9. The method of claim 6, wherein the second material of the coupling segment comprises stainless steel and the first material of either the first or second wire segments comprises nickel-titanium.

10. The method of claim 6, wherein the wire has an outer diameter, and wherein heating the coupling segment comprises controlling the heat such that the indent penetrates a penetration distance into one of the first and second wire segments, and wherein the penetration distance is no more than fifty percent of the wire outer diameter.

11. The method of claim 10, further comprising controlling the heat such that the indent penetrates a penetration distance into one of the first and second wire segments, and wherein the penetration distance is no more than twenty percent of the wire outer diameter.

12. The method of claim 6, wherein the indent is formed by welding the coupling segment with a laser such that a laser beam is applied directly to the coupling segment and such that the laser is not applied directly to either the first or second wire segments.

13. The method of claim 12, wherein the laser beam is applied to the coupling segment in a direction that is transverse to the axial length of the wire.