Abstract:
A process for joining two discrete wire components without the need of a third component, wherein material from the end of one wire component is removed to form a female end and the end of the other wire is formed into a male end. The male may be secured within the female end by conventional means. The female end may be formed by electrical discharge machining or laser drilling.

Description:
BACKGROUND 
     Metallic wires are widely used in medical procedures, a common example being the guidewires used to locate intravascular devices such as angioplasty catheters. For various reasons, it is often desirable to join two discrete wire elements. For example, using different metal alloys can impart distinct handling characteristics to each wire element. By varying properties such as elasticity, strength and torqueability in each wire element, the overall handling of the guidewire can be varied or improved. 
     Conventional means for joining discrete wire elements involves the use of a third component, such as a hypotube. One end of each wire element is plunge ground and then inserted into the joining hypotube. The wire elements then can be secured to the hypotube, and thus to each other, by soldering or gluing. These prior art methods can be improved upon because the hypotube itself is expensive and increases manufacturing time due to the handling required to glue each wire element into the hypotube. 
     Accordingly, there is a need for improved wire joining processes that allow discrete wire elements to be joined without the use of a third element. There is also a need for wire joining processes that facilitate manufacturing and decrease costs. Additionally, it would be desirable to have a wire joining technique that produces a joint with a smooth continuous outer surface at the joint. 
     SUMMARY 
     The invention is directed to a process for forming a small diameter elongated device for use in a medical procedure, such as a guidewire, by joining a first elongated member to a second elongated member by forming a male end at an extremity formed of a first continuous material of the first elongated member, forming a female end at an extremity formed of a second continuous material of a second elongated member, inserting the male end into the female end, and permanently securing the male end to the female end. In one embodiment, formation of the female end is achieved by forming a hole by electrical discharge machining. In another embodiment, formation of the female end consists of forming a hole by laser drilling. Other focused energy methods are also suitable for forming the female end. Forming the male end can be carried out by mechanical abrasion, such as plunge grinding. Friction filting, crimping, soldering, gluing, brazing, laser welding, combinations thereof, or other suitable means may also be used to permanently secure the male end within the female end. 
     The invention is also directed to an elongated device for performing a medical procedure with a first elongated member having a male end at an extremity formed of a first continuous material permanently secured within a female end at an extremity of a second elongated member, the extremity of the second elongated member being formed of a second continuous material. The male and female ends being formable by the methods discussed above. In one embodiment, one elongated member is formed from stainless steel while the other elongated member is formed from a shape memory material such as Nitinol. In other embodiments, any suitable biocompatible material may be used for the elongate members or extremities thereof, including other metals, polymeric compositions or composites. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view, partially in section, of a three component joint formed by conventional prior art methods. 
     FIG. 2 is an elevational view, partially in section, of an elongate member with a female end at an extremity and an elongate member with a male end at an extremity, embodying features of the invention. 
     FIG. 3 is an elevational view, partially in section, of the elongate members shown in FIG. 2 secured together and embodying features of the invention. 
     FIG. 4 is a cross sectional view of the elongate members shown in FIG. 3 taken along lines  4 — 4  in FIG.  3 . 
     FIG. 5 is an elevational view in partial section of a guidewire having features of the invention. 
     FIG. 6 is a transverse cross sectional view of the guidewire of FIG. 5 taken along lines  6 — 6  in FIG.  5 . 
     FIG. 7 is a transverse cross sectional view of the guidewire of FIG. 5 taken along lines  7 — 7  in FIG.  5 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a portion of a guidewire  10  with wire joint  12  formed by conventional methods, having a first core wire  14  and a second core wire  16  coaxially disposed within hypotube  18 . First and second core wires  14  and  16  are secured to hypotube  18  in a conventional manner, such as soldering, gluing or welding. The requirement of the hypotube to join the core wire segments necessitates two points of attachment. The hypotube joint creates two transition points  20  and  22  that are larger in diameter than the nominal diameter of the first and second core wires  14  and  16 . 
     FIGS. 2-4 show a portion of a guidewire  24  joined by methods having features of the invention. Specifically, FIG. 2 shows a first core wire  25  having a female end  26  at an extremity  27 . As shown in FIG. 2, extremity  27  of the first core wire  25  is formed of a continuous material which is a monogeneous structural extension of the first core wire  25  generally. The continuous material of the first core wire  25  extends to the extremity  27  and female end  26  without any additional components or materials. A hole  28  of the female end  26  can be formed by electrical discharge machining (EDM). Depending on the axial depth and diameter of hole  28 , the cycle time for a hole EDM on a guidewire end will be about 10-30 sec. The hole  28  of the female end  26  may also be formed by other suitable focused energy removal means, such as laser drilling. The removal method should be operable with the precise tolerances required to form a small diameter hole in the wire. Second core wire  30  has a male end  31  configured to mate with hole  28  of female end  26 . The male end  31  may be formed by removing material from the end of core wire  30  by any suitable means so as to produce a reduced diameter portion  31 A. The reduced diameter portion  31 A extends axially from a flanged portion  33 . An abrasive operation such as plunge grinding may be used to form the male end  31 . Other means of forming male end  31  include drawing the wire, pressing the wire, melting the wire and molding it or chemical removal of the wire material. Extremity  32  of second core wire  30  is formed of a continuous material which is a homogeneous structural extension of the second core wire  30  generally. The continuous material of the second core wire  30  extends axially to extremity  32  and male end  31  without any additional components or materials. 
     As shown in FIG. 3, and the cross section of, FIG. 4, male end  31  fits closely within female end  26  and the two ends may be secured by soldering, gluing, welding, brazing and the like, to form wire joint  34 . Alternatively, male end  31  and female end  26  may be configured so that press fitting them generates sufficient friction to secure them together. It is also possible for the joint  34  to be swaged or crimped to secure the wire cores  26  and  30  at joint  34 . Regardless of the method of attachment, it is important to allow the transmission of torque through the joint  34  to maintain steerability of the guidewire  24 . Joining core wires  26  and  30  as shown in FIG.  3  and discussed above requires only one point of attachment and creates only one effective transition point  36 . These features improve the reliability of guidewire  24  by creating fewer failure points and improving the crossing characteristics by creating a joint  34  with a smooth continuous outer surface at the transition point  36 . 
     The joining methods of the invention can allow a guidewire  40 , shown in FIG. 5, to be formed with two adjacent components joined together to impart different handling characteristics to each section. In the embodiment shown in FIG. 5, an elongated proximal core portion  41  or a proximal section  41  is formed from stainless steel while a distal core portion  42  or a distal section  42  is formed from a nickel-titanium allow having pseudo-elastic or super-elastic characteristics, such as NiTi, commonly called NITINOL. Other metals having super- or pseudo-elastic properties may also be desirable. The invention is not limited to metals as other suitable bio-compatible materials such as polymers or composites may be used. 
     The proximal section  41  of the guidewire  40  is generally about 130 to about 140 cm in length with an outer diameter of about 0.006 to 0.018 inch for coronary use. The distal section  42  can have nominal transverse dimensions similar to those of proximal section  41 , however, the distal section  42  typically has one or more tapered distal portions  43  and  44  which taper distally to a reduced diameter or transverse dimension. Larger diameter guidewires up to about 0.038 inch may be employed in peripheral arteries and other body lumens. Guidewire  40  may also have a flexible body member such as a helical coil  45  disposed about the distal section  42 . A shapable member  46 , which may be the distal extremity of the distal section  42 , or a separate shaping ribbon  46 , as shown in FIG. 5, is secured to the distal end  47  of the distal section  42 . The distal section  42  extends through the helical coil  45  and is secured to a rounded plug  48  at a distal end  51  of the helical coil  45 . The lengths of the tapered distal portions  43  and  44  can range from about 2 to about 20 cm, depending upon the stiffness or flexibility desired in the final product. The helical coil  45  is about 20 to about 45 cm in length, has an outer diameter about the same size as the diameter of the proximal section  41 , and is made from wire about 0.002 to 0.003 inch in diameter. The shapable member  46  can have a ribbon with a rectangular transverse cross-section, usually having dimensions of about 0.001 by 0.003 inch. 
     The proximal section  41  has a female end  52  with a hole  52 A disposed at a distal extremity or end  53  of the proximal section  41 . A male end  54  with a reduced diameter portion  54 A extending proximally from a flanged portion  54 B is disposed at a proximal extremity or end  55  of distal section  42 . The female end  52  and male end  54  can be engaged and secured in a similar fashion to the female end  28  and the male end  32  of the embodiment shown in FIG.  3 . The reduced diameter portion  54 A of the male end  54  can have a length of about 0.005 to about 0.20 inch, specifically about 0.02 to about 0.06 inch. The depth of hole  52 A of the female end  52  should be comparable to the length of the reduced diameter portion  54 A of the male end  54 . 
     Described herein are preferred embodiments, however, one skilled in the art that pertains to the present invention will understand that there are equivalent alternative embodiments. Although the described embodiments have comprised guidewires, the invention can be used to create other solid, elongated, small diameter medical devices from two or more discrete sections. For example, devices such as pacing leads may be formed using the methods disclosed herein.