Abstract:
Disclosed is a guide wire having a coil surrounding a core of the guide wire and a stiffness transition element. The stiffness transition element is configured to provide a smooth stiffness transition from the distal end of the guide wire to the coil and/or the core of the guide wire. The stiffness transition element may be formed of any medical grade polymer.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to guide wires. More specifically, the invention relates to a novel approach to making a smoother transition in stiffness along the length of a guide wire which is more stiff at the proximal end and less stiff at the distal end. Those skilled in the art will recognize the benefits of applying the present invention to similar fields not discussed herein. 
     BACKGROUND OF THE INVENTION 
     Guide wires are used in a variety of medical applications including intravascular, gastrointestinal, and urological. A common vascular application is Percutaneous Transluminal Coronary Angioplasty (PTCA). This procedure can involve inserting a guide wire through an incision in the femoral artery near the groin, advancing the guide wire over the aortic arch, into a coronary artery, and across a lesion to be treated in the heart. Similarly, angioplasty performed in other parts of the anatomy is called Percutaneous Transluminal Angioplasty (PTA) and may also involve the use of a guide wire. Typical vascular guide wires are 50 cm or 300 cm in length, and are 0.010-0.038 inches in diameter depending upon the application. 
     Common gastrointestinal uses of guide wires include endoscopic procedures in which an endoscope may be inserted into the mouth and advanced through the esophagus to the bile duct, the cystic duct, or the pancreatic duct. A guide wire is then threaded through a lumen in the endoscope and into the bile duct, cystic duct, or pancreatic duct. Once the distal tip of the guide wire is located in a position desired to be treated, a catheter having a medical instrument on it distal end is advanced over the guide wire and to the treatment area. The guide wire and the catheter may then be observed through the endoscope as treatment occurs. 
     Urological uses of guide wires include the placement of ureteral stents. Ureteral stenting is required when the normal flow of urine from the kidney into the bladder is compromised perhaps by tumor growth, stricture, or stones. Generally, the procedure involves the insertion of a ureteroscope through the urethra and into the bladder. A guide wire is then advanced through the ureteroscope and into a ureter. The wire is then forced through the compromised portion of the ureter. Once the guide wire is in place, a ureteral stent is advanced over the guide wire and into position in the ureter. The guide wire may then be removed and the stent will maintain the patency of the fluid path between the kidney and the bladder. The procedures described above are but a few of the known uses for guide wires. 
     Pushability, kink resistance, torqueability and bendability are closely related and important features of a guide wire. It is important that force applied at the proximal end of a guide wire is completely transferred to the distal end of the guide wire. A guide wire must exhibit good bendability. This characteristic is a balance between adequate flexibility to navigate a tortuous lumen and suitable rigidity to support tracking of another device such as a catheter. Torqueability is closely related to the torsional rigidity of the wire and is ultimately demonstrated by how well rotation imparted to the proximal end of the guide wire is translated to the distal end of the guide wire. 
     Kink resistance is also an important characteristic of a guide wire. Kink resistance is closely related to the stiffness of the wire. Very stiff wires often provide good pushability (axial rigidity) but poor kink resistance. Kink resistance is measured by the ability of the guide wire to be forced into a relatively tight bend radius without permanently deforming the wire. 
     Many guide wires use stiffness by creating a transition from relatively more stiff in the proximal end to relatively less stiff in the distal end. This provides the best combination of pushability and the ability to navigate tortuous vessels. The transition in stiffness may easily be seen by simply bending the wire about an arch. FIG. 1 depicts a prior art wire  10  which shows with a flat spot  20  in the arch of the wire. A potential kink point may be created where the transition is not smooth. Furthermore, the unsmooth or flat transition region causes resistance when the wire is advanced through a vessel. The ideal transition is a smooth and continuous transition from stiffer to less stiff. The ideal transition is depicted in FIG. 2 where wire forms a smooth and continuous arch. 
     Several different types of guide wires are well known in the art. One type of wire is characterized by a solid metal core surrounded by a metal coil. Typical metals for the core may include spring steels and stainless steels. The distal tip of the core may also be ground to a taper to provide added flexibility near the tip. Coils may be made of the same variety of metals used as core materials. The coil may be made of round wire or flat wire and may surround the entire length of the core or only a portion of the core. The coil usually is formed by helically wrapping the wire around a mandrel, removing the mandrel, and inserting the core into the coil. The pitch of the wire may be varied along the length of the coil to vary the stiffness of the coil. 
     Traditional coil over core wires provide good axial stiffness and hence improved possibility. Traditional coil over core wires also provide dramatically improved kink resistance over stainless steel wires and achieve a smooth transition in stiffness by using a ground core. Some coil over core wires also use a polymer jacket or sleeve to provide improved lubricity and wire movement. However, a flat spot in the stiffness transition may be created where the sleeve stops leaving only the coil over core construction. A coil over core wire having at least a portion covered by a polymer would therefore be improved if it had a smoother transition near the termination of the polymer sleeve. 
     SUMMARY OF THE INVENTION 
     The present invention improves upon the prior art by providing a coil over core guide wire having a smooth stiffness transition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a prior art guide wire bent about an arch. 
     FIG. 2 depicts an ideal guide wire bent about an arch. 
     FIG. 3 depicts an embodiment of the invention. 
     FIG. 4 depicts another embodiment of the invention. 
     FIG. 5 depicts another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description should be read with reference to the drawings in which like elements in different drawing are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. 
     Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements. All other elements employ that which is known to those skilled in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that may also be used. 
     Construction of a coil over core guide wire is described in copending patent application Ser. No. 09/078,946, filed May 14, 1998, which is herein incorporated by reference. 
     FIG. 3 depicts an embodiment of the invention where core wire may be formed of any biocompatible plastic or metal. Core wire  30  may be formed of a variety of metals including stainless steals such as 316, Eligiloy, or MP35N. Core wire  30  may also be formed of alloys of nickel and titanium such as Nitinol where the nickel titanium alloy is heat treated such that the wire is linearly elastic or superelastic. Core wire  30  may be about 125-300 cm in length and may further have a tapered distal portion  40 . 
     Surrounding core wire  30  may be a coil  50 . Coil  50  may be formed of any biocompatible metal or plastic. Coil  50  may be formed of stainless steals or nickel titanium alloys. Coil  50  may be formed of flat ribbon or wire that is ovoid, rectangular or round in cross-section. Coil  50  may have tightly packed turns where each turn touches the preceding turn or may have loosely spaced turns. Coil  50  may further have turns which change in spacing or which change in pitch along the length of coil  50 . 
     Coil  50  may have an interior diameter which is greater than the outside diameter of core wire  30  or may have an interior diameter which is approximately equal to the outside diameter of core wire  30 . The diameter of coil  50  may vary along the length of the coil. In a preferred embodiment, the coil  50  may have a uniform diameter along its entire length. Where core wire  30  has a tapered portion  40 , the inside diameter of the coil  50  may be greater than the outside diameter of the tapered portion  40  which thereby forms an annular space  60 . 
     Surrounding tapered portion  40  is polymer tip  70 . Polymer tip  70  may best, formed of any suitable medical grade polymer including Plexar, nylon, polypropylene, polyurethane, polyethylene, silicone and polyether glycol. In a preferred embodiment, polymer tip  70  may be formed from urethane. Tip  70  has a distal portion  73  and a proximal portion  76  where distal portion  73  may generally be of a diameter approximately equal to the outside diameter of coil  50  and proximal portion  76  may generally have a outside diameter less than the inside diameter of coil  50 . Second annular space  65  may be formed between the outside of proximal portion  76  and the inside of coil  50 . 
     Annular space  65  may be filled with a transition element  80 . Transition element  80  may be formed of any suitable medical grade polymer including silicone. In a preferred embodiment, transition element  80  may be formed of a polymer having a hardness that is less than the hardness of tip  76  where tip  76  may be about 45 D and transition element  80  may be approximately 25 D. 
     Wire  10  may be assembled by placing transition element  80  about proximal portion  76  and then sliding the assembled tip  70  and transition element  80  over core  30  and into annular space  60 . Following this step, the entire assembly may be bond together using common bonding practices including adhesives. Alternatively, wire  10  may be heated to cause transition element  80  and polymer tip  70  to flow together. Transition element  80  and polymer tip  70  may also flow into coil  50  and ultimately become bonded to wire  10 . 
     Alternatively, polymer tip  70  may be formed without proximal portion  76  (not shown). Wire  10  may then be assembled by placing transition element  80  into annular space  60 . Tip  70  may then be place about core  30 . Wire  10  may then be subject to heating sufficient to cause polymer tip  70  to flow into the annular space formed between the inside diameter of transition element  80  and core  30 . Ultimately then, transition element  80  may bond to core  30 , coil  50  and tip  70 . 
     FIG. 4 depicts an alternative embodiment of the invention where like elements are similarly numbered. In this embodiment, transition element  80  may be formed to closely fit about tapered portion  40 . The outside diameter of transition element  80  may be sized such that an annular space is formed between transition element  80  and the inside diameter of coil  50 . Polymer tip  70  may then have a proximal section  76  which may fit into the annular space formed between the outside diameter of transition element  80  and the inside diameter of coil  50 . The entire assembly may then be bonded as previously described. Alternatively, polymer tip  70  may be formed without proximal section  76  (not shown) and heated such that polymer tip  70  flows into the annular space formed between the outside diameter of transition element  80  and the inside diameter of coil  50 . 
     FIG. 5 depicts another embodiment of the invention where like elements are similarly numbered. In this embodiment, transition element  80  may be closely formed to fit about tapered portion  40 . Transition element  80  may further have an outside diameter which may approximately the same as the inside diameter of coil  60 . Transition element  80  may be positioned about tapered portion  40  such that the distal end of transition element does not match with the distal end of coil  60  and thereby leaves an annular space distal of transition element  80  which is formed by the space between the outside diameter of tapered section  40  and the inside diameter of coil  60 . Polymer tip  70  may then be formed with a proximal portion  76  sized to fit in the annular space formed by the space between the outside diameter of tapered section  40  and the inside diameter of coil  60 . The entire tip assembly may then be bonded as previously described. 
     Polymer tip  70  may be formed without a proximal section  76  (not shown). The tip assembly may then be bonded by heating wire  10  such that polymer tip  70  flows into the annular space formed by the space between the outside diameter of tapered section  40  and the inside diameter of coil  60 . 
     Alternatively, transition element  80  may have its distal end aligned with the distal end of coil  50 . The tip assembly may then be bonded as described above. 
     While the specification describes the preferred designs, materials, methods of manufacture and methods of use, those skilled in the art will appreciate the scope and spirit of the invention with reference to the appended claims.