Patent Publication Number: US-2022226618-A1

Title: Mold for forming solder distal tip for guidewire

Description:
BACKGROUND 
     This invention relates to the field of guidewires for advancing intraluminal devices such as stent delivery catheters, balloon dilatation catheters, atherectomy catheters and the like within body lumens. 
     In a typical coronary procedure a guiding catheter having a preformed distal tip is percutaneously introduced into a patient&#39;s peripheral artery, e.g., femoral or brachial artery, by means of a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. There are two basic techniques for advancing a guidewire into the desired location within the patient&#39;s coronary anatomy, the first is a preload technique which is used primarily for over-the-wire (OTW) devices and the second is a bare wire technique which is used primarily for rapid exchange type systems. With the preload technique, a guidewire is positioned within an inner lumen of an OTW device such as a dilatation catheter or stent delivery catheter with the distal tip of the guidewire just proximal to the distal tip of the catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire is first advanced out of the distal end of the guiding catheter into the patient&#39;s coronary vasculature until the distal end of the guidewire crosses the arterial location where the interventional procedure is to be performed, e.g., a lesion to be dilated or a dilated region where a stent is to be deployed. The catheter, which is slidably mounted onto the guidewire, is advanced out of the guiding catheter into the patient&#39;s coronary anatomy over the previously introduced guidewire until the operative portion of the intravascular device, e.g., the balloon of a dilatation or a stent delivery catheter, is properly positioned across the arterial location. Once the catheter is in position with the operative means located within the desired arterial location, the interventional procedure is performed. The catheter can then be removed from the patient over the guidewire. Usually, the guidewire is left in place for a period of time after the procedure is completed to ensure reaccess to the arterial location. For example, in the event of arterial blockage due to dissected lining collapse, a rapid exchange type perfusion balloon catheter can be advanced over the in-place guidewire so that the balloon can be inflated to open up the arterial passageway and allow blood to perfuse through the distal section of the catheter to a distal location until the dissection is reattached to the arterial wall by natural healing. 
     With the bare wire technique, the guidewire is first advanced by itself through the guiding catheter until the distal tip of the guidewire extends beyond the arterial location where the procedure is to be performed. Then a rapid exchange (RX) catheter is mounted onto the proximal portion of the guidewire which extends out of the proximal end of the guiding catheter, which is outside of the patient. The catheter is advanced over the guidewire, while the position of the guidewire is fixed, until the operative means on the RX catheter is disposed within the arterial location where the procedure is to be performed. After the procedure, the intravascular device may be withdrawn from the patient over the guidewire or the guidewire advanced further within the coronary anatomy for an additional procedure. 
     Conventional guidewires for angioplasty, stent delivery, atherectomy and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil or a tubular body of polymeric material disposed about the distal portion of the core member. A shapeable member, which may be the distal extremity of the core member or a separate shaping ribbon, which is secured to the distal extremity of the core member, extends through the flexible body and is secured to the distal end of the flexible body by soldering, brazing or welding which forms a rounded distal tip. Torqueing means are provided on the proximal end of the core member to rotate, and thereby steer, the guidewire while it is being advanced through a patient&#39;s vascular system. 
     For certain procedures, such as when delivering stents around a challenging take-off, e.g., a shepherd&#39;s crook, tortuosities or severe angulation, substantially more support and/or vessel straightening is frequently needed from the guidewire than normal guidewires can provide. Guidewires have been commercially introduced for such procedures which provide improved distal support over conventional guidewires, but such guidewires are not very steerable and in some instances are so stiff that they can damage vessel linings when advanced therethrough. What has been needed and heretofore unavailable is a guidewire which provides a high level of distal support with acceptable steerability and little risk of damage when advanced through a patient&#39;s vasculature. 
     In addition, conventional guidewires using tapered distal core sections as discussed above can be difficult to use in many clinical circumstances because they have an abrupt stiffness change along the length of the guidewire, particularly where the tapered portion begins and ends. As a guidewire having a core with an abrupt change in stiffness is moved through tortuous vasculature of a patient, the physician moving the guidewire can feel the abrupt resistance as the stiffness change is deflected by the curvature of the patient&#39;s vasculature. The abrupt change in resistance felt by the physician can hinder the physician&#39;s ability to safely and controllably advance the guidewire through the vasculature. What has been needed is a guidewire that does not have an abrupt change in stiffness, particularly in the portions of the distal section that are subject to bending in the vasculature and guiding catheter. The present invention satisfies these and other needs by providing distal tip integrity, kink resistance, enhanced torque response, improved distal tip radiopacity, and a smooth transition region. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the invention a guidewire has a radiopaque inner coil and a substantially non-radiopaque outer coil. The inner coil and the outer coil are attached to the distal end of the guidewire and the outer coil covers the inner coil and extends proximally along the guidewire proximal of a proximal end of the inner coil. The inner coil is formed from a radiopaque material so that the physician can easily detect the location of the distal end of the guidewire under fluoroscopy during a procedure. Both the inner coil and the outer coil can be formed from a single strand of wire or a multifilar strand of wire. 
     In another embodiment, a mold is used for forming a solder distal tip or solder joint at the distal end of the guidewire. The solder distal tip attaches the distal end of the guidewire and the distal end of the inner coil and the distal end of the outer coil (if present) together. It is important that the solder distal tip be uniform from one guidewire to the next, and repeatable in structural formation. A mold, including a split mold, provides a bullet shaped solder tip or a micro-J shape tip at the distal end of the guidewire to attach the inner and outer coils to the guidewire. Other shapes of solder tips are contemplated such as cone shape, truncated cone shape, and a solder joint having a textured surface. 
     In another embodiment, a laser is used to form dimples on the solder joint connecting the distal end of the guidewire. A laser is used to form dimples on the distal end of the solder joint such that the dimples resemble the dimples on a golf ball and can have specific spacing and patterns. The laser can be programmed to provide dimples that are spaced apart and have specific diameters and depths depending on the requirements of the user. 
     In another embodiment, the present invention guidewire increases the torqueability of the guidewire without negatively affecting the bending stiffness and functionality of the guidewire by using different cross-section shapes of the coils. For example, the different cross-section shapes of the coils can include I-beam, vertical rectangular, vertical ellipse, square, peanut shape, vertical hexagonal, horizontal hexagonal, and horizontal ellipse cross-sections. Considering the constraints due to manufacturing, dimensions, and tolerances, the I-beam, peanut shape, vertical rectangular and vertical ellipse shaped cross-sections are more favorable than a conventional round cross-section coil, for increasing torquability without negatively affecting the bending stiffness of the guidewire. The different cross-section shaped coils can be used to form a single wire coil or a multifilar coil. 
     In another embodiment a guidewire tip shaping tool forms a micro-J shape in the distal tip of the guidewire. The shaping tool is provided to the physician with the guidewire so that the physician can select the amount of bend in the distal end of the guidewire using the shaping tool. Traditionally, the physician would bend the distal end of the guidewire with his/her hands, which lacked control of the bend angle and shape of the bend. The shaping tool includes a number of cavities having a different angular orientation and depth so that the physician can select the length of the bend and the angle of the bend in the distal tip of the guidewire. The shaping tool is spring loaded toward the open position so that the guidewire distal end can be inserted into a cavity. Once the guidewire is inserted into a cavity, the physician gently presses the ends of the shaping tool to overcome the spring force and shift an inner tube having the cavity relative to an outer tube to form the bend in the distal tip of the guidewire. The predetermined angle and length of the cavities provide a consistent micro-J shape for the physician to use. 
     In another embodiment of the invention, the distal section of the guidewire is reduced in cross-section to be more flexible when navigating tortious vessels. In this embodiment, a parabolic distal section of the guidewire includes a significant portion of the distal section having been ground down to form a continuous taper. The continuous taper is formed by a parabolic grind along the distal section of the guidewire. The parabolic grind provides a smooth curvilinear transition along the distal section of the guidewire that is highly flexible and yet maintains a linear change in stiffness thereby providing excellent torque and tactical feedback to the physician when advancing the guidewire through tortuous anatomy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational view of a prior art guidewire depicting a coil at the distal end of the guidewire. 
         FIG. 2  is an elevational view of a guidewire of the invention depicting an inner coil and an outer coil at the distal end of the guidewire. 
         FIG. 3  is an elevational view of a multifilar guidewire for use as an inner coil or an outer coil on a guidewire. 
         FIG. 4A  is an elevational view of an eight filar strand coil for use as an inner or outer coil on the distal end of the guidewire. 
         FIG. 4B  is a longitudinal cross-sectional view of the eight filar strand coil of  FIG. 4A . 
         FIG. 5  is a chart depicting the torque analysis for guidewires of the invention having different filar strand coils. 
         FIG. 6  is a graph depicting the guidewires shown in  FIG. 5  and showing the radiopacity of the distal portion of the guidewires including the coils. 
         FIG. 7A  is an elevational view of a mold for forming a solder joint on the distal end of a guidewire. 
         FIG. 7B  is a cross-sectional view taken along lines  7 B- 7 B of the mold of  FIG. 7A . 
         FIG. 8A  is an elevational view of a mold for forming a solder joint on the distal end of a guidewire. 
         FIG. 8B  is an elevational view of the split mold of  FIG. 8A . 
         FIG. 9A  is a cross-sectional view of a mold used for forming a solder joint at the distal end of a guidewire and depicting the cavity for receiving a molten metal. 
         FIG. 9B  is a top view of the solder joint formed by the mold of  FIG. 9A . 
         FIG. 9C  is an elevational view of the solder joint formed by the mold of  FIG. 9A . 
         FIG. 10A  is an elevational view of a mold for forming a solder joint having a micro-J shape. 
         FIG. 10B  is an elevational view of a mold for forming a solder joint having a micro-J shape. 
         FIG. 11A  is a top view of a joint depicting a series of dimples formed by a laser. 
         FIG. 11B  is an elevational view of the joint of  FIG. 11A . 
         FIG. 12A  is a top view of a joint depicting a series of dimples formed by laser. 
         FIG. 12B  is an elevational view of the joint of  FIG. 12A . 
         FIG. 12C  is an enlarged top view of the joint of  FIG. 12A . 
         FIG. 12D  is a side view depicting one dimple formed in the joint depicted in  FIG. 12C . 
         FIG. 12E  is a chart depicting test data comparing the time to pass through a lesion for the laser dimpled guidewire compared to a commercially available guidewire. 
         FIG. 13  is an elevational view of a prior art coil having a circular or round cross-section wire. 
         FIG. 14  is a chart depicting the elastic modulus, yield strength, and ultimate strength of  304 V stainless steel. 
         FIGS. 15A and 15B  are elevational and front views of a prior art coil having a circular or round cross-section. 
         FIGS. 16A and 16B  are elevational and front views respectively, of a coil having an I-beam cross-section. 
         FIGS. 17A and 17B  are elevational and front views respectively, of a coil having a vertical rectangular cross-section. 
         FIGS. 18A and 18B  are elevational and front views respectively, of a coil having a vertical ellipse cross-section. 
         FIGS. 19A and 19B  are elevational and front views respectively, of a coil having a square cross-section. 
         FIGS. 20A and 20B  are elevational and front views respectively, of a coil having a vertical hexagonal configuration. 
         FIGS. 21A and 21B  are elevational and front views respectively, of a coil having a horizontal hexagonal cross-section. 
         FIGS. 22A and 22B  are elevational and front views respectively, of a coil having a flat cross-section. 
         FIGS. 23A and 23B  are elevational and front views respectively, of a coil having a horizontal elliptical cross-section. 
         FIG. 24  depicts the torque response of single wire coils having different cross-sections shown in  FIGS. 15A-23B . 
         FIG. 25  is a chart showing the bending stiffness of the coils having different cross-sections as depicted in  FIGS. 15A-23B . 
         FIG. 26  is an elevational view of a distal end of a guidewire inserted into a fixture depicting the angular shape of the micro-J bend in the distal tip of the guidewire. 
         FIG. 27A  is an exploded perspective view of a shaping tool for forming a micro-J bend in the distal end of a guidewire. 
         FIG. 27B  is an elevational perspective view of a shaping tool for forming a micro-J bend in the distal end of a guidewire. 
         FIG. 28A  is an elevational view of a shaping tool in an open position for forming a micro-J bend in the distal end of a guidewire. 
         FIG. 28B  is an elevational view of a shaping tool in a closed position forming a micro-J bend in the distal end of the guidewire. 
         FIG. 29  is an enlarged circular view taken along lines  29 - 29  depicting a channel and a cavity for receiving the distal end of a guidewire. 
         FIG. 30  is an enlarged circular view of the cavity of  FIG. 29  in which a guidewire has been inserted through the channel and in to the cavity and is being bent into a micro-J shape. 
         FIG. 31  is an elevational view of a prior art guidewire depicting a distal section having multiple tapered sections. 
         FIG. 32  is an elevational view of a guidewire depicting a distal section having a parabolic grind profile. 
         FIG. 33  is a graph depicting the bending stiffness along the distal section of the guidewires shown in  FIGS. 31 and 32 . 
         FIG. 34  is a schematic depicting the tapered distal section of a prior art guidewire kinking in a side branch vessel. 
         FIG. 35  is a graph of a 0.014 inch diameter guidewire depicting a distal section having a parabolic grind profile. 
         FIG. 36  is a graph of a 0.014 inch diameter guidewire depicting a distal section having a parabolic grind profile. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Prior Art Guidewires 
     Prior art guidewires typically include an elongated core wire having a flexible atraumatic distal end. A prior art guidewire is shown in  FIG. 1  and includes an elongated core member  11  with a proximal core section  12 , a distal core section  13 , and a flexible body member  14  which is fixed to the distal core section. The distal core section  13  has a tapered segment  15 , a flexible segment  16  which is distally contiguous to the tapered segment  15 , a distal end  13   a,  and a proximal end  13   b.  The distal section  13  may also have more than one tapered segment  15  which have typical distally decreasing tapers with substantially round transverse cross sections. 
     The core member  11  may be formed of stainless steel, NiTi alloys or combinations thereof. The core member  11  is optionally coated with a lubricious coating such as a fluoropolymer, e.g., TEFLON® available from DuPont, which extends the length of the proximal core section. Hydrophilic coatings may also be employed. The length and diameter of prior art guidewire  10  may be varied to suit the particular procedures in which it is to be used and the materials from which it is constructed. The length of the guidewire  10  generally ranges from about 65 cm to about 320 cm, more typically ranging from about 160 cm to about 200 cm, and preferably from about 175 cm to about 190 cm for the coronary anatomy. The guidewire diameter generally ranges from about 0.008 inch to about 0.035 inch (0.203 to 0.889 mm), more typically ranging from about 0.012 inch to about 0.018 inch (0.305 to 0.547 mm), and preferably about 0.014 inch (0.336 mm) for coronary anatomy. 
     The flexible segment  16  terminates in a distal end  18 . Flexible body member  14 , preferably a coil, surrounds a portion of the distal section of the elongated core  13 , with a distal end  19  of the flexible body member  14  secured to the distal end  18  of the flexible segment  16  by the body of solder  20 . The proximal end  22  of the flexible body member  14  is similarly bonded or secured to the distal core section  13  by a body of solder  23 . Materials and structures other than solder may be used to join the flexible body  14  to the distal core section  13 , and the term “solder body” includes other materials such as braze, epoxy, polymer adhesives, including cyanoacrylates and the like. 
     The wire from which the flexible body  14  is made generally has a transverse diameter of about 0.001 to about 0.004 inch, preferably about 0.002 to about 0.003 inch (0.05 mm). Multiple turns of the distal portion of the coil may be expanded to provide additional flexibility. The coil may have a diameter or transverse dimension that is about the same as the proximal core section  12 . The flexible body member  14  may have a length of about 2 to about 40 cm or more, preferably about 2 to about 10 cm in length. A flexible body member  14  in the form of a coil may be formed of a suitable radiopaque material such as platinum or alloys thereof or formed of other material such as stainless steel and coated with a radiopaque material such as gold. 
     The flexible segment  16  has a length typically ranging about 1 to about 12 cm, preferably about 2 to about 10 cm, although longer segments may be used. The form of taper of the flexible segment  16  provides a controlled longitudinal variation and transition in flexibility (or degree of stiffness) of the core segment. The flexible segment is contiguous with the core member  11  and is distally disposed on the distal section  13  so as to serve as a shapable member. 
     Guidewire Having Radiopaque Inner Coil 
     In keeping with the invention, in one embodiment shown in  FIGS. 2-6 , a guidewire  30  has an elongated core member  32  with a proximal core section  34  and a distal core section  36 . The distal core section  36  is preferably tapered, having a tapered segment  38  that tapers to a smaller diameter moving from the proximal end  40  of the guidewire toward the distal end  42  of the guidewire. The elongated core member  32  is preferably formed from stainless steel, however, it also can be formed from other metals or metallic alloys known in the art. 
     In order to improve radiopacity, the guidewire  30  shown in  FIGS. 2-6  includes a radiopaque inner coil  44  positioned over the elongated core member at the distal end  42  thereof. The inner coil  44  may be 3 cm in length and have a distal end  46  that is coterminous with the distal end  42  of the elongated core member  32 . While 3 cm is a preferred length for the radiopaque inner coil  44 , the length of the inner coil  44  can range from 0.5 cm to 15 cm as necessary to satisfy the needs of the physician. The radiopaque inner coil  44  has a proximal end  48  with multiple coils  50  extending from the proximal end  48  to the distal end  46 . The radiopaque inner coil  44  is made from a radiopaque material taken from the group of radiopaque metals including platinum (Pt), palladium (Pd), iridium (Ir), tungsten (W), tantalum (Ta), rhenium (Re) and gold (Au). In one embodiment, shown in  FIG. 2 , the radiopaque inner coil  44  is formed from a single filar coil  50  of wire, and the diameter can vary as required for a balance in radiopacity, flexibility, torquability and kink resistance (durability). In another embodiment, shown in  FIG. 3 , the radiopaque inner coil  44  is formed from a four filar coil  52  of wire. The four filar coil  52  can be made with drawn, filled tubing (tube filled radiopaque material or sandwiched) which is known in the prior art. The inner coil  44  can be formed using any number of filars, such as the eight filar coil shown in  FIGS. 4A and 4B . In one embodiment, the eight filar coil of  FIGS. 4A and 4B  is 31 cm long, has an outer diameter of 0.0135±0.0005 inch, an inner diameter of 0.0095 inch, a pitch of 0.193 inch, a wire diameter of 0.002 inch, and a spacing between the eight filar segments of 25% of the wire diameter. These dimensions are representative and can vary depending upon different needs. Importantly, all of the various coil shapes can be formed of the radiopaque metals listed herein so that the radiopaque inner coil  44  is radiopaque and easily seen by the physician under fluoroscopy. 
     The embodiment in  FIGS. 2-6  also includes a non-radiopaque outer coil  56  that has an inner diameter  58  that is greater than an outer diameter  60  of the radiopaque inner coil  44  and greater than the outer diameter of the elongated core member  32 . The non-radiopaque outer coil  56  is formed from a non-radiopaque material including stainless steel (SS), cobalt-chromium (CoCr), and nickel-titanium (NiTi) alloys. The non-radiopaque outer coil can range in length from 10 cm to 60 cm from a distal end  62  to a proximal end  64 . In one embodiment, the non-radiopaque outer coil  56  is 30 cm long. 
     As shown most clearly in  FIG. 2 , the distal end  46  of the radiopaque inner coil  44 , the distal end  42  of the guidewire  30 , and the distal end  62  of the non-radiopaque outer coil  56  all are connected together by solder, glue, weld or braze. Preferably, a solder ball  66  is formed at the distal end  42  of the guidewire  30  in a known manner to connect the radiopaque inner coil  44  to the non-radiopaque outer coil  56  and to the guidewire distal end  42 . It is important to emphasize that the distal end  46  of the radiopaque inner coil  44  preferably does not contact the distal end  62  of the non-radiopaque outer coil  56 , they are connected together by the solder ball  66 , but after the solder ball  66  is formed, there may be direct contact with each other. The distal end  46  of the radiopaque inner coil  44  does contact the distal end  42  of the elongated core member  32 . The proximal end  48  of the radiopaque inner coil  44  is connected to the elongated core member  32  by first solder joint  70 , weld, glue, or braze, in a known manner. The proximal end  48  of the radiopaque inner coil  44  is not attached to the non-radiopaque outer coil  56 . The proximal end  64  of the non-radiopaque outer coil  56  is attached to the elongated core member  32  by second solder joint  72 , weld, glue, or braze, in a known manner. The first solder joint  70  is proximal of the solder ball  66  and distal of the second solder joint  72 . The proximal end  64  of the non-radiopaque outer coil  56  is not connected to any portion of the radiopaque inner coil  44 , thereby providing a seamless outer surface  68  along non-radiopaque outer coil  56  with no solder joint with the radiopaque inner coil to create a stiffness problem. Preferably, as shown in  FIG. 2 , there is a gap between the elongated core member  32  and the inner coil  44  and the outer coil  56 , and a gap between the inner coil  44  and the outer coil  56  Like the radiopaque inner coil  44 , the non-radiopaque outer coil  56  can be formed from the single filar coil  50 , a four filar coil  56  ( FIG. 3 ), or any number of filar coils such as the eight filar coil shown in  FIGS. 4A and 4B . 
     As shown in the graph in  FIG. 5 , experiments were conducted to determine the effects of multifilar coils on torque. In  FIG. 5 , the Straight Torque was measured for a guidewire having an inner and outer coil with only one filar, a guidewire having an inner and outer coil with four filars, six filars, eight filars, and an inner and outer coil that is laser cut in the form of a vertical rectangle. As can be seen in  FIG. 5 , the single filar coils and multifilar coils of the invention compare favorably in torque performance. 
     Testing also was conducted on guidewires of the invention to measure radiopacity, as seen in  FIG. 6 . The guidewires in Groups  1 - 6  have a radiopaque inner coil and a non-radiopaque outer coil, as disclosed in  FIG. 2 . The radiopacity of the radiopaque inner coil compares favorably under fluoroscopy compared to the commercially available WHISPER® guidewire sold by Abbott Cardiovascular Systems, Santa Clara, Calif. 
     In one embodiment, shown in  FIG. 2 , a proximal section  74  of the guidewire  30  has a silicone based hydrophobic coating and a polytetrafluoroethylene coating (PTFE). A distal section  76  has a polyvinylpyrrolidone hydrocoat coating (PVP). Typically, the distal end  42  of the guidewire  30  is uncoated. 
     Mold For Forming Solder Distal Tip 
     Guidewires are available in many different configurations including tip load, support profile, and materials of construction, all selected by a physician for specific clinical case requirements. For certain situations it has been perceived that a guidewire distal tip with a specific geometry provides the physician a mechanical advantage in navigating a tortuous path or occluded segment. In this embodiment, the characteristics of molten solder flow is overcome to contain the molten solder flow within a predetermined shape. Currently, a solder joint is formed at the distal tip of the guidewire attaching the elongated core wire to the outer coils. This solder joint is formed utilizing a conventional soldering iron to heat and flow the solder onto the core wire and secure the coils to the core wire when solidified. The present invention creates a soldered tip by a different means, and allows a specific shape to be achieved by casting the molten solder in a predetermined shape. 
     As shown in  FIGS. 7A-10B , a mold  80  is used to cast the soldered tip, which overcomes many obstacles both in cost and manufacturability. Using the mold  80  to form a predetermined soldered shape provides not only the intended geometry of the solder joint, but also performs the necessary solder bond attaching the guidewire elongated core wire to the outer coils (see  FIGS. 2-6  for example). The mold could be machined as simple as a bullet shaped tip  82  or it could be machined to include a small angular feature to what is referred to as a micro-J shaped tip  84 . Utilizing mold  80  to perform this solder tip operation allows the engineering team the ability to change the configuration to suit the requirements for the product being produced. 
     The mold  80  is made as a solid mold constructed of ceramic or other suitable material able to withstand the temperature required to receive molten solder. The mold  80  has a cavity  86  which receives the molten solder and the distal tip of the guidewire elongated core wire, and the distal end of any coils, if present. The shape of the cavity  86  determines the shape of the solder joint, such as the bullet shaped tip  82  and the micro-J shaped tip  84 . 
     A more complex shape is achieved by utilizing a split mold  90  where a first shell  92  and a second shell  94  are held together while the solder is molten, and then separated to release the solder tip  88 . The split mold  90  has the solder tip  88  configuration machined into a first face  96  and the mirror image machined into a second face  98 . The split mold  90  can be machined as the bullet shaped tip  82  or to include a small angular feature to form the micro-J shaped tip  84 . Various other solder tip  88  shapes can be formed by the spilt mold  90  such as cone shaped, truncated cone shaped, and a textured surface. 
     The method to form the solder tip  88  includes placing the molds into a heating apparatus and allowing the solder to become molten. Once molten, the distal tip of a guidewire elongated core wire is submerged into the mold cavity  86  allowing solder to flow onto the distal tip and the first few winds of the outer coil (if present). A thermally conductive material can be placed around segments of the outer coil, just above the mold cavity  86 , to prevent solder from flowing to undesirable places and control the precise placement of the solder tip  88 . Once the solder has flowed to the specified area, the split mold  90  is rapidly cooled allowing the solder to solidify and bond the guidewire distal tip and coils together. Once cooled, the part may be withdrawn from mold  80 , or the first and second shells  92 ,  94  are separated, and the solder tip  88  can be removed. 
     Utilizing mold  80  to form the solder tip  88  allows the engineering team the ability to quickly change the configuration for the product being produced. 
     Additionally, the first face  96  and the second face  98  can be modified to provide some type of feature or texture depending on the needs of the specific product driven by the application. The mold  80  may possess some form of texture or even have grooves, either raised or recessed, to allow a specific outer surface geometry as required for specified product requirements. For example, as shown in  FIGS. 9A-9C , split mold  90  has angular grooves  100  formed in the mold cavity  86  so that the solder tip  88  has matching angular grooves  102 . 
     While the vast majority of guidewires will use solder to form the bond at the distal tip and connect the coils, some guidewires may use epoxy or another similar material instead of solder. The foregoing description relating to  FIGS. 7A-10B  relating to the solder tip  88  applies as well to other suitable metals and epoxy. 
     Laser To Form Dimpled Joint 
     Generally, most commercially available guidewires have guidewire tips made from solder material or weld material and have a smooth, dome-shaped surface. Such guidewires encounter challenges when used to cross calcified and fibrous tissues, to treat chronic total occlusions (CTO). Certain commercially available guidewires are designed to have higher tip loads in order to treat CTO and penetrate through complex and stenosed lesions. Optimal wire strength, tip load and tip shape help with push-ability and maneuvering the guidewire through the lesions, however, with a smooth tip surface likely will have challenges engaging calcified and fibrous tissues resulting tip deflection and failure to penetrate through the lesion. In one embodiment, shown in  FIGS. 11A-12D , a laser (not shown) is used to form a textured or roughened surface  154  on the solder/weld joint  156  at the distal tip of the guidewire  150 . Commercial lasers, such as a fiber laser, are capable of a focused spot of approximately 0.001 inch, and can provide random or tightly stitched patterns as shown in  FIGS. 11A and 11B , or provide spaced apart dimples  158  as shown in  FIGS. 12A-12C . The dimples  158  resemble the dimples on a golf ball and can have specific spacing and patterns. In one embodiment, the laser creates a series of dimples  158  that have a diameter of 0.001 inch and are spaced apart 0.001 inch. In another embodiment, the dimples  158  have a diameter in the range from 0.0005 inch to 0.005 inch and have spacing between dimples  158  in the range from 0.0005 inch to 0.005 inch. In another embodiment, the laser creates dimples  158  having a diameter of 0.001 inch and spaced apart by 0.0005 inch, which forms the textured surface  154 . It is also possible to provide greater spacing between the dimples  158  to provide a mechanical advantage in specific clinical cases. The laser can be programmed to provide areas on the solder/weld joint  156  that are left untouched (i.e., smooth), depending on the application. The ablated patterns (dimples  158 ) are easily modified by simply altering the laser frequency, grid spacing (spaced apart dimples  158 ), or programming dimple by dimple to achieve an optimal configuration. 
     The dimples  158  also have a depth dimension  160  and a diameter  162  as shown in  FIG. 12D . Preferably, the dimples  158  have a depth dimension  160  ranging from 0.5μ to 1.5μ, and more preferably 1.0 μ. 
     Similarly, the radius dimension  162  of dimples  158  can range from 0.3μ to 6.0μ, and preferably from 2.0μ to 4.0μ, and more preferably 3.0μ. The process involves utilizing a commercially available fiber laser, with the wire tip fixture end on, to selectively soften and dimple the solder/weld surface of the guidewire tip where the beam is directed. This process is performed without disrupting the solder/weld structural integrity of the solder or weld material due to the extremely fast pulse rate of the laser providing focused heating only where the beam is targeted. In one embodiment, the cycle time for the laser process is 50 ms, which allows for a modified tip texture in a time that is acceptable in a production environment. Higher or lower laser cycle times are acceptable depending on the composition of the solder/weld and the size and depth of the dimples. 
     In addition to using a commercially available laser, the dimples  158  can be formed by other processes including bead blasting, chemical etching, or mechanical impact, as long as the integrity of the solder/weld joint  156  is maintained. 
     The dimples  158  can be formed on the solder/weld joint  156  after the joint has been formed on the distal tip  152  of the guidewire  150 . Alternatively, the solder/weld joint  156  is manufactured at a component level and the dimples  158  are then formed on the joint. Thereafter, the solder/weld joint  156  with the pre-formed dimples  158  can be attached to the distal tip  152  of the guidewire  150 . 
     As shown in  FIG. 12E , an experiment was conducted comparing lesion crossing performance of the laser dimpled guidewire with commercially available guidewires. Testing was performed on a clinically relevant Chronic Total Occlusion (CTO) model to determine the time to pass the guidewire through the lesion. The round dots represent the time in seconds it took the guidewire to pass through the lesion, while the triangular dots represent those guidewires that were unable to pass through the lesion. As can be seen in  FIG. 12E , the laser dimpled guidewire performed substantially better than a commercially available guidewire and a wire with no dimples in terms of consistently better passing times, and no failed attempts to pass through the lesion. 
     Coils With Different Cross Section Shapes 
     Generally, the distal end of a guidewire should have a low support profile to make it flexible enough for cross-ability purposes. Therefore, the distal end of the core wire is ground (tapered) and covered with a coil to make it flexible and atraumatic (see e.g.,  FIGS. 2-3 ). Also, the coil will assist with keeping the outer diameter of the guidewire consistent. Prior art coils are formed from a wire with a circular cross section ( FIG. 13 ) and cut with a laser. 
     For the next generation guidewires, good torque response without negatively affecting the bending stiffness of the guidewire is an important functional attribute. 
     In the present invention, multiple wire cross-sections were designed to improve the functionality of the guidewires. Finite Element Analysis (FEA using ABAQUS commercial software) was performed on these guidewire cross sections to identify the effect of different cross-sections on torque response and bending stiffness. 
     The present invention increases the torquability without negatively affecting the bending stiffness and functionality of guidewire using different cross-section shapes of coils. As shown in  FIGS. 15A-23B , the different embodiments include circle  178  (prior art), I-beam  180 , vertical rectangular  182 , vertical ellipse  183 , square  184 , vertical hexagonal  186 , horizontal hexagonal  188 , flat  190 , and horizontal ellipse  192  cross-sections. FEA demonstrates that the more material removed away from the Neutral Axis (N. A.) of the coil wire, increases the torquability while decreasing the bending stiffness. Coils with different cross-sections were created and subjected to torque while keeping the other parameters such as material and volume of the coil wires constant. For this study, the coil material considered was 304V stainless steel.  FIG. 14  shows the material properties for 304V stainless steel. In order to keep the volume constant, the cross-sectional area, the length, the nominal diameter, and the pitch for the wires were kept constant. 
     Coils having different cross sections with the same length, pitch, mean diameter and cross-sectional area (dimensions scaled up to  100 ) are shown in  FIGS. 15A-23B .  FIG. 24  shows the torque response of single coils with different cross-sections analyzed by ABAQUS using the provided material properties. The torsional stiffness of the I-beam is the highest followed by the rectangular and vertical ellipse cross-sections. A peanut shaped cross-section wire also showed high torsional stiffness ( FIG. 24 ).  FIG. 25  shows the bending stiffness of the coils with different cross-sections. Therefore, by changing the cross-section of the wire of a coil from circular to I-beam, the torque response increased up to 250% while decreasing the bending stiffness by 50%. Considering the constraints due to manufacturing, dimensions and tolerances the I-beam, peanut, vertical rectangular and vertical ellipse shapes are more favorable than the conventional round cross-section coils, depending on the application or other limitations. 
     In  FIGS. 15A-23B , the shapes and sizes related to the coils  178 ,  180 ,  182 ,  183 ,  184 ,  186 ,  188 ,  190  and  192  are for illustrative purposes and to ensure the parameters such as length, pitch, mean diameter and cross-sectional area of the coil wires were constant for testing purposes. 
     The coils  180 ,  182 ,  183 ,  184 ,  186 ,  188 ,  190  and  192  can be used with the guidewire  30  shown in  FIGS. 2-6  and can be used as either an inner coil or an outer coil. 
     Guidewire Tip Shaping Tool—Micro J 
     Guidewires are sold either in a straight or pre-formed “J” shaped configuration. Generally, the distal tip of the guidewires are micro “J” shaped to assist with maneuverability. Wires can be shaped by the manufacturer or by the physician using a shaping tool provided with the guidewire. Shaping by the manufacturer is an automated process, which is more repeatable and does not compromise the integrity of the wire. The majority of users prefer a straight wire and shape the tips themselves. Guidewire manufactures provide a mandrel and introducer to assist physicians with the wire shaping. 
     It has been determined that users do not have good control in how they shape the wire and can easily damage the wire. Testing shows that there is an optimal angle (i.e., ˜20°-30°) and distance from the tip (2-3 mm) that can significantly help with the wire performance. Even though physicians know what specifications they want in the bend, due to the size, most of the physicians are nowhere close to the intended optimal dimensions. Also, there is a higher risk of the wire losing integrity and functional performance if the physician performs the shaping. 
     In this embodiment, shown in  FIGS. 26-30 , a micro “J” shaping tool can be shipped with the guidewires or can be sold as a standalone accessory. This shaping tool will have pre-defined existing slots where a physician can decide the angle as well as the distance from the tip to form the micro-J bend. This tool has a universal design and will be compatible with all manufacturers guidewires as well. 
     In this embodiment, shown in  FIGS. 27A-30 , a shaping tool  200  includes a first member  202  and a second member  204 , and multiple cavities  206  having different depths and shapes. A channel  208  extends through a wall  210  of the first member  202  and provides access for the distal end  212  of the guidewire  214 . The second member  204  is slidably contained in the first member  202  and a third member  205  is inserted into a slot  207  in the first member  202  to hold the second member  204  in the first member  204 . The third member  205  can be glued or laser welded in the slot  207 , but it allows for longitudinal movement or sliding between the first member  202  and the second member  204 . A pair of springs  216  are spring biased to keep the spacing tool  200  in an open position  218 . In the open position  218 , the distal end  212  of the guidewire  214  can be inserted through channel  208  and advanced into one of the cavities  206  (see  FIG. 27B ). To form the micro-J tip, the user pushes the end of the second member  204  in the direction of the arrow in  FIGS. 28A and 28B , which overcomers the spring force of springs  216 . As shown in  FIGS. 28A-30 , the second member  204  slides relative to the first member  202  to closed position  220 . In the closed position  220 , the cavities  206  have shifted relative to the channels  208  so that the guidewire distal end  212  will bend the predetermined angle and the bend will be set at a predetermined length from an end  222  of the distal end  212 . When the user releases pressure on the end of the shaping tool  200 , the springs  216  spring open and move the first member  202  to the open position  218  so that the guidewire  214  can be removed from the cavity  206 . While the cavities  206  depict angular bends of 25° and 30°, a range of angular bends from 5° to 40° is contemplated. Similarly, the length of the bend from the distal end  220  to the unbent portion of the guidewire  214  is preferably 1 mm or 2 mm, however, the length can range from 0.5 mm to 5 mm. 
     Parabolic Grind Profile 
     In another embodiment of the invention, the distal section of the guidewire is reduced in cross-section to be more flexible when navigating tortuous vessels, such as coronary arteries. The distal section of the guidewire must be both flexible and pushable, that is the distal section must flex and be steerable through the tortuous arteries, and also have some stiffness so that it can be pushed or advanced through the arteries without bending or kinking. A prior art guidewire is shown in  FIG. 31  and has a distal section comprised of tapered sections and core sections with no taper. The resulting bending stiffness is shown in the graph in  FIG. 33  wherein the bending stiffness decreases at each tapered position, and the bending stiffness remains constant along the core section that is not tapered. The tapered distal section of the prior art guidewire of  FIG. 31  provides abrupt changes in bending stiffness that can reduce the tactile feel to the physician when advancing the guidewire through tortuous anatomy. In fact, in some prior art guidewires, the abrupt change in bending stiffness can result in the distal tip of the guidewire to kink or prolapse into a side branch vessel as shown schematically in  FIG. 34 . Prolapse can be dangerous to the patient in that the artery can be damaged or punctured. Importantly, it is preferred to maintain the outer diameter of the core section as far distal as possible to maintain torque. Each tapered section loses torque, which is critical in advancing the guidewire through tortuous vessels. 
     In keeping with the invention, a parabolic distal section  232  of a guidewire  230  is shown in  FIG. 32  wherein a significant portion of the distal section has been ground to form a continuous taper. More specifically, the continuous taper is formed by a parabolic grind along parabolic distal section  232  of the guidewire  230 . The parabolic grind provides a smooth curvilinear transition along section  232  that is highly flexible and yet maintains a linear change in stiffness as shown in the graph of  FIG. 33 . Not only is parabolic distal section  232  flexible, but it has a linear change in stiffness thereby providing excellent torque and tactile feedback to the physician when advancing the guidewire through tortuous anatomy. A tapered section  234  that is not curvilinear (not a parabolic grind section) is located on the guidewire  230  distal of the parabolic distal section  232  and it provides reduced bending stiffness and a linear change in bending stiffness as shown in the graph of  FIG. 33 . 
     Bending stiffness can be measured in a variety of ways. Typical methods of measuring bending stiffness include extending a portion of the sample to be tested from a fixed block with the sample immovably secured to the fixed block and measuring the amount of force necessary to deflect the end of the sample that is away from the fixed block a predetermined distance. A similar approach can be used by fixing two points along the length of a sample and measuring the force required to deflect the middle of the sample a fixed amount. Those skilled in the art will realize that a large number of variations on these basic methods exist including measuring the amount of deflection that results from a fixed amount of force on the free end of a sample, and the like. Other methods of measuring bending stiffness may produce values in different units of different overall magnitude, however, it is believed that the overall shape of the graph will remain the same regardless of the method used to measure bending stiffness. 
     The parabolic grind profiles for a 0.014 inch diameter guidewire are shown in  FIGS. 35 and 36  respectively. The guidewire in  FIG. 35  has an 11 gram tip load and the guidewire in  FIG. 36  has a 14 gram tip load. The unit of measure on the Y-axis is in inches and the X-axis is in centimeters. In both  FIGS. 35 and 36 , two parabolic grind profiles are separated by a uniform diameter core wire segment. More specifically, each graph shows a first parabolic grind profile starting at approximately 23.1 cm from the distal tip of the guidewire and ending at approximately 17.9 cm from the distal tip. Further, each graph shows a second parabolic grind starting at approximately 4.8 cm from the distal tip. The uniform diameter core wire section is between the parabolic grind sections, and there is a uniform diameter core wire section starting at approximately 1.2 cm from the distal tip. The parabolic grind profile shown in  FIGS. 35 and 36  provide guidewires that have a linear change in stiffness, are flexible, and still maintain a high degree of torque to the guidewire distal end to navigate tortuous arteries and other vessels. 
     Conventional materials and manufacturing methods may be used to form the parabolic grind profiles of the disclosed guidewires. Those skilled in the art can use computerized grinding machines to form the parabolic grind profiles disclosed herein. 
     While the invention has been illustrated and described herein in terms of its use as a guidewire, it will be apparent to those skilled in the art that the guidewire can be used in all vessels in the body. All dimensions disclosed herein are by way of example. Other modifications and improvements may be made without departing from the scope of the invention.