Abstract:
Alternative designs, materials and combinations for guidewires. Some embodiments pertain to a guidewire having a stainless steel elongated core member. A nickel-titanium reinforcing member may be located about a distal region of the core member having a reduced diameter, wherein a portion of the distal region of the core member extends beyond the reinforcing member. The nickel-titanium member may have added physical characteristics providing superior flexibility. An outer member may be placed about the distal portion of the core wire and extend over the reinforcing member.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention generally pertains to guidewires, and more particularly to guidewires including a reinforcing member including a nickel-titanium alloy. More particularly the invention pertains to guidewires having a stainless steel core and a reinforcing member including a nickel-titanium alloy located in a distal region.  
       BACKGROUND OF THE INVENTION  
       [0002]     A wide variety of guidewires have been developed for medical use, for example intravascular use. Intravascular guidewires are commonly used in conjunction with intravascular devices such as catheters to facilitate navigation through the vasculature of a patient. Because the vasculature of a patient may be very tortuous, it is desirable to combine a number of performance features in a guidewire. For example, it is sometimes desirable that the guidewire have a relatively high level of pushability and torqueability, particularly near its proximal end. It is also sometimes desirable that a device be relatively flexible, particularly near its distal end. A number of different guidewire structures and assemblies are known, each having certain advantages and disadvantages. However, there is an ongoing need to provide alternative guidewire structures and assemblies.  
       SUMMARY OF THE INVENTION  
       [0003]     The invention provides several alternative designs, materials and combinations in a guidewire with improved characteristics.  
         [0004]     One embodiment includes a guidewire having an elongated core member with a reinforcing member disposed about a portion of the distal region of the core member. A distal portion of the core member extends beyond the reinforcing member. An outer member is positioned over the distal portion of the core member and extends over at least a portion of the reinforcing member.  
         [0005]     Another embodiment provides a guidewire including an elongated core member, wherein at least a portion of the distal region of the core member includes stainless steel. A reinforcing member preferably formed of a nickel-titanium alloy is disposed about a portion of the distal region of the core member, wherein the distal end of the reinforcing member terminates proximal of a distal portion of the distal region of the core member. An outer member is positioned over at least a portion of the reinforcing member and the portion of the core member distal of the reinforcing member.  
         [0006]     Another embodiment provides a guidewire configured for use in a patient&#39;s body, the guidewire having an elongated inner core member including stainless steel. The core member includes at least a proximal portion having a first cross-sectional area, an intermediate portion having a second cross-sectional area, and a distal portion having a ribbon profile. Preferably, the first cross-sectional area is larger than the second cross-sectional area, which is larger than the ribbon profile.  
         [0007]     An elongated reinforcing member is disposed about the intermediate portion of the core member. The reinforcing member preferably includes a nickel-titanium alloy. The reinforcing member may be a coil, tubular member or at least one ribbon wire helically wrapped about the core member. The reinforcing member is preferably of a different material than the intermediate portion of the core member. Therefore, providing characteristics not otherwise present in the reinforced portion.  
         [0008]     A spring tip, preferably including stainless steel, is positioned about the distal portion of the core member and extends over the reinforcing member. The spring tip preferably has an outside diameter substantially equal to the diameter of the proximal portion of the core member adjacent the spring tip. Substantially equivalent diameters in this region provide for a smooth transition along the guidewire that enables medical devices to more easily pass along the guidewire during a medical procedure.  
         [0009]     The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures, and Detailed Description which follow more particularly exemplify these embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:  
         [0011]      FIG. 1  is a schematic plan view of a guidewire generally;  
         [0012]      FIG. 2  is a partial cross-sectional view of the distal portion of a guidewire in accordance with the invention;  
         [0013]      FIG. 2A  is an orthogonal cross-sectional view of the guidewire in  FIG. 2 ;  
         [0014]      FIG. 3A  is a plan view of an alternative reinforcing member for a guidewire in accordance with the invention;  
         [0015]      FIG. 3B  is a plan view of an alternative reinforcing member for a guidewire in accordance with the invention;  
         [0016]      FIG. 4  is a partial cross-sectional view of a variation of the distal portion of the guidewire in  FIG. 3 ;  
         [0017]      FIG. 4A  is an orthogonal cross-sectional view of the guidewire in  FIG. 4 ;  
         [0018]      FIG. 5  is a partial cross-sectional view of another embodiment of the distal portion of a guidewire;  
         [0019]      FIG. 6  is a cross-sectional view of an alternative embodiment of the distal portion of a guidewire in accordance with the invention;  
         [0020]      FIG. 7  is a cross-sectional view of a variation of the distal portion of the guidewire in  FIG. 6 ;  
         [0021]      FIG. 8  is a cross-sectional view of a variation of the distal portion of the guidewire in  FIG. 6 ;  
         [0022]      FIG. 9  is a cross-sectional view of an alternative embodiment of the distal portion of a guidewire in accordance with the invention;  
         [0023]      FIG. 10  is a partial cross-sectional view of another embodiment of the distal portion of a guidewire; and  
         [0024]      FIG. 11  is a partial cross-sectional view of an alternative embodiment of a guidewire in accordance with the invention. 
     
    
       [0025]     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification.  
         [0027]     All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure.  
         [0028]     Weight percent, percent by weight, wt %, wt-%, % by weight, and the like are synonyms that refer to the concentration of a substance as the weight of that substance divided by the weight of the composition and multiplied by 100.  
         [0029]     The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).  
         [0030]     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.  
         [0031]     The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.  
         [0032]     Refer now to  FIG. 1 , which is a schematic plan view of one example embodiment of a guidewire  10 . The guidewire  10  includes a proximal section  11  defining a proximal end  13 , and a distal section  15  defining a distal end  17 . A distal tip  12  is located near distal end  17 .  
         [0033]     It can be seen that guidewire  10  may include a core member or wire  14 . The distal section  15  includes a proximal portion  16  and a distal portion  18 . Core wire  14  can be made of any suitable materials including metals, metal alloys, polymers, or the like, or combinations or mixtures thereof. Some examples of suitable metals and metal alloys include stainless steel, such as 304v stainless steel; nickel-titanium alloy, such as linear elastic or superelastic (i.e., pseudo elastic) nitinol, nickel-chromium alloy, nickel-chromium-iron alloy, cobalt alloy, tungsten, tungsten alloy, Elgiloy, MP35N, or the like; or other suitable materials.  
         [0034]     The word nitinol was coined by a group of researchers at the United States Naval Ordinance Laboratory (NOL) who were the first to observe the shape memory behavior of this material. The word nitinol is an acronym including the chemical symbol for nickel (Ni), the chemical symbol for titanium (Ti), and an acronym identifying the Naval Ordinance Laboratory (NOL). In some embodiments, nitinol alloys can include in the range of about 50 to about 60 weight percent nickel, with the remainder being essentially titanium. It should be understood, however, that in other embodiments, the range of weight percent nickel and titanium, and/or other trace elements may vary from these ranges. Within the family of commercially available nitinol alloys are categories designated as “superelastic” (i.e., pseudo elastic) and “linear elastic” which, although similar in chemistry, exhibit distinct and useful mechanical properties.  
         [0035]     In some embodiments, a superelastic alloy, for example a superelastic Nitinol, can be used to achieve desired properties. Such alloys typically display a substantial “superelastic plateau” or “flag region” in its stress/strain curve. Such alloys can be desirable in some embodiments because a suitable superelastic alloy will provide a reinforcing member that exhibits some enhanced ability, relative to some other non-superelastic materials, of substantially recovering its shape without significant plastic deformation, upon the application and release of stress, for example, during placement of the catheter in the body.  
         [0036]     In some other embodiments, a linear elastic alloy, for example a linear elastic Nitinol, can be used to achieve desired properties. For example, in some embodiments, certain linear elastic nitinol alloys can be generated by the application of cold work, directional stress and heat treatment such that the material fabricated does not display a substantial “superelastic plateau” or “flag region” in its stress/strain curve. Instead, in such embodiments, as recoverable strain increases, the stress continues to increase in a somewhat linear relationship until plastic deformation begins. In some embodiments, the linear elastic nickel-titanium alloy is an alloy that does not show any martensite/austenite phase changes that are detectable by DSC and DMTA analysis over a large temperature range. For example, in some embodiments, there are no martensite/austenite phase changes detectable by DSC and DMTA analysis in the range of about −60° C. to about 120° C. The mechanical bending properties of such material are, therefore, generally inert to the effect of temperature over a broad range of temperature. In some particular embodiments, the mechanical properties of the alloy at ambient or room temperature are substantially the same as the mechanical properties at body temperature. In some embodiments, the use of the linear elastic nickel-titanium alloy allows the reinforcing member to exhibit superior “pushability” around tortuous anatomy. One example of a suitable nickel-titanium alloy exhibiting at least some linear elastic properties is FHP-NT alloy commercially available from Furukawa Techno Material Co. of Kanagawa, Japan. Additionally, some examples of suitable nickel-titanium alloy exhibiting at least some linear elastic properties include those disclosed in U.S. Pat. Nos. 5,238,004 and 6,508,803, which are incorporated herein by reference.  
         [0037]     In at least some embodiments, portions or all of core wire  14  may also be doped with, made of or otherwise include a radiopaque material. Radiopaque materials are understood to be materials capable of producing a relatively bright image on a fluoroscopy screen or another imaging technique during a medical procedure. This relatively bright image aids the user of device  10  in determining its location. Some examples of radiopaque materials can include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloy, polymer material loaded with a radiopaque filler, and the like. In some embodiments, it is also contemplated that a separate radiopaque member or a series of radiopaque members, such as radiopaque coils, bands, tubes, or other such structures could be attached to the guidewire core wire or incorporated into the core wire by plating, drawing, forging, or ion implantation techniques, and the like.  
         [0038]     In some embodiments, a degree of MRI compatibility is imparted into guidewire  10 . For example, to enhance compatibility with Magnetic Resonance Imaging (MRI) machines, it may be desirable to make core wire  14 , or other portions of the medical device  10 , in a manner that would impart a degree of MRI compatibility. For example, core wire  14 , or portions thereof, may be made of a material that does not substantially distort the image and create substantial artifacts (artifacts are gaps in the image). Certain ferromagnetic materials, for example, may not be suitable because they may create artifacts in an MRI image. Core wire  14 , or portions thereof, may also be made from a material that the MRI machine can image. Some materials that exhibit these characteristics include, for example, tungsten, Elgiloy, MP35N, nitinol, and the like, and others.  
         [0039]     The entire core wire  14  can be made of the same material, or in some embodiments, can include portions or sections made of different materials. In some embodiments, the material used to construct core wire  14  is chosen to impart varying flexibility and stiffness characteristics to different portions of core wire  14 . For example, proximal section  11  and distal section  15  may be formed of different materials, for example materials having different moduli of elasticity, resulting in a difference in flexibility. In some embodiments, the material used to construct proximal section  11  can be relatively stiff for pushability and torqueability, and the material used to construct distal section  15  can be relatively flexible by comparison for better lateral trackability and steerability. For example, proximal section  11  can be formed of straightened 304v stainless steel wire or ribbon, and distal section  15  can be formed of a straightened super elastic or linear elastic alloy, for example a nickel-titanium alloy wire or ribbon.  
         [0040]     In embodiments where different portions of core wire  14  are made of different material, the different portions can be connected using any suitable connecting techniques. For example, the different portions of the core wire can be connected using welding, soldering, brazing, adhesives, or the like, or combinations thereof. Additionally, some embodiments can include one or more mechanical connectors or connector assemblies to connect the different portions of the core wire that are made of different materials. The connector may include any structure generally suitable for connecting portions of a guidewire. One example of a suitable structure includes a structure such as a hypotube or a coiled wire which has an inside diameter sized appropriately to receive and connect to the ends of the proximal portion and the distal portion. Some other examples of suitable techniques and structures that can be used to interconnect different shaft sections are disclosed in U.S. Patent Publication Nos. 2003-0069521 and 2003-0069520, which are incorporated herein by reference.  
         [0041]     The length of core member  14  (and/or device  10 ), or the length of individual portions thereof, is typically dictated by the length and flexibility characteristics desired in the final medical device. For example, proximal section  11  may have a length in the range of about 20 to about 300 centimeters or more and distal section  15  may have a length in the range of about 3 to about 50 centimeters or more. It can be appreciated that alterations in the length of sections  11 / 15  can be made without departing from the spirit of the invention.  
         [0042]     Core wire  14  can have a solid cross-section, but in some embodiments, can have a hollow cross-section. In yet other embodiments, core wire  14  can include a combination of areas having solid cross-sections and hollow cross-sections. Moreover, core wire  14 , or portions thereof, can be made of rounded wire, flattened ribbon, or other such structures having various cross-sectional geometries. The cross-sectional geometries along the length of shaft  14  can be constant or can vary. For example,  FIG. 2  depicts core wire  14  as having a round cross-sectional shape. It can be appreciated that other cross-sectional shapes or combinations of shapes may be utilized without departing from the spirit of the invention. For example, the cross-sectional shape of core wire  14  may be oval, rectangular, square, polygonal, and the like, or any suitable shape.  
         [0043]     As shown in  FIG. 2 , distal section  15  may include one or more tapers or tapered regions. In some embodiments distal region  18  may be tapered and have an initial outside size or diameter that can be substantially the same as the outside diameter of proximal section  11 , which then tapers to a reduced size or diameter. For example, in some embodiments, distal section  15  can have an initial outside diameter that is in the range of about 0.010 inches to about 0.040 inches that tapers to a diameter in the range of about 0.001 inches to about 0.005 inches. The tapered regions may be linearly tapered, tapered in a curvilinear fashion, uniformly tapered, non-uniformly tapered, or tapered in a step-wise fashion. The angle of any such tapers can vary, depending upon the desired flexibility characteristics. The length of the taper may be selected to obtain a more (longer length) or less (shorter length) gradual transition in stiffness. Although  FIG. 2  depicts distal section  15  of core wire  14  as being tapered, it can be appreciated that essentially any portion of core wire  14  may be tapered and the taper can be in either the proximal or the distal direction. As shown in  FIG. 2 , the tapered region may include one or more portions where the outside diameter is narrowing, for example the tapered portions, and portions where the outside diameter remains essentially constant, for example constant diameter portions. The number, arrangement, size, and length of the narrowing and constant diameter portions can be varied to achieve the desired characteristics, such as flexibility and torque transmission characteristics. The narrowing and constant diameter portions as shown in  FIG. 2  are not intended to be limiting, and alterations of this arrangement can be made without departing from the spirit of the invention.  
         [0044]     The tapered and constant diameter portions of the tapered region may be formed by any one of a number of different techniques, for example, by centerless grinding methods, stamping methods, and the like. The centerless grinding technique may utilize an indexing system employing sensors (e.g., optical/reflective, magnetic) to avoid excessive grinding of the connection. In addition, the centerless grinding technique may utilize a CBN or diamond abrasive grinding wheel that is well shaped and dressed to avoid grabbing the core wire during the grinding process. In some embodiments, core wire  14  can be centerless ground using a Royal Master HI-AC centerless grinder. Some examples of suitable grinding methods are disclosed in U.S. patent application Ser. No. 10/346,698 filed Jan. 17, 2003, which is herein incorporated by reference.  
         [0045]     As shown in  FIG. 2 , a reinforcing member  20  may be disposed about a proximal portion  16  of the distal section  15  of the core wire  14 . A distal portion  18  of the distal section  15  extends distally beyond the reinforcing member  20 . The reinforcing member may be a tubular segment  20  formed of a variety of materials including metals, metal alloys, polymers, and the like. Some examples of material for use in the tubular segment  20  include stainless steel, nickel-titanium alloy, nickel-chromium alloy, nickel-chromium-iron alloy, cobalt alloy, or other suitable materials. In a preferred embodiment, the tubular segment  20  includes nickel-titanium alloy for its superior characteristics such as pushability, with a preferred embodiment further utilizing a stainless steel as a core member  14 .  
         [0046]     As more clearly shown in  FIGS. 3A and 3B , tubular segment  20  may include at least one groove or cut  24 . The groove or cut  24  may enhance the properties, such as flexibility, of the tubular segment  20 . The groove or cut  24  may extend through substantially the entire thickness of the tube, or the groove or cut  24  may extend only partially through the thickness of the tube (such as a score line). As shown in  FIG. 3A , a plurality of grooves or cuts  24  may be used to acquire the necessary flexibility. As shown in  FIG. 3B , the groove or cut  22  may be helically formed along the length of the tubular segment  20  or a portion thereof. The helical groove or cut  22  may extend only partially through the thickness of the tube (such as a score line) or may extend through substantially the entire thickness of the tube. The pitch of the helical groove or cut  22  may be selected in order to provide desired functionality, or the pitch may vary along the length of the tubular segment  20 . The tubular segment  20  may include one or more additional helical grooves or cuts  22  or a combination of grooves or cuts  24  and helical grooves or cuts  22 . It is understood that the width and depth of the groove or cut  22 ,  24  may be of a wide range as may be necessary to attain the desired properties of the tubular segment  20 . The groove or cut  22 ,  24  may be made by any of a variety of techniques known in the art, such as a laser cutter or a plasma cutter.  
         [0047]     In some embodiments, an outer member is disposed about at least a portion of the distal section  15  of the core member  14 . The outer member may extend from the distal end  17  of guidewire  10  to a point proximal of the distal end  17 . The outer member may extend over at least a portion of the reinforcing member, preferably extending substantially over the entire reinforcing member. The outer member may have an outer diameter substantially the same as the diameter of the proximal section  11  of core wire  14 , or the outer diameter of the outer member may be larger or smaller than that of the adjacent portion of the core wire  14 .  
         [0048]     As shown in  FIG. 2 , the outer member may be a coil  30 . The coil  30  may be disposed about the distal section  15  of the guidewire  10 . The coil  30  can be formed of a variety of materials including metals, metal alloys, polymers, and the like. Some examples of materials for use in the coil  30  include stainless steel, nickel-chromium alloy, nickel-chromium-iron alloy, cobalt alloy, or other suitable materials. Some additional examples of suitable materials include straightened super elastic or linear elastic alloy (e.g., nickel-titanium) wire, or alternatively, a polymer material, such as a high performance polymer. In some embodiments, the coil  30  or portions thereof can be made of, include or be coated with a radiopaque material such as gold, platinum, tungsten, or the like, or alloys thereof.  
         [0049]     The coil  30  can be formed of round or flat ribbon ranging in dimensions to achieve the desired flexibility. In some embodiments, the coil  30  can be a round ribbon in the range of about 0.001 inches to about 0.015 inches in diameter, and can have a length in the range of about 0.1 to about 20 inches. However, other dimensions are contemplated.  
         [0050]     The coil  30  can be wrapped in a helical fashion by conventional winding techniques. The pitch of adjacent turns of the coil  30  may be tightly wrapped so that each turn touches the succeeding turn or the pitch may be set such that the coil  30  is wrapped in an open fashion.  
         [0051]     A distal tip  32  may be positioned at the distal end  17  of guidewire  10 . The distal tip  32  may be a solder, polymer, or other material known in the art. The distal tip  32  may include a radiopaque material, making the location of the distal tip within a body region more visible when using certain imaging techniques, for example, fluoroscopy techniques. Any suitable radiopaque material known in the art can be used. Some examples include precious metals, tungsten, barium subcarbonate powder, and the like, and mixtures thereof. The distal tip  32  may be located distal of coil  30 . The distal tip, or a portion thereof, may be located within the distal portion of coil  30 .  
         [0052]     A variation of the distal section  15  of guidewire  10  is shown in  FIG. 4 . The distal section  15  of guidewire  10  is substantially the same as in  FIG. 2 , except for the relative spacing between the tubular segment  20  and the coil  30 . As best shown in  FIG. 4A , the tubular segment  20  is located adjacent to the coil  30 , whereas in  FIG. 2A , there is a space between the tubular segment  20  and the coil  30 . The relative spacing between the tubular segment  20  and the coil  30  may provide unique characteristics of the distal section  15  that may be desirable during a procedure.  
         [0053]     An alternative embodiment of the distal section  15  of the guidewire  10  is shown in  FIG. 5 . Core wire  14  includes a proximal portion  40 , an intermediate portion  42 , and a distal portion  44 . A taper  41  is located between proximal portion  40  and intermediate portion  42  in order to transition from a first cross-section in proximal portion  40  to a second cross-section in intermediate portion  42 . A taper  43  is located between intermediate portion  42  and distal portion  44  in order to transition from the second cross-section in intermediate portion  42  to a third cross-section in distal portion  44 . The tapering and constant cross-sectional area portions as shown in  FIG. 4  are not intended to be limiting, and alterations of this arrangement can be made without departing from the spirit of the invention as discussed earlier.  
         [0054]     In one preferred embodiment, a reinforcing member  50  is disposed about the intermediate portion  42  of the core wire  14 . The reinforcing member may provide desired characteristics in the region of the intermediate portion  42  of the core wire  14  which may be inadequately provided by the material used in that portion of the core wire  14 . For example, the core wire may be stainless steel having superior properties of flexibility and steerability. The reinforcing member may be a nickel-titanium alloy providing enhanced pushability and torqueability to the intermediate portion. In some embodiments, the distal portion  44  may be ribbon shaped providing desired flexibility characteristics at the distal end  17  of the guidewire  10 . The distal portion  44  may be shape formed prior to a medical procedure to provide a desired curved tip for enhanced navigation through a tortuous vascular system.  
         [0055]     The reinforcing member in  FIG. 5  is a coil  50 . The coil  50  may be disposed about the distal section  15  of the guidewire  10 . The coil  50  can be formed from a variety of materials including metals, metal alloys, polymers, and the like. The coil  50  may preferably include nickel-titanium alloy. Some other examples of material for use in the coil  50  include stainless steel, nickel-chromium alloy, nickel-chromium-iron alloy, cobalt alloy, a polymer material such as a high performance polymer, or other suitable materials. In some embodiments, the coil  50  or portions thereof can be made of, include or be coated with a radiopaque material such as gold, platinum, tungsten, or the like, or alloys thereof. In a preferred embodiment, a nickel-titanium alloy coil to is used with a stainless steel core  14 .  
         [0056]     The coil  50  can be formed of wire ranging in dimensions to achieve the desired flexibility. In some embodiments, the wire can be round wire, rectangular wire, or flat ribbon. Wire of other cross-sectional areas is also contemplated in the invention. The coil  50  can be wrapped in a helical fashion by conventional winding techniques. The pitch of adjacent turns of the coil  50  may be tightly wrapped so that each turn touches the succeeding turn or the pitch may be set such that the coil  50  is wrapped in an open fashion.  
         [0057]     As can been seen in  FIG. 5 , the coil  50  may be disposed about the intermediate portion  42  of core wire  14 . The coil  50  may end proximal of the distal portion  44  of the core wire  14 . The coil  50  may provide desired characteristics in the region of the intermediate portion  42  of the core wire  14  which may be inadequately provided by the core wire  14 .  
         [0058]      FIG. 6  shows an alternative embodiment of the distal section  15  of the guidewire  10 . In  FIG. 6 , the reinforcing member is a helically wrapped wire  60  wound about a portion of the distal section  15  of core wire  14 . The helically wrapped wire  60  may be a single strand wound about the core wire  14 , or may comprise a plurality of wires  60  wound about the core wire  14 . In an embodiment having a plurality of wires  60 , such as is shown in  FIG. 6 , a first strand may be wound in one direction and a second strand wound in an opposing direction. However, wrapping a plurality of wires  60  in the same or similar direction is contemplated within the scope of the invention.  
         [0059]     In some embodiments, the helically wrapped wire  60  can be round wire, rectangular wire, or flat ribbon. Wire of other cross-sectional areas is also contemplated in the invention. The helically wrapped wire  60  may be formed from a variety of materials including metals, metal alloys, polymers, fibers, and the like. The wire  60  may preferably include nickel-titanium alloy. Some other examples of material for use in the wire  60  include stainless steel, nickel-chromium alloy, nickel-chromium-iron alloy, cobalt alloy, a polymer material such as a high performance polymer, or other suitable materials. In some embodiments, the wire  60  or portions thereof can be made of, include or be coated with a radiopaque material such as gold, platinum, tungsten, or the like, or alloys thereof. In a preferred embodiment, the helically wrapped wire includes nickel-titanium alloy, and the core contains stainless steel.  
         [0060]     In some other embodiments, a polymer jacket tip or combination coil/polymer tip can be used. The polymer jacket tip may extend over at least a portion of the core wire. The outer diameter of the polymer tip may be substantially the same as the diameter of a region of the core wire, or it may be larger or smaller in diameter. A polymer tip having a substantially similar outer diameter may create a smooth transition from a region of the core wire located adjacent to the polymer tip. The smooth transition allows medical devices to be delivered over the guidewire with minimal interference through a transition section, thus increasing efficiency of a medical procedure while reducing the possibility of inadvertent damage to a body region.  
         [0061]     For example, in the embodiment shown in  FIG. 7 , an outer polymer member  170  is disposed over a portion of the core wire  114 . In this embodiment, a polymer tip guidewire is formed by including a polymer sheath  170  extending over at least a portion of the distal section  115  of the core wire  114 , and forms a rounded tip  132  over the distal end  117  of core member  114 . The polymer sheath  170  can be made from any material that can provide the desired strength, flexibility or other desired characteristics. The polymer sheath  170  can, in some non-limiting embodiments, have a length that is in the range of about 1.0 inches to about 25.0 inches, an inner diameter that is in the range of about 0.003 inches to about 0.010 inches and an outer diameter that is in the range of about 0.010 inches to about 0.035 inches.  
         [0062]     The use of a polymer can serve several functions, such as improving the flexibility properties of the guidewire assembly. Choice of polymers for the sheath or sleeve  150  will vary the flexibility of the guidewire. For example, polymers with a low durometer or hardness will make a very flexible or floppy tip. Conversely, polymers with a high durometer will make a tip which is stiffer. The use of polymers for the sleeve can also provide a more atraumatic tip for the guidewire. An atraumatic tip is better suited for passing through fragile body passages. Finally, a polymer can act as a binder for radiopaque materials, as discussed in more detail below.  
         [0063]     Some suitable materials include polymers, and like material. Examples of suitable polymer material include any of a broad variety of polymers generally known for use as guidewire polymer sleeves. In some embodiments, the polymer material used is a thermoplastic polymer material. Some examples of some suitable materials include polyurethane, elastomeric polyamides, block polyamide/ethers (such as PEBAX™), silicones, and co-polymers. The sleeve may be a single polymer, multiple layers, or a blend of polymers. By employing careful selection of materials and processing techniques, thermoplastic, solvent soluble and thermosetting variants of these materials can be employed to achieve the desired results.  
         [0064]     Further examples of suitable polymeric materials include but are not limited to poly(L-lactide) (PLLA), poly(D,L-lactide) (PLA), polyglycolide (PGA), poly(L-lactide-co-D,L-lactide) (PLLA/PLA), poly(L-lactide-co-glycolide) (PLLA/PGA), poly(D, L-lactide-co-glycolide) (PLA/PGA), poly(glycolide-co-trimethylene carbonate) (PGA/PTMC), polyethylene oxide (PEO), polydioxanone (PDS), polycaprolactone (PCL), polyhydroxylbutyrate (PHBT), poly(phosphazene), poly D,L-lactide-co-caprolactone) (PLA/PCL), poly(glycolide-co-caprolactone) (PGA/PCL), polyanhydrides (PAN), poly(ortho esters), poly(phosphate ester), poly(amino acid), poly(hydroxy butyrate), polyacrylate, polyacrylamid, poly(hydroxyethyl methacrylate), polyurethane, polysiloxane and their copolymers.  
         [0065]     In some embodiments, the sheath  170  or portions thereof can include or be doped with radiopaque material to make the sheath  170  or portions thereof more visible when using certain imaging techniques, for example fluoroscopy techniques. Any suitable radiopaque material known in the art can be used. Some examples include precious metals, tungsten, barium subcarbonate powder, and the like, and mixtures thereof. In some embodiments, the polymer can include different sections having different amounts of loading with radiopaque material. For example, the sheath or sleeve  150  can include a distal section having a higher level of radiopaque material loading, and a proximal section having a correspondingly lower level of loading.  
         [0066]     The sheath  170  can be disposed around and attached to the guidewire assembly  110  using any suitable technique for the particular material used. In some embodiments, the sheath  170  can be attached by heating a sleeve of polymer material to a temperature until it is reformed around the guidewire assembly  110 . In some embodiments, the sheath  170  can be attached using heat-shrinking techniques. In other embodiments, the sheath or sleeve  170  can be co-extruded with the core wire  114 . The sheath  170  can be finished, for example, by a centerless grinding or other method to provide the desired diameter and to provide a smooth outer surface.  
         [0067]      FIG. 8  shows an alternative embodiment of a guidewire having a distal section  215 . The guidewire includes a reinforcing member  250  disposed on a tapered portion  242  of the core wire  214 . It is therefore contemplated that the reinforcing member  250  may be located on a portion of the core wire  214  having a variable cross-section. The tapered portion  242  is located between proximal region  240  and distal region  244 . Distal region  244  may be of a circular cross-section or may be ribbon shaped. Outer polymer layer  270  may be disposed over at least a portion of the distal region  215 . Alternatively, a coil could overlay the reinforcing member  250 , as in  FIG. 2 .  
         [0068]      FIG. 9  shows an alternative embodiment of a distal region  315  of a guidewire. The guidewire includes a core wire  314  having a continuous taper from a proximal tapered portion  342 , through a distal tapered portion  344 , to the distal end  317  of the core wire  314 . A reinforcing member  350  is disposed on at least a portion of the tapered portion  342 ,  344 . An outer polymer member  370  extends over at least a portion of the tapered portion  342 ,  344 , and preferably extends to a proximal portion  340  of the core wire  314 .  
         [0069]     Other embodiments of the invention incorporate similar elements of the invention in additional configurations. Additional figures have been included to further describe the invention. However, selected embodiments depicted in the drawings are not intended to limit the scope of the invention  
         [0070]     For example,  FIG. 10  combines a reinforcing member comprising a tubular member  420  like that of  FIG. 2  with a polymer sleeve  470  like that in  FIG. 7 . The tubular member  420  is disposed on a distal portion  415  of the core wire  414 . The tubular member  420  may have cuts, grooves, or similar features as disclosed with tubular member  20 .  
         [0071]      FIG. 11  depicts an additional embodiment in accordance with the invention. Helically wrapped wire  560  is disposed along at least a portion of the distal region  515  of core wire  514 . As in  FIG. 5 , helically wrapped wire  560  may be a single strand or a plurality of strands. Additionally, in a preferred embodiment, helically wrapped wire  560  includes a first strand wound about a portion of the core wire  514  and a second strand wound about the portion of the core wire  514  in an opposing direction. Polymer sleeve  570  is positioned over at least a portion of the distal region  515 . The polymer sleeve  570  preferably has an outside diameter substantially the same as the diameter of the core wire  514  adjacent the polymer sleeve  570 .  
         [0072]     Additionally, in some embodiments, a coating, for example a lubricious (e.g., hydrophylic) or other type of coating, may be applied over portions or all of the core wire, reinforcing member, outer member, or other portions of the guidewire. Hydrophobic coatings such as fluoropolymers provide a dry lubricity which improves guidewire handling and device exchanges. Lubricious coatings improve steerability and improve lesion crossing capability. Suitable lubricious polymers are well known in the art and may include hydrophilic polymers such as polyarylene oxides, polyvinylpyrolidones, polyvinylalcohols, hydroxy alkyl cellulosics, algins, saccharides, caprolactones, and the like, and mixtures and combinations thereof. Hydrophilic polymers may be blended among themselves or with formulated amounts of water insoluble compounds (including some polymers) to yield coatings with suitable lubricity, bonding, and solubility. Some other examples of such coatings and materials and methods used to create such coatings can be found in U.S. Pat. Nos. 6,139,510 and 5,772,609, which are incorporated herein by reference. In some embodiments, the more distal portion of the guidewire is coated with a hydrophilic polymer as discussed above, and the more proximal portions are coated with a fluoropolymer, such as polytetrafluoroethylene (PTFE).  
         [0073]     Additionally, other structures, such as radiopaque markers, safety and/or shaping ribbons (coiled or uncoiled), additional coils or reinforcing members, and the like, may be incorporated into the guidewire construction.  
         [0074]     The present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the instant specification. It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the invention. The scope of the invention is, of course, defined in the language in which the appended claims are expressed.