Abstract:
A guidewire having a super elastic core surrounded by a shape memory polymer jacket. The super elastic core wire permits the guidewire to be navigated through tortuous vasculature without undergoing plastic deformation, and the shape memory polymer jacket permits the guidewire to be shaped by the physician.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to intravascular guidewires. More specifically, the present invention relates to intravascular guidewires utilizing super elastic materials.  
         BACKGROUND OF THE INVENTION  
         [0002]    Intravascular guidewires are commonly used to navigate through a patient&#39;s vascular system for the diagnosis and treatment of a wide variety of vascular disorders. Guidewires conventionally utilize a stainless steel or nitinol (super elastic) core wire. Stainless steel core wires are advantageous because they are shapeable, but are disadvantageous because they may become deformed in tortuous vascular anatomy. Nitinol core wires are advantageous because they do not become deformed in tortuous vasculature, but are disadvantageous because they are not shapeable. Thus, there is a need for a guidewire that offers both advantages, namely a guidewire that is shapeable and that is not readily deformed in tortuous vasculature.  
         SUMMARY OF THE INVENTION  
         [0003]    To address this need, the present invention provides several design alternatives. For example, in one embodiment, the present invention provides a guidewire having a super elastic core wire surrounded by a shape memory polymer jacket. The super elastic core wire permits the guidewire to be navigated through tortuous vasculature without undergoing plastic deformation, and the shape memory polymer jacket permits the guidewire to be shapeable. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a plan view of a guidewire according to the present invention, in combination with a balloon catheter;  
         [0005]    [0005]FIG. 2 is a foreshortened longitudinal cross-sectional view of a distal portion of a guidewire of the present invention, showing a polymer jacket surrounding a distal tip of a core wire;  
         [0006]    [0006]FIG. 3 is a foreshortened longitudinal cross-sectional view of a portion of a guidewire of the present invention, showing a polymer jacket surrounding a mid portion of a core wire; and  
         [0007]    [0007]FIGS. 4 and 5 are side views of a distal tip portion of a guide wire showing a polymer jacket surrounding a distal portion of a spring tip and core wire, wherein the distal tip is deformed about a cylinder-shaped object. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The detailed description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.  
         [0009]    Refer now to FIG. 1 which illustrates a plan view of a guidewire  10  in combination with an intravascular device  100 . In this particular example, the intravascular device  100  comprises a balloon catheter, but those skilled in the art will recognize that guidewires may be used alone or in combination with a wide variety of intravascular devices for coronary, peripheral and cerebral use, including balloon catheters, guide catheters, diagnostic catheters, micro-catheters, etc. For purposes of illustration only, intravascular device  100  is shown to be a balloon catheter  100  having an elongate shaft  100 , a proximally disposed manifold  104 , and a distally disposed inflatable balloon  106 , all of which are conventional in the art. Guidewire  10  may extend through the entire length of the balloon catheter  100 , and includes a proximal end  12  and a distal tip portion  14 . The guidewire  10  may have a size (length and diameter) to navigate coronary, peripheral and/or cerebral vasculature, depending on the particular clinical application, and the distal tip portion  14  may be shaped to facilitate steering in such vascular anatomy.  
         [0010]    As seen in FIG. 2, the guidewire  10  may include a core wire  20  with a polymer jacket  50  surrounding a distal tip portion  14  thereof. Alternatively, the polymer jacket  50  may surround a mid portion of the guidewire  10  as shown in FIG. 3. As shown in FIGS. 4 and 5, a radiopaque coil  40  may surround a distal portion  14  of the core wire  20 , with a distal weld  42  connecting the distal end of the coil  40  to the distal end of the core wire  20  (not visible in FIGS. 4 and 5). In this latter instance, the polymer jacket  50  may surround the core wire  20  and the radiopaque coil  40 . As a further alternative, the polymer jacket  50  may surround an inner polymer jacket (not shown) disposed on the core wire  20 , resulting in a multi-layered polymer jacket arrangement, with layer thicknesses that may vary, but preferably do not exceed the proximal profile of the guidewire. In all embodiments, the polymer jacket  50  may incorporate radiopaque filler.  
         [0011]    In all embodiments illustrated, the polymer jacket  50  may surround the core wire  20  and/or radiopaque coil  40  to establish contact therebetween or to establish an annular space therebetween. In addition, the polymer jacket  50  may surround and encase the core wire  20  and/or radiopaque coil  40  to encase the distal tip  14  as shown in FIGS. 2, 4 and  5 , or merely surround a portion thereof without encasing as shown in FIG. 3.  
         [0012]    Core wire  20  may comprise a stainless steel metal or a super elastic metal such as nitinol (nickel titanium alloy) for purposes of navigating tortuous vasculature without causing plastic deformation thereof. Polymer jacket  50  may comprise a polymer and may have suitable dimensions and material characteristics that render the polymer jacket  50  more stiff than the distal tip portion  14  of the super elastic core wire  20  which it surrounds. As used herein, stiff or stiffness refers to the collective property defined by material characteristics and shape, as conventionally used in mechanical engineering design. In particular, the cross-sectional bending moment and the flexural modulus of the polymer jacket  50  may be selected such that when the tip  14  is deformed into a shape within the elastic limit of the super elastic core wire  20 , and beyond the elastic limit of the polymer, the tip  14  substantially retains the shape, although some recoil may occur.  
         [0013]    The polymer jacket  50  may comprise a shape memory polymer such as shape memory polyurethane available from Mitsubishi, polynorbornene polymers and copolymers (including blends with polyethylene and Kraton), polycaprolactone or (oligo)caprolactone copolymer, polymethylmethacylate, PLLA or PL/D LA copolymer, PLLA PGA copolymer, PMMA, cross-linked polyethylene, cross-linked polyisoprene, polycyclooctene, styrene-butadiene copolymer, or photocrosslinkable polymer including azo-dye, zwitterionic and other photoschromic materials (as referenced in  Shape memory Materials,  Otsuka and Wayman, Cambridge University press, ®1998).  
         [0014]    With a shape memory polymer, the distal tip  14 , including polymer jacket  50 , core wire  20 , and/or radiopaque coil  40 , may be deformed into the desired shape. By way of example, not limitation, the distal tip portion  14  may be deformed about a cylindrical object  90  to impart a J-tip shape as shown in FIG. 4, or a bent-L shape as shown in FIG. 5. Although only basic shapes are shown, it is contemplated that a wide variety of simple and complex shapes may be achieved with the present invention. While the desired shape is maintained, the polymer jacket  50  may be subjected to heat at a temperature at or above the glass transition temperature (or near the melt temperature) of the shape memory polymer, and subsequently cooled to a temperature below the glass transition temperature. Once cooled, the distal tip  14  may be released from the constrained shape.  
         [0015]    After releasing the distal tip  14  from the constrained shape, the elastic forces of the super elastic core wire  20  work against the polymer jacket  50 , biasing the shape of the distal tip back to the original (e.g., straight) configuration. However, the polymer jacket  50  has sufficient stiffness, by virtue of its size and its material properties, to substantially oppose, if not completely offset, the biasing force of the super elastic core wire  20 . The biasing force of the core wire  20  may be reduced by reducing the size (e.g., diameter) thereof, and the opposing force of the polymer jacket  50  may be increased by increasing the size (cross-sectional area moment) and/or the flexural modulus thereof. Thus, by substantially opposing, if not completely offsetting, the biasing force of the super elastic core wire  20 , the polymer jacket  50  substantially maintains the deformed shape, although some recoil may occur. To compensate for such recoil, the deformed shape may be exaggerated relative to the desired final shape.  
         [0016]    The distal tip  14  may be re-shaped by re-deforming the distal tip  14  and exposing the polymer jacket  50  to heat at a temperature at or above the glass transition temperature (or near the melt temperature) of the shape memory polymer, and subsequently cooled to a temperature below the glass transition temperature. The original (e.g., straight) configuration of the distal tip  14  may be recaptured by exposing the polymer jacket  50  to heat at a temperature at or above the transformation temperature of the shape memory polymer, followed by cooling. The distal tip  14  may be repeatedly shaped without compromising shapeability or guidewire performance.  
         [0017]    The polymer jacket  50  may surround the distal tip portion  14  as shown in FIG. 2 or a mid portion of the core wire  20  as shown in FIG. 3. To accommodate the polymer jacket  50  and to provide a uniform outer profile, the core wire  20  may be ground to have a single taper or a series of tapers as shown in FIG. 2 or ground to define a recess as shown in FIG. 3.  
         [0018]    In FIG. 2, the distal portion  14  of the core wire  20  includes a series of tapers to accommodate the polymer jacket  50  and to provide a gradual reduction in stiffness toward the distal end thereof. For example, the core wire  20  may have a proximal uniform diameter portion  22  having a diameter of about 0.007 to 0.038 inches and a length “A” of about 100 to 260 cm, a mid uniform diameter portion  26  having a diameter of about 0.003 to 0.010 inches and a length “C” of about 5 to 30 cm, and a distal uniform diameter portion  30  having a diameter of about 0.0015 to 0.005 inches and a length “E” of about 5 to 30 cm. Alternatively, distal portion  30  may comprise a flat ribbon having a thickness of 0.0015 to 0.005 inches. The core wire  20  may also include tapered portions  24 / 28  between the uniform diameter portions  22 / 26 / 30 , having tapering diameters and lengths “B” and “D” of about 0.1 to 10 cm to provide a smooth transition between the uniform diameter portions  22 / 26 / 30 . As an alternative, the core wire  20  may have a continuous taper terminating in a radiopaque tip, and covered by the polymer jacket  50 .  
         [0019]    In FIG. 3, a mid portion (i.e., a portion that is proximal of the distal end and distal of the proximal end) of the core wire  20  is provided with an optional recess having a uniform diameter portion  34  and two tapered portions  32 / 36 . The position of the recess  34  and thus the position of the polymer jacket  50  in this embodiment is dictated by the length “F” of the proximal uniform diameter portion  22  and the length “J” of the distal uniform diameter portion  38 . The length “H” of the recess portion  34  may be selected depending on the desired shapeable length of the core wire  20 . The lengths “G” and “I” of the tapered portion  32 / 36  may be the same or similar to that of tapered portions  24 / 28  described previously.  
         [0020]    Those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departures in form and detail may be made without departing from the scope and spirit of the present invention as described in the appended claims.