Abstract:
A stent-delivery catheter includes a balloon having an intermediate body, tapered end portions and at least one circumferential groove adjacent a transition between the intermediate body and a tapered end portion. While the balloon is deflated, the groove allows the tapered end portion of the balloon to function as a dam to retain a stent on the balloon. This abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to intraluminal stenting, and in particular, to a catheter having a grooved stent delivery balloon.  
         BACKGROUND OF THE INVENTION  
         [0002]    Intraluminal stenting is useful in treating tubular vessels in the body which are narrowed or blocked and it is an alternative to surgical procedures that intend to bypass such an occlusion. When used in endovascular applications, the procedure involves inserting a prosthesis into an artery and expanding it to prevent collapse of the vessel wall.  
           [0003]    Percutaneous transluminal angioplasty (PTCA) is used to open coronary arteries which have been occluded by a build-up of cholesterol fats or atherosclerotic plaque. Typically, a guide catheter is inserted into a major artery in the groin and is passed to the heart, providing a conduit to the ostia of the coronary arteries from outside the body. A balloon catheter and guidewire are advanced through the guiding catheter and steered through the coronary vasculature to the site of therapy. The balloon at the distal end of the catheter is inflated, causing the site of the stenosis to widen. Dilation of the occlusion, however, can form flaps, fissures or dissections which may threaten re-closure of the dilated vessel. Implantation of a stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel. Reducing the possibility of restenosis after angioplasty reduces the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.  
           [0004]    A stent is typically a hollow, generally cylindrical device formed from wire(s) or a tube and the stent is commonly intended to act as a permanent prosthesis. A stent is deployed in a body lumen from a radially contracted configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be either radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient material while the device-expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during an angioplasty procedure by using a balloon catheter bearing the compressed stent which has been loaded onto the balloon. The stent radially expands as the balloon is inflated, forcing the stent into contact with the body lumen, thereby forming a support for the vessel wall. Deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by means of the balloon catheter.  
           [0005]    A balloon of appropriate size and pressure is first used to open the lesion. The process can be repeated with a stent loaded onto a balloon. Direct stenting involves simultaneously performing angioplasty and stent implantation using a stent mounted on a dilatation balloon. After the balloon is withdrawn, the stent remains as a scaffold for the injured vessel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the appended drawings in which:  
         [0007]    [0007]FIG. 1 is a longitudinal view of a balloon in accordance with the invention;  
         [0008]    FIGS.  2 - 5  are enlarged, longitudinal portions (FIGS. 2, 4 and  5  in section) of balloons in accordance with the invention, showing several alternative embodiments of circumferential grooves;  
         [0009]    [0009]FIG. 6 is a longitudinal view of a balloon catheter in accordance with the invention, shown with the balloon deflated;  
         [0010]    [0010]FIG. 7 is a longitudinal view of a stent delivery balloon catheter in accordance with the invention, shown with a stent mounted thereon and the balloon deflated; and  
         [0011]    [0011]FIG. 8 shows the embodiment of FIG. 7 wherein the balloon has been inflated to deliver the stent in a vessel of a patient. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Applicant&#39;s invention is useful with any expandable stent, such as those stents designed for delivery by a balloon. The stent may be generally cylindrical, and it may be mounted on a tubular balloon. FIG. 1 shows balloon  10 , which can retain a stent thereon during delivery. Proximal and distal circumferential grooves  15 ,  20 , respectively, surround balloon  10  adjacent the transitions between intermediate body  12  and proximal and distal cones  25 ,  30 , respectively. Intermediate body  12  may be generally cylindrical in shape, and it may be centrally located between proximal and distal cones  25 ,  30 . Proximal and distal cones  25 ,  30  terminate in proximal and distal ends  35 ,  40 , respectively, which are adapted to be mounted on catheter shaft  50 , as shown in FIG. 6.  
         [0013]    In FIG. 1, proximal circumferential groove  15  is substantially U-shaped when viewed in longitudinal section, and the diameters of balloon  10  measured distal and proximal to groove  15  are substantially equal. Distal circumferential groove  20  is an alternative embodiment to groove  15  and is flat-bottomed, or rectangular in longitudinal section. FIGS.  2 - 5  show several other alternative embodiments of circumferential grooves in balloon  10 . As shown in FIG. 2, circumferential groove  115  is substantially C-shaped in longitudinal section. Groove  115  may also be described as being generally circular in longitudinal section, with an open arc portion. Groove  115  is also shown as being optionally filled with flexible material  45 . Any of the circumferential grooves in the invention may be partially or fully filled with flexible material  45 , as will be described further below.  
         [0014]    As shown in FIG. 3, circumferential groove  215  is substantially U-shaped. in longitudinal section. However, groove  215  is located toward the cone side of the transition between cylindrical intermediate body  12  and cone  225 , such that the diameters of balloon  10  measured distal and proximal to groove  215  are substantially unequal.  
         [0015]    As shown in FIG. 4, circumferential groove  315  is substantially W-shaped in longitudinal section. Groove  315  may also be considered as two U-shaped circumferential grooves formed adjacent each other. As shown in FIG. 5, circumferential groove  415  is, in longitudinal section, a polygon with an open side.  
         [0016]    Balloon  10  can be made according to stretch blow molding processes that are well known to those skilled in the arts of dilatation and stent delivery balloons. Molds used in balloon forming typically have hollow intermediate sections with removable end inserts for forming cones, and are made of metal such as brass. In known alternatives, balloon molds may be unitary tubular chambers that have been thermo-formed of a high temperature material such as glass. Circumferential grooves  15 ,  20 , and their alternatives shown herein can be formed during conventional stretch blow molding, thus providing a generally uniform wall thickness throughout the balloon regions that include grooves  15 ,  20 .  
         [0017]    A balloon mold can be adapted in a variety of ways to form balloon  10  with circumferential grooves  15 ,  20 . In a first example, ring members may be inserted inside a balloon mold such that balloon  10  forms around the ring members to create circumferential grooves  15 ,  20 . The ring members can be cast, molded or machined of any material that will retain its shape during balloon forming, such as a metal, a ceramic, a thermoset polymer or a thermoplastic having a sufficiently high melting temperature. A conventional multi-part mold may have one or more internal grooves adapted to retain the ring members in the desired position within the mold. For instance, ring retaining grooves may be machined adjacent the interface between a mold center section and the mating removable inserts. In a second example, a unitary glass balloon mold (see U.S. Pat. No. 5,163,989) can be formed to capture the ring members within the inner chamber. Balloon  10  can be made from single or multiple layers of thermoplastics such as polyolefins, polyurethanes, polyamides, blends or block copolymers that include these materials, or other polymers known to be suitable for dilatation and stent delivery balloons.  
         [0018]    Circumferential grooves  15 ,  20  create a partial mechanical disengagement between balloon intermediate body  12  and cones  25 ,  30 . The partial disengagement permits adjacent body  12  and cones  25 ,  30  to move differently in the radial direction, comparable to the way a rolling diaphragm works in the axial direction. For example, if intermediate body  12  is radially restrained during inflation of balloon  10 , then circumferential grooves  15 ,  20  will allow a limited radial expansion of cones  25 ,  30 , thus creating radial steps at both ends of intermediate body  12 . These radial steps can be heat set into balloon  10 , and can act as dams to prevent stent  60  from sliding off of balloon  10 .  
         [0019]    Any of the circumferential grooves disclosed herein can be partially or completely filled with flexible material  45 , as mentioned above. The addition of such a material to a circumferential groove can reinforce or enhance the dam effect created by the radial steps at the ends of intermediate body  12 . Substances selected for flexible material  45  may be elastic or inelastic, thermoplastic or thermoset polymers, and may be foamed to enhance flexibility. Flexible material  45  may also comprise a formulation typically used for coating medical devices, including balloons, to either reduce or enhance friction properties. Elastic or elastomeric materials may provide a high coefficient of friction relative to the material of balloon  10 , thus enhancing stent retention thereon. To avoid separation between flexible material  45  and balloon  10 , material  45  should be adhered to balloon  10 , either by inherent adhesive properties of the material, or by a separate bonding component.  
         [0020]    [0020]FIG. 7 shows a stent delivery balloon catheter in accordance with the invention, and which has been made as follows. Balloon  10  is mounted on catheter shaft  50 . Balloon  10  is deflated about shaft  50 , and stent  60  is crimped or compressed about intermediate body  12 . With stent  60  held in the radially compressed configuration, inflation pressure is applied to balloon  10 . In response to this internal pressure, circumferential grooves  15 ,  20  allow limited expansion of cones  25 ,  30  to form proximal and distal steps  65 ,  70 , respectively. Heat setting of balloon  10  imparts thereto a memory of the shapes of steps  65 ,  70 . Heat setting can be performed with or without internal pressure in balloon  10 .  
         [0021]    Alternatively, steps  65 ,  70  may be formed after deflation of balloon  10  by wrapping balloon  10  around shaft  50  and crimping stent  60  around intermediate body  12 . During stent crimping, circumferential grooves  15 ,  20  allow cones  25 ,  30  to retain a larger deflated profile than that of intermediate body  12 . In this way, steps  65 ,  70  can be formed without pressurizing balloon  10 .  
         [0022]    The invention may be practiced with one or more circumferential grooves adjacent the ends of intermediate body  12  of balloon  10 . For example, a single groove  20  may be formed in balloon  10  adjacent the transition between intermediate body  12  and distal cone  30 . Alternatively, a single groove  15 , may be formed in balloon  10  adjacent the transition between intermediate body  12  and proximal cone  25 . As shown in FIG. 4, two or more grooves may be formed next to each other adjacent a transition between intermediate body  12  and a cone. Any combinations of alternative embodiments of circumferential grooves are also possible, with or without flexible filler materials.