Abstract:
A stent, a system for delivering a stent and a method of assembling a stent on a stent delivery shaft. The stent delivery system comprises a delivery shaft and a stent configured to be positioned about the delivery shaft. The stent includes an extension extending circumferentially from a portion of the stent to a free end, thereby defining a shoulder surface. A belt has a first portion fixed relative to the delivery shaft and a second portion positioned circumferentially about at least a portion of the stent to retain the stent in an at least partially constrained configuration. A release wire is configured to releasably engage at least a portion of the belt to retain the belt. The shoulder surface engages at least a portion of the belt to minimize axial movement of the belt during release of the release wire from engagement with the belt.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to endoluminal devices, particularly stents and grafts for placement in an area of a body lumen that has been weakened by damage or disease, such as an aneurysm of the abdominal aorta, and more particularly to a stent and a corresponding system for deployment thereof. 
     Medical devices for placement in a human or other animal body are well known in the art. One class of medical devices comprises endoluminal devices such as stents, stent-grafts, filters, coils, occlusion baskets, valves, and the like. A stent typically is an elongated device used to support an intraluminal wall. In the case of a stenosis, for example, a stent provides an unobstructed conduit through a body lumen in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside and/or outside thereof. A covered stent is commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), a stent-graft, or endograft. 
     An endograft may be used, for example, to treat a vascular aneurysm by removing or reducing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, an endograft is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the endograft, typically restrained in a radially compressed configuration by a sheath, crocheted or knit web, catheter or other means, is delivered by an endograft delivery system or “introducer” to the site where it is required. The introducer may enter the vessel or lumen from an access location outside the body, such as purcutaneously through the patient&#39;s skin, or by a “cut down” technique in which the entry vessel or lumen is exposed by minor surgical means. 
     U.S. Patent Application Publication No. US 2004/0138734, which is incorporated herein in its entirety by reference, describes systems and methods for the delivery of stents, endovascular grafts, and the like.  FIG. 1  herein illustrates a delivery system  10  of such publication for delivering a variety of expandable intracorporeal devices; for example, an expandable endovascular graft  11 . One such expandable endovascular graft  11  useful for delivery and deployment at a desired site within a patient is disclosed in U.S. Pat. No. 6,395,019, which is hereby incorporated by reference in its entirety. 
     Delivery system  10  in  FIG. 1  has an elongate shaft  12  with a proximal section  13 , a distal section  14 , a proximal end  15  and a distal end  16 . The distal section  14  has an elongate belt support member in the form of a guidewire tube  17  disposed adjacent a portion of the expandable endovascular graft  11 . A guidewire  18  is disposed within guidewire tube  17 . A plurality of belts  21 ,  22 , and  23  are secured to the guidewire tube  17  and are circumferentially disposed about portions of the endovascular graft  11 .  FIG. 1  shows the belts in a configuration that constrains the endovascular graft  11 . First and second release members  24  and  25  releasably secure belts  21 ,  22 , and  23  in a constraining configuration as shown. 
     As defined herein, the proximal end of the elongate shaft is the end  15  proximal to an operator of the delivery system  10  during use. The distal end of the elongate shaft is the end  16  that enters and extends into the patient&#39;s body. The proximal and distal directions for the delivery system  10  and endovascular graft  11  loaded within the delivery system  10  as used herein are the same. This convention is used throughout the specification for the purposes of clarity, although other conventions are commonly used. 
     Belts  21 - 23  extend circumferentially about the respective portions of the expandable intracorporeal device  11  and are releasably locked together by one or more release members  24  and  25 . U.S. Patent Application Publication No. US 2004/0138734 discloses various belt and release wire configurations that may be utilized to secure stents and the like. 
     To deploy the graft  11 , the release wires  24  and  25  are pulled proximally, in a desired sequence, such that the release wires  24  and  25  disengage from the end loops of the belts  21 ,  22  and  23 . It is desired to provide a system and method to minimize the axial force required on the release wires  24  and  25  to release the belts  21 ,  22  and  23 . 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention may provide a stent comprising a plurality of substantially axially extending struts; and an extension coupled to one of the struts and extending circumferentially therefrom to a free end, thereby defining a shoulder surface at angle approximately 90° or less relative to a longitudinal axis of the stent strut. 
     In another aspect, the invention may provide a stent delivery system comprising a delivery shaft and a stent configured to be positioned about the delivery shaft. The stent includes an extension extending circumferentially from a portion of the stent to a free end, thereby defining a shoulder surface. A belt has a first portion fixed relative to the delivery shaft and a second portion positioned circumferentially about at least a portion of the stent to retain the stent in an at least partially constrained configuration. A release wire is configured to releasably engage at least a portion of the belt to retain the belt. The shoulder surface engages at least a portion of the belt to minimize axial movement of the belt during release of the release wire from engagement with the belt. 
     In yet another aspect, the invention may provide a method of assembling a stent on a stent delivery shaft, the method comprising fixing a first portion of a belt relative to the delivery shaft; positioning a stent about a portion of the delivery shaft; positioning a second portion of the belt circumferentially about at least a portion of the stent to retain the stent in a constrained configuration; engaging at least a portion of the belt with a release wire to maintain the belt about the stent; and engaging at least a portion of the belt with an extension extending circumferentially from a portion of the stent and defining a shoulder surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view in partial section of a prior art endovascular stent graft delivery system. 
         FIG. 2  shows a flat pattern of an embodiment of a stent in accordance with one or more aspects of the invention. 
         FIG. 3  is a side elevation view illustrating the stent of  FIG. 2  positioned about an embodiment of a delivery system in accordance with one or more aspects of the invention. 
         FIG. 4  is a side elevation view illustrating an embodiment of a delivery shaft with a belt positioned thereabout. 
         FIG. 5  shows a flat pattern of an alternative embodiment of a stent in accordance with one or more aspects of the invention. 
         FIG. 6  is a side elevation view illustrating the stent of  FIG. 5  positioned about an embodiment of a delivery system in accordance with one or more aspects of the invention. 
         FIG. 7  shows a flat pattern of another alternative embodiment of a stent in accordance with one or more aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
     Referring to  FIG. 2 , a stent  30  that is a first embodiment of the present invention is illustrated. Stent  30  includes a plurality of struts  32  extending axially between the opposed ends  31 ,  33  thereof. The stent  30  can be oriented in either direction, that is, the end  33  may represent the proximal end or the distal end of the stent  30 , depending on the application. Both ends  31 ,  33  have a plurality of crowns adjoining adjacent struts  32 . The end  33  of stent  30  has a plurality of connecting members  36  configured to connect the stent  30  to a graft or other structure. The illustrated stent  30  structure is merely a representative example, and the invention is not intended to be limited to such. The stent  30  of the present invention can have various structures and is not limited to the strut structure illustrated herein. For example, the stent  30  may have a body defined by a lattice structure or a helical structure. 
     Along one or more of the struts  32 , a barb  40  may be provided. The barbs  40  are preferably formed integrally with the struts  32 , but may otherwise be manufactured, for example, as a separate component attached to the struts  32 . The stent struts  32  and the barbs  40  are preferably self expanding, that is, upon release of a constraining force, the struts  32  will move radially apart and the barbs  40  will extend radially outward. Other configurations, for example, balloon expansion, are also contemplated within the present invention. 
     Referring to  FIGS. 3 and 4 , a belt  44  is positioned about the stent  30  and secured to maintain the stent  30  in at least a partially constrained configuration. In the present embodiment, opposite ends  43  and  45  of the belt  44  are separately wrapped about the delivery shaft  60 . Both ends  43  and  45  are secured to the delivery shaft  60 , for example, via adhesive, welding, bonding or any other suitable means. Two intermediate belt portions  47  and  49  extend from the bonded portions and are intertwined to define an eye loop  50  at a free portion of the belt  44  configured to receive a release wire  70  to maintain the stent  30  in the at least a partially constrained configuration. As illustrated in  FIGS. 3 and 4 , in the present embodiment, intermediate belt portion  47  is returned upon itself to form a partial loop portion  51  through which the release wire  70  extends. Intermediate belt portion  49  extends tangentially from the delivery shaft  60  and extends over the release wire  70 . 
     While the release wire  70  is illustrated as engaging only one belt, the release wire  70  may extend through multiple stent belts  44  or a single stent belt  44 . Various belt and release wire configurations and sequences are described in U.S. Patent Application Publication No. US 2004/0138734, which is incorporated herein in its entirety by reference. 
     To provide general axial containment of the belt  44 , a circumferential groove  42  is preferably ground about the stent  30 . While the groove  42  provides general axial containment, belts of prior art systems have been found to move in conjunction with the release wire due to the friction force created between the belt and the release wire. The friction force may provide undesired resistance to removal of the release wire. Such undesired resistance to removal of the release wire may be further enhanced if a portion of the belt moves axially, thereby creating a pivot motion which may pinch or otherwise trap the release wire. 
     Referring to  FIGS. 2 and 3 , the stent  30  of the present embodiment of the invention includes an extension  80  extending circumferentially from one of the struts  32  to define a shoulder surface  82 . In the present embodiment, the extension  80  is formed integrally with the strut  32  during stamping of the stent  30 . Provision of the extension  80  on the stent  30  allows the extension  80  to be accurately positioned relative to the intended position of the belt  44 . In the present embodiment, the shoulder surface  82  is positioned slightly proximal of the groove  42 . The shoulder surface  82  preferably extends at an angle Ø relative to the longitudinal axis of the strut. With such an arrangement, the shoulder surface  82  guides the belt  44  toward the junction  84  between the shoulder surface  82  and the strut  32  and reduces the changes the belt  44  will slip past the extension  80  in the proximal direction. 
     Referring to  FIG. 3 , it is preferable that the extension  80  is provided on the strut  32  which is the last strut  32  that the free portion of the belt  44  passes over. As such, the eye loop  50  positioned about the release wire  70  biases the release wire  70  toward the extension  80 , thereby moving the intermediate portion  49  toward the shoulder surface  82 . However, the extension  80  may be provided on any of the other struts  32  if such will be aligned adjacent the release wire  70 . 
     As further illustrated in  FIG. 3 , it is also preferable that the extension  80  be axially positioned such that it is proximally adjacent the intermediate belt portion  49  which extends tangentially from the delivery shaft  60  as opposed to the intermediate belt portion  47  that is returned upon itself. With such an arrangement, the intermediate belt portion  49  extends from under the strut  32  over the release wire such that it crosses the shoulder surface  82 . However, the extension  80  may be otherwise axially positioned. For example, in the embodiment illustrated in  FIG. 6 , the extension  80 ′ is positioned axially adjacent the returned intermediate belt portion  47 , however, the extension  80 ′ still contacts the eye loop  50  and maintains the axial position of the belt  44 . 
     The belt  44  can be made from any high strength, resilient material that can accommodate the tensile requirements of the belt members and remain flexible after being set in a constraining configuration. Typically, belt  44  is made from solid ribbon or wire of a shape memory alloy such as nickel titanium or the like, although other metallic or polymeric materials are possible. Belt  44  may also be made of braided metal filaments or braided or solid filaments of high strength synthetic fibers such as Dacron®, Spectra or the like. The release wire  70  is generally made from a biocompatible high strength alloy such as stainless steel, but can also be made from any other suitable materials. Examples include other metallic alloys such as nickel titanium, non-metallic fibers such as carbon, polymeric materials, composites thereof, and the like. The diameter and stiffness of the release wire  70  can be selected in accordance with the diameter and stiffness of the belt  44 . The configuration of the belt  44  may vary to suit the particular embodiment of the delivery system. As set forth above, various belt and release wire configurations and sequences are described in U.S. Patent Application Publication No. US 2004/0138734, which is incorporated herein in its entirety by reference. 
     The delivery shaft  60  illustrated herein may have various configurations. For example, the delivery shaft  60  may be a catheter, a guide wire lumen, a solid shaft or any other suitable structure. Similarly, while the belts  44  are illustrated as directly connected to the delivery shaft  60  without any additional support, belt bushings, standoff tubes and the like may be provided to secure, support and direct the belt  44 . 
     Referring to  FIGS. 5 and 6 , a stent  30 ′ that is an alternative embodiment of the present invention is shown. The stent  30 ′ is similar to the previous embodiment and like elements are numbered alike. Stent  30 ′ includes a extension  80 ′ that is formed integrally formed with the strut  32  axially aligned with the groove  42  such that the shoulder surface  82 ′ is within the axial confines of the groove  42 . Additionally, the shoulder surface  82 ′ is at angle Ø which is substantially perpendicular to the strut  32 . The junction  84 ′ is still configured to receive a portion of the belt  44 . As explained above with respect to  FIG. 6 , the extension  80 ′ is positioned axially adjacent the returned intermediate belt portion  47 , however, the extension  80 ′ still contacts the eye loop  50  and maintains the axial position of the belt  44 . The extension  80 ′ has a circumferential length such that the extension  80 ′ does not pass under the release wire  70 , but instead terminates prior to reaching the release wire  70 . 
     Referring to  FIG. 7 , a stent  30 ″ that is an another alternative embodiment of the present invention is shown. The stent  30 ″ is similar to the previous embodiments and like elements are numbered alike. Stent  30 ″ includes a extension  80 ″. The extension  80 ″ is formed as part of a separate shoulder member  100  that is interconnected with the strut  32 . The shoulder member  100  may be crimped, adhered, welded, bonded or otherwise fixed relative to the strut  32 . The shoulder member  100  is axially aligned such that the shoulder surface  82 ″ is axially aligned in a desired relationship with respect to the groove  42 . In the illustrated embodiment, the contact face  82 ″ is aligned directly with an axial edge of the groove  42  and the shoulder surface  82 ″ is at angle Ø which is substantially perpendicular to a longitudinal axis of the strut  32 . The position of the extension  80 ″ relative to the intermediate belt portions  47  and  49  can be controlled by positioning the shoulder member  100  prior to interconnection and/or by controlling the direction of winding of the belt  44  with respect to the delivery shaft  60 .