Stent and delivery system for deployment thereof

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.

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'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. 1herein illustrates a delivery system10of such publication for delivering a variety of expandable intracorporeal devices; for example, an expandable endovascular graft11. One such expandable endovascular graft11useful 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 system10inFIG. 1has an elongate shaft12with a proximal section13, a distal section14, a proximal end15and a distal end16. The distal section14has an elongate belt support member in the form of a guidewire tube17disposed adjacent a portion of the expandable endovascular graft11. A guidewire18is disposed within guidewire tube17. A plurality of belts21,22, and23are secured to the guidewire tube17and are circumferentially disposed about portions of the endovascular graft11.FIG. 1shows the belts in a configuration that constrains the endovascular graft11. First and second release members24and25releasably secure belts21,22, and23in a constraining configuration as shown.

As defined herein, the proximal end of the elongate shaft is the end15proximal to an operator of the delivery system10during use. The distal end of the elongate shaft is the end16that enters and extends into the patient's body. The proximal and distal directions for the delivery system10and endovascular graft11loaded within the delivery system10as used herein are the same. This convention is used throughout the specification for the purposes of clarity, although other conventions are commonly used.

Belts21-23extend circumferentially about the respective portions of the expandable intracorporeal device11and are releasably locked together by one or more release members24and25. 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 graft11, the release wires24and25are pulled proximally, in a desired sequence, such that the release wires24and25disengage from the end loops of the belts21,22and23. It is desired to provide a system and method to minimize the axial force required on the release wires24and25to release the belts21,22and23.

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.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 2, a stent30that is a first embodiment of the present invention is illustrated. Stent30includes a plurality of struts32extending axially between the opposed ends31,33thereof. The stent30can be oriented in either direction, that is, the end33may represent the proximal end or the distal end of the stent30, depending on the application. Both ends31,33have a plurality of crowns adjoining adjacent struts32. The end33of stent30has a plurality of connecting members36configured to connect the stent30to a graft or other structure. The illustrated stent30structure is merely a representative example, and the invention is not intended to be limited to such. The stent30of the present invention can have various structures and is not limited to the strut structure illustrated herein. For example, the stent30may have a body defined by a lattice structure or a helical structure.

Along one or more of the struts32, a barb40may be provided. The barbs40are preferably formed integrally with the struts32, but may otherwise be manufactured, for example, as a separate component attached to the struts32. The stent struts32and the barbs40are preferably self expanding, that is, upon release of a constraining force, the struts32will move radially apart and the barbs40will extend radially outward. Other configurations, for example, balloon expansion, are also contemplated within the present invention.

Referring toFIGS. 3 and 4, a belt44is positioned about the stent30and secured to maintain the stent30in at least a partially constrained configuration. In the present embodiment, opposite ends43and45of the belt44are separately wrapped about the delivery shaft60. Both ends43and45are secured to the delivery shaft60, for example, via adhesive, welding, bonding or any other suitable means. Two intermediate belt portions47and49extend from the bonded portions and are intertwined to define an eye loop50at a free portion of the belt44configured to receive a release wire70to maintain the stent30in the at least a partially constrained configuration. As illustrated inFIGS. 3 and 4, in the present embodiment, intermediate belt portion47is returned upon itself to form a partial loop portion51through which the release wire70extends. Intermediate belt portion49extends tangentially from the delivery shaft60and extends over the release wire70.

While the release wire70is illustrated as engaging only one belt, the release wire70may extend through multiple stent belts44or a single stent belt44. 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 belt44, a circumferential groove42is preferably ground about the stent30. While the groove42provides 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 toFIGS. 2 and 3, the stent30of the present embodiment of the invention includes an extension80extending circumferentially from one of the struts32to define a shoulder surface82. In the present embodiment, the extension80is formed integrally with the strut32during stamping of the stent30. Provision of the extension80on the stent30allows the extension80to be accurately positioned relative to the intended position of the belt44. In the present embodiment, the shoulder surface82is positioned slightly proximal of the groove42. The shoulder surface82preferably extends at an angle Ø relative to the longitudinal axis of the strut. With such an arrangement, the shoulder surface82guides the belt44toward the junction84between the shoulder surface82and the strut32and reduces the changes the belt44will slip past the extension80in the proximal direction.

Referring toFIG. 3, it is preferable that the extension80is provided on the strut32which is the last strut32that the free portion of the belt44passes over. As such, the eye loop50positioned about the release wire70biases the release wire70toward the extension80, thereby moving the intermediate portion49toward the shoulder surface82. However, the extension80may be provided on any of the other struts32if such will be aligned adjacent the release wire70.

As further illustrated inFIG. 3, it is also preferable that the extension80be axially positioned such that it is proximally adjacent the intermediate belt portion49which extends tangentially from the delivery shaft60as opposed to the intermediate belt portion47that is returned upon itself. With such an arrangement, the intermediate belt portion49extends from under the strut32over the release wire such that it crosses the shoulder surface82. However, the extension80may be otherwise axially positioned. For example, in the embodiment illustrated inFIG. 6, the extension80′ is positioned axially adjacent the returned intermediate belt portion47, however, the extension80′ still contacts the eye loop50and maintains the axial position of the belt44.

The belt44can 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, belt44is 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. Belt44may 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 wire70is 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 wire70can be selected in accordance with the diameter and stiffness of the belt44. The configuration of the belt44may 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 shaft60illustrated herein may have various configurations. For example, the delivery shaft60may be a catheter, a guide wire lumen, a solid shaft or any other suitable structure. Similarly, while the belts44are illustrated as directly connected to the delivery shaft60without any additional support, belt bushings, standoff tubes and the like may be provided to secure, support and direct the belt44.

Referring toFIGS. 5 and 6, a stent30′ that is an alternative embodiment of the present invention is shown. The stent30′ is similar to the previous embodiment and like elements are numbered alike. Stent30′ includes a extension80′ that is formed integrally formed with the strut32axially aligned with the groove42such that the shoulder surface82′ is within the axial confines of the groove42. Additionally, the shoulder surface82′ is at angle Ø which is substantially perpendicular to the strut32. The junction84′ is still configured to receive a portion of the belt44. As explained above with respect toFIG. 6, the extension80′ is positioned axially adjacent the returned intermediate belt portion47, however, the extension80′ still contacts the eye loop50and maintains the axial position of the belt44. The extension80′ has a circumferential length such that the extension80′ does not pass under the release wire70, but instead terminates prior to reaching the release wire70.

Referring toFIG. 7, a stent30″ that is an another alternative embodiment of the present invention is shown. The stent30″ is similar to the previous embodiments and like elements are numbered alike. Stent30″ includes a extension80″. The extension80″ is formed as part of a separate shoulder member100that is interconnected with the strut32. The shoulder member100may be crimped, adhered, welded, bonded or otherwise fixed relative to the strut32. The shoulder member100is axially aligned such that the shoulder surface82″ is axially aligned in a desired relationship with respect to the groove42. In the illustrated embodiment, the contact face82″ is aligned directly with an axial edge of the groove42and the shoulder surface82″ is at angle Ø which is substantially perpendicular to a longitudinal axis of the strut32. The position of the extension80″ relative to the intermediate belt portions47and49can be controlled by positioning the shoulder member100prior to interconnection and/or by controlling the direction of winding of the belt44with respect to the delivery shaft60.