Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent combined with surgical delivery system
Reexamination Certificate
1997-07-18
2003-09-02
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent combined with surgical delivery system
C623S001230, C623S001200
Reexamination Certificate
active
06613072
ABSTRACT:
FIELD OF THE INVENTION
This invention is a medical device and a method of using it. The device is a foldable stent or stent-graft which may be percutaneously delivered with (or on) a catheter, typically an endovascular catheter, to a body cavity or lumen and then expanded. It may also be delivered via surgical (or other) techniques. The expandable stent structure utilizes torsional members which distribute bending and folding loads in such a way that the stent is not plastically deformed. The stent's configuration allows it to be folded or otherwise compressed to a very small diameter prior to deployment without changing the length of the stent. The graft component cooperating with the stent is tubular and preferably is blood-compatible material which may, if desired, be reinforced with fibers. The stent is able to provide collapsible support for otherwise frangible graft material.
The invention also involves procedures for folding stents and for deploying stents or stent-grafts which have been folded, bound, or otherwise collapsed to significantly smaller diameters for insertion into a human or animal body. When used with super-elastic alloys, the stent may be collapsed at a convenient temperature either above or, preferably, below the transition temperature of the alloy. The deployment procedures may involve the use of an outer sleeve to maintain the stent or stent-graft at a reduced diameter or may involve one or more external or internal “slip-lines” or “tether wires” to hold and then to release the device.
BACKGROUND OF THE INVENTION
Treatment or isolation of vascular aneurysms or of vessel walls which have been thinned or thickened by disease has traditionally been done via surgical bypassing with vascular grafts. Shortcomings of this procedure include the morbidity and mortality associated with surgery, long recovery times after surgery, and the high incidence of repeat intervention needed due to limitations of the graft or of the procedure. Vessels thickened by disease are currently sometimes treated less invasively with intraluminal stents that mechanically hold these vessels open either subsequent to or as an adjunct to a balloon angioplasty procedure. Shortcomings of current stents include the use of highly thrombogenic materials (stainless steels, tantalum, ELGILOY) which are exposed to blood, the general failure of these materials to attract and support functional endothelium, the irregular stent/vessel surface that causes unnatural blood flow patterns, and the mismatch of compliance and flexibility between the vessel and the stent.
Important to this invention is the use of less invasive intraluminal delivery and, desirably, placement of a nonthrombogenic blood-carrying conduit having a smooth inner lumen which will endothelize. One desirable biologic material for the inner layer of the inventive stent-graft is collagen-based and, although it will fold with ease, is otherwise fairly frangible or inelastic in that it has very little ability to stretch. Mounting a collagen tube on the outside of or as a part of a balloon-expandable stent will usually cause the tube to tear. Mounting such a tube on the inside of a balloon expandable stent will yield a torn irregular surface exposed to blood flow. Further, balloon expandable devices that rely upon plastic deformation of the stent to achieve a deployed shape are subject to abrupt closure as a result of trauma when the devices are placed in a vessel near the skin surface or across a joint or ligament. Those self-expanding stents which rely on the shortening of the stent upon radial expansion at deployment may cause vessel tearing problems similar to those observed with the use of balloon expandable devices. Obviously, stents which shorten during deployment are also subject to deployment placement inaccuracies.
The most desired variations of this invention involve a stent-graft which is self-expanding, which does not shorten upon delivery, which has excellent longitudinal flexibility, which has high radial compliance to the vessel lumen, and exposes the blood to a smooth, nonthrombogenic surface often capable of supporting endothelium growth.
The inventive device may be delivered in a reduced diameter and expanded to maintain the patency of any conduit or lumen in the body. An area in which the inventive stent and stent graft is particularly beneficial is in the scaffolding of atherosclerotic lesions in the cardiovascular system to establish vessel patency, prevention of thrombosis, and the further prevention of restenosis after angioplasty. In contrast to many of the stents discussed below having metallic struts intruding into the blood flow in the vessel lumen which generate turbulence and create blood stasis points initiating thrombus formation, the smooth, continuous surface provided by the preferred tubular collagen-based inner conduit of our invention provides a hemodynamically superior surface for blood flow. the stent and stent-graft may also be employed in any body cavity, opening, or lumen where a device such as is described here is appropriate.
The absence of gaps or holes in the graft structure between stent struts of our invention allows the tacking of both large and small flaps and tears in the vessel wall. These flaps disrupt blood flow and attract thrombus. The disruption of the natural anti-thrombotic covering of endothelium only worsens the condition. When collagen-based materials are used, the collagen-based barrier interposed between blood and a disrupted or injured portion of the vessel wall serves to mask injured intimal or medial layers from blood, thereby preventing thrombus formation and intimal proliferation which may lead to restenosis.
The stent-graft acts as a mechanical barrier preventing tissue from proliferating into or impinging the lumen. The nature of the bioactivity of the collagen and the smoother flow characteristics at the blood-contacting surface are conducive to endothelial cell attachment and growth thereby assuring the long-term blood compatibility of the device.
Mechanically, the preferred stent structures (described in U.S. patent application Ser. Nos. 08/221,815 and 08/222,263 both filed on Apr. 1, 1994 by Lau et al, the entirety of which are incorporated by reference) provide a good combination of radial strength and flexibility. The preferred stent structures are also radially resilient and may be completely crushed or flattened and yet spring open again once the obstructive loading is removed. This ability is important for use in exposed portions of the body around the peripheral vasculature or around joints. The stent-graft can sustain a crushing traumatic blow or compression from the bending of a joint and still return to the open configuration once the load is removed.
With regard to delivery, the inventive self-expansion mechanism and procedure eliminates the need for a balloon catheter and the associated balloon rupture problems often associated with balloons. In addition, the absence of the bulk of the balloon allows a smaller delivery profile to be achieved. Unlike some other self-expanding stent designs, this stent-graft maintains a constant length throughout the expansion process. Thus, the stent-graft would not have some of the positioning problems associated with other many self-expanding stents. In treating longer lesions, our self-expanding design eliminates the need for special long balloons or repositioning of the balloon between inflations in order to expand the entire length of the stent.
Stents
The stents currently described in the open literature include a wide variety of different shapes.
Wallsten, U.S. Pat. No. 4,655,771, suggests a vascular prosthesis for transluminal implantation which is made up of a flexible tubular body having a diameter that is varied by adjusting the axial separation of the two ends of the body relative to each other. In general, the body appears to be a woven device produced of various plastics or stainless steel.
U.S. Pat. No. 4,760,849, to Kroph, shows the use of a ladder-shaped coil spring which additionally may be use
Hartigan William M.
Lam Sharon
Lau Lilip
Maroney Charles T.
Gore Enterprise Holdings Inc.
Morgan & Finnegan , LLP
Prebilic Paul B.
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