Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent in combination with graft
Reexamination Certificate
1997-07-21
2003-02-11
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent in combination with graft
C623S001220, C623S023700, C606S195000
Reexamination Certificate
active
06517570
ABSTRACT:
FIELD OF THE INVENTION
This invention is a medical device and a method of using it. The device is a foldable stent-graft which may be percutaneously delivered with (or on) an endovascular catheter or via surgical techniques or using other suitable techniques and then expanded. The stent-graft uses a kink-resistant stent structure and an interior graft which is attached to the stent in such a way that the graft does not kink and yet the stent is able to conform to curves in the blood vessel lumen.
The expandable stent structure preferably has a helically deployed torsional member with an undulating shape which is wound to form the generally cylindrical shape deployed as the stent. The helical winding desirably is aligned to allow the undulations in adjacent turns of the helix to be in phase. The adjacent undulating shapes may be held in that phased relationship using a flexible linkage, typically made of a polymeric material. The stent may also be of a ring configuration. The stent may be flared to promote smooth blood flow and to assure that the stent will remain in its chosen position.
The graft component cooperating with the stent is tubular and mounted on the interior of the stent. Although it may be made of any of a variety of materials, it preferably is an expanded polyfluorocarbon. The graft component may be attached to the stent in a variety of ways but desirably is bound to the flexible linkage which holds the stent windings in phase (or to the stent structure itself) at a number of sliding attachment points. This manner of attachment allows the stent to slide locally with respect to the graft structure or, in the case of the helically wound stent structure, allows the adjacent undulating shapes in adjacent helical turns to slide longitudinally with respect to each other as the stent is bent and still support the shape of the graft.
The stent-graft may be used to reinforce vascular irregularities, to provide a smooth nonthrombogenic interior vascular surface for diseased areas in blood vessels, or to increase blood flow past a diseased area of a vessel by mechanically improving the interior surface of the vessel. The inventive stent-graft is especially suitable for use within smaller vessels between 2 mm and 6 mm in diameter but is equally suitable for significantly larger vessels. The inventive stent-graft may be self-expandable; it is kink-resistant, easily bent along its longitudinal axis, and does not change its length during that expansion.
Included in the invention are methods for coupling the stent structure to the graft to optimize the flexibility and the kink resistance of the resulting stent-graft.
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, in a preferred aspect, placement of a nonthrombogenic blood-carrying conduit having a smooth inner lumen.
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 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-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 inner conduit of our invention provides a hemodynamically superior surface for blood flow.
Mechanically, the linked helical stent structure used in the stent-graft provides a good combination of radial strength and flexibility. The structure is also radially resilient. It can 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 self-expansion mechanism eliminates the need for a balloon catheter and the associated balloon rupture problems often associated with that delivery procedure. 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 does 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.
The impermeability of the preferred stent-graft makes it suitable for shunting and thereby hydraulically isolating aneurysms. The expansile properties derived from the stent structure provide a secure anchor to the vessel wall.
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 used as a filter in certain situations.
Porter, U.S. Pat. No. 5,064,435, suggests a stent made up of two or more tubular stent segments which may be deployed together so to produce a single axial length by a provision of overlapping areas. This concept is to permit the use of segments of known length, which, when deployed, may be used together in overlapping fashion additively to provide a stent of significant length.
Quan-Gett, U.S. Pat. No. 5,151,105, discloses an implantable, collapsible tubular sleeve apparently of an outer band and an inner spring used to maintain the sleeve in a deployed condition.
Wall, U.S. Pat. No. 5,192,307, suggests a stent having a number of holes therein and which is expandable using an angioplasty balloon so to allow ratchet devices or ledges to hold the stent in an open position once it is deployed.
Perhaps of more relevance are the patents using wire as the stent material.
Gianturco, in U.S. Pat. Nos. 4,580,568 and 5,035,706, describes stents formed of stainless steel wir
Lau Lilip
Maroney Charles
Gore Enterprise Holdings Inc.
Morgan & Finnegan , LLP
Prebilic Paul B.
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