Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1997-10-23
2002-11-05
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001140
Reexamination Certificate
active
06475233
ABSTRACT:
FIELD OF THE INVENTION
In general, the present invention relates to percutaneous transluminal devices and methods which are used to treat obstructed (sclerotic) vessel lumina in humans. In particular, the present invention is an improved stent that requires low expansion pressure for deployment and improved embedding of the struts within the vessel wall.
BACKGROUND OF THE INVENTION
Cardiovascular disease is commonly accepted as being one of the most serious health risks facing our society today. Diseased and obstructed coronary arteries can restrict the flow of blood and cause tissue ischemia and necrosis. While the exact etiology of sclerotic cardiovascular disease is still in question, the treatment of narrowed coronary arteries is more defined. Surgical construction of coronary artery bypass grafts (CABG) is often the method of choice when there are several diseased segments in one or multiple arteries. Conventional open heart surgery is, of course, very invasive and traumatic for patients undergoing such treatment. In many cases, less traumatic, alternative methods are available for treating cardiovascular disease percutaneously. These alternate treatment methods generally employ various types of balloons (angioplasty) or excising devices (atherectomy) to remodel or debulk diseased vessel segments. A further alternative treatment method involves percutaneous, intraluminal installation of one or more expandable, tubular stents or prostheses in sclerotic lesions. Intraluminal endovascular prosthetic grafting is an alternative to conventional vascular surgery. Intraluminal endovascular grafting involves the percutaneous insertion into a blood vessel of a tubular prosthetic graft and its delivery via a catheter to the desired location within the vascular system. The alternative approach to percutaneous revascularization is the surgical placement of vein, artery, or other by-pass segments from the aorta onto the coronary artery, requiring open heart surgery, and significant morbidity and mortality. Advantages of the percutaneous revascularization method over conventional vascular surgery include obviating the need for surgically exposing, removing, replacing, or by-passing the defective blood vessel, including heart-lung by-pass, opening the chest, and general anesthesia.
Stents or prostheses are known in the art as implants which function to maintain patency of a body lumen in humans and especially to such implants for use in blood vessels. They are typically formed from a cylindrical metal mesh which expand when internal pressure is applied. Alternatively, they can be formed of wire wrapped into a cylindrical shape. The present invention relates to an improved stent design which by its specifically configured struts can facilitate the deployment and embedment of the stent within a vessel and is constructed from a manufacturing process which provides a controlled and superior stress yield point and ultimate tensile characteristics.
Stents or prostheses can be used in a variety of tubular structures in the body including, but not limited to, arteries and veins, ureters, common bile ducts, and the like. Stents are used to expand a vascular lumen or to maintain its patency after angioplasty or atherectomy procedures, overlie an aortic dissecting aneurysm, tack dissections to the vessel wall, eliminate the risk of occlusion caused by flaps resulting from the intimal tears associated with primary interventional procedure, or prevent elastic recoil of the vessel.
Stents may be utilized after atherectomy, which excises plaque, cutting balloon angioplasty, which scores the arterial wall prior to dilatation, or standard balloon angioplasty to maintain acute and long-term patency of the vessel.
Stents may be utilized in by-pass grafts as well, to maintain vessel patency. Stents can also be used to reinforce collapsing structures in the respiratory, biliary, urological, and other tracts.
Further details of prior art stents can be found in U.S. Pat. No. 3,868,956 (Alfidi et. al.); U.S. Pat. No. 4,739,762 (Palmaz); U.S. Pat. No. 4,512,338 (Balko et. al.); U.S. Pat. No. 4,553,545 (Maass et. al.); U.S. Pat. No. 4,733,665 (Palmaz); U.S. Pat. No. 4,762,128 (Rosenbluth); U.S. Pat. No. 4,800,882 (Gianturco); U.S. Pat. No. 4,856,516 (Hillstead); U.S. Pat. No. 4,886,062 (Wiktor); U.S. Pat. No. 5,102,417 (Palmaz); U.S. Pat. No. 5,104,404 (Wolff); U.S. Pat. No. 5,192,307 (Wall); U.S. Pat. No. 5,195,984 (Schatz); U.S. Pat. No. 5,282,823 (Schwartz et. al.); U.S. Pat. No. 5,354,308 (Simon et. al.); U.S. Pat. No. 5,395,390 (Simon et. al), U.S. Pat. No. 5,421,955 (Lau et. al.); U.S. Pat. No. 5,443,496 (Schwartz et. al.); U.S. Pat. No. 5,449,373 (Pinchasik et. al.); U.S. Pat. No. 5,102,417 (Palmaz); U.S. Pat. No. 5,514,154 (Lau et. al); and U.S. Pat. No. 5,591,226 (Trerotola et. al.).
In general, it is an object of the present invention to provide a stent or prosthesis which can be readily expanded and embedded into an obstruction or vessel wall with low dilatation pressure thereby minimizing the trauma and damaged imparted to the vessel wall during deployment of the stent.
It is also an object of the present invention to utilize a specifically designed configuration of the outer strut surface to facilitate embedment of the stent structure into the obstruction and vessel wall with low dilatation pressure.
Another object of the present invention is to employ a manufacturing process which optimizes the stress-strain curve characteristics that achieves an increased yield strength and ultimate tensile strength when compared to the other non-wire prior art stents.
SUMMARY OF THE INVENTION
The present invention is directed to an expandable stent which is relatively flexible along its longitudinal axis to facilitate delivery through tortuous body lumens, but which is stiff and stable enough radially in an expanded condition to maintain the patency of a body lumen such as an artery when implanted therein. In addition, the struts of the present invention have a specific trapezoidal, triangular or reduced radii configuration projecting radially outward that functions to reduce the forces necessary to penetrate the vessel wall with the stent thereby minimizing trauma or damage imparted to the wall during deployment.
The invention generally includes a plurality of radially expandable loop elements which are relatively independent in their ability to expand and to flex relative to one another. The individual radially expandable elements of the stent (cross-section of a strut) are dimensioned such that the aspect ratio of the height to width minimizes twisting or rotation during expansion. Interconnecting elements or a backbone extends between the adjacent loop elements to provide increased stability and a preferable position for each loop to prevent warping of the stent upon the expansion thereof. The resulting stent structure is a series of radially expandable loop elements which are spaced longitudinally close enough so that the obstruction, vessel wall and any small dissections located at the treatment site of a body lumen may be dilated or pressed back into position against the lumenal wall. The outward projecting strut surface converges towards the terminal end and is configured in a trapezoidal, triangular or rounded shape to facilitate embedment of the strut into the vessel wall utilizing low dilatation pressure. The individual loop elements may bend relative to adjacent loop elements without significant deformation, cumulatively providing a stent which is flexible along its length and about its longitudinal axis but is still very stiff in the radial direction in order to resist collapse.
The presently preferred structure for the expandable loop elements which form the stent of the present invention are generally a circumferential undulating or alternating loop pattern which comprises one of the radially expandable cylindrical elements. The transverse cross-section of the undulating component of the loop element preferably has an aspect ratio of about one to one (base to height) thereby minimizing any tendency
Interventional Technologies Inc.
Kilpera, Esq. Michael E.
Snow Bruce
Vidas Arrett & Steinkraus
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