Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1998-07-22
2001-12-04
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001150
Reexamination Certificate
active
06325824
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to self-expanding endoprosthesis devices, in particular self-expanding intraluminal vascular grafts, generally called stents, adapted to be implanted in a body lumen, such as carotid arteries, coronary arteries, peripheral arteries, veins, or other vessels to maintain the patency of the lumen. These devices are frequently used in the treatment of atherosclerotic stenosis in blood vessels especially after percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA) procedures, with the intent to reduce the likelihood of restenosis of a vessel. Stents are also used to support a body lumen, tack-up a flap or dissection in a vessel, or in general where the lumen is weak to add support. The present invention also relates to an intraluminal vascular graft that can be used in essentially any body lumen.
In expandable stents that are delivered with expandable catheters, such as balloon catheters, the stents are positioned over the balloon portion of the catheter and are expanded from a reduced diameter to an enlarged diameter greater than or equal to the inner diameter of the arterial wall, by inflating the balloon. Stents of this type can be expanded to an enlarged diameter by deforming the stent, by engagement of the stent walls with respect to one another, and by one way engagement of the stent walls together with endothelial growth onto and over the stent. Other stents are self-expanding, through the properties of the material constituting the stent or by design. Examples of intravascular stents can be found in U.S. Pat. No. 5,292,331 (Boneau); U.S. Pat. No. 4,580,568 (Gianturco); U.S. Pat. No. 4,856,516 (Hillstead); U.S. Pat. No. 5,092,877 (Pinchuk); and U.S. Pat. No. 5,514,154 (Lau et al.), which are incorporated herein by reference in their entirety.
The problems with some prior art stents, especially those of the expandable type, is that they are often stiff and inflexible. Often, the expandable type stents are formed from stainless steel alloys and the stents are constructed so that they are expanded beyond their elastic limit. Such stents are permanently deformed beyond their elastic limits and are capable of holding open a body lumen and maintaining patency of the body lumen. There are several commercially available stents that are widely used and generally implanted in the coronary arteries after a PTCA procedure.
Stents also are implanted in vessels that are closer to the surface of the body, such as in the carotid arteries in the neck or in peripheral arteries and veins in the leg. Because these stents are so close to the surface of the body they are particularly vulnerable to impact forces that can partially or completely collapse the stent and thereby block fluid flow in the vessel. Since the prior art stents are plastically deformed, once collapsed or crushed they will remain so, permanently blocking the vessel. Thus, the prior art stents can pose an undesirable condition to the patient.
Other forces can impact the prior art stents and cause similar partial or total vessel blockage. Under certain conditions, muscle contractions might cause the prior art stents to partially or totally collapse and restrict blood flow in the vessel in which they are implanted.
Attempts have been made to make stents out of shape memory alloys (see discussion infra), but dislodgment from the implant site may result if these prior art stents are temporarily crushed due to external forces.
What has been needed and heretofore unavailable in the prior art stents is a stent that is formed from a metal alloy having crush-resistant and recovery properties and, importantly, that will not dislodge from the implant site if it is temporarily crushed due to external forces. The present invention satisfies these needs.
SUMMARY OF THE INVENTION
The present invention is directed to a method for maintaining the patency of a body lumen, including providing a substantially cylindrically-shaped stent having crush-resistant superelastic properties; implanting the stent in the body lumen; and providing projections which form on an outer wall surface of the stent and thereby at least partially penetrate the inner wall surface of the body lumen, thus facilitating the attachment of the stent to the inner wall surface of the body lumen so that as an external force is applied to the body lumen, the stent temporarily at least partially collapses, and the stent returns to the substantially cylindrical shape to thereby maintain the patency of the body lumen when the external force is removed.
One object of the present invention is to provide a method of maintaining the patency of a vessel via a stent while minimizing both the risk of permanent vessel collapse and the risk of dislodgment of the stent from the implant site if the stent is temporarily crushed due to external or internal forces. In one preferred method a crush-resistant superelastic stent may be made from a material including a nickel-titanium alloy. The stent of the present invention is placed under stress by collapsing it to a delivery diameter. Once the stent is positioned in a body lumen, it will expand in the radial direction upon a reduction of stress applied to the stent. During expansion of the stent, projections form on the outer wall surface of the stent. These projections at least partially penetrate the inner wall surface of the body lumen. If an external force is then applied to the body lumen, the stent temporarily at least partially collapses. However, due to the projections, the inner surface of the body lumen is held fast to the outer wall surface of the stent. Therefore, the body lumen temporarily collapses with the stent and the stent will not migrate within the body lumen. The stent then quickly regains its former expanded shape due to its superelastic qualities.
In another preferred method, the stent may be constructed of a shape memory alloy, such as a nickel-titanium alloy. The stent is designed to expand in the radial direction when inserted into a body lumen and upon reaching a transition temperature that is below normal body temperature. The stent further exhibits crush-resistant superelastic qualities. Again, during expansion of the stent, projections form on the outer wall surface of the stent. These projections at least partially penetrate the inner wall surface of the body lumen. If an external force is then applied to the body lumen, the stent temporarily at least partially collapses. However, due to the projections, the inner surface of the body lumen is held fast to the outer wall surface of the stent. Therefore, the body lumen temporarily collapses with the stent and the stent will not migrate within the body lumen. The stent then quickly regains its former expanded shape due to its superelastic qualities.
Other features and advantages of the present invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings.
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Advanced Cardiovascular Systems Inc.
Fulwider Patton Lee & Utecht LLP
Stewart Alvin
Willse David H.
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