Surgery – Instruments – Internal pressure applicator
Reexamination Certificate
2001-02-27
2003-04-29
Hale, Gloria M. (Department: 3765)
Surgery
Instruments
Internal pressure applicator
C623S001150, C606S108000
Reexamination Certificate
active
06554848
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to self-expanding endoprosthetic devices. In particular, the present invention relates to 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.
For example, during PTCA procedures, it is common to use a dilation catheter to expand a diseased and partially occluded coronary artery so that blood freely flows. Despite the beneficial aspects of PTCA procedures and its widespread and accepted use, it has several drawbacks, including the possible development of restenosis and perhaps acute thrombosis and sub-acute closure. This recurrent stenosis has been estimated to occur in seventeen to fifty percent of patients despite the initial PTCA procedure being successful. Restenosis is a complex and not fully understood biological response to injury of a vessel which results in chronic hyperplasia of the neointima. This neonintimal hyperplasia is activated by growth factors which are released in response to injury. Acute thrombosis is also a result of vascular injury and requires systemic antithrombotic drugs and possibly thrombolytics as well. This therapy can increase bleeding complications at the catheter insertion site and may result in a longer hospital stay. Sub-acute closure is a result of thrombosis, elastic recoil, and/or vessel dissection.
Several procedures have been developed to combat restenosis and sub-acute or abrupt closure, one of which is the delivery and implantation of an intravascular stent. Stents are widely used throughout the United States and in Europe and other countries. Generally speaking, the stents can take numerous forms, however, most common is a generally cylindrical hollow tube that holds open the vascular wall at the area that has been dilated by a dilation catheter. One highly regarded stent used and sold in the United States is marketed under the tradename ACS Multi-Link Stent, which is made by Advanced Cardiovascular Systems, Inc., Santa Clara, Calif.
For 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 delivery diameter to an enlarged deployment diameter greater than or equal to the inner diameter of the arterial wall by inflating the balloon. Stents of this type are expanded to an enlarged diameter through deformation of the stent, which then engages the vessel wall. Eventual endothelial growth of the vessel wall covers over the stent.
Other stents are self-expanding where the expansion occurs through the properties of the material constituting the stent. Examples of intravascular stents can be found in U.S. Pat. No. 5,292,331 to Boneau; U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 4,856,516 to Hillstead; U.S. Pat. No. 5,092,877 to Pinchuk; and U.S. Pat. No. 5,514,154 to Lau et al.
One problem 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 are constructed so that they are expanded beyond their elastic limit. Such stents are permanently deformed beyond their elastic limits in order to hold open a body lumen and to maintain the patency of the body lumen. By the same token, since the material is stressed beyond its elastic limit into the plastic region, the material becomes stiff and inflexible.
There are several commercially available stents that are widely used and generally implanted in the coronary arteries after a PTCA procedure. Another class of stents is 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 these prior art stents are plastically deformed, once collapsed or crushed, they remain collapsed, 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 occlusion. Under certain conditions, muscle contractions might cause the prior art stents to partially or totally collapse and to restrict blood flow in the vessel in which they are implanted.
Such important applications as mentioned above have prompted stent designers to use superelastic or shape memory alloys in their stent to exploit the materials'properties. An example of such shape memory alloy stents is disclosed in, for example, European Patent Application Publication No. EP0873734A2, entitled “Shape Memory Alloy Stent.” This publication suggests a stent for use in a lumen in a human or animal body having a generally tubular body formed from a shape memory alloy which has been treated so that it exhibits enhanced elastic properties.
The evolution of superelastic and shape memory alloy stents progressed to use of ternary elements in combination with nickel-titanium alloys to obtain specific material properties. Use of a ternary element in a superelastic stent is shown in, for example, U.S. Pat. No. 5,907,893 to Zadno-Azizi et al. As a general proposition, there have been attempts at adding a ternary element to nickel-titanium alloys as disclosed in, for instance, U.S. Pat. No. 5,885,381 to Mitose et al.
Another goal has been to design stents that are capable of easy passage through tortuous anatomies such as those found in a coronary artery. One design entails a nitinol stent having a multiplicity of undulating longitudinal struts that can readily change their lengths in the longitudinal direction so as to provide increased longitudinal flexibility for the stent. An example of such a construction is shown in U.S. Pat. No. 5,879,370 to Fischell et al.
Designing stents for extremely curved and highly tortuous anatomies requires a stent that can bend sufficiently without the struts kinking. To address this kinking problem, one concept is to construct a tubular stent with helically-arranged undulating members having a plurality of helical turns. Linking members formed by rings are laced or interwoven between the undulations in adjacent turns of the helical undulating members. U.S. Pat. No. 6,042,605 to Martin et al. discloses such a construction. The linked undulating elements facilitate bending of the stent.
The foregoing stent designs address the problems with delivering a straight length stent into a tortuous anatomy. These designs, do not, however, address the problems with deploying a straight length stent in an extremely curved vessel. Indeed, when a straight length stent is deployed in a curved vessel, the stent tends to straighten the curved vessel to follow the form of the stent. It is believed that the straightening forces of the stent is damaging to the health of the vessel, may create emboli, and may generate intimal flaps that promote restenosis.
One possible solution suggests assembling a composite stent piecemeal at the curved vessel delivery site by using short modular sections. This approach is disclosed in U.S. Pat. No. 5,824,037 to Fogarty et al. In this design, modular sections of the prosthesis may be selectively combined to form a composite prosthesis having characteristics that are tailored to the specific requirements of the patient. Each prosth
Boylan John F.
Huter Benjamin C.
Advanced Cardiovascular Systems Inc.
Fulwider Patton Lee & Utecht LLP
Hale Gloria M.
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