US 20050090894 A1
A stent having helical elements, a geometry for improved crimping, and a good stent-to-vessel ratio is disclosed. In one embodiment, the stent has a plurality of first helical segments and a plurality of second opposing helical segments. The first helical segments are comprised of a plurality of first expandable elements and the second helical segments are comprised of a plurality of second helical elements. The expandable elements are joined to each other by a plurality of struts. When the stent is crimped a portion of one of the first expandable elements nest within another portion of the same expandable element and a portion of two first expandable elements nestle between the same two portions of second expandable elements.
17. A stent having a generally cylindrical main body, the main body comprising:
a plurality of helical segments, at least one helical segment crossing another helical segment; and
wherein the stent has a crimped diameter and an expanded diameter that is 3-6 times the crimped diameter.
18. The stent of
21. The stent of
22. The stent of
This application claims the benefit of U.S. Provisional Application No. 60/267,778, filed on Feb. 9, 2001, which is hereby incorporated in its entirety by reference, and it is a continuation-in-part of U.S. patent application Ser. No. 09/511,481, filed on Feb. 23, 2000, which is also hereby incorporated in its entirety by reference and which is a continuation of U.S. patent application Ser. No. 09/094,402, filed Jun. 10, 1998 (now U.S. Pat. No. 6,117,165).
1. Field of the Invention
The present invention relates to intraluminal endoprosthetic devices known as stents. In particular, the present invention relates to stents having helical elements with a geometry that allows the stent to be readily crimped onto a delivery device.
2. Description of Related Art
Stents are prosthetic devices that are implanted in the lumen of a vessel inside the body to provide support for the vessel's wall. Structural support from stents is particularly important in angioplasty procedures. Typically, stents are implanted within a vessel system to reinforce vessels that are partially occluded, collapsing, weakened, or abnormally dilated. More generally, stents can be used inside any physiological conduit or duct, including—for example—arteries, veins, bile ducts, the urinary tract, alimentary tracts, the tracheobronchial tree, a cerebral aqueduct or the genitourinary system. Stents may be used in both humans and animals.
There are typically two types of stents: self expanding stents and balloon expandable stents. Self expanding stents automatically expand once they are released and assume a deployed, expanded state. A balloon expandable stent is expanded using an inflatable balloon catheter. The balloon is inflated to plastically deform the stent. Balloon expandable stents may be implanted by mounting the stent in an unexpanded or crimped state on a balloon segment of a catheter. The catheter, after having the crimped stent placed thereon, is inserted through a puncture in a vessel wall and moved through the vessel until it is positioned in the portion of the vessel that is in need of repair. The stent is then expanded by inflating the balloon catheter against the inside wall of the vessel. Specifically, the stent is plastically deformed by inflating the balloon so that the diameter of the stent is increased and remains at an increased state. In some situations, the vessel in which the stent is implanted may be dilated by the stent itself when the stent is expanded.
The Palmaz-Schatzt™ stent, which is disclosed in the Handbook of Coronary Stents by Patrick W. Serruys et al. (Martin Dunitz, LTD 1998), is an example of a balloon expandable stent that had been implanted in hundreds of thousands of patients. The Palmaz-Schatz™ stent, like other known stents, has certain limitations. These include, but are not limited to: (i) low stent-to-vessel ratio uniformity, (ii) comparative rigidity of the stent in a crimped as well as deployed state, and (iii) limited flexibility making delivery and placement in narrow vessels difficult. Stent-to-vessel ratio generally refers to the degree that the vessel wall is supported by the stent in its expanded state and preferably should be uniform throughout the length of the stent. Furthermore because the Palmaz-Schatz™ stent consists of one or more bridges that connect a number of consecutively slotted tubes, there are a number of bare areas in the vessel after the expansion of the stent. These shortfalls are common to many stents. Id. at 36.
The present invention is directed to expandable stents that have geometries that allow them to be readily crimped onto a balloon delivery device. In one embodiment, the stent may be comprised of a plurality of first helical segment having a first helical angle with respect to the longitudinal axis of the stent and a plurality of second helical segments that have a second helical angle. The helical segments are capable of expanding and contracting circumferentially, i.e., they expand or contract along the circumference of the stent. In this embodiment, when the stent is crimped, at least one portion of one first helical segment, along with at least one portion of a second first helical element, nestle between the same two portions of two separate second helical segments.
In one embodiment of the present invention, the stent is comprised of a plurality of first expandable elements and a plurality of second expandable elements. The first expandable element may have a segment that nests within another segment of the same first expandable element. In some embodiments, the first expandable elements are joined together by struts to form first helical segments and the second expandable elements are joined together by struts to form second helical segments. The first and second helical segments may have different helical angles or different pitches. In some embodiments, the first and second helical segments share common struts.
In some embodiments of the present invention, the stent may be comprised of a plurality of cells. Each cells may be comprised of first and second elements that are alternatively joined together (i.e., each first element is joined to two second elements and each second element is joined to two first elements to form a polygon). The polygon may be amorphous or may have a definite shape. When the stent is crimped a portion of each first of the elements that make up the cell nestles between portions of the second elements of the cell. In some embodiments, the first and second elements may touch each other when the stent is crimped. A plurality of struts joins the cells to form a stent body. In addition portions of a first element may nest within other portions of the same first element and a portion of a second element may also nest within a portion of the same first element.
The present invention is directed to an expandable stent having a geometry that is well-suited for crimping the stent onto a delivery device. In some, but not necessarily all embodiments of the present invention, the stents may have an expanded diameter that is 3 to 6 times that of its crimped diameter. In addition, in some—but not necessarily all—embodiments the stent-to-vessel ratios may be better than 15%.
In one embodiment of the present invention, as is shown in
As is discussed further below, in some embodiments, the first helical segments 120 a and 120 b may be comprised of a plurality of filament segments and likewise the second helical segments 150 a and 150 b may be comprised of a plurality of filament segments. In some embodiments the total length of the sum of all the filament segments comprising the first helical segment may be longer than the total length of the filament segments comprising the second helical segment. In some cases, the first and second helical segments may share common filament segments.
As is shown in
As is shown in
In some embodiments, as is shown in
As is shown in
The stents of the present invention provide a geometry that improves their crimpability. For example, one embodiment of the present invention may have a crimped diameter of less than 2.0 mm and an expanded diameter of 6.0-12.0 mm, or greater. The stent may be crimped onto a PTA Balloon at a diameter of 1.50 mm and it may be manufactured from a tube having a diameter of approximately 0.030 to 0.500 inches. Of course, other sized tube may be used. And stents may be manufactured in a wide variety of sizes for a wide variety of applications.
In one embodiment of the present invention, when the stent is crimped, a first portion of the first expandable element 300 nests within another portion of the same first expandable element 300. For example, as is shown in
In some embodiments of the present invention, when the stent is crimped, a portion of a second expandable element 350 nests within a portion of the first expandable element 300. For example, as is shown in
In some embodiments of the present invention, when the stent is crimped, portions from two separate first expandable elements 300 may nestle between the same portions of two separate second expandable segments 350. As is shown in
As is illustrated by
As is shown in
Cell geometry may be such that each cell expands at a relatively constant rate. For example, in the embodiment shown in
As is shown in
The foregoing embodiments and description is intended to illustrate the various and broad-ranging features of the present invention and is not intended to limit the scope or spirit of the present invention. The present invention may be embodied in numerous forms other than those specifically described above. For example, and without limitation, the first elements 300 and the second elements 350 may take numerous forms and shapes other than those shown. This may result in a first helical segment having a total filament length that is greater than or less than that of a second helical element. In addition, the stents of the present invention may be manufactured from materials with techniques that are readily known in the art, such as for example, by laser cutting tubes, which are manufactured from appropriate stent materials. Thus, although the embodiments described herein refer to different elements and segments within the same stent, those skilled in the art will recognize that the stent of the present invention may be comprised of a single continuous piece of material or it may be comprised of multiple disparate filaments or segment pieces joined together by well-known techniques.