Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1999-11-16
2003-07-01
Milano, Michael J. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
Reexamination Certificate
active
06585758
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to endoluminal stents, grafts, and/or prostheses and, more specifically, to stents having multiple longitudinal sections of different stent architecture.
BACKGROUND OF THE INVENTION
A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft.
A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the prosthesis, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or “introducer” to the site where it is required. The introducer may enter the body through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the prosthesis to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the prosthesis), whereupon the prosthesis expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Various types of stent architectures are known in the art, including many designs comprising a filament or number of filaments, such as a wire or wires, wound or braided into a particular configuration. Included among these wire stent configurations are braided stents, such as is described in U.S. Pat. No. 4,655,771 to Hans I. Wallsten and incorporated herein by reference, the '771 Wallsten patent being only one example of many variations of braided stents known in the art and thus not intended as a limitation of the invention described herein later. Braided stents tend to be very flexible, having the ability to be placed in tortuous anatomy and still maintain patency. This flexibility of braided stents make them particularly well-suited for treating aneurysms in the aorta, where often the lumen of the vessel becomes contorted and irregular both before and after placement of the stent.
Braided stents also have several disadvantages, however. One such disadvantage is that the radial strength on the end of the braided stent is typically substantially less than the radial strength in the middle of the stent. Insufficient radial strength on the stent ends can result in an incomplete seal or migration of the device after implantation. Although flaring the ends or covering the stent with a graft can enhance the radial strength of the ends, the radial strength may still be insufficient. Also, when a braided stent is placed around a curve so that the end of the stent terminates within the curve, tapering of the stent end can result. This can also result in poor end sealing and migration. This phenomenon is particularly prevalent in stents greater than 16 mm in diameter. Although such tapering can be minimized by optimizing braid characteristics such as for example, wire count, wire diameter, and end flare, this tapering effect is still of significant concern.
A number of other stent designs are known in the art having greater radial strength but also having less flexibility than braided stents. Such stent designs can be combined with a braided stent design to produce a multi-segment stent having a flexible, braided stent member in the middle and less-flexible, higher-radial-strength stent members on the ends. Referring now to
FIG. 18
, one known way of combining such stents is merely to implant a braided stent
180
across a region to be repaired (not shown), and then to implant a higher-radial-strength stent
182
overlapping one or both ends
184
of the braided stent to more strongly anchor the braided stent to the lumen (not shown). Such a procedure, however, requires the implantation of multiple stents.
Referring now to
FIGS. 1 and 2
, it is also known, for example, to attach a braided stent member
2
to radially strong, rigid tubular stent end members
1
and
11
. Braided stent member
2
comprises meshing wires
7
that criss-cross to form knots or overlaps
8
. Wires
7
of braided stent member
2
are welded to flanges
6
of tubular stent end members
1
and
11
in pairs. This configuration is described in detail in U.S. Pat. No. 5,383,892 to Cardon et al. (hereinafter “Cardon”).
In another configuration, described in detail in U.S. Pat. No. 5,817,126 to Imran, strands or ribbons of metal are attached to opposite ends comprising slotted metal stents. The strands or ribbons are then intertwined to form a braided middle section.
The configuration disclosed in Cardon and Imran, however, while being applicable for providing a braided stent joined to a slotted metal stent, does not address joining a flexible, filamentary braided stent to a more rigid, wound filamentary stent. Filamentary stents of various winding configurations are well-known in the art, having various degrees of flexibility or rigidity. Inasmuch as such wound filamentary stents do not have discrete flanges as shown in
FIGS. 1 and 2
and described in Cardon or flat areas of slotted metal for joining ribbons or strands as described in Imran, a wound filamentary stent cannot be joined to a braided filamentary stent as described in Cardon or Imran. It may also be desirable to provide more continuity between the end and middle sections than is offered by the mere welding of the ends of the wires or ribbons of the braided section to flanges or other elements of the slotted metal ends, such welding points potentially forming weak spots in the overall stent construction. Additionally, it may be desired to provide stents with variable radial strength sections having diameters larger than can be readily provided by slotted metal stents. In particular, it is desirable to provide multi-section stents wherein the flexible middle section and the more rigid end sections all comprise filamentary stents.
SUMMARY OF THE INVENTION
According to an embodiment of the invention, a multi-section filamentary stent comprises a braided section, which is a cylindrical mesh of a first set of filaments, and at least one wound section, which is connected to the braided section and which comprises a second set of one or more filaments in a repeating configuration having at least one bent portion. For example, a braided center section may be connected between two wound end sections. The repeating configuration of the second set of filaments in the wound section may comprise: a zig-zag configuration, an overlapping zig-zag configuration, a helical configuration, a non-helical configuration, or a configuration having polygonal cells. The polygonal cells may comprise hexagonal cells or overlapping hexagonal cells. At least one continuous filament may be a member of both the first set of filaments in the braided section and the second set of filaments in the wound section, serving to connect the two sections. In one exemplary configuration, at least one continuous filament may extend from the wound section into the braided section as a redundant filament, a tracer filament, or a redundant tracer filament.
The braided section is preferably connected to the wound section by virtue of at least one of the filaments being a member of both sets of filaments. The sections may also be connected to
Chouinard Paul F.
Haverkost Patrick A.
Bui Vy Q.
Milano Michael J.
RatnerPrestia
Sci-Med Life Systems, Inc.
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