Textiles: braiding – netting – and lace making – Processes and products – Braided
Reexamination Certificate
1998-04-30
2001-05-29
Stryiewski, William (Department: 3765)
Textiles: braiding, netting, and lace making
Processes and products
Braided
C087S001000, C087S002000, C087S005000, C087S013000
Reexamination Certificate
active
06237460
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self-expanding stent for a medical device to be introduced into a cavity of a human or animal body. More particularly, the present invention relates to a braided or woven filament medical stent having a tubular body which is radially expandable and retractable between a first diameter, corresponding to a compressed state of the stent, and a second diameter, greater than the first, corresponding to a resting state of the stent, and is axially expansible and retractable between a first length, corresponding to the working state, and a second length, less than the first, corresponding to the resting state. For purposes herein, the term “self-expanding stent” is intended to mean that, when brought into its working position (i.e., a radially compressed and axially extended position), the stent, once released, tends spontaneously to substantially recover its resting position (i.e., a radially expanded and axially contracted position). Also, the term “medical device to be introduced into a cavity of a human or animal body” as used herein should be taken to mean, for example, luminal endoprostheses, catheters, dilators, grafts and the like which can be introduced, for example, into the vascular, esophageal, urinary, urethral, or biliary cavities and other tubular ducts of the body. Further, the terms “woven”, “braided” and “plaited” are used interchangeably herein and are intended to be understood in their broadest sense to require an over-under interlacing of a plurality of filaments.
2. State of the Art
Braided or woven filament medical stents which are used as vascular, esophageal or other dilators have been known for a long time (See, e.g., GB-1,205,743). These stents, formed by a tubular plaited structure of individual filaments include, in the resting state, filaments forming a fairly small angle with respect to a longitudinal axis of the tube (e.g., 30°). Stents with a relatively small directed angle do not offer a sufficient capacity for radial expansion when they are released after having been radially compressed. Their crushing resistance is also insufficient when they are used in cavities of the body whose walls exert a strong radial pressure on the stent introduced.
It has consequently been sought to overcome these drawbacks by providing a plaited structure of individual filaments with a larger angle so that, in the resting state of the stent, the filaments exhibit an angle greater than 45°, preferably of at least 60°, with respect to a longitudinal axis of the stent (See, e.g., U.S. Pat. Nos. 4,655,711 and 4,954,126). However, stents with a large braiding angle have a great drawback. Indeed, the tubular stent must be extended to two to three times its initial length in order to be capable of being inserted in a vascular introducer. It then occupies from 40 to 50% of the length of the introducer, and stiffens it and renders it difficult to pass through the femoral artery through which introduction into the body is generally initiated. On release, the tubular structure retracts by two to three times in length. It is therefore very difficult to estimate the length which will be deployed in the internal cavity of the body treated. This may lead to serious problems, as it is difficult to estimate the exact location where the stent will be anchored. For example, a length of stent may be deployed beyond a vascular bifurcation and thus lead to undesirable artery closure when the stent is provided with a covering, as is the case for luminal endoprostheses. In another case, if the deployed length is too short, the aneurysm treated will not be closed. Finally, it has been observed that stents with a large plaiting angle do not exhibit good resistance to blood pressure inside the aneurysms treated.
Other filament-based tubular plaited structures, which are used in devices to be introduced into the human body, are also described, in particular, in Patent #EP-A-0,183,372, U.S. Pat. Nos.3,509,883, 5,061,275 and 5,171,262.
SUMMARY OF THE INVENTION
According to the invention, the problems mentioned hereinabove have been solved by an self-expanding stent as described at the outset, in which the tubular body comprises first flexible rigid filaments which are arranged side by side in a number at least equal to two and thus form first multiple filaments wound along a first helicoid direction around a longitudinal axis of the tubular body, and second flexible rigid filaments which are arranged side by side in a number at least equal to two and thus form second multiple filaments wound along a second helicoid direction opposite to the first, each multiple filament wound in one of the said helicoid directions crossing multiple filaments wound in the other helicoid direction according to a plaited arrangement. Such a stent exhibits high dimensional and geometrical stability, without requiring a large Plaiting angle and the accuracy on release of this stent is therefore greatly increased.
In the braided or woven arrangement of the filaments, in some embodiments, a first multiple filament will, when crossing over with a second multiple filament, pass above the latter and, during the subsequent cross-over, pass below the second filament then crossed, and so on. In other embodiments, the first multiple filament passes above a second multiple filament having two or more successive cross-overs and will then only pass below a second multiple filament after a plurality of successive cross-overs, and so on. Mixed plaited arrangements (e.g., two over, one under) may also be provided, as can plaited structures formed partially of double filaments and monofilaments.
According to a particular form of the invention, the tubular body formed by plaited multiple filaments has at least at one of its ends, in the resting state, a flaring in which the multiple filaments follow a helix with increasing radii. Such an embodiment is particularly advantageous for treating, for example, aortic aneurysms in which contraction of the proximal or distal neck of the aneurysm occurs. The stent according to the invention, and in particular at its flared end, resists crushing by the arterial wall due to contraction of the neck. The radial expansion of the flared part of the stent furthermore promotes the absence of migration along the wall of the cavity in which it is to be applied and applies leakproofness to the distal neck of the aneurysm.
According to one highly advantageous embodiment of the invention, the ends of the stent are flared so that the stent assumes the shape of a hyperboloid. As will be discussed hereinafter, this embodiment has the great advantage of very simple manufacture and perfect reproducibility of the plaiting angle.
According to another aspect of the invention, in the resting state, the tubular body includes multiple filaments oriented at an angle equal to, and preferably less than 45° with respect to the longitudinal axis of the stent. According to the invention, the plaiting angle need not be high in order to obtain good dimensional stability properties. A significant improvement in the release of the stent in the cavity in which it is to be applied consequently results.
According to another advantageous embodiment of the invention, a stent-graft is provided with an expandable covering applied to at least one of an external wall surface and an internal wall surface of the stent body. Such a covering may be applied onto the stent using any known technique, for example in accordance with the teaching of Patent #EP-A-0,603,959. This makes it possible to form, for example, luminal endoprostheses with a diameter of 40 mm when resting, the covering of which is made of polycarbonate-urethane or other fibers with a fiber diameter of 5-25 &mgr;m. The diameters of such endoprostheses may then be reduced to a diameter of 4 to 5 mm for insertion in an introducer. The graft covering may take many forms and may be produced using other well-known techniques without departing from the scope of the invention.
The invention
Corvita Corporation
Ratner & Prestia
Stryiewski William
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