Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1998-11-13
2001-02-20
Buiz, Michael (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
Reexamination Certificate
active
06190403
ABSTRACT:
FIELD OF USE
The present invention is an expandable stent for insertion into a vessel of a human body for the purpose of creating and maintaining the patency of that vessel.
BACKGROUND
In U.S. Pat. No. 5,697,971 Fischell et al describe a balloon expandable stainless steel vascular stent with two different cell types. Cells containing an “H”-shaped link to provide strength and cells having an “S”-shaped link to provide increased flexibility and the ability to “unjail” side branch arteries. In addition, “S” links of the Fischell, et al invention attach to the strut members at the center of the end of the end struts. This increases the length of the “S” link along the longitudinal axis of the stent as compared with off-center attachment points. Finally, the “H” link of the Fischell et al prior art stent increases the relative strength of the section of the stent where it is used by shortening the distance between adjacent sets of strut members as compared to the distance between adjacent strut members for the “S” links.
SUMMARY OF INVENTION
The current invention is a comparatively thick-walled vascular stent comprising sets of strut members connected by flexible links. This design uses a script “N” shaped flexible link instead of the “S” link described by Fischell et al in U.S. Pat. No. 5,697,971. The “N” links, instead of touching or overlapping during crimping, are designed to nest one into the other, allowing the stent to be both thick-walled and to crimp down without overlap onto a low profile balloon. The “N” links are attached to the strut members not at the center like the “S” links in the prior art, but off center near the end of the curved end strut portion of each strut member. This off center attachment point allows for a more flexible link without increasing the cell size of the expanded stent. Small cell size is desirable to limit plaque prolapse into the lumen of the expanded stent. It is also desirable to replace the “H” link described by Fischell et al in the prior art with a short “J”-shaped, flexible link that will keep the struts close together for strength but unlike the “H” link will not detract from the stent's flexibility. To enhance flexibility, the wire width of the “N” and “J” links should be less than 0.10 mm. The relatively thin strut width with thick wall allows the “J” and “N” links to easily lengthen and shorten during stent delivery into the body while still allowing the stent to retain a considerable degree of radial strength.
An alternative embodiment of the flexible thick-walled stent has also been envisioned where the “N” link has certain curved segments to further minimize stent cell size. It is also conceived to increase flexibility by using “M”-shaped or “W”-shaped links each having additional undulations as compared to the “N” link.
Thus an object of this invention is to have a multi-cell, thick-walled stent with at least two different types of closed perimeter cells where every cell includes at least one longitudinally extending flexible link.
Another object of this invention is to have a stent with flexible links designed to nest inside each other when the stent is crimped down onto the balloon of a balloon catheter so as to reduce the stent profile (i.e., to reduce the outer diameter).
Another object of this invention is to have a stent with flexible links having the shapes of a “J”, inverted “J”, an “N”, inverted “N”, a sine wave, “M” or “W”.
Another object of this invention is to have a stent with flexible links that are attached off center to the curved ends of the strut members.
Still another objective of this invention is to have a multi-cell stent with short flexible links forming the part of the perimeter of one type of cell and longer flexible links forming part of the perimeter of a second type of cell.
Still another objective of this invention is to have a thick-walled stent with “N” shaped links where two of the three vertical segments of the “N” are curved to minimize the longitudinal extent of the link and thus minimize cell size for the expanded stent.
Still another object of this invention is to have flexible links between sets of strut members where the ratio of link width to link wall thickness is less than 1.0.
Still another object of this invention is to have the struts at the ends of the stent be of a shorter length as compared to struts at a central location so as to enhance the radial strength at the ends of the stent.
Still another objective of this invention is to have a stent in which the sets of strut members are constructed from several connected arcs of different radii with no straight segments.
Still another objective of this invention is to have a stent adapted for implantation at the ostium of a vessel, the stent having an extremely flexible distal section and a less flexible proximal section, the proximal section being radially stronger than the distal section after stent expansion to its nominal diameter.
These and other important objects and advantages of this invention will become apparent from the detailed description of the invention and the associated drawings provided herein.
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Fischell David R.
Fischell Robert E.
Majercak David C.
Bui Vy Q.
Buiz Michael
Cordis Corporation
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