Self-expanding stent with time variable radial force

Details Self-expanding stent with time variable radial force Self-expanding stent with time variable radial force

2000-10-26

2003-12-16

McDermott, Corrine (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Arterial prosthesis

Stent structure

C623S001150

Reexamination Certificate

active

06663664

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to expandable endoprosthesis devices, generally called stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel, to maintain the patency thereof. Stents are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or removed by atherectomy or other means, to help improve the outcome of the procedure and reduce the possibility of restenosis.
Stents are generally cylindrically shaped devices which function to hold open, and sometimes expand, a segment of a blood vessel or other arterial lumen, such as a coronary artery. Stents are usually delivered in a compressed condition to the target site and then deployed at that location into an expanded condition to support the vessel and help maintain it in an open position. They are particularly suitable for use to support and hold back a dissected arterial lining which can occlude the fluid passageway there through.
A variety of devices are known in the art for use as stents and have included coiled wires in a variety of patterns that are expanded after being placed intraluminally on a balloon catheter; helically wound coiled springs manufactured from an expandable heat sensitive metal; and self-expanding stents inserted in a compressed state for deployment into a body lumen.
One of the difficulties with prior art stents involves restenosis, which is recurrent stenosis, or narrowing, in a body lumen after a corrective procedure. Restenosis is a multifactorial problem believed to be caused by stimulatory processes stemming from the presence of thrombus, a foreign body reaction to the stent, and stent injury to the endothelium and lumen wall from deployment and the stent's pressure against the lumen wall. A related difficulty for prior art stents involves use in connection with intercoronary brachytherapy. Brachytherapy is traditionally a procedure for treatment of cancer, or other proliferative diseases and the like, wherein radiation is used at or near the target site within the body. The radiation has an antiproliferative effect, meaning that rapidly dividing cells are affected most by the DNA damage induced by the radiation, which leads to apoptosis, or cell death, upon division. Thus, brachytherapy has the positive effect of potentially reducing restenosis after angioplasty or stenting, but it also presents new challenges for prior art stents.
Due to cellular damage and inhibition resulting from brachytherapy, a phenomenon known as positive vessel remodeling has been observed in vivo, which vessel lumen enlargement and, sometimes, medial thinning. Positive remodeling is beneficial to the extent that the vessel is still fully functional. The typical balloon expandable, prior art stent, because of its constant size after expansion, may either prevent positive remodeling from occurring or may be left exposed in the lumen after the lumen wall recedes. Such an exposed stent greatly increases the risk of thrombosis.
Due to the cellular damage and death resulting from brachytherapy, a phenomenon known as positive vessel remodeling has been observed in vivo, where new cells eventually grow and “remodel” the body lumen walls. The typical prior art stent, because of its constant radial expansion and force, may either prevent the positive remodeling from occurring or may be left exposed in the lumen after the lumen wall recedes.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the blood vessel. Stents manufactured from expandable heat sensitive materials usually allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent. Other self-expanding stents may use SIM alloys to allow the stent to move between contracted and expanded positions.
Typical stent delivery systems for implanting self-expanding stents at the target site include an inner lumen upon which the compressed or collapsed stent is mounted and an outer restraining sheath which is initially placed over the compressed stent prior to deployment. When the stent is to be deployed in the body vessel, the outer sheath is moved in relation to the inner lumen to “uncover” the compressed stent, allowing the stent to move to its expanded condition.
Balloon expandable stents have the advantage of a high radial strength that is capable of holding open a tight stenosis. This stenosis is initially expanded by the force of a high pressure balloon. However, such a stent requires this dilitation to occur all at once. There is the alternative of simply deploying a self-expanding stent, and allowing the lumen to be slowly dilated over time to produce less injury. High levels of vessel injury are directly correlated with the greater levels of restenosis. However, a traditional manner of utilizing self-expanding stents requires predilating the lesion with a balloon, deploying the stent, and then postdilating the stent with another balloon. These many manipulations in the lesion increase the amount of vessel injury and endothelial denudation. Compared to this, the single step of deploying the self-expanding stent is attractive if the acute outcome is acceptable. The other issue, already mentioned, regarding balloon expandable stents is that if positive remodeling occurs, the stent is left exposed in the vessel. These two aspects, the ability to gradually expand the lesion over time, and expand with the vessel in a more passive sense, are compelling reasons to consider self-expanding stents over balloon expandable stents, particularly when used in conjunction with brachytherapy. Use of self-expanding stents to either hold open a previously tight stenosis, or to start the process of opening a lesion without completing predilatation, can require a high initial radial force. Compared to balloon expandable stents, usually of 316L stainless steel, achieving a high initial radial strength with NiTi alloys can be more of a challenge.
Currently, a high initial radial force for a self-expanding stent is accomplished by either oversizing the stent (to increase the strength) or by placing more metal in the stent (i.e., by making the struts thicker and wider). However, oversizing may lead to excessive vessel injury as the stent continues to exert a force against the vessel wall once implanted. For this reason, there is currently a concern that oversizing the stent by a large amount, in order to exert a large initial force, may be detrimental, as the stent will keep pushing the vessel wall possibly causing injury. Moreover, oversizing or increasing the amount of metal in the stent changes the way in which the stent functions biologically. For example, increasing the amount of metal results in a stent having thicker struts and increases the stent to artery ratio, which may not be desirable for every stent application. The stent to artery ratio is defined as the percentage of the vessel wall area covered by the stent struts. With balloon expandable stents, there is a known and preferred range of stent to artery ratio, strut thickness and width. When engineering a self-expanding stent, one challenge is designing a stent which expands to a final diameter, as dictated by the reference vessel size of the body lumen in which the stent is to be implanted, while exerting a radial force at this final diameter that is not

Affiliated with

Also associated with

Rating

Self-expanding stent with time variable radial force does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Self-expanding stent with time variable radial force, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Self-expanding stent with time variable radial force will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3176328