Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1998-01-16
2001-01-30
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001170
Reexamination Certificate
active
06179867
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to expandable endoprosthesis devices, generally known as stents, which are designed for implantation in a patient s body lumen, such as blood vessels to maintain the patency thereof. These devices are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), or percutaneous transluminal angioplasty (PTA), or removed by atherectomy or other means.
Stents are generally cylindrically-shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other lumen such as a coronary artery. They are particularly suitable for use to support the lumen or hold back a dissected arterial lining which can occlude the fluid passageway therethrough.
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 and shaped in a zigzag pattern. One of the difficulties encountered using prior stents involved maintaining the radial rigidity needed to hold open a body lumen while at the same time maintaining the longitudinal flexibility of the stent to facilitate its delivery and accommodate the often tortuous path of the body lumen.
Another problem area has been the limiting range of expandability. Certain prior art stents expand only to a limited degree due to the uneven stresses created upon the stents during radial expansion. This necessitates providing stents with a variety of diameters, thus increasing the cost of manufacture. Additionally, having a stent with a wider range of expandability allows the physician to redilate the stent if the original vessel size was miscalculated.
Another problem with the prior art stents has been contraction of the stent along its longitudinal axis upon radial expansion of the stent. This can cause placement problems within the artery during expansion.
Various means have been described to deliver and implant stents. One method frequently described for delivering a stent to a desired intraluminal location includes mounting the expandable stent on an expandable member, such as a balloon, provided on the distal end of an intravascular catheter, advancing the catheter to the desired location within the patient's body lumen, inflating the balloon on the catheter to expand the stent into a permanent expanded condition and then deflating the balloon and removing the catheter.
What has been needed is a stent which has an enhanced degree of flexibility so that it can be readily advanced through tortuous passageways and radially expanded over a wider range of diameters with minimal longitudinal contraction to accommodate a greater range of vessel diameters, all with minimal longitudinal contraction. The expanded stent must also of course have adequate structural strength (hoop strength) to hold open the body lumen in which it is expanded. The present invention satisfies this need.
SUMMARY OF THE INVENTION
The present invention is directed to stents of enhanced longitudinal flexibility and configuration which permit the stents to expand radially to accommodate a greater number of different diameter vessels, both large and small, than heretofore was possible. The stents of the instant application also have greater flexibility along their longitudinal axis to facilitate delivery through tortuous body lumens, but remain highly stable when expanded radially, to maintain the patency of a body lumen such as an artery or other vessel when implanted therein. The unique patterns of the stents of the instant invention permit both greater longitudinal flexibility and enhanced radial expansibility and stability compared to prior art stents.
Each of the different embodiments of stents of the present invention include a plurality of adjacent cylindrical elements which are generally expandable in the radial direction and arranged in alignment along a longitudinal stent axis. The cylindrical elements are formed in a variety of serpentine wave patterns transverse to the longitudinal axis and containing a plurality of alternating peaks and valleys. At least one interconnecting member extends between adjacent cylindrical elements and connects them to one another. These interconnecting members insure minimal longitudinal contraction during radial expansion of the stent in the body vessel. The serpentine patterns contain varying degrees of curvature in regions of the peaks and valleys and are adapted so that radial expansion of said cylindrical elements are generally uniform around their circumferences during expansion of the stents from their contracted conditions to their expanded conditions.
The resulting stent structures are a series of radially expandable cylindrical elements which are spaced longitudinally close enough so that small dissections in the wall of a body lumen may be pressed back into position against the lumenal wall, but not so close as to compromise the longitudinal flexibility of the stent both when being negotiated through the body lumens in their unexpanded state and when expanded into position. The serpentine patterns allow for an even expansion around the circumference by accounting for the relative differences in stress created by the radial expansion of the cylindrical elements. Each of the individual cylindrical elements may rotate slightly relative to their adjacent cylindrical elements without significant deformation, cumulatively providing stents which are flexible along their length and about their longitudinal axis, but which are still very stable in the radial direction in order to resist collapse after expansion.
Each of the stents of the invention can be readily delivered to the desired lumenal location by mounting them on an expandable member of a delivery catheter, for example a balloon, and passing the catheter-stent assembly through the body lumen to the implantation site. A variety of means for securing the stents to the expandable member on the catheter for delivery to the desired location is available. It is presently preferred to compress the stent onto the unexpanded balloon. Other means to secure the stent to the balloon include providing ridges or collars on the inflatable member to restrain lateral movement, using bioabsorbable temporary adhesives, or a retractable sheath to cover the stent during delivery through a body lumen.
The presently preferred structures for the expandable cylindrical elements which form the stents of the present invention generally have a circumferential serpentine pattern containing a plurality of alternating peaks and valleys. The degrees of curvature along adjacent peaks and valleys are designed to compensate for the stresses created during expansion of the stent so that expansion of each of the peaks and valleys is uniform relative to one another. This novel structure permits the stents to radially expand from first smaller diameters to any number of second larger diameters since stress is distributed more uniformly along the cylindrical elements. This uniformity in stress distribution reduces the tendency of stress fractures in one particular region and allows high expansion rates.
The different stent embodiments also allow the stents to expand to various diameters from small to large to accommodate different-sized body lumens, without loss of radial strength and limited contraction of longitudinal length. The open reticulated structure of the stents provides low mass allowing for the perfusion of blood over a large portion of the arterial wall which can improve the healing and repair of a damaged arterial lining.
In one presently preferred embodiment, the ability of the stent to treat larger diameter vessels results from increasing the number of units of the repeating pattern of peaks and valleys so that the starting compressed diameter is larger than in prior
Advanced Cardiovascular Systems Inc.
Fulwider Patton Lee & Utecht LLP
Snow Bruce
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