Implantable and lumen-supporting stents and related methods of manufacture and use

The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Applications No. 60/981,433 filed Oct. 19, 2007 which is incorporated by reference herein in its entirety.

This invention relates to implantable medical devices. More specifically, the invention relates to implantable and lumen-supporting stents. Still more specifically, it relates to such stents for the treatment or inhibition of stenoses in coronary or peripheral vessels in humans.

Cardiovascular disease, including atherosclerosis, is the leading cause of death in the United States. The medical community has developed a number of methods and devices for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary vessel narrowing.

An important development for treating atherosclerosis and other forms of vascular narrowing is percutaneous transluminal angioplasty, hereinafter referred to as “angioplasty.” The objective of angioplasty is to enlarge the lumen of an affected vessel by radial hydraulic expansion. The procedure is accomplished by inflating a balloon within the narrowed lumen of the affected vessel. Radial expansion of the affected vessel occurs in several different dimensions, and is related to the nature of the plaque narrowing the lumen. Soft, fatty plaque deposits are flattened by the balloon, while hardened deposits are cracked and split to enlarge the lumen. The wall of the affected vessel itself is also stretched when the balloon is inflated.

Unfortunately, while the affected vessel can be enlarged thus improving blood flow, in some instances the vessel re-occludes chronically (“restenosis”), or closes down acutely (“abrupt reclosure”), negating the positive effect of the angioplasty procedure. Such restenosis or abrupt reclosure frequently necessitates repeat angioplasty or open heart surgery. While such restenosis or abrupt reclosure does not occur in the majority of cases, it occurs frequently enough that such complications comprise a significant percentage of the overall failures of the angioplasty procedure, for example, twenty-five to thirty-five percent of such failures.

To lessen the risk of restenosis and abrupt closure, various devices have been proposed for mechanically keeping the affected vessel open after completion of the angioplasty procedure. Such endoprostheses (generally referred to as “stents”), are typically inserted into the vessel, positioned across the lesion or stenosis, and then expanded to keep the passageway clear. The stent provides a scaffold which overcomes the natural tendency of the vessel walls of some patients to renarrow, thus maintaining the openness of the vessel and resulting blood flow.

While stents and stent applications of the type described have been found to work well in a number of patients, there is still room for improvement. First, various areas of the vasculature and different treatment sites call for stents with different characteristics. For example, a stent that must travel through a tortuous and highly-curved area of the vasculature to reach a particular treatment site would benefit from enhanced flexibility characteristics that are not necessarily needed in a stent used to treat an easily-accessible treatment site. Likewise, a stent that will be deployed at an area of a vessel that has a branch or bifurcation would benefit from flexibility characteristics not necessarily needed in a stent used to treat a relatively straight and uniform portion of a vessel.

Further, as stents are presently used, there can be an abrupt transition between the area of a vessel that is contacted by the stent (and thus receiving the benefits of the stent) and those portions of the vessel that are not. This abrupt transition between stented and unstented portions of a vessel can exacerbate the physiological trauma found at a treatment site. Thus, in some instances, a stent with characteristics that provide for a less abrupt transition between stented and unstented portions of a vessel may be advantageous.

Notwithstanding the foregoing, however, another frequent observation is that balloon expanded stents first deploy open under balloon inflation at their ends, with middle portion of the stent to follow. This is often referred to as “dog-boning” and has been suspected to result, in some cases, in increased trauma at end margins of treated areas. Because stent ends can deploy before middle stent regions and at lower balloon pressures, it would be considered advantageous to provide a new and improved stent that counteracts this with more uniform stent expansion. In particular cases where a stent may maintain a design with particularly beneficial lateral flexibility over its length, it would be desirable to also provide features at or adjacent the ends to result in a more uniform expansion over the length and including the stent ends.

Characteristics that result in low restenosis rates are also considered highly beneficial for most stent uses, such as for example for endovascular stents in particular. One such beneficial characteristic would be one that combats restenosis at locations along or adjacent the treatment site where restenosis is more frequently observed to occur, such as for example the area of the vessel nearest to the proximal (e.g. “upstream” portion, as related to blood flow) end of the stent. Other such characteristics include for example enhanced tissue-device interface between the stent and tissue being implanted. Such enhancements may for example reduce trauma, reduce a restenotic or other undesired biological response to the implant, or otherwise benefit other aspects of the stent\'s intended use. In one particular regard, a pattern chosen for a stent scaffold, such as per undulating sinusoidal or “serpentine” strut-crown scaffolds most frequently used, may impact their capabilities in their use and/or with respect to outcomes. According to one more specific example, relative stiffnesses (including lateral, radial, or both) and geometries of crowns, struts, the connections or transitions between “segments” along a stent, and how these aspects relate to each other within an overall design, can have distinct impact on their in vivo use and outcomes.

It is also to be appreciated that certain stents, and their respective features related to their performance, are relatively small to the basic human observation skills such as sight and touch. The difference between features of one stent and another may appear very subtle, or not even readily noticeable, to initial visual or tactile observation. However, such otherwise subtle changes in or differences between such features may significantly impact the use of these devices, especially where intended for percutaneous transluminal delivery and chronic in vivo implantation within dynamic biological tissues such as blood vessels.

While endolumenal vascular stents have clearly become the most prominent type of stents used in medicine, it is also appreciated that stents may be, and have been, implanted in other regions of the body. For example, stents have been either proposed or used in other body lumens or spaces, such as without limitation within gastrointestinal tract, pulmonary system, urinary tract system, etc.

Various needs still remain for providing stents with improved features, including without limitation in order to beneficially improve various combinations of performance aspects such as trackability, visibility, expansion characteristics (e.g. uniformity of expansion, recoil, etc.), material fatigue and yield failure, tissue-device interface, surface coating adhesion and integrity, local drug delivery, and biological response and outcomes from their implantation.

One aspect of the present disclosure provides a stent system with an improved stent. According to one embodiment, the stent includes improved expansion characteristics. According to another embodiment, the stent includes improved lateral bending characteristics. In one particular embodiment, the stent undergoes lateral or radial deflection with strain distribution primarily at transition regions between struts and crown shoulders on opposite sides of crown peaks of the stent\'s filamental pattern. In another embodiment, the stent includes geometry along crown regions that differ from strut geometry, providing enhanced deflection characteristics in combination with enhanced characteristics along the strut, such as for example for drug delivery or visibility.

Another aspect of the present disclosure is an implantable medical stent system with a radially expandable stent comprising a filamental structure in a pattern surrounding a bore to form a substantially tubular wall along a length relative to a longitudinal axis. The filamental structure comprises at least one arcuate crown with a crown peak having a radius of curvature located along a reference axis, and first and second arcuate crown shoulders on first and second sides, respectively, of the reference axis. The filamental structure also comprises at least one pair of adjacent first and second elongated struts extending from the first and second crown shoulders, respectively.

The arcuate crown peak comprises at least one of: (a) a peak width that is greater than at least one of first and second shoulder widths along the first and second respective crown shoulders; (b) an outer radius of curvature about a first center that is offset from a second center of an inner radius of curvature; and (c) a radial expansion characteristic with a strain distribution that is substantially lower than along at least one of the first and second crown shoulders. According to a further mode, the crown peak comprises a combination of at least two of these particularly beneficial features. In a still further embodiment, the crown peak comprises each of these features.

Another aspect of the present disclosure is an implantable medical stent system with a radially expandable stent comprising a plurality of adjacent circumferential segments that comprise patterned filamental structures that surround a bore and are arranged in series along a length relative to a longitudinal axis to thereby form a substantially tubular wall along the length. Each pair of adjacent segments is connected by at least one of a plurality of connections between segments.