Patent Application
20080177376
1. Field of the Invention
The present invention relates generally to a stent with improved flexibility. More specifically, the present invention relates to a welded stent having increased flexibility at the welded connections.
2. Description of Related Art
A stent is a prosthesis that is inserted into a body lumen and used, for example, for treating stenoses, strictures, and/or aneurysms therein. In the event of a stenosed vessel, a stent may be used to prop open the vessel after an angioplasty procedure. Once opened, the stent forms to the inner wall of the vessel, remains in place, and may help prevent restenosis. Additionally, in the event of an aneurysm or weakened vessel wall, stents may be used to provide support to, and reinforce the vessel wall.
To perform such functions, stents in the past have included many different structures. For example, previously disclosed stents include coiled stainless steel springs, helical wound springs, and generally serpentine configurations with continuous waves of generally sinusoidal character. Some of these stents self deploy when placed in the vessel, whereby stent expansion is primarily achieved by removing a restraint mechanism holding the stent in a constricted state. Other types of stents rely on alternate means to deploy, for example, use of a balloon catheter system, whereby balloon dilation expands and deploys the stent.
One of the major complications associated with using stents has been thrombosis. This complication is caused by clotting in the vicinity of the stent and is associated with high morbidity and mortality. It has been shown that the better the stent apposition against the vessel wall and the larger the lumen, the less likely that this complication will occur. A further complication is restenosis, which is caused by tissue proliferation around the angioplasty site. To minimize the potential for restenosis, the stent should cover the lesion and not leave any significant gaps in which restenosis may occur. The stent should also adhere to the inner wall of the vessel as much as possible.
Accordingly, when a stent deploys in a restricted vessel, adequate radial strength is required to overcome the strictures and ensure apposition of the stent to the vessel wall. Radial strength is a force produced by the stent acting at all points on the vessel wall in an outwardly direction perpendicular to the vessel wall. Stents are designed with circumferential rings to provide most of the radial strength needed to overcome radial forces pushing inwardly against the stent as the stent expands.
Many stents also include longitudinal links that primarily act to attach longitudinally adjacent circumferential rings, but also add radial strength and stent stability. Once the stent is fully deployed, in addition to providing adequate radial strength, the stent must provide adequate vessel wall coverage, hereinafter referred to as scaffolding affect. Scaffolding affect is defined as the amount of area of the vessel wall covered by the stent, once the stent is fully deployed. The circumferential rings and longitudinal links connecting the circumferential rings have traditionally provided the needed scaffolding affect. Other stents include welded connections between longitudinally adjacent circumferential rings.
Further, to meet the demands of adequate radial strength and scaffolding affect, conventional stents have been designed with circumferential rings manufactured with adequate ring width, which were then continuously connected at each peak and valley or trough by longitudinal links. However, such conventional stents suffer from predilation stent longitudinal rigidity. Predilation or crimped stent longitudinal rigidity is a resistance to movement and decreased flexibility of the stent along the stent's longitudinal axis. Accordingly, predilation longitudinal stent rigidity makes it much harder and oftentimes even impossible to thread the stent through long tortuous vessels and past constrictions and lesions.
Past attempts have been made to overcome predilation stent longitudinal rigidity. Such attempts have included designs with decreased ring width, often referred to as decreased wire gauge, which resulted in increased longitudinal flexibility but decreased radial strength. These conventional designs have resulted in inadequate stent apposition and/or inadequate vessel wall support. Additionally, past attempts to increase longitudinal flexibility have included designs where longitudinal links are not attached to each peak and valley of the circumferential ring. Thus, only some of the peaks and valleys of adjacent circumferential rings are connected by longitudinal links. This increases longitudinal flexibility but decreases the scaffolding affect of the stent. The decreased scaffolding affect creates areas where the vessel wall is not adequately covered by the stent, which may lead to thrombosis and/or restenosis.
Additionally, in order to meet the requirements of drug eluting stents, conventional stent substrates have been designed with circumferential elements manufactured with adequate ring/strut/apex width, which were then continuously connected at each peak and valley by longitudinal links. However, such conventional stents may suffer from abrasion or damage due to adjacent apexes (i.e., peaks and valleys) interacting during crimping and tracking, which may be caused by the close proximity of adjacent apexes coming into contact with one another due to links or weld not providing adequate clearance. This interaction may cause abrasion or damage during the coating of the stent with a drug and/or polymer or during tracking of the stent through the anatomy.
Accordingly, there arises the need for a stent, which provides adequate radial strength, scaffolding affect, with increased apex spacing and longitudinal flexibility. It is among the objects of the present invention to provide a stent that overcomes the foregoing shortcomings and meets the needs discussed above.
One aspect of the present invention provides a stent having improved longitudinal flexibility and minimal apex to apex (i.e., peak to valley) interaction between adjacent rings.
In an embodiment of the present invention, a stent is provided. The stent includes a first ring having a plurality of peaks and a plurality of valleys, a second ring having a plurality of peaks and a plurality of valleys, and a connector connecting one of the peaks of the first ring to one of the valleys of the second ring. The connected peak of the first ring includes a deformed portion that extends towards the connected valley of the second ring.
Another aspect of the present invention provides a method for manufacturing a stent with improved longitudinal flexibility and increased apex to apex spacing between adjacent rings.
In an embodiment of the present invention, a method for manufacturing a stent is provided. The method includes forming a first ring having a plurality of peaks and a plurality of valleys, forming a second ring having a plurality of peaks and a plurality of valleys, deforming a portion of at least one of the peaks of the first ring, and connecting the deformed portion to one of the valleys of the second ring.
In another embodiment of the present invention, a method for manufacturing a stent is provided. The method includes forming a first ring having a plurality of peaks and a plurality of valleys, forming a second ring having a plurality of peaks and a plurality of valleys, connecting one of the peaks of the first ring to one of the valleys of the second ring, and deforming a portion of the connected peak of the first ring.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
The foregoing and other features and advantages of the invention will be apparent from the following, more detailed description of the preferred embodiment of the invention, as illustrated with reference to the Figures. While specific embodiments are discussed in detail, it should be understood that this is done for illustrative purposes only. A person skilled in the art will recognize that other embodiments can be used without departing from the spirit and scope of the invention.
Each ring 12 may be formed from a single piece of material, such as a metal wire, or each ring/element 12 may be cut from a metal tube. For rings 12 that are formed from a single wire, the ends of the wire may be welded together so as to form a continuous ring. The material used to fabricate the rings 12 can be made of an inert, biocompatible material with high corrosion resistance that can be plastically deformed at low-moderate stress levels such as tantalum, or moderate to high stress levels such as L605, MP35N, or any other high work hardening rate material. Other acceptable materials include, but are not limited to, nickel titanium, stainless steel, titanium ASTM F63-83 Grade 1, niobium, cobalt-chromium (Co—Cr) alloys, and other cobalt-based alloys. A self-expanding device can be made by the use of superelastic NiTi, such as nitinol. As discussed in further detail below, a single ring may be connected to an adjacent ring with a connector 22, such as a weld 24, so as to form a flexible connection between the rings.
As shown in greater detail in
As discussed in further detail below, the deformed portions 26a, 26b may be created by work hardening (e.g., cold-working) the material in the peak 14a and the valley 15b, respectively, such that the material plastically deforms, thereby creating the recesses 30a, 30b and the extensions 32a, 32b. As a result of work hardening the material, the deformed portions 26a, 26b may have a hardness that is greater than the hardness of the non-deformed portions 28a, 28b of the peak 14a and the valley 15b, respectively.
In an embodiment, the material in the deformed portions 26a, 26b have a hardness that is at least about 20%, and preferably between about 20% and about 40%, higher than the hardness of the material in the non-deformed portions 28a, 28b due to the work hardening of the material. For example, in an embodiment, the ring 12a may be made from annealed stainless steel, or Co—Cr alloy having a Vickers hardness of about 220 HV, while the hardness of the material of the deformed portion 26a that has been work-hardened may be about 300 HV, which is an increase of about 36%.
Of course, the actual amount of increase in hardness of the material in the deformed portion 26a will depend on the material, the degree of deformation, the working temperature, and the amount and duration of pressure that is applied to the material. The same considerations apply to the deformation of the valley 15b of the adjacent ring 12b, if applicable. In some embodiments, only the peak of one ring is deformed and is connected to a non-deformed valley of an adjacent ring. The illustrated embodiment is not intended to be limiting in any way.
By creating the deformed portions 26a, 26b in the peak 14a and the valley 15b, respectively, by work hardening the material, not only are the extensions 32a, 32b created, but the strength of the extensions 32a, 32b may be increased. This may allow the connection between the peak 14a and the valley 15b to be more flexible, yet stronger. Increased flexibility may be achieved by allowing the non-deformed portions 28a, 28b of the peak 14a and the valley 15b in the adjacent rings 12a, 12b, respectively, to be spaced apart at a greater distance than other connected peaks and valleys, such as the peak 14a′ and valley 15b′ illustrated in
For example, as discussed above, in the conventional welded stent 10′, the weld 24′ has a length of d1. However, in the embodiment illustrated in
The weld 24 may be created by conventional welding techniques, including but not limited to butt welding, resistance welding, and/or laser welding. In addition, it is contemplated that the connector 22 may not be in the form of a weld per say, and may be created by soldering or brazing.
In an embodiment, heat may be generated at the peak 14a and the valley 15b with a laser, so as to cause the material in the peak 14a and the valley 15b to flow together, thereby creating the weld 24. As the weld 24 is created, an inert gas, such as argon or helium, may be used to flood the weld area at a sufficient flow rate to prevent oxidation so that the weld 24 does not become brittle. Of course, other welding techniques may be used, and the above-described method should not be considered to be limiting in any way.
A support 46 may be placed inside the ring 12 so that it contacts an inside surface 48 of the peak 14a, as shown in
In another embodiment, the deformed portions 26a, 26b may be formed simultaneously by using an apparatus 52 illustrated in
In another embodiment, that peak 14a and the valley 15b of adjacent rings 12a, 12b may first be welded together, as shown in
While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.
