Patent Application
20150148887
The present invention relates generally to expandable tubular structures capable of insertion into small spaces in living bodies and, more particularly, concerns a stent or stent-like structure which is capable of substantial and/or repeated flexing at points along its length either in the compressed or deployed configuration without mechanical failures and with no substantial changes in its geometry.
A stent is a tubular structure that, in a radially compressed or crimped state, may be inserted into a confined space in a living body, such as an artery or other vessel. After insertion, the stent may be expanded radially to enlarge the space in which it is located. Stents are typically characterized as balloon-expanding (BX) or self-expanding (SX). A balloon-expanding stent requires a balloon, which is usually part of a delivery system, to expand the stent from within and to dilate the vessel. A self expanding stent is designed, through choice of material, geometry, or manufacturing techniques, to expand from the crimped state to an expanded state once it is released into the intended vessel. In certain situations higher forces than the expanding force of the self expanding stent are required to dilate a diseased vessel. In this case, a balloon or similar device might be employed to aid the expansion of a self expanding stent.
Stents are typically used in the treatment of vascular and non-vascular diseases. For instance, a crimped stent may be inserted into a clogged artery and then expanded to restore blood flow in the artery. Prior to release, the stent would typically be retained in its crimped state within a catheter and the like. Upon completion of the procedure, the stent is left inside the patient's artery in its expanded state. The health, and sometimes the life, of the patient depend upon the stent's ability to remain in its expanded state. Stents and stent-like devices, while often used as permanent implants, can be used as temporary medical devices or components to be implanted in the body.
Many available stents are flexible in their crimped state in order to facilitate the delivery of the stent, for example within an artery. Few are flexible after being deployed and expanded. Yet, after deployment, in certain applications, a stent may be subjected to substantial flexing or bending, axial compressions and repeated displacements at points along its length, for example, when stenting the superficial femoral artery. This can produce severe strain and fatigue, resulting in failure of the stent.
A similar problem exists with respect to stent-like structures. Stent-like structures are similar in construction as a stent such that they can compress to a smaller diameter or dimension, and can then expand in the body to a larger diameter or dimension. Stent-like devices are also placed in a vessel including arteries, veins ducts, esophagus, urinary tracts, urethra and colon. The stent or stent-like devices may support the vessel, act as a biased force, hold another component in place either temporarily or permanently, act as an anchor, prevent tissue or other biomaterial prolapse and block or divert flow.
Similar to a stent, stent-like devices may be used to keep a vessel open or to open a vessel, act as a biased force, hold another component in place either temporarily or permanently, act as an anchor, block flow or divert flow. In some cases, they may be used in part to hold another item, device or component in place. An example would be a stent-like structure used with other components in a catheter-based valve delivery system. Such a stent-like structure holds a valve which is placed in a vessel. A second example would be a stent-like structure used to divert flow as may be needed in treatment of an aneurysm. A third example would be a stent-like structure used to anchor another device or component. A fourth example would be a stent-like structure to aid in the revascularization of a vessel which has expanded or otherwise become misshapen from an aneurysm, weak vessel wall or other cause. A fifth example would be a bifurcation device such as an abdominal aortic aneurysm device where the construction would have at least one section with the stent-like structure discussed herein. Many other examples, including filters and variable diameter catheter shafts or components, can use the stent-like construction.
For the purposes of this disclosure, a stent will refer to both a stent and a stent-like device unless otherwise noted.
In accordance with the present invention, a stent or a stent-like structure is constructed to have different types of tubular portions along its length. In general, there are strut portions and helical portions, where the strut portions are constructed primarily to provide radial expansion and radial strength, and the helical portions are constructed primarily to permit repeated flexing and axial compression and expansion. However, both the struts and helical portions, and the integration of the two typically contribute to all of the stent attributes. The flexing and axial compression are likely to be required simultaneously, so the stent structure permits repeated and substantial flexing while in an axially compressed or expanded state, and it permits axial compression while in a flexed state. Preferably, strut portions are provided between helical portions or helical portions are provided between strut portions. In a preferred embodiment, the stent is self-expanding and strut portions and helical portions alternate along the length of the stent. The stents when used in pair can have helical strut portions which are mirrored images of each other or where the helical strut portions just have an opposite pitch. When two stents are used as a pair, the connecting elements can be helical coils which form the helical portion or can be made of other connecting elements that are helical, straight or undulating in structure.
The stent is preferably constructed so that, in the expanded state the helical portions permit axial compression or expansion of about 20% (preferably between 15% and 25%) and simultaneously permit bending with a minimum bending radius of about twice the average diameter of the device (preferably between 1.5 to 2.5 the average diameter of the device or component).
In accordance with yet another aspect of the invention, a helical portion is made of joining elements which extend helically about the axis of the stent between locations on two different strut portions. A joining element is bi-directional, in that it extends first in one circumferential direction and then the other between the two locations and has a peak, and the circumferential distance of the peak from a location is more than approximately 15% (preferably between 10% and 20%) of the circumference of the stent when it is in its expanded state.
In accordance with one aspect of the invention the helical portions are constructed to permit axial compression or expansion of about 30% and simultaneously permit bending with a minimum bending radius equal to about twice the average diameter of the device or component. In accordance with another aspect of the invention, a helical portion is made of joining elements which extend helically about the axis of the stent between points on two different strut portions which are spaced apart circumferentially by a distance which is more than approximately 25% (preferably 20% to 30%) of the circumference of the stent when it is in its expanded state.
In accordance with yet another aspect of the invention, the stent has a main body defined by an axial sequence of helical segments lying about the stent axis and each defining a complete turn of the helix. The two strut portions between which a helical portion extends include adjacent helical segments. A helical portion is made of joining elements which extend helically about the axis of the stent between points on two strut portions which are spaced apart circumferentially by a distance which is more than approximately 25% (preferably between 20% and 30%) of the circumference of the stent when it is in its expanded state. The main body may include an elongated element extending generally helically about the stent axis and having a series of wave-like struts extending along its length. In this case, a joining element is connected between struts on adjacent strut portions which are spaced apart circumferentially by a distance which is greater than approximately twice the circumferential extent of a strut.
In accordance with another aspect of the invention, a helical portion is made of helical elements which extend helically about the axis of the stent between points on two different strut portions which are spaced apart circumferentially by a distance which is more than approximately 25% (e.g. 20% to 30%), preferably more than approximately 50% (e.g. 40% to 60%) of the circumference of the stent (which is equivalent to an extent of 90 degrees about the axis of the stent) when it is in its expanded state.
In accordance with yet another aspect of the invention, a helical portion is made of helical elements which extend helically about the axis of the stent between locations on two different strut portions. In one embodiment a helical element is bi-directional, in that it extends first in one circumferential direction and then the other between the two locations and has a peak.
In accordance with yet another aspect of the invention, a stent has a plurality of axially spaced strut portions defining generally tubular axial segments of the stent and constructed to be radially expandable. A helical portion is interposed axially between two strut portions, and the helical portion has a plurality of helical elements connected between circumferentially spaced locations on two strut portions. A helical element extends helically between these locations, and at least part of the helical portion has a greater diameter than a strut portion when the stent is in an expanded state. In an alternate embodiment, at least part of the helical portion has a smaller diameter than the strut portion when the strut is in an expanded state.
In one embodiment, the helical element is wound at least 90 degrees between strut elements connected to the helical element. In another embodiment, the helical element is wound at least 360 degrees between strut elements connected to the helical element.
In an alternate embodiment, stent grafts are formed of a biocompatible graft material covering the outside, inside or both the outside and inside of the stent. The stent graft can have any embodiment of a stent structure of the present invention. Stent graft devices are used, for example, in the treatment of aneurysms, dissections and tracheo-bronchial strictures. The stent can also be coated with a polymer and/or drug eluting material as are known in the art.
In accordance with yet another aspect of the invention, a stent or stent like device is constructed at least in part such that the coils are placed as closely together as possible, the cell sizes are minimized, the metal-to-metal gaps are minimized and/or the metal coverage is maximized such that the device can in part divert flow in a vessel or could minimize vessel wall prolapse in a vessel with softer tissue, such as for treatment of saphenous vein graft disease, which may with a less dense construction squeeze between and protrude from the mesh. The construction of this embodiment could be such that the center or near the center is denser to cover, for example, the neck of an aneurysm or an artereovenous fistula. An artereovenous fistula is also referred to as an AV fistula.
In accordance with yet another aspect of the invention, a stent or stent like device is constructed at least in part such that the coils are placed as closely together as possible, the cell sizes are minimized, the metal-to-metal gaps are minimized and/or the metal coverage is maximized such that the device can in part divert flow in a vessel. A second device is constructed similarly but has an opposite pitch as the first device. These two devices are intended to be implanted one right after the other or together such that they over lap at least in part to maximize the flow diversion. The second device can be longer, shorter, or the same length as the first device. The construction of this embodiment could be such that the center or near the center is denser to cover, for example, the neck of an aneurysm. However, the construction could be such that the stents are intended to overlap such that a portion of each stent extends out of the other stent. In any case, the intended area of overlap between the two devices is designed to maximize flow diversion.
In accordance with yet another aspect of the invention, one device has an opposite pitch from a second device. The devices are used together to treat an AV fistula such that one device is placed in the artery of the AV fistula and one device is placed in the vein of the AV fistula. The two devices can be provided together in a kit or separately.
In accordance with yet another aspect of the invention, a stent or stent like device pair is constructed such that each device has a helical strut with an opposite pitch from the other. The two devices can have helical coils connecting neighboring windings of the struts or other connecting links such as an undulating links or straight links. The two devices can be provided together in a kit or separately.
In accordance with yet another aspect of the invention, a flow diverter type construction is shaped to have a dog bone type shape such that the inside diameter is less than the diameter at both ends.
In accordance with yet another aspect of the invention, a stent or stent like device is constructed such that at least part of the center section is tubular and one end tapers down to a smaller diameter or a solid ring. Such an embodiment may be preferred for construction of a permanent or temporary filter or revascularization device.
In accordance with yet another aspect of the invention, a stent or stent like device is constructed such that at least part of the center section is tubular and both ends taper down to a smaller diameter or a solid ring. The center tubular section may be relatively long or not be long at all forming almost a point at which the two ends join at a larger diameter. Such an embodiment may be preferred for construction of a permanent or temporary filter or revascularization device.
In accordance with yet another aspect of the invention, a stent or stent like device is constructed such that valve material can be attached to the structure. In this embodiment, there may need to be holes or rings to facilitate attachment of the valve material.
In accordance with yet another aspect of the invention, a stent or stent like device is constructed such that the device can anchor itself or another device with sufficient radial strength, barbs, and/or tapered ends or mid-section.
In accordance with yet another aspect of the invention, a stent or stent like device is used in the construction of a bifurcation device in at least one of the three legs.
The foregoing description, as well as further objects, features, and advantages of the present invention will be understood more completely from the following detailed description of presently preferred, but nonetheless illustrative embodiments in accordance with the present invention, with reference being had to the accompanying drawings, in which:
NOTE: All figures could represent a flow diverter or a similar stent-like device requiring denser coverage to in part divert flow or in part prevent vessel wall or something in the vessel wall from protruding through the device. All figures could also be used in the construction of a bifurcation device.
Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts.
Stent 10 is made from a common material for self expanding stents, such as Nitinol nickel-titanium alloy (Ni/Ti), as is well known in the art. Typically, the stent is laser cut from tubing, for example, with a diameter of about 5 mm (
Stent 10 is generally made up of strut portion 12 and helical portion 14 with axially aligned strut portion 12 alternating with helical portion 14. In a preferred embodiment, strut portion 12 is positioned at either end of stent 10. Strut portion 12 being radially expandable upon deployment. Each strut portion 12 includes strut ring 16 having a pattern of wave-like strut elements 16a that progresses circumferentially about the stent. Each strut element 16a has a width equal to the peak to peak distance around the stent and a length equal to the peak-to-peak distance along the length of the stent. It will be appreciated that strut ring 16 could be partially straightened (stretched vertically in
Each helical portion is made up of a plurality of side-by-side helical elements 18, each of which is helically wound about an axis of stent 10. Helical portion 14 is expandable radially upon deployment and compressible, expandable and bendable in a deployed state. Helical elements 18 can be connected between opposed individual wave portions of strut element 16a of different strut portions 12. In this embodiment, each helical element 18 makes a complete rotation about the surface of stent 10. However, they can make a partial rotation or more than one rotation. The helical portion is preferably constructed to permit repeated axial compression or expansion of about 20% (preferably between 15% and 25%) and simultaneously permit bending with a minimum bending radius of about twice the average diameter of the device (preferably between 1.5 to 2.5 the average diameter of the device or component), all without failure.
Improved flexibility and axial compression can generally be accomplished if helical element 18 is wound at least 90 degrees between strut elements 16a connected to helical elements 18. Alternatively, helical element 18 is wound at least 360 degrees between strut elements 16a connected to helical elements 18.
In a right-handed helical portion 14R, the elements 18 progress clockwise about the surface of stent 10 and, in a left-handed helical portion 14L, they progress counterclockwise. Helical elements 18 essentially float and permit relatively large displacements about and along the stent axis between the two strut ring portions at either end. In this embodiment, it will be appreciated that the diameter of the stent at each helical portion 14R, 14L is the same as the diameter of the stent at the strut portions 12 on either side. However, this need not be the case, as will become evident from additional embodiments discussed below. A benefit of using left-handed and right-handed helical portions is that when the stent deploys the two portions rotate in opposite directions, maintaining the relative rotational positions of different axial portions of the stent.
When all portions of the stent have the same diameter, the helical portions may not have as much outward force on a vessel as the strut portions when the strut is expanded. The geometry of
Nitinol structures have a biased stiffness, such that the force required to collapse the structure back towards the collapsed state is generally greater than the force that continues to dilate the diseased vessel when the stent is in its expanded state. With some self expanding Nitinol stents, a balloon is used to assist the expansion/dilation of the vessel. The biased stiffness is enough to support the open vessel, but the outward force may not be enough to open the vessel (or it may take a longer period of time). A stent with the type of geometry shown in
Preferably, helical elements 46 are axially abutted, forming a type of spring which permits a great deal of flexibility and axial expansion, while strut member 42 provides radial strength and retains the stent in its expanded condition.
Stents 40B′ and 40C′ have the advantage that the flexible helical elements are distributed more continuously along the length of the stent and may provide more continuous flexibility.
Those skilled in the art will appreciate that various modifications to stent 40B′ or 40C′ are possible, depending upon the requirements of a particular design. For example, it might be desirable to connect fewer than all of strut elements 44a in a particular winding to a subsequent winding, reducing the number of helical elements 46. Helical elements 46 can extend for less or for any integer or non-integer multiple of a rotation. A stent could also be made of a plurality of tubular sections each having the construction of stent 40B′ or 40C′ and joined lengthwise by another type of section.
Stent graft 100 comprises a continuous covering of graft material 102 covering stent 10, as shown in
Stent graft 110 comprises a plurality of sections 111 of graft material 112 covering the stent structure, as shown in
Stent graft 120 comprises a plurality of sections 121 of graft material 122 covering the stent structure, as shown in
Stent graft 130 comprises a continuous covering of graft material 132, as shown in
Stent graft 140 comprises a continuous covering of graft material 142, as shown in
Stent graft 150 comprises a continuous covering of graft material 152, as shown in
Stent graft 160 comprises a continuous covering of graft material 162, as shown in
Stent graft 170 comprises a plurality of sections 171 of graft material 172 covering stent 10, as shown in
Stent graft 180 comprises a plurality of sections 181 of graft material 182 covering stent 10, as shown in
The helical elements of the stent shown in
In
An additional method can be provided to crimp the stent such that the length of helical portions is shorter in the crimped state than in the expanded state. For example, if the stent of
As described above, one preferred embodiment of the stent is to permit repeated axial compression or expansion of about 20% and simultaneously permit bending with a twice the average diameter of the device. One method to construct a stent of the present invention with a specific target for flexibility is to vary the ratio between the sum of the gap space in the helical portion to the overall length. By increasing that ratio, the flexibility of the stent increases. This ratio will also be approximately the maximum axial compression the stent will allow. It will be appreciated that the maximum axial compression for safety may be limited by other factors such as strain in the helical elements.
Helical portion 303 that is adjacent to the strut portion 302 comprises helical elements 18 that are connected to every strut element 301 of strut portion 302. Helical portion 303 can provide a high percentage of surface area for optimized delivery of a drug or other therapeutic agent. Strut portion 304 is connected to helical portion 303 by helical element 18 at every strut element 16a on side 320 of strut portion 304 and is connected to helical portion 309 at every other strut element 16a on side 321 of strut portion 304. Helical portion 309 provides a lower percentage of surface area and greater flexibility than helical portion 303. This type of configuration can provide a transition from a stiffer helical portion that has a high percentage of surface area to a more flexible helical portion.
Helical portion 309 has a higher ratio of the sum of gap lengths 323 to length 324 of helical portion 309 than the sum of gap lengths 325 to length 326 of helical portion 303, so that helical portion 309 will generally have greater flexibility.
Strut portion 306 has half as many strut elements 305 as strut portions 302 or 304 and therefore generally has more open area compared to strut portion 302 or strut portion 304. An advantage of a stent including a portion having a larger open area than other portions of the stent is that the larger open portion of the stent can be placed over an arterial bifurcation and not impede blood flow. Whereas the strut portion with a higher strut element density may impede blood flow.
The stent structure of the present invention, namely flexible helical portions flanked on either side by strut portions, provide an optimized structure where the strut portions stabilize a naturally unstable helical structure, and the helical portions provide net flexibility. There is substantial design optimization potential in combining various embodiments of the two portions.
The flexible stents and stent grafts of the present invention may be placed within vessels using procedures well known in the art. The flexible stents and stent grafts may be loaded into the proximal end of a catheter and advanced through the catheter and released at the desired site. Alternatively, the flexible stents and stent grafts may be carried about the distal end of the catheter in a compressed state and released at the desired site. The flexible stents or stent grafts may either be self-expanding or expanded by means such as an inflatable balloon segment of the catheter. After the stent(s) or stent graft(s) have been deposited at the desired intralumenal site, the catheter is withdrawn.
The flexible stents and stent grafts of the present invention may be placed within body lumen such as vascular vessels or ducts of any mammal species including humans, without damaging the lumenal wall. For example, the flexible stent can be placed within a lesion or an aneurysm for treating the aneurysm. In one embodiment, the flexible stent is placed in a super femoral artery upon insertion into the vessel, the flexible stent or stent grafts provides coverage of at least about 50% of the vessel.
Although presently preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that many additions, modifications, and substitutions are possible without departing from the scope and spirit of the invention as defined by the accompanying claims. For example, a stent could be made with only right-handed or only left-handed helical portions, or the helical portions could have multiple reversals in winding direction rather than just one. Also, the helical portions could have any number of turns per unit length or a variable pitch, and the strut rings and/or helical portions could be of unequal length along the stent. Devices intended for use in pairs could have helical strut portions with windings in opposite directions or could have section of device pairs intended to overlap with windings in opposite directions. Further, a device could have circumferential struts with helical sections interposed. Pairs of such devices could have sections intended to overlap in use with windings in opposite directions. All such devices intended for use together could be sold together in a kit or sold separately.
This application claims the benefit of U.S. Provisional Patent Application No. 61/172,485, filed Apr. 24, 2009 and U.S. Provisional Patent Application No. 61/226,965 filed Jul. 20, 2009, the entirety of both of which applications are hereby incorporated by reference into this application.
| Number | Date | Country | |
|---|---|---|---|
| 61226965 | Jul 2009 | US | |
| 61172485 | Apr 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12767588 | Apr 2010 | US |
| Child | 14548772 | US |
