US 20050075716 A1
Luminal prostheses comprise adjacent expansible segments, typically serpentine ring segments joined by sigmoidal links. By properly orienting the sigmoidal links and aligning hinge regions on adjacent serpentine rings, enhanced opening characteristics can be obtained. Additionally, by varying the mechanical characteristics of adjacent serpentine rings, program expansion of the luminal prostheses over their lengths may be obtained. The disclosed prostheses also have controllable opening characteristics and can be crimped to small diameters.
1. A radially expansible luminal prosthesis including a scaffold comprising:
a plurality of serpentine ring segments including struts connected by circumferentially offset hinge regions, each hinge region having an apex and side regions disposed on either side of the of the apex; and
links between at least some of the hinge regions on adjacent serpentine rings, wherein the links are attached on the sides of the hinge regions, and all links have substantially similar sigmoidal shapes.
2. A radially expansible luminal prosthesis as in
3. A radially expansible luminal prosthesis as in
4. A radially expansible luminal prosthesis as in
5. A radially expansible luminal prosthesis as in
6. A radially expansible luminal prosthesis as in
wherein at least one of the ring segments opens at a different rate or in a different amount than at least one other ring segment when exposed to the same radially outward force.
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8. A radially expansible luminal prosthesis as in
9. A radially expansible luminal prosthesis as in
10. A radially expansible luminal prosthesis as in
11. A radially expansible luminal prosthesis as in
12. A radially expansible luminal prosthesis as in
13. A radially expansible luminal prosthesis as in
14. A radially expansible luminal prosthesis including a scaffold comprising:
a plurality of serpentine ring segments including struts connected by hinge regions being circumferentially offset with apices and side regions disposed on either side of the apices; and
links extending between and connecting at least some of the hinge regions on adjacent serpentine rings, wherein each link is attached on a side of each connected hinge region and wherein all the links have substantially similar sigmoidal shapes.
15. A radially expansible luminal prosthesis as in
16. A radially expansible luminal prosthesis as in
17. A radially expansible luminal prosthesis as in
18. A radially expansible luminal prosthesis as in
19. A radially expansible luminal prosthesis as in
20. A radially expansible luminal prosthesis including a scaffold comprising:
a plurality of serpentine ring segments including struts connected by hinge regions having apices and side regions, wherein the side regions are disposed on either side of the of the apices; and
links between at least some of the hinge regions on adjacent serpentine rings, wherein the links are attached on the sides of the hinge regions and all links have substantially similar sigmoidal shapes.
21. A radially expansible luminal prosthesis as in
22. A radially expansible luminal prosthesis including a scaffold comprising:
a plurality of serpentine ring segments including struts and hinge regions disposed between the struts, each hinge region having an apex and side regions disposed on either side of the apex;
links extending from one of the side regions of at least some of the hinge regions and connecting at least some of the adjacent serpentine rings, wherein all links have substantially similar sigmoidal shapes; and
cells formed by a boundary defined by adjacently joined serpentine ring segments and a pair of radially adjacent links connecting the adjacent serpentine rings, wherein each cell has a shape which is a multiple of the smallest cell.
23. A radially expansible luminal prosthesis as in
The present application is a continuation of U.S. patent application Ser. No. 09/565,560 (Attorney Docket No. 020460-000100/______), filed May 4, 2000, the full disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to radially expansible luminal prostheses, such as vascular stents and grafts.
Luminal prostheses are provided for a variety of medical purposes. For example, luminal stents can be placed in various body lumens, such as blood vessels, the ureter, urethra, biliary tract, and gastrointestinal tract, for maintaining patency. Luminal stents are particularly useful for placement in atherosclerotic sites in blood vessels or fistula or bypass grafts. Luminal grafts can be placed in blood vessels to provide support in diseased regions, such as aortic abdominal, and other aneurysms.
Both stent and graft prostheses must meet certain mechanical criteria to function successfully. In particular, such prostheses should be at least partly flexible or articulated (i.e., adjacent expansible ring segments are connected by links that articulate relative to one another) over their lengths so that they may be advanced through tortuous body lumens, such as those of the coronary vasculature. In addition, the prostheses should have controllable length change properties, either to maintain their original length or to have the ability to elongate or foreshorten, as desired, when the prostheses assume an expanded configuration. Further such prostheses must have sufficient mechanical strength, particularly hoop strength after they are expanded, in order to mechanically augment the luminal wall strength and thus maintain lumen patency. The ability to meet these requirements is severely limited in the case of stents and grafts which are delivered in a radially constrained or collapsed configuration. Such prostheses must radially expand at a target site within the body lumen, so any adaptations which are intended to enhance flexibility must not interfere with the ability to radially expand or to maintain strength once expanded.
Prior luminal prostheses often have structures which present a risk of injury as they are endoluminally delivered (i.e., tracked) to and/or released at a target site within a patient's body lumen. In particular, many vascular stents comprise a plurality of circumferentially connected and spaced-apart ring segments which deform circumferentially as the stent is radially expanded. The Palmaz stent described in U.S. Pat. Nos. 5,102,417 and 4,776,337, is typical of such stents. Such stent designs can present challenges in both delivery and deployment. For example a phenomenon called “flaring” occurs when the longitudinal elements of the distal or proximal end of the prosthesis are bent outward to assume a crown-like configuration due to bending forces placed on these elements as the prosthesis passes through tortuous body passageways. Flaring can create the same deleterious effects as the previously described fish scaling phenomenon, injuring or traumatizing the blood vessel wall as the prosthesis is delivered or tracked within the blood vessel. In addition, flaring may increase a tendency for stent movement relative to a delivery balloon, thus causing an improperly deployed stent or, possibly, dislodging the undeployed stent completely from the catheter.
In addition to challenges during delivery, prior luminal prostheses can suffer problems during expansion, particularly during balloon expansion of malleable stents. For example, it has been found that balloon expansion of vascular stents often results in the ends of the stent expanding preferentially compared to the center of the stent. Such “dog-bone” expansion inhibits sufficient expansion of the center or ends of the stent, thus leaving a restricted luminal area in the fully deployed stent. Conversely, sometimes it will be desired to flare the ends of the stent in order to lock the stent in place and prevent the ends of the stent from collapsing after deployment. The ability to program stent expansion over the length of the stent has generally been lacking in prior stent designs.
A still further problem experienced by many prior stent designs is a lack of vessel coverage after expansion. It will be appreciated that the ability to support luminal patency and inhibit hyperplasia and other luminal in-growth can be enhanced if relative coverage of the luminal wall area by the expanded stent is increased. Thus, stent designs which afford a greater luminal wall coverage, or which minimize the free space between stent structures, while minimizing the amount of stent material used may be advantageous. Such increase of luminal wall coverage, however, should not be achieved at the expense of “crimpability.” Particularly for vascular applications, it is desirable that the diameter of the stent be reduced as much as possible during delivery, e.g., when crimped over a delivery balloon. By minimizing the crimped-stent diameter, both trackability and the ability to cross smaller lesions and access more distal lesions will be enhanced. In addition, a larger crimped-stent diameter may increase the risk of stent movement relative to the deployment balloon which, in turn, could cause an improperly deployed stent or even loss of the undeployed stent from the catheter. The ability to reduce the stent diameter is generally limited by the amount of material in the stent itself. Thus, designs which increase the ability of the stent to cover the luminal wall without significantly reducing the “crimpability” would be particularly desirable.
For these reasons, it would be desirable to provide improved stent, graft, and other luminal prostheses. In particular, it would be desirable to provide improved luminal prostheses which exhibit a high degree of flexibility with minimum losses of hoop strength and luminal wall coverage after the prostheses are expanded. For example, the design should be such that the expanded prostheses will conform to both curved and straight vessels with minimal or no straightening or other unintended deformation of the vessel wall. Such luminal prostheses should be trackable, preferably being both flexible and presenting minimum risk of injury to the luminal wall as they are being delivered. In particular, the prostheses should avoid “fish scaling” and should be highly “crimpable” so that the prostheses diameter during delivery can be reduced. The luminal prostheses will preferably further display superior expansion characteristics. In particular, the prostheses designs should permit selective programming of the expansion characteristics along the length of the prostheses. For example, the designs should permit preferential expansion over the central portion of the prosthesis, or alternatively at either or both ends of the prostheses depending on the particular application in which the prosthesis is to be used. Still further preferably, upon expansion the prostheses should display superior luminal wall coverage and adequate to superior hoop strength in order to best maintain patency of the body lumen being treated. At least some of these objectives will be met by the luminal prostheses described and claimed hereinafter.
2. Description of the Background Art
Stents having expansible ring segments joined by sigmoidal links and axial beams are described in WO 99/17680. Stents comprising expansible rings including struts and hinges where the hinges are configured to have different opening forces are described in U.S. Pat. No. 5,922,020. EP 662 307 describes an expansible stent having serpentine elements with varying degrees of curvature to provide controlled expansion characteristics. WO 00/003,662 describes a stent delivery balloon which preferentially opens a center region of a stent as the balloon is expanded. U.S. Pat. No. 6,017,365, describes a stent with serpentine segments with non-linear struts and sigmoidal links. Other patents of interest include U.S. Pat. Nos. 4,776,337; 5,102,417; 6,017,362; 6,015,429; and 6,013,854.
The present invention provides improved luminal prostheses suitable for endoluminal placement within body lumens, particularly blood vessels, and most particularly coronary and peripheral arteries. The luminal prostheses may be in the form of stents, intended for maintaining luminal patency, or may be in the form of grafts, intended for protecting or enhancing the strength of a luminal wall. Generally, the term “stent” will be used to denote a vascular or other scaffold structure comprising expansible components, such as ring segments, which when expanded form an open lattice or framework which is disposed against the luminal wall. In contrast, the term “graft” will generally denote such as luminal scaffold which is covered by a liner, membrane, or other permeable or impermeable layer which covers at least a portion of the scaffold. The drawings included herein are generally directed at stent structures, but it will be appreciated that corresponding graft structures could be provided by incorporating a liner, membrane, or the like, on either the outer or inner surfaces of the stent.
The luminal prostheses of the present invention will be radially expansible, usually by the application of a radially outward internal force to expand a minimally resilient (usually malleable) prosthesis structure. Such radially outward internal force will usually be provided by an inflatable balloon, and such balloon expansible stents are well-known in the art and described in the background references which have been cited above and are incorporated herein by reference. Alternatively, at least some of the radially expansible luminal prostheses of the present invention may be self-expanding. By fabricating the prostheses from a resilient material, usually a metal, such as spring stainless steel, a nickel-titanium alloy (such as Nitinol® alloy), or the like, the prosthesis can be designed to have a large (fully expanded) diameter in an unconstrained state. The diameter of the prosthesis can be reduced by applying a radial constraint, e.g., by placing the prosthesis within a sleeve, tube, or other constraining structure. In that way, the self-expanding prosthesis can be delivered while constrained and deployed by releasing the constraint at the target site within the body lumen. The general principles of constructing self-expanding stents and other luminal prostheses are also well-known in the art and described in at least some of the background references which have previously been incorporated herein.
In a first aspect of the present invention, a radially expansible luminal prostheses comprises a plurality of serpentine ring segments including struts connected by hinge regions. The struts may be straight or may have non-linear configurations, e.g., being curved, wavy, or the like. The use of non-linear struts may be advantageous in order to increase the area of the strut which engages the luminal wall after expansion without significantly reducing flexibility and/or crimpability of the strut. The hinge regions are usually formed by a short curved or C-shaped region which permits the connected struts to reverse direction in order to define the serpentine ring pattern. Adjacent serpentine rings are joined by sigmoidal links, i.e., S-shaped elements which may be malleable or elastically deformable in order to allow the adjacent segments to flex relative to each other during prosthesis delivery and expansion. The sigmoidal links are attached to a side of the hinge region, typically located at the point where the hinge attaches to or transforms into the strut. The use of such sigmoidal links is beneficial since it permits the longitudinal expansion or contraction of the prosthesis to accommodate length changes as the prosthesis is expanded. Such links further permit bending of the prosthesis since they allow differential motion of adjacent serpentine rings. Such flexibility is particularly advantageous since it allows improved tracking of the prosthesis as it is delivered to an endoluminal location. The sigmoidal links also improve the conformability of the expanded prosthesis when placed in a native vessel, artificial graft, or other body lumen location. Such a structure distinguishes prior art designs where a sigmoidal link is attached at or near the apex of the link. By attaching the sigmoidal link closer to the strut, the adjacent ring segments can be positioned closer to each other. Moreover, because the links attach away from the apex of the hinge region, stress at the apex is reduced and uniform expansion of each ring segment is enhanced.
In a second aspect of the present invention, the apexes of opposed hinge regions on adjacent serpentine rings will be circumferentially offset. That is, the hinge regions apices on at least some (often all) of the serpentine rings will be aligned with the trough regions on the adjacent serpentine ring. In this way, the hinge regions are circumferentially offset so that the circumferential length of the sigmoidal links connecting proximate hinge regions can be reduced. Such a design also allows for adjacent serpentine rings to be closer together to allow for improved vessel coverage upon prosthesis expansion. Such a design also permits an increase in the diameter of the curved portions of the sigmoidal link which further improves stress distribution and opening characteristics of the prosthesis. Preferably, the luminal prostheses of the present invention will both have the sigmoidal links attached to the sides of the hinge regions and have the hinge regions circumferentially offset in order to achieve the greatest improvement in flexibility, crimpability, and uniform expansion characteristics.
The sigmoidal links will preferably have a S-shaped geometry with two outer connecting legs joined to a central leg by U-shaped joints. In some instances, it might also be possible to provide Z-shaped sigmoidal links, but those will generally be less preferred. In connecting the sigmoidal links to the hinge regions of the serpentine rings, the outer connecting legs will generally be oriented in the annular or circumferential direction and attach to the hinge region on its side.
In a further aspect of the present invention, a radially expansible luminal prosthesis comprises a plurality of ring segments which are expansible in response to a radially outward force. The ring segments may comprise serpentine rings, as generally described above, or may comprise zig-zag segments, box segments, or other conventional prosthesis ring patterns. The expansion characteristics of the luminal prosthesis may be varied over the length of the prostheses by controlling or programming the characteristics of each of the adjacent expansible ring segments. For example, different ring segments can be controlled to have different cross-sectional areas, e.g., differing widths, thicknesses or both, so that the amount of radially outward force needed to open the stent is lesser or greater. Alternatively, in the case of serpentine or zig-zag ring patterns, the strut length may be varied in order to control the force needed to open the stent. That is, ring segments having a greater strut length will open with a lesser force since the increased strut length will leverage the force applied to a hinge region so that the hinge region will open sooner. Other techniques for controlling the expansion characteristics of an individual ring segment may also be employed, such as those described in U.S. Pat. No. 5,922,020, the full disclosure of which has previously been incorporated herein by reference. Depending on the objective, the ring segments near either or both ends of the prosthesis may be programmed to open more or less readily so that, when applying a constant radially outward force along the length of the prosthesis, the stent will first open either at both ends or in the middle. It will be appreciated that by employing balloons which also have variable expansion characteristics, such as those described in WO 00/03662, a wide variety of prosthesis expansion characteristics can be provided over the length of the prosthesis.
The present invention provides luminal prostheses intended for endoluminal placement in body lumens, particularly within the vascular system for the treatment of cardiovascular disease, such as vascular stenoses, dissections, aneurysms, and the like. The prostheses, however, are also useful for placement in other body lumens, such as the ureter, urethra, biliary tract, gastrointestinal tract and the like, for the treatment of other conditions which may benefit from the introduction of a reinforcing or protective structure within the body lumen.
The prostheses are preferably placed endoluminally. As used herein, “endoluminally” will mean placement through a body opening or by percutaneous or cutdown procedures, wherein the prosthesis is translumenally advanced through the body lumen from a remote location to a target site in the lumen. In vascular procedures, the prostheses will typically be introduced “endovascularly” using a catheter over a guidewire under fluoroscopic guidance. The catheters and guidewires may be introduced through conventional access sites to the vascular system, such as through the femoral artery, or brachial, subclavian or radial arteries, for access to the coronary arteries.
A luminal prosthesis according to the present invention will usually comprise at least two radially expansible, usually cylindrical, ring segments. Typically, the prostheses will have at least four, and often five, six, seven, eight, ten, or more ring segments. At least some of the ring segments will be adjacent to each other but others may be separated by other non-ring structures.
By “radially expansible,” it is meant that the segment can be converted from a small diameter configuration (used for endoluminal placement) to a radially expanded, usually cylindrical, configuration which is achieved when the prosthesis is implanted at the desired target site. The prosthesis may be minimally resilient, e.g., malleable, thus requiring the application of an internal force to expand and set it at the target site. Typically, the expansive force can be provided by a balloon, such as the balloon of an angioplasty catheter for vascular procedures. As will be described below, the present invention preferably provides sigmoidal links between successive unit segments which are particularly useful to enhance flexibility and crimpability of the prosthesis.
Alternatively, the prosthesis can be self-expanding. Such self-expanding structures are provided by utilizing a resilient material, such as a tempered stainless steel or a superelastic alloy such as a Nitinol® alloy, and forming the body segment so that it possesses its desired, radially-expanded diameter when it is unconstrained, i.e. released from the radially constraining forces of a sheath. In order to remain anchored in the body lumen, the prosthesis will remain partially constrained by the lumen. The self-expanding prosthesis can be tracked and delivered in its radially constrained configuration, e.g., by placing the prosthesis within a delivery sheath or tube and removing the sheath at the target site.
The dimensions of the luminal prosthesis will depend on its intended use. Typically, the prosthesis will have a length in the range from about 5 mm to 100 mm, usually being from about 8 mm to 50 mm, for vascular applications. The small (radially collapsed) diameter of cylindrical prostheses will usually be in the range from about 0.5 mm to 10 mm, more usually being in the range from 0.8 mm to 1.25 mm for vascular applications. The expanded diameter will usually be in the range from about 1.5 mm to 50 mm, preferably being in the range from about 2.5 mm to 30 mm for vascular applications.
The ring segments may be formed from conventional materials used for body lumen stents and grafts, typically being formed from malleable metals, such as 300 series stainless steel, or from resilient metals, such as superelastic and shape memory alloys, e.g., Nitinol® alloys, spring stainless steels, and the like. It is possible that the body segments could be formed from combinations of these metals, or combinations of these types of metals and other non-metallic materials. Additional structures for the body or unit segments of the present invention are illustrated in U.S. Pat. Nos. 5,195,417; 5,102,417; and 4,776,337, the full disclosures of which are incorporated herein by reference.
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The sigmoidal links 28 are adjoined to the hinge regions 26 a so that a first outer leg segment 30 connects to the hinge region at its base i.e., where the hinge opens into the strut 24. Similarly, a second outer leg segment 32 is joined to hinge region 26 a on the adjacent serpentine ring 22 at the base of that hinge region. The legs 30 and 32 are generally oriented in a circumferential or annular direction at the point where they attach to the hinge regions 26 a. The legs are joined by a pair of U-shaped regions which join a central leg 34 to complete the sigmoidal link. This design of the sigmoidal link has a number of advantages. For example, by orienting the leg segments 30 and 32 circumferentially, the legs can move circumferentially past each other to accommodate radial crimping of the prosthesis as well as facilitate radial opening of the stent. Additionally, the structure permits axially shortening and elongation to permit bending of the prosthesis as it is being introduced through tortuous regions of a blood vessel or other body lumen.
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The dimensions of the hinges, struts, sigmoidal links, and the like, of the luminal prostheses of the present invention may vary considerably depending on the intended use. Exemplary dimensions intended for a coronary stent (
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In the particular embodiment of
Under other circumstances, however, it may be desired to preferentially open the end portions of the luminal prosthesis first. In such instances, the luminal prosthesis 30 could be modified so that the end segments 32 a-32 c and 32 k-32 m open preferentially with respect to the central ring segments 32 d-32 j. A variety of other opening characteristics, such as tapered would also be possible. For example, a tapered opening could be achieved by providing a stiffness gradient where segments at one end, such as 32 a, are the least stiff with ring segments becoming progressively stiffer in the direction of ring segment 32 m.
Differential expansion of different ring segments can be achieved in a variety of ways. For example, as shown in
Referring now to
In an optional aspect of the present invention, at least some of the serpentine ring segments may employ non-linear struts. As shown in
Referring now to
While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.