Stent-graft with rails
A stent-graft with increased longitudinal flexibility that is deployed within a body lumen for supporting the lumen and repairing luminal aneurysms. In a preferred embodiment, the stent-graft is located and expanded within a blood vessel to repair aortic aneurysms. The stent-graft is comprised of an expandable stent portion, an expandable graft portion and at least one elongated rail. The stent portion and graft portion are moveable between the terminal ends of the rail(s) and relative to the rails so that it can conform to the shape of a vessel in which it is deployed. The stent-graft provides increased longitudinal flexibility within a vessel. Also, the stent-graft of the present invention does not kink after expansion, and thus, eliminates the potential for the graft portion occluding the blood flow lumen of the vessel in which it is deployed. Moreover, the wear on the graft is reduced and its longevity increased.
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This application claims the benefit of and incorporates by reference U.S. Provisional Patent Application No. 60/403,361 filed on Aug. 15, 2002.
FIELD OF THE INVENTIONThe present invention relates to a stent-graft for use as a prosthetic within a body lumen to support the lumen, and particularly, to a stent-graft having improved longitudinal structural flexibility and graft wear that can be used within a body to support a lumen.
BACKGROUND OF THE INVENTIONIt is generally known to insert a resiliently expandable stent into a body lumen, such as a blood vessel, to provide radial hoop support within the lumen in the treatment of atherosclerotic stenosis and other conditions. For example, it is generally known to open a blocked cardiac blood vessel by conventional methods (e.g., balloon angioplasty or laser ablation) and to keep that blood vessel open using an expandable stent.
Stents are tubular structures formed of biocompatible materials, usually metals like stainless steel or Nitinol, which are radially expandable. The radial strength of the stent material keeps the stent and the lumen into which the stent is deployed in an open configuration. Expandable stents typically include a mesh-like surface pattern of slots or holes cut therein so that a balloon can expand the stent after the stent has been deployed into the body lumen and positioned at a predetermined location. However, these mesh-like surface patterns also permit the passage of endothelial and other cells through the openings in the stents that can cause restenosis of the vessels. For example, the mesh-like surface patterns can permit thrombus formations and plaque buildup within the vessel.
Expandable stents have been combined with coverings of biocompatible materials to form “stent-grafts” that provide benefits in addition to those provided by conventional expandable stents. For example, the expandable stent-grafts can be used as a graft within a body lumen, such as a blood vessel. Intraluminal vascular stent-grafts can be used to repair aneurysmal vessels, particularly aortic arteries, by inserting an intraluminal vascular stent-graft within the aneurysmal vessel so that the prosthetic stent-graft support the vessel and withstand the forces within the vessel that are responsible for creating the aneurysm.
Polytetrafluroethylene (PTFE) has been used as a material from which to fabricate blood vessel grafts or prostheses used to replace damaged or diseased vessels. This is partially because PTFE is extremely biocompatible causing little or no immunogenic reaction when placed within the human body. Additionally, in a preferred form, expanded PTFE (ePTFE) has been used. This material is light and porous and is potentially colonized by living cells becoming a permanent part of the body. The process of making ePTFE of vascular graft grade is well known.
Enclosing a stent with ePTFE can create a vascular prosthetic that limits the amount of cellular material that can enter the stent and the blood vessel. However, such a stent-graft tends to be rather inflexible. Conventional stent-grafts tend not to conform to the natural curved shape of the blood vessel in which they are deployed. In particular, conventional stent-grafts can be longitudinally inflexible (i.e., along a length of the stent portion and the graft portion), and therefore tend to be resistant to transverse deformation. As a result, these stent-grafts may not effectively seal the intended aneurysm(s) within the blood vessel in which the stent-graft is deployed.
Conventional stent-grafts include circumferential support members (hoops) that are securely spaced from each other and from the ends of the stent portion so that they do not experience relative axial movement. The spacing between adjacent support elements is maintained by rigid connections or bridge elements (sometimes referred to in the art as “bridges”) between adjacent support elements and at least one elongated member that extends from a first end of the stent portion to a second end of the stent portion. The circumferential support members are also secured to the graft portion of material extending along the stent portion so that the graft portion cannot move along the length of the stent portion. These secure, rigid connections prevent the support elements and the graft portion from moving longitudinally along the elongated member(s) of the stent and prevent the stent-graft from conforming to the curvature of the blood vessel in which it is deployed. The interaction of the conventional stent material and the conventional graft material, along with the large expanded diameter of a stent-graft, create conformability, performance and manufacturing issues that are in addition to those issues associated with conventional stents and discussed in copending U.S. patent application Ser. No. 10/100,986 which is hereby incorporated by reference. For example, poor longitudinal flexibility of the stent-graft can lead to kinking of the graft portion and the ultimate occlusion of the flow lumen. Additional disadvantageous of conventional stent-grafts can include graft wear on the stent portion, blood leakage through suture holes in the graft portion that receive the sutures that anchor the graft portion to the stent portion and labor intensive manufacturing processes.
There is a need in the art for a stent-graft that is longitudinally flexible, while providing a smooth inner surface for blood flow.
SUMMARY OF THE INVENTIONThe present invention relates to a stent-graft with increased longitudinal flexibility relative to conventional stent-grafts. Longitudinal flexibility as used herein relates to the flexibility of the stent-graft structure (or portions thereof) to move relative to its major, longitudinal axis of extension. The stent-graft is deployed within a body lumen for supporting the lumen and repairing luminal aneurysms. In a preferred embodiment, the stent-graft is located and expanded within a blood vessel to repair aortic aneurysms.
In an embodiment, the stent-graft can be comprised of an expandable stent portion, an expandable graft portion and at least one elongated rail. The stent portion and graft portion are moveable between the terminal ends of the rail(s) and relative to the rails so that the stent-graft can conform to the shape of a vessel in which it is deployed. Additionally, longitudinally adjacent circumferential support elements of the stent portion can be secured together by at least one bridging element. Alternatively, each circumferential support elements can be free of a connection to a longitudinally adjacent circumferential support element. The use of the rail(s) and the bridging elements allows the support elements to separate as needed, assume the outer radius of a vessel bend and shorten to assume an inner radius of a vessel bend. The stent-graft eliminates the poor longitudinal flexibility associated with conventional stent-grafts. As a result, the stent-graft of the present invention provides greater resistance to kinking after expansion, and thus, eliminates the potential for the graft portion occluding the blood flow lumen. Moreover, the wear on the graft is reduced and its longevity increased.
Furthermore, according to an aspect of the present invention, the graft portion of the stent-graft is coupled to at least one longitudinal extending rail at locations spaced from the ends of the stent-graft. In one embodiment, the graft portion is coupled to the rails at the locations spaced from the ends of the stent-graft without the use of sutures that would extend through the graft portion and compromise the fluid retention integrity of the graft portion at these spaced locations. Instead, circumferential coupling members positioned about the graft portion and secured to the graft portion can receive the rails. These coupling members include circumferentially spaced openings that receive the rail(s). Alternatively, the rails extend through cauterized holes that were mechanically created in a substrate of the graft portion. Passing the rail(s) through these openings and holes reduces manufacturing costs and time. Passing the rail(s) also provides greater expanded longitudinal flexibility, prevents apices of the stent portion from protruding into the graft portion and the blood vessel and reduces wear on the material forming the graft portion. The securing of the rail(s) relative to the graft portion according to the present invention eliminates the blood leakage that is typically seen with conventional stent-grafts that employ sutures. In this or any of the embodiments discussed herein, the ends of the graft portion may be secured to the stent portion by sutures.
BRIEF DESCRIPTION OF THE DRAWINGSThe present invention will be even better understood with reference to the attached drawings, in which:
Referring to the figures where like numerals indicate the same element throughout the views,
The stent portion 20 includes a plurality of spaced, circumferentially extending support elements (hoops) 22. Each circumferential support element 22 is generally annular in shape as shown in
Stainless steel, metal alloys, shape-memory alloys, super elastic alloys and polymeric materials used in conventional stents are representative examples of materials from which circumferential stent portion 20 and its support elements 22 can be formed. The alloys can include NiTi (Nitinol). The polymers for circumferential support elements 22 may, for example, be bioabsorbable polymers so that the stent can be absorbed into the body instead of being removed.
In a first embodiment, illustrated in
In the embodiment illustrated in
In the embodiment shown in
Furthermore, the peripheral location at which bridge element(s) 24 are provided between respective adjacent support elements 22 has an effect on longitudinal flexibility. For example, if two bridge elements are provided between a respective pair of adjacent support elements 22 at diametrically opposite sides of the support elements 22, then, generally, the longitudinal flexibility there between is at a maximum at diametrically opposite sides of the support elements 22 located at about 90 degrees from the bridge elements 24, and decreases along the circumference of the support elements 22 in a direction approaching the respective bridge elements 24.
For the foregoing reasons, it may be useful or otherwise beneficial to provide, for example, one bridge element 24 between adjacent support elements 22, as illustrated in
In an alternative embodiment illustrated in
As shown in
Rails 50 are desirably sufficiently flexible to accommodate bends, curves, etc. in a blood vessel. In one embodiment, the rails 50 are free of longitudinal expansion. Also, the rails 50 may be made from, for example and without limitation the following biocompatible materials: metals, metallic alloys including those discussed above, glass or acrylic, and polymers including bioabsorbable polymers. The rails 50 can have any form. For example, the rails 50 can be solid cylindrical members, such as wires or extrusions with a circular, elliptical or other known cross sections. Alternatively, the rails 50 can be ribbons or spring wires.
In contrast to bridge elements 24 which are generally the same thickness and the circumferential support element 22 that they join and thus relatively inflexible, the thickness of the rails 50 can be designed to provide a desired degree of flexibility to a given stent-graft 10. Each rail 50 can have a thickness (diameter) of about 0.001 inch to about 0.010 inch. In an embodiment, each rail 50 has a thickness of about 0.0011 inch to about 0.005 inch. In another embodiment, each rail 50 has a thickness of about 0.005 inch. The rails 50 can be passed or “snaked” through the circumferential support elements 22 as discussed in copending U.S. patent application Ser. No. 10/100,986, which has been incorporated by reference. Additionally, the rails 50 can be passed through the stent portion 20 and the graft portion 100 as discussed below.
At least some of rails 50 may include end structures for preventing the circumferential support elements 22 from unintentionally passing beyond the ends 54, 56 of the rails 50. The end structures may have several forms as illustrated in copending U.S. patent application Ser. No. 10/100,986, which has been incorporated by reference. In an example, the end structures may be mechanical protrusions or grasp structures by which the endmost circumferential support elements 22 are fixed in place relative to the ends 54, 56 of rails 50. In yet another embodiment, the structures may also be a weld (made by, for example, a laser) for bonding a portion of an endmost circumferential support element 22 to ends 54, 56 of rails 50.
As illustrated in
In the embodiment illustrated in
The struts 14 of the stent portion 20 can have substantially any radial thickness that provides them with the needed strength to support the graft portion i 00 and a blood vessel when deployed and expanded within the vessel. Each strut 14 has a substantially low profile that will not damage the vessel as it is deployed. In one example, the struts 14 can have a radial thickness of between about 0.0001 inch and about 0.020 inch. In an embodiment, the radial thickness is about 0.002 inch to about 0.008 inch. In another embodiment, the struts 14 have a radial thickness of between about 0.004 inch and about 0.005 inch. These thicknesses provide the stent-graft 10 with the needed structural and expansion properties to support the graft 100, to support the vessel in which it is deployed and the longitudinal flexibility to conform to the natural elongated shape of the vessel.
In an embodiment, the areas of the curved members 16 are formed to have the same radial thickness as that of the struts 14 in order to accommodate the apparatus 17 and the received rail(s) 50. In another embodiment, the areas of the curved members 16 are formed with a greater radial thickness than the struts 14 in order to accommodate the apertures 17. For example, the radial thickness of the curved members 16 can be between about 0.001 inch and about 0.006 inch greater than that of the struts 14. The apertures 17 can have a diameter of about 0.005 inch for receiving the rails 50. Between the rails 50 where expansion occurs, the thickness could be about 0.004 inch. A stent portion 20 having 0.002 inch thick strut 14 walls could have a curved member 16 with a radial thickness of about 0.009 inch where the rails 50 are passed.
In the embodiments illustrated in
Each aperture 39 can have a diameter that is large enough to slidably receive a rail 50. The diameter of each aperture 39 can be between about 0.0014 inch and about 0.012 inch. In an embodiment, the rail receiving area has an opening of between about 0.0014 inch and 0.006 inch. However, any diameter that slidably receives a rail 50 could also be used.
In alternative embodiments illustrated in
In a first embodiment illustrated in
In the embodiment illustrated in
In either embodiment illustrated in
As illustrated in
In any of the above-discussed embodiments, the illustrated graft portion 100 is formed of a well known biocompatible materials such as woven polyester including polyester terphthalate (PET, polyester, formerly available under the Dupont Trademark “Dacron”), polytetrafluroethylene (PTFE, Teflon) and fluorinated ethylene propylene (FEP, Teflon with additives for melt processing). Other polymer fabrics could be used including polypropylene, polyurethane, including porous polyurethane, and others. In an embodiment, the biocompatible material is expanded Polytetrafluroethylene (ePTFE). Methods for making ePTFE are well known in art, and are also described in U.S. Pat. No. 4,187,390 issued to Gore on Feb. 5, 1980, which is hereby incorporated herein by reference. The graft portion 100 can be formed of either woven or a non-woven material(s).
The porous structure of ePTFE consists of nodes interconnected by very small fibrils. The ePTFE material provides a number of advantages when used as a prosthetic vascular graft. The ePTFE is highly biocompatible, has excellent mechanical and handling characteristics, does not require preclotting with the patient's blood, heals relatively quickly following implantation, and is thromboresistant. Further, ePTFE has a microporous structure that allows natural tissue ingrowth and cell endothelialization once implanted into the vascular system. This contributes to long-term healing and graft patency.
The graft portion 100 can be surrounded by the rails 50 and the stent portion 20 as illustrated in
Each coupling member 60 is sized to be circumferentially and longitudinally coextensive with a portion of the outer surface of the graft portion 100. The coupling members 60 can extend 360 degrees around the circumference of the graft portion 100 or only partially around the circumference of the graft portion 100. For example, each coupling member 60 may extend only about 270 or 180 degrees around the circumference of the graft portion 100. The coupling members 60 expand with the stent portion 20 and the graft portion 100 when the stent-graft 10 is expanded within a vessel using either self-expansion or a balloon.
Each coupling member 60 is formed of a known material such as those discussed above relating to the graft portion 100 including PTFE, ePTFE, FEP, woven PET (DACRON), PET film, or any polymer that can be bonded to the exterior of the graft portion 100 and permits the smooth and easy passage of the rails 50 through their associated passageways 62, hereinafter referred to as “openings 62”. The material for each coupling member 60 can vary depending on the material used for the graft portion 100.
As shown in
In an embodiment, the number of coupling members 60 will be equal to the number of support elements 22 that extend around the graft portion 100. As illustrated in
In an alternative embodiment, the coupling member 60 includes a first circumferentially extending member secured to the outer surface 104 of the graft portion 100 and a second circumferentially extending member positioned over the first member. In this embodiment, the openings 62 are formed between the two circumferentially extending members.
In any of the above embodiments relating to
In the alternative embodiment illustrated in
In an alternative embodiment, shown in
In the embodiments illustrated in
In the embodiment illustrated in
Portions of the loops 200 on the exterior of the graft portion 100 and in-between the interior regions 202 form arches 210 along the outer surface of the graft portion 100. The arches 210 slidably receive the rails 50 so that the graft portion 100 can move along the rails 50 and relative to the support elements 22. While rounded arches 210 are illustrated, any shaped opening that slidably receives the rails 50 can be used. For example, the opening of the arches 210 can include a rectangular, elliptical or triangular shape. The arches 210 each include an opening sized to receive the rails 50. These opening can be between about 0.0014 inch and about 0.012 inch. In an embodiment, the arch openings can be between about 0.0014 inch and about 0.006 inch. In an embodiment, the arch openings can be about 0.005 inch.
Each arch 210 is spaced from circumferentially spaced arches 210 by a distance that is substantially equal to the circumferential spacing of the adjacent rails 50. The adjacent arches 210 can be equally spaced from each other around the circumference of the graft portion 100. Alternatively, adjacent arches 210 can be circumferentially spaced at different intervals around the circumference of the graft portion 100 to provide different flexion capabilities to the stent graft 10. Each arch 210 can be spaced from an adjacent arch 210 by a distance of about 0.10 inch to about 0.30 inch. In one embodiment, adjacent arches 210 are spaced from each other by a distance of about 0.155 inch.
The support elements 22 comprise the diamond shaped support members 30 shown in
The movement of the support elements 22 along the length of the stent-graft 10 and relative to the rails 50 and graft portion 100 can be limited by one or both of the longitudinal peaks 34, 35 abutting against a support element 200. As shown in
Unlike the other embodiments (for example the embodiment illustrated in
In another alternative embodiment, the graft portion 100 can include integral, spaced areas that receive the rails 50 formed of the material used to form the graft portion 100. These spaced areas have an increased thickness with respect to the remainder of the graft portion 100.
The present invention also includes introducing an agent, including those set forth in U.S. patent application Ser. No. 60/426,366, which is hereby incorporated by reference, into a body using the above-discussed stent-graft 10. In a preferred embodiment, the agent(s) is carried by one or more of the rails 50 or the graft portion 100 and released within the body over a predetermined period of time. For example, these stents can deliver one or more known agents, including therapeutic and pharmaceutical drugs, at a site of contact with a portion of the vasculature system or when released from a carrier as is known. These agents can include any known therapeutic drugs, antiplatelet agents, anticoagulant agents, antimicrobial agents, antimetabolic agents and proteins. These agents can also include any of those disclosed in U.S. Pat. No. 6,153,252 to Hossainy et al. and U.S. Pat. No. 5,833,651 to Donovan et al., both of which are hereby incorporated by reference in their entirety. Local delivery of these agents is advantageous in that their effective local concentration is much higher when delivered by the stent than that normally achieved by systemic administration.
The rails 50, which have a relatively low elastic modulus (i.e. low force to elastic deformation) in their transverse direction, may carry one or more of the above-referenced agents for applying to a vessel as the vessel moves into contact with the agent carrying rail(s) 50 after deployment of the stent-graft 10 within the vessel. These agents can be applied using a known method such as dipping, spraying, impregnation or any other technique described in the above-mentioned patents and patent applications that have been incorporated by reference. Applying the agents to the rails 50 avoids the stresses at focal areas as seen in the struts of traditional stents. In this manner drug coatings applied to the stent rails 50 may be used with support elements formed of materials that are otherwise unsuitable for coating.
It is contemplated that the various elements of the present invention can be combined with each other to provide the desired flexibility. For example, the rails 50 can be formed of one or more radiopaque materials. Additionally, the support element designs can be altered and various support element designs that permit the passage of the rails could be used. Similarly, the number, shape, composition and spacing of the rail elements can be altered to provide the stent with different properties. Additionally, the device can have varying numbers and placement of the bridge elements. The properties of any individual stent would be a function of the design, composition and spacing of the support elements, rails and bridge elements.
Thus, while there have been shown and described and pointed out fundamental novel features of the present invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, and in the method illustrated and described, may be made by those skilled in the art without departing from the spirit of the invention as broadly disclosed herein.
Claims
1. A stent-graft comprising:
- an elongated stent portion extending about an axis;
- a graft portion being at least partially coextensive with said stent portion; and
- at least one rail element extending along a length of said stent-graft, each rail element being movably coupled to said stent portion and/or said graft portion such that at least a portion of said stent portion and said graft portion are freely movable along a portion and relative to each rail element.
Type: Application
Filed: Oct 19, 2004
Publication Date: May 12, 2005
Applicant: GMP Cardiac Care, Inc. (Fort Lauderdale, FL)
Inventors: Kenneth Solovay (Weston, FL), Thomas Jacobs (Delray Beach, FL)
Application Number: 10/967,207