Abstract:
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.

Description:
RELATED APPLICATION  
       [0001]     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 INVENTION  
       [0002]     The 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 INVENTION  
       [0003]     It 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.  
         [0004]     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.  
         [0005]     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.  
         [0006]     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.  
         [0007]     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.  
         [0008]     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.  
         [0009]     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 INVENTION  
       [0010]     The 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.  
         [0011]     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.  
         [0012]     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 DRAWINGS  
       [0013]     The present invention will be even better understood with reference to the attached drawings, in which:  
         [0014]      FIG. 1  illustrates a stent-graft according to an embodiment of the present invention;  
         [0015]      FIG. 2  is an enlarged view of a portion of the stent-graft shown in  FIG. 1 ;  
         [0016]      FIG. 3  illustrates a graft portion and rail receiving coupling members of the stent-graft shown in  FIG. 1 ;  
         [0017]      FIG. 4  is an enlarged view of an end of the graft portion and rail receiving coupling members illustrated in  FIG. 3 ;  
         [0018]      FIG. 5  is an end view of the graft portion and rail receiving coupling members shown in  FIG. 3 ;  
         [0019]      FIG. 6  illustrates an opening of a rail receiving coupling member along the circumference of the stent graft;  
         [0020]      FIG. 7  is a side view of the rail receiving coupling members with at least two rails extending along the length of the stent-graft;  
         [0021]      FIG. 8  is a perspective view of the rail receiving coupling members spaced along the stent-graft with the graft portion and stent portion removed;  
         [0022]      FIG. 9  illustrates a portion of an alternative stent-graft embodiment according to the present invention;  
         [0023]      FIGS. 10 and 11  illustrate portions of an additional alternative stent-graft embodiment according to the present invention;  
         [0024]      FIGS. 12-15  illustrate another alternative embodiment of the stent-graft according to the present invention in which the rails are extended through cauterized openings in the graft portion;  
         [0025]      FIG. 16  illustrates a graft portion of a stent-graft according to another embodiment of the present invention;  
         [0026]      FIG. 17  illustrates a stent-graft according to the present invention including the graft portion illustrated in  FIG. 16 ; and  
         [0027]      FIGS. 18-20  illustrate a vascular support member including rail receiving coupling members according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]     Referring to the figures where like numerals indicate the same element throughout the views,  FIG. 1  illustrates a stent-graft  10  according to the present invention. The stent-graft  10  includes a graft portion  100  and a stent portion  20  with flexible elongated rail elements  50 . The stent portion  20  provides support to the graft portion  100  when the stent-graft  10  is deployed and located in an expanded condition within a portion of a mammalian body such as a vascular lumen.  
         [0029]     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  FIG. 1 . Each circumferential support element  22  is made from a flexible, biocompatible material (i.e., from a material that is, for example, non-reactive and/or non-irritating). In one embodiment, the stent portion  20  can be formed from a tube of biocompatible material. For example, the stent portion  20  can be formed by laser cutting the stent portion  20  and its support elements  22 , etc. from the tube. In another embodiment, each circumferential support element  22  is made from medical-grade metal wire formed as a closed loop (i.e., as an annular hoop) in a known manner, including, for example, micro-welding two ends of a wire segment together.  
         [0030]     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.  
         [0031]     In a first embodiment, illustrated in  FIGS. 1 and 2 , each circumferential support element  22  has a sinusoidal or otherwise undulating form, such as a wave shape. As shown in  FIGS. 1 and 2 , the undulating form of the support elements  22  includes peaks  12  and troughs  13  (space behind the peaks). The troughs  13  include the open spaces between adjacent substantially linear struts  14  that are connected to a curved member  16  that forms the respective peak  12 . Each peak  12  points in a direction that is opposite that of the immediately preceding or following, circumferentially positioned peak  12 . The same is true of the troughs  13 . Each trough  13  points in a direction that is opposite the immediately preceding or following, circumferentially positioned trough.  
         [0032]     In the embodiment illustrated in  FIGS. 1 and 2 , the peaks  12  all face in the one direction, toward a first end  54  of the stent  20 . Similarly, the troughs  13  all face in one direction, toward a second end  56  of the stent  20 , which is opposite the first end. Each circumferential support element  22  is connected to a longitudinally adjacent circumferential support element  22  by a respective bridge element  24  ( FIGS. 1 and 2 ). As shown, the bridge elements  24  connect peaks of adjacent and circumferentially out-of-phase peaks  12  of adjacent support elements  22 . As a result, adjacent support elements  22  can be rigidly spaced from each other at the area where they are joined by the bridge element  24 .  
         [0033]     In the embodiment shown in  FIGS. 1 and 2 , only a limited number of bridge elements  24  are provided between respective adjacent support elements  22 . For example, adjacent support elements  22  may be connected to each other by between about one and three bridge elements  24 . In an embodiment, only one bridge element  24  extends between adjacent support elements  22 . If too many bridge elements  24  are provided between adjacent support elements, the coupling between the support elements  22  becomes similar to providing a rigid coupling between support elements, such that the desired longitudinal flexibility according to the present invention is lost. By providing only a limited number of bridge elements  24  (including, without limitation, one bridge element  24 ), the resultant assembly can still provide a good approximation of using completely independent circumferential support elements  22 .  
         [0034]     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 .  
         [0035]     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  FIG. 1 . Furthermore, it may be additionally useful to offset each bridge element  24  from a longitudinally adjacent bridge element  24  in a circumferential direction, as is also illustrated in  FIG. 1 . The circumferential offset can be staggered by one set of peaks  12  along the length of the stent portion  20  between adjacent support elements  22 . Alternatively, the bridge elements  24  can be circumferentially offset by up to 180 degrees for adjacent pairs of support elements  22 . The above-discussed circumferential offset embodiments provide the structural integrity benefits of using a bridge element  24 , but distribute the resultant restriction in longitudinal flexibility so that no one transverse direction of stent deflection is overly restricted.  
         [0036]     In an alternative embodiment illustrated in  FIG. 9-15 , the circumferential support elements  22  are formed by a plurality of connected, substantially diamond shaped support members  30 . Each diamond shaped support member  30  has a first circumferential peak  32  and a second circumferential peak  33  that point in opposite circumferential directions. Each support member  30  also includes a first longitudinal peak  34  and a second longitudinal peak  35  that point toward different ends of the stent portion  20 . Circumferentially successive diamond shaped support members  30  are connected to each other at a junction  36  that is formed as part of the support element  22  during the pressing or molding of the support elements  22 . Alternatively, the junctions  36  can be applied using conventional techniques such as welding, hooks or friction fitting.  
         [0037]     As shown in  FIGS. 1 and 2 , the support elements  22  are freely mounted on flexible, elongated rail elements  50  (hereinafter “rails”) such that the support elements  22  can move along the rails  50 . The rails  50  extend along the length of the stent-graft  10  between the outermost peaks  12  of terminal support elements  22  at a first end  54  and the innermost peaks  12  of the terminal support element  22  at a second end  56 . As illustrated, the terminal support elements  22  can extend beyond the terminal ends of the graft-portion  100 .  
         [0038]     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.  
         [0039]     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.  
         [0040]     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 .  
         [0041]     As illustrated in  FIG. 1 , the stent portion  20  can include eight rails  50  that extend between the ends  54 ,  56 . However, it is also contemplated that any number of rails  50  up to the number of peaks  12  along the circumference of the support element  22  could be used. For example, if the support elements  22  include three sets of peaks  12 , then three rails  50  could be used. If the support elements included fourteen sets of peaks  12 , then up to fourteen rails  50  could be used. In between the support elements  22  at the terminal ends  54 ,  56 , the support elements  22  that are connected to each other by the bridge elements  24  are free to move along the rail(s)  50 . These remaining support elements  22  slide along the rail(s)  50  so that the stent  50  can conform to the shape of the blood vessel. It is also contemplated that the terminal support elements  22  can move along the rails  50 .  
         [0042]     In the embodiment illustrated in  FIG. 1 , the circumferential support elements  22  include apertures  17  in the curved members  16  through which the rails  50  extend. Apertures  17  extend through the peaks  12  in a direction that is substantially parallel to the length of the stent portion  20 . These apertures  17  retain and orient the supporting rail(s)  50  in a direction parallel to the length of the stent-graft  10 . Also, in an embodiment, the rails  50  are completely contained within the walls (within the outer surface) of the stent-graft  10  so that they do not protrude beyond the outer surface of the stent-graft  10 .  
         [0043]     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.  
         [0044]     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.  
         [0045]     In the embodiments illustrated in  FIGS. 9-15  and  17 , the rails  50  extend through apertures  39  located at the first and second longitudinal peaks  34 ,  35  of the support elements  22 . In a first embodiment, the areas of the support members  30  forming longitudinal peak  34  and longitudinal peak  35  and surrounding apertures  39  can have the same radial thickness as that of longitudinal struts  37  extending between the peaks  32 - 35 . In an alternative embodiment, the areas surrounding apertures  39  can have a greater radial thickness than that of the longitudinal struts  37 . As discussed above, the radial thickness of the areas surrounding apertures  39  can be between about 0.001 inch and about 0.006 inch greater than that of the struts  37 . For example, a diamond shaped support member  30  having struts  37  with a radial thickness of about 0.002 inch could have a longitudinal peak  34 ,  35  with a radial thickness of between about 0.006 inch and about 0.009 inch.  
         [0046]     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.  
         [0047]     In alternative embodiments illustrated in  FIGS. 18-20 , the rails  50  are slidably received within rail receiving members  130  that extend from a surface of the support member  30  forming the support element  22 . These rail receiving members  130  slidably couple a rail  50  to the support element  22 . As illustrated, the rail receiving members  130  are located proximate the longitudinal peaks  34 ,  35  of their respective support member  30 . However, the rail receiving members  130  could be located at other positions along the length of their respective support elements  22 . Any of the above-discussed embodiments can include support elements  22  having the rail receiving members  130 .  
         [0048]     In a first embodiment illustrated in  FIG. 18 , the rail receiving members  130  are located proximate the longitudinal peaks  34 ,  35  of the support members  30 . The receiving members  130  of this embodiment include an arm  137  with a groove  139  that receives the rail  50 . The groove  139  has a bearing surface that is sized large enough to couple the support element  22  to the rail  50 , while still permitting movement of the support element  22  along the rail  50  and relative to the graft portion  100 .  
         [0049]     In the embodiment illustrated in  FIG. 19 , each receiving member  130  can include two opposing arms  158  that are offset from each other along the length of the support member  30 . Like arm  137 , each arm  158  includes a groove  159  sized to couple the support member  30  to the rail  50  while permitting sliding movement of the support member and stent portion  20  relative to the rails  50 .  
         [0050]     In either embodiment illustrated in  FIGS. 18 and 19 , the arms  137 ,  158  can be formed by being punched, or otherwise mechanically formed, from a portion of its support member  30 . Alternatively, the arms  137 ,  158  could be secured to their respective support members  30  by welding or other known connection techniques. Each arm  137 ,  158  can be formed to extend inwardly away from its support member  30  in the direction of the graft portion  100 . In such an embodiment, the arms  137 ,  158  are not intended to contact the inner surface of the vessel into which the stent-graft  10  is deployed. Alternatively, the arms  137 ,  158  of the receiving members  130  can project outwardly away from the stent portion  100  and the outer surface of their support members  30  that are intended to contact the inner wall of the vessel in which the stent-graft  10  is deployed. As with the above-discussed embodiments, the grooves  139 ,  159  provide rail receiving areas having openings of between about 0.0014 inch and 0.012 inch. In an embodiment, the rail receiving areas of grooves  139 ,  159  has an opening of between about 0.0014 inch and 0.006 inch.  
         [0051]     As illustrated in  FIG. 20 , the rail receiving members  130  can also include a pair of opposing, cooperating arms  163  that form a groove  164  into which the rail  50  can be snap fitted. The groove  164  is sized to receive the rail  50  such that the support member  30  is coupled to the rail  50  and free to move longitudinally along the rail  50  as discussed above with respect to the other embodiments. The arms  163  can be formed as discussed above with respect to the embodiments illustrated in  FIGS. 18 and 19 . Additionally, the arms  163  can extend from either the inner or outer surfaces of their respective support members  30  as discussed above with respect to the embodiments illustrated in  FIGS. 18 and 19 .  
         [0052]     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).  
         [0053]     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&#39;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.  
         [0054]     The graft portion  100  can be surrounded by the rails  50  and the stent portion  20  as illustrated in  FIGS. 1-17 . In the first embodiment, illustrated in  FIGS. 1-8 , the stent-graft  10  includes a plurality of circumferentially extending, rail receiving coupling members  60  that are spaced from each other along the length of the graft portion  100 . The rail receiving coupling members  60  eliminate the need to suture the stent portion  20  to the graft portion  100  at locations spaced from the ends of the graft portion  100 .  
         [0055]     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.  
         [0056]     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 .  
         [0057]     As shown in  FIGS. 6 and 7 , the openings  62  are formed between the inner surface of the coupling member  60  and the outer surface  104  of the graft portion  100  so that the openings  62  retain their open position before and after the rails  50  have been passed through. The openings  62  are equally or unequally spaced around the circumference of the coupling members  60 . In an embodiment, the openings  62  are axially aligned along the length of the graft portion  100 . However, in an alternative embodiment, the openings  62  of adjacent coupling members  60  can be circumferentially offset relative to each other. The number of openings  62  circumferentially spaced about the coupling member  60  will equal the number of rails used for the stent-graft  10 . For example, if the stent-graft  10  includes five rails  50 , then each longitudinally spaced coupling member  60  could include at least five openings  62 .  
         [0058]     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  FIG. 5 , each coupling member  60  is formed of a single layer  64  of material secured to the outer surface of the graft portion  100  by ultrasonic welding, adhesive bonding, thermal fusing or other known manners. In this embodiment, the rails  50  extend between the inner surface  63  of each coupling member  60  at a respective opening  62  and the outer surface  104  of the graft portion  100 .  
         [0059]     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.  
         [0060]     In any of the above embodiments relating to  FIGS. 1-8 , the coupling members  60  are secured to the graft portion  100  and the stent portion  20  while receiving the rails  50  so that the coupling members  60  can move along and relative to the rails  50 . The coupling members  60  can be secured to the support elements  22  by welding or other known conventional securing techniques. In an alternative embodiment, the coupling members  60  can extend through slots in the support elements  22  or they can be adhesively secured in recesses formed on the inner surfaces of the support elements  22 .  
         [0061]     In the alternative embodiment illustrated in  FIGS. 9-11 , the coupling members  60  can be positioned along the length of the stent-graft  10  and oriented so that their openings  62  are circumferentially offset from the openings  62  of longitudinally adjacent coupling member(s)  66 ,  68 . As shown in  FIG. 9 , coupling member  66  can have openings  62  that are positioned within the openings in circumferentially spaced support members  30  so that a respective rail  50  passes through the opening  62  in the coupling member  60  at point A that is between the longitudinal peaks  34 ,  35  of the support members  30 . The coupling member  60  then passes under the circumferentially adjacent rail(s)  50  that extends through the immediately, circumferentially adjacent support member(s)  30  (See  FIG. 9 ). The openings  62  of the immediately, longitudinally adjacent coupling member  68  are circumferentially offset from those of coupling member  66  so that the rail  50  passes through the openings  62  of the adjacent coupling member  68  at point B. As a result, immediately, longitudinally adjacent coupling members  60  ( 66 ,  68 ) slidably receive circumferentially spaced rails  50  at offset points. This can increase the stability of the stent-graft  10  without reducing its ability to conform to the shape of the vessel in which it is deployed.  
         [0062]     In an alternative embodiment, shown in  FIGS. 10 and 11 , the longitudinally spaced coupling members  60  receive the rails  50  outside the support members  30  at point B. In this embodiment, the openings  62  of longitudinally adjacent coupling members  60  are circumferentially and longitudinally aligned.  
         [0063]     In the embodiments illustrated in  FIGS. 12-15 , the rails  50  could extend through cauterized openings in the graft portion  100  in place of using the coupling members  60 . Hence, in these alternative embodiments, immediately, circumferentially adjacent rails  50  could be extended through cauterized openings  80  in the graft portion  100  at longitudinally and/or circumferentially offset points (A, B) as shown in  FIGS. 9 and 12 . Alternatively, the adjacent rails  50  could be extended through cauterized openings  80  the graft portion  100  at circumferentially and/or longitudinally aligned locations B, as shown in  FIG. 14 . In any of the above-discussed embodiments, the graft portion  100  will move with support elements  22  as the support elements  22  move along the rails  50 .  
         [0064]     In the embodiment illustrated in  FIGS. 16 and 17 , the rails  50  pass through circumferentially extending retainer coupling members  200 , hereinafter referred to as “loops 200”. Unlike coupling members  60  shown in  FIG. 9 , the loops  200  have interior regions  202  that pass through openings  195  in the graft portion  100  and extend along an inner surface of the graft portion  100 . The openings  195  can be welded, cauterized or otherwise closed about the loops  200  using other known techniques. In an embodiment, the loops  200  can be formed of yam that is stronger than the graft portion  100 . In an embodiment, the loops  200  are formed of a PET,  80  denier loop yam. The loops  200  can also be formed of any of the materials discussed above with respect to the graft portion  100 . The loops  200  can also be formed of a solid polymer fiber, braid, film, or the like. It is also possible to bond or otherwise secure the loops  200  to the graft portion  100 .  
         [0065]     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.  
         [0066]     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.  
         [0067]     The support elements  22  comprise the diamond shaped support members  30  shown in  FIGS. 9 and 17 . However, as with the above-discussed embodiments, other known shapes may also be used. Similar to the embodiments illustrated in  FIGS. 9-15 , the support elements  22  shown in  FIG. 17  include apertures  39  and are free of a connection to the loops  200 . The support elements  22  (FIG.  17 ) are moveable along the rails  50  in a direction that is substantially parallel to the length of the graft portion  100  as discussed above.  
         [0068]     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  FIG. 17 , the arches  210  of the loops  200  can act as a stop for the longitudinal movement of the support element  22 . Therefore, the total distance that the support elements  22  move along the rails  50  can be controlled and limited by the spacing between the loops  200  along the length of the graft portion  100 . In one embodiment, each loop  200  can be spaced from adjacent loops  200  along the length of the graft portion  100  by the same distance as the coupling members  60  so that the support elements  22  can move a distance that permits the stent-graft  10  to conform to the shape of the vessel in which the stent-graft  10  is deployed. The spacing between adjacent loops  200  (and  60 ) can be less than the distance that each support element  22  extends in a direction parallel to the length of the stent-graft  10 .  
         [0069]     Unlike the other embodiments (for example the embodiment illustrated in  FIG. 1 ), each support elements  22  illustrated in  FIG. 17  is free of a connection to a longitudinally adjacent support element  22  by a bridging element. As a result, the support elements  22 , illustrated in  FIG. 17 , can move independently relative to each other along the length of the graft portion  100 . Also, like the embodiments discussed above, the rails  50  can include a single, continuous member with multiple turns ( FIG. 17 ), a plurality of separate members with at least one turn that are circumferentially spaced from adjacent members around the graft portion  100 , or separate, individual members that are free of turns and that are free of a direct, secured attachment to an adjacent rail  50 . As used herein, the term “rail” includes each of these arrangements.  
         [0070]     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 .  
         [0071]     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.  
         [0072]     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.  
         [0073]     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.  
         [0074]     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.