Abstract:
The present invention embodies an endovascular graft having an attachment frame connection mechanism that allows placement of the main body component in vasculature in combination with limb components. Various limb component-to-main body component attachment mechanisms are provided which ensure a reliable bond while facilitating a smaller delivery profile.

Description:
This application is a divisional of U.S. application Ser. No. 10/090,472, filed Mar. 4, 2002, which is a continuation-in-part of U.S. application Ser. No. 09/562,595, filed May 1, 2000. This application claims the benefit of U.S. Provisional Application Ser. No. 60/360,323, filed Feb. 26, 2002, entitled Endovascular Grafting Device, which contents are incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to methods for delivering and deploying an endovascular graft within the vasculature of a patient and more specifically to a modular grafting system used to treat vasculature. 
     It is well established that various fluid conducting body or corporeal lumens, such as veins and arteries, may deteriorate or suffer trauma so that repair is necessary. For example, various types of aneurysms or other deteriorative diseases may affect the ability of the lumen to conduct fluids and, in turn, may be life threatening. In some cases, the damage to the lumen is repairable only with the use of prosthesis such as an artificial vessel or graft. 
     For repair of vital lumens such as the aorta, surgical repair is significantly life threatening or subject to significant morbidity. Surgical techniques known in the art involve major surgery in which a graft resembling the natural vessel is spliced into the diseased or obstructed section of the natural vessel. Known procedures include surgically removing the damaged or diseased portion of the vessel and inserting an artificial or donor graft portion inserted and stitched to the ends of the vessel which were created by the removal of the diseased portion. More recently, devices have been developed for treating diseased vasculature through intraluminal repair. Rather than removing the diseased portion of the vasculature, the art has taught bypassing the diseased portion with a prosthesis and implanting the prosthesis within the vasculature. An intra arterial prosthesis of this type has two components: a flexible conduit, the graft, and the expandable framework, the stent (or stents). Such a prosthesis is called an endovascular graft. 
     It has been found that many abdominal aortic aneurysms extend to the aortic bifurcation. Accordingly, a majority of cases of endovascular aneurysm repair employ a graft having a bifurcated shape with a trunk portion and two limbs, each limb extending into separate branches of vasculature. Currently available bifurcated endovascular grafts fall into two categories. One category of grafts are those in which a preformed graft is inserted whole into the arterial system and manipulated into position about the area to be treated. This is a unibody graft. The other category of endovascular grafts are those in which a graft is assembled in-situ from two or more endovascular graft components. This latter endovascular graft is referred to as a modular endovascular graft. Because a modular endovascular graft facilitates greater versatility of matching the individual components to the dimensions of the patient&#39;s anatomy, the art has taught the use of modular endovascular grafts in order to minimize difficulties encountered with insertion of the devices into vasculature and sizing to the patient&#39;s vasculature. 
     Although the use of modular endovascular grafts minimize some of the difficulties, there are still drawbacks associated with the current methods. Drawbacks with current methods can be categorized in three ways; drawbacks associated with delivery and deployment of the individual endovascular graft components, drawbacks associated with the main body portion, and drawbacks associated with securing the limb portions to the main body portion. 
     The drawbacks of current methods of joining the limb components of a modular endovascular graft to the main graft component include disruption of the junction over time and leakage at the connection site of the components. The junctions conventionally used in the art may depend upon friction between the overlapping components to hold them in place relative to each other. In other cases, the overlapping portion of one component may be adapted to form a frustoconical shape compatible with the overlapping portion of the other component. This serves to enhance the frictional connection between the components and provides a degree of mechanical joining. However, certain of these junctions relies primarily upon radial pressure of a stent to accomplish the joint-seal between the components and may be disrupted by the high shear forces generated by the blood flow and shrinkage of the aneurysm sac during the natural healing process. Once the junction between modular components of an endovascular graft has been disrupted, blood may flow into the aneurysm sac, a condition known as “endoleak” that can cause repressurization of the aneurysm that leads to death or severe injury to the patient. 
     Furthermore, even if the junction between the components is not disrupted, leakage may still occur. The limb components used in friction-fit designs often are composed of a stent-like exoskeleton over a layer of graft material. This means that the seal is between the graft material of the limb support portion of the main body component and the stent structure of the limb component. Since the stent is not a closed structure, it is still possible for blood to leak between the limb component and the main body component. 
     With regard to the method of joining the limb components of a modular endovascular graft to the main body component, there therefore exists a need for structure and a method that provides a leak-proof seal that will not be disrupted by blood flow or physiologic remodeling over time. 
     The devices and methods of the present invention address these and other needs. 
     SUMMARY OF THE INVENTION 
     Briefly and in general terms, the present invention embodies an endovascular graft composed of individual components delivered individually and assembled in-vivo and methods for delivering, deploying and assembling the same. 
     Throughout this specification, the term “proximal” shall mean “nearest to the heart”, and the term “distal” shall mean “furthest from the heart.” Additionally, the term “ipsi-lateral” shall mean the side for example of the limb of a bifurcated graft which is deployed using the same path through the vasculature that was used to deploy the main body component, and the term “contra-lateral” shall mean the side for example of the limb of a bifurcated graft which is deployed using a second path through the vasculature which is catheterized after the main body component has been deployed. Furthermore, the term “inferior” shall mean “nearest to the technician”, and the term “superior” shall mean “farthest from the technician.” 
     In one aspect, the invention is directed toward limb components and methods of attaching them to the main body component of an endovascular graft that provide a leak-resistant seal between the graft material of the components that will not be disrupted by blood flow or physiologic remodeling over time. Two primary concepts are contemplated; attachment via hooks or barbs that penetrate the graft material components and mechanical attachment that does not require penetration of the graft material of the components. 
     In a preferred embodiment of the invention, the limb component is attached to the limb portion of the main body component by a frame or self-expanding stent at the proximal or superior end of the limb component that is either inside the limb component or external the limb component with graft material folded over it. The limb can be manufactured with the hooks already through its graft. When the proximal end of the limb component is inserted and deployed within the distal end of the limb support portion of the main body component, radially extending components in the form, for example, of hooks or barbs incorporated within the self-expanding stent penetrate the graft material of the limb support portion of the main body component to form a graft-to-graft bond. 
     Trauma and wear on the graft material may be reduced in several ways. The limb component can have pre-fabricated holes cut in the graft that allow the hooks and barbs to pass through, thereby reducing trauma and wear to the limb component graft. 
     The bond between the limb component and limb support portion of the main body component can be strengthened in several ways. Tufting or the placement of fuzzy yarn on the outside of the limb component graft and inside the limb support portion of the main body component promotes blood clotting which forms a better seal. Additionally, the stent hooks and barbs can be angled caudally (toward the feet) such that the blood flow causes better penetration of the graft material and resistance to axial displacement of the components. 
     In an alternate embodiment of the invention, the limb component is attached to the limb support portion of the main body component by a mechanical joint formed between the distal end of the limb support portion and the proximal end of the limb component that utilizes the natural blood flow in the vessel to strengthen the bond. The distal end of the limb support portion of the main body component has an inner cuff, inward taper, or inner flap that is designed to receive the limb component when it is deployed. Conversely, the limb component proximal end has a stent with outward protrusions, outward taper, or outer flap that engages the inner side of the limb support portion distal end when it is deployed. The axial pressure of the natural blood flow inside the vessel helps to maintain the joint between the components. Additionally, the distal end of the limb support portion of the main body component may contain a tapered inner sleeve that facilitates funneling blood flow into the attached limb component. 
     In another alternate embodiment, the limb component is attached to the limb support portion of the main body component by a radially adjustable structure or a “lasso” that tightens around the limb component as it is deployed within the limb support portion. The “lasso” consists of a thread connected to two slip-knots; one located at the distal end of the limb support portion of the main body component and the other located proximal of the first. When the proximal end of the limb component is deployed within the limb support portion of the main body component, the radial expansion of the self-expanding frame or stent at the proximal end of the limb component causes the most proximal slip-knot on the limb support portion to expand, which, in turn, tightens the slip-knot at the distal end of the limb support portion around the limb component. 
     Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view, depicting a limb component and attachment stents of the present invention with the graft material partially removed to show the internal stent; 
         FIG. 2  is a partial perspective view of an alternate embodiment of the limb component depicted in  FIG. 1  with pre-fabricated holes for the limb attachment stent in the graft material; 
         FIG. 3  is a side elevation, partial cross-sectional view of a main body component already implanted at the treatment site with the limb support portions floating freely and the limb component depicted in  FIG. 1  inserted in a compressed state inside one of the limb support portions; 
         FIG. 4  is a side elevation, partial cross-sectional view of a main body component already implanted at the treatment site with the limb support portions floating freely and the limb component depicted in  FIG. 1  deployed inside one of the limb support portions; 
         FIG. 5  is a partial perspective view of an alternate embodiment of the limb component depicted in  FIG. 1  with the proximal end of the graft material folded over the external limb attachment stent and attached to the limb component; 
         FIG. 6  is a partial perspective view depicting a traditional embodiment of the main body and limb components with fuzzy yarns attached to the internal limb attachment stent of the limb support portion and the external limb attachment stent of the limb component, the graft material partially removed to show the tufting of the limb support portion internal stent; 
         FIG. 7  is a partial perspective view of an alternate embodiment of the main body and limb components of the present invention with the main body component limb support portion having a tapered inner layer and internal sealing material and the limb component having an internal support stent and external sealing material, the graft material and sealing material partially removed to show the limb support portion internal taper and limb component internal stent; 
         FIG. 8  is a view of the main body component limb support portion depicted in  FIG. 7  from the distal end; 
         FIG. 9  is a view of the limb component depicted in  FIG. 7  from the proximal end; 
         FIG. 10A  is a side elevation, partial cross-sectional view of a main body component depicted in  FIG. 7  already implanted at the treatment site with the limb support portions floating freely and the limb component depicted in  FIG. 7  inserted in a compressed state inside one of the limb support portions; 
         FIG. 10B  is a side elevation, partial cross-sectional view a main body component depicted in  FIG. 7  already implanted at the treatment site with the limb support portions floating freely and the limb component depicted in  FIG. 7  deployed inside one of the limb support portions; 
         FIG. 11A  is a partial perspective view of an alternate embodiment of the main body and limb components of the present invention where the limb support portion of the main body component has a “lasso” attached to the distal end and the limb component has an internal support stent; 
         FIG. 11B  is a partial perspective view depicting the joint formed when the limb component shown in  FIG. 11A  is deployed within the limb support portion of the main body component shown in  FIG. 11A ; 
         FIG. 12A  is a partial perspective view of an alternate embodiment of the main body and limb components of the present invention where the limb support portion of the main body component has a tapered portion and a “bell-bottom” distal portion with support stents and the limb component has an internal support stent; 
         FIG. 12B  is a partial perspective view depicting the joint formed when the limb component shown in  FIG. 12A  is deployed within the limb support portion of the main body component shown in  FIG. 12A ; 
         FIG. 13  is a schematic view of an alternate stent design of the present invention in which separate proximal and distal cell portions are connected by cell connectors between the wishbone areas of the struts of the proximal and distal cell portions; 
         FIG. 14A  is a partial perspective view depicting the proximal end of a limb component of the present invention with an external proximal stent utilizing the alternate stent design shown in  FIG. 13  and held in a compressed state by a sheath that is shown as transparent; 
         FIG. 14B  is a partial perspective view depicting the proximal end of a limb component of the present invention with an internal proximal stent utilizing the alternate stent design shown in  FIG. 13  with the proximal cell portions extending beyond the proximal end of the limb component and held in a compressed state by a sheath that is shown as transparent; 
         FIG. 14C  is a partial perspective view depicting the “umbrella” or grappling pattern produced when the sheath in  FIG. 14B  is retracted distally to expose the upper cell portions of the stent; 
         FIG. 15  is a schematic partial cross-sectional view of the upper cell portions of the stent utilizing the alternate stent design shown in  FIG. 13  which is partially deployed and indicating pertinent dimensions; 
         FIG. 16A  is a partial perspective view depicting the proximal end of a limb component of the present invention where the graft material is folded over itself to provide additional support for the area where there is the largest separation between stent struts and the graft material is partially removed to show the internal stent; 
         FIG. 16B  is a cross-sectional view along line  16 B- 16 B of  FIG. 16A ; 
         FIG. 17A  is a partial perspective view depicting the proximal end of a limb component of the present invention with a graft material patch attached over an unattached external stent and the graft material patch partially removed to show the stent; 
         FIG. 17B  is a cross-sectional view along line  17 B- 17 B of  FIG. 17A ; 
         FIG. 18A  is a partial perspective view depicting the proximal end of a limb component of the present invention where the graft material is folded over an unattached external stent and the graft material is partially removed to show the stent; 
         FIG. 18B  is a cross-sectional view along line  18 B- 18 B of  FIG. 18A ; 
         FIG. 19A  is a partial perspective view depicting the proximal end of a limb component of the present invention where a graft belt is attached over an external stent; 
         FIG. 19B  is a cross-sectional view along line  19 B- 19 B of  FIG. 19A ; 
         FIG. 19C  is a view of the limb component depicted in  FIG. 19A  from the proximal end; 
         FIG. 20A  is a partial perspective view depicting the proximal end of a limb component of the present invention where two graft belts are attached over an external stent having attachment hooks or barbs; 
         FIG. 20B  is a cross-sectional view along line  20 B- 20 B of  FIG. 20A ; 
         FIG. 20C  is a view of the limb component depicted in  FIG. 20A  from the proximal end; 
         FIG. 21A  is a partial perspective view depicting the proximal end of a limb component of the present invention where the graft material is folded over the connector eyelets of an external stent; and 
         FIG. 21B  is a cross-sectional view along line  21 B- 21 B of  FIG. 21A ; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to an endovascular graft which is assembled in-vivo from components, and methods for attaching and securing the individual components. 
       FIG. 1  shows a limb component  80  that is one aspect of the present invention. The limb component has a proximal end  81  with a proximal stent  84 , a distal end  82  with a distal stent  85 , and graft material  83 . The proximal stent  84  is located internal to the graft material and is self-expanding with a series of caudal hooks or barbs  86  which puncture the graft material of the main body limb portion  33  when the stent  84  is deployed. The proximal stent  84  is designed to be attached to a limb support portion  33 ,  34  of the main body component  30  of a bifurcated endovascular graft (see  FIGS. 3 and 4 ). The distal stent  85  is also self-expanding and is designed to be attached to the vessel wall to anchor the distal end  82  of the limb component  80 . Although shown external to the graft material with a series of caudal hooks or barbs  86 , the distal stent  85  can be located internal to the graft material and may be of any type known within the art. Note that the hooks or barbs  86  at the proximal end  81  are angled in the distal direction, which is the direction of blood flow in the vessel. This angling helps to ensure better attachment of the limb component  80  to the main body component  30 . The barbs on the distal end  82  of the limb point opposite to the blood flow. When the limb component  80  is compressed for delivery, the hooks or barbs  86  of the stents  84 ,  85  are also at least partially compressed. 
       FIG. 2  depicts an alternate embodiment of the limb component  80  shown in  FIG. 1 . The limb component  180  has relief holes  87  that are spaced around the circumference of the proximal end  81  of the graft material  183  to correspond to the hooks or barbs  86 . The proximal stent  84  is attached to the graft material  183  using sutures  88  such that the hooks or barbs  86  protrude through the holes  87  when the limb component  180  is compressed for delivery, thereby preventing the compressed hook or barb  86  from tearing the graft material  183 . It is contemplated that relief holes  87  may also be utilized for an internal stent  85  near the distal end  82  of the limb component  180  or whenever is desired to prevent tearing of the graft material by a compressed stent having hooks or barbs. 
     In a preferred embodiment, the limb component  180  proximal stent  84  is cut from a Nitinol tube using a laser beam and has five hooks  86  equally spaced around its circumference at 72 degrees apart. The stent  84  is heat-set for its final expanded diameter using a process known in the art, with the hooks  86  set at an approximately 45 degree angle using a inner mandrel and outer cylindrical tube, the stent  84  “electro polished”, and the hooks  86  sharpened. The stent  84  is sutured inside the limb components  180  graft material  183  which has five holes  87  equally-spaced around its circumference. The holes  87 , pre-punctured using a hot pin to melt the graft material  183 , or ultrasonically punched, allow the five stent hooks  86  to protrude through the graft material  183  when the limb component  80  is compressed for delivery. When the limb component  80  is deployed within the limb support portion  33 ,  34  of a main body component  30 , the stent  84  will expand, thereby causing the hooks  86  to penetrate the graft material of the main body component  30 , forming a seal and anchoring the limb component  80  within the main body component  30 . A balloon can also be used to set the hooks. A “tug” in the distal direction can also set the hooks. 
     Referring to  FIGS. 3 and 4 , the method for joining the limb component  80  to the main body component  30  is shown. With the main body component  30  already implanted within the patient&#39;s vasculature  160 , the limb component  80  is inserted in its compressed state within one of the limb support portions  34  of the main body component  30 . The hooks or barbs  86  penetrate the limb graft before it is compressed. Once the limb component  80  is positioned properly, it is deployed. When the proximal end  81  of the limb component  80  is deployed, the radial force of the proximal stent  84  causes the hooks or barbs  86  to penetrate the graft material of the main body component  30  limb support portion  34 , thereby locking the two components together and forming a seal between two layers of graft material. This graft-to-graft seal resists blood leakage better than the traditional stent-to-graft seal. The direction of blood flow (shown by arrow in  FIG. 4 ) strengthens the seal by forcing the limb component  80  in the distal direction, thereby imbedding the hooks or barbs  86  in the graft material. 
     Furthermore, there is no pre-determined attachment point within the limb support portion  34  of the main body component  30 . Therefore, the technician can position the proximal end  81  of the limb component  80  anywhere within the limb support portion  34 , thereby allowing him to adjust the length of the limb component  80  between the main body component  30  limb support portion  34  distal end and the limb component  80  distal end  82  attachment point within the iliac “landing zone.” 
     Moreover, several limbs  80  can be “chained” together, allowing the technician to customize the length of the limb section to the vasculature of individual patients or to correct for misjudgment of the length between the main body component  30  and the iliac “landing zone.” It is contemplated that the graft material of the main body component  30  and limb component  80  can be polyethylene terephthalate (e.g. Dacron®) or PTFE (e.g. Teflon®) or any other similar material known in the art. It is further contemplated that the limb component  80  stent  84 ,  85  material can be Nitinol, Elgiloy, stainless steel, or any similar material known in the art that is either self-expanding or balloon expandable. 
       FIG. 5  depicts another alternate embodiment of the limb component  80  shown in  FIG. 1 . The limb component  380  has an external proximal stent  184  with hooks or barbs  86 . The proximal stent  184  is covered by the limb component  380  graft material  83  which is folded over from a point proximal the stent  184  and attached to itself at a point distal the stent  184 , thereby forming an inner graft portion  90  and outer graft portion  91  at the proximal end  81  of the limb component  380 . Hooks or barbs  86  on the proximal stent  184  protrude through the outer graft portion  91 . When the limb component  380  is deployed, the hooks or barbs  86  penetrate the graft material of the main body component  30  limb support portion  33 ,  34 , thereby forming a mechanical interconnection between them. Although the mechanical interconnection is between the hook or barbs  86  of the limb component  380  and graft material of the limb support portion  33 ,  34 , the graft-to-graft contact between the outer graft portion  91  of the limb component  380  and the graft material of the limb support portion  33 ,  34  provides a better seal against blood leakage between the components than proximal stent  184 -to-graft contact would. 
     It is contemplated that tufting  92  can also be used where the seal between the limb component and main body component is achieved by traditional methods. For example,  FIG. 6  depicts a limb component  580  with an external proximal stent  184  that is to be deployed within the limb support portion  134  of a main body component  130  with an internal distal stent  52 . The seal is formed by the main body component  130  internal distal stent  52  that resists the expansion of the limb component  580  external proximal stent  184 . Tufting  92  on the outside of the limb component  580  graft material  83  protrude through the external proximal stent  184 . Likewise, tufting  92  on the inside of the limb support portion  134  graft material protrude through the internal distal stent  52 . The tufting  92  will fill spaces between the stents  52 ,  184  and graft material as well as spaces between the two stents  52 ,  184 , thereby promoting blood clotting, improving the seals, and reducing blood leakage. The location of the stents  52 ,  184  in  FIG. 6  is intended for demonstration purposes only as it is contemplated that tufting  92  may be used to improve the seal anytime stents are used. 
     Alternately, the components may be attached without hooks or barbs which can lead to deterioration or tearing of the graft material.  FIGS. 7-9  depict one such method. The main body component  330  is defined by a limb support portion  334  that has a tapered inner graft layer  66  and an outer graft layer  67 . The outer graft layer  67 , which parallels the profile of the main body component  330 , is further defined by a sealing material  68  around the inner circumference. The sealing material  68 , which may be formed of graft material or plastic, forms a pattern such as a saw-tooth pattern. The tapered inner graft layer  66  is attached to the inner circumference of the outer graft layer  67  proximal the sealing material  68 , thereby creating a funnel for blood flow into the attached limb component  680 . The limb component  680  has a self-expanding internal stent  84  at its proximal end  81 . The limb component  680  is further defined by a sealing material  93  that is secured external the graft material  83 . The sealing material  93  is similar to that on the limb support portion  334 , but with an inverse pattern. 
       FIGS. 10A and 10B  depict the joint formed between the main body component  330  and limb component  680  using this method. The main body component  330  is deployed first in the patient&#39;s vasculature. The flow of blood (indicated by the arrow) helps to keep the tapered inner layer  66  of the limb support portion  334  open. The limb component  680  is inserted and partially deployed within the outer graft layer  67  of the limb support portion  334  such that the inner layer  66  of the limb support portion  334  is inside the limb component  680 , but the sealing material  93  of the limb component  680  does not engage the sealing material  68  of the limb support portion  334 . The partially-deployed limb component  680  is moved distally such that the edges of its sealing material  93  pattern are slightly distal the corresponding edges of the limb support portion  334  sealing material  68  pattern and the limb component  680  is then fully deployed. The flow of blood (shown by the arrow) forces the inner layer  66  of the limb support portion  334  to expand and thereby causes the limb component  680  to advance distally. The radial expansion of the limb component  680  proximal stent  84  causes the limb component  680  sealing material  93  to engage the limb support portion  334  sealing material  68 , thereby preventing further distal migration of the limb component  680 . The resulting mechanical joint between the limb component  680  and limb support portion  334  sealing materials  93 ,  68  provides better resistance to distal migration of the limb component  680  than traditional methods, such as a frictional joint, without deterioration or tearing of the graft material  83 . It is contemplated that this method may be used to join any two components where the first-deployed component has a tapered inner graft layer and an outer graft layer with sealing material on its inner surface and the second component, with an internal self-expanding stent and sealing material external the graft material, is deployed within the first component such that the first component tapered inner layer is inside the second component. 
     An alternative method of attaching components without hooks or barbs is depicted in  FIGS. 11A and 11B . The main body component  430  is defined by a limb support portion  434  which has a “lasso”. The “lasso” has a proximal loop  75 , a distal loop  76 , and a transition portion  77 . The “lasso” may be formed by two slipknots attached or laced through the graft material and connected by a thread or a single thread that is laced through the graft material and attached at both ends such that the loops cannot move along the axis of the graft. The “lasso” is further defined by a length (indicated as L 1  In  FIG. 11A ). Wire, suture material, ribbon, rope, or string may be used instead of thread. The limb component  80  is defined by a self-expanding internal stent  183  at the proximal end  81 . The proximal stent  183  is further defined by a proximal end  94 , a distal end  95 , and an axial length (indicated as L 2  in  FIG. 11A ). The total length of the material used to create the two “lasso” loops minus the transition length is less than twice the circumference of the expanded limb component  80  such that expanding one of the loops causes the other loop to constrict to a diameter less than that of the limb component  80 . However, the total length of the material used to create the two “lasso” loops and transition portion must be sufficient to preclude the expansion of one loop from causing the other loop to constrict so much that it occludes the limb component  80 . Furthermore, the length of the “lasso” is less than the axial length of the limb component  80  proximal stent  183  (L 1 &lt;L 2 ) such that the limb component  80  may be positioned and the “lasso” proximal loop  75  expanded by the deployed stent  183  proximal end  94  while the “lasso” distal loop  76  constricts around the stent  183  distal end  95 . 
       FIG. 11B  depicts the joint formed between the main body component  430  and limb component  80  using this method. The main body component  430  is deployed first. The limb component  80  is delivered in a compressed state and positioned such that the limb support portion  434  proximal loop  75  is directly above the proximal end  94  of the limb component proximal stent  183  and the limb support portion distal loop  76  is directly above the distal end  95  of the limb component proximal stent. When the limb component  80  proximal stent  183  is deployed, the radial force of the proximal end  94  causes the limb support portion  434  proximal loop  75  to expand, thereby causing the limb support portion  434  distal loop  76  to contract around the distal end  95  of the stent  183 . The resulting joint between the components is both mechanical, between the radial force of the distal end  95  of the stent  183  and the constricted distal loop  76 , and frictional, between the limb component  80  and limb support component  434  graft materials. Such a joint provides better resistance to distal migration of the limb component  80  than traditional methods, such as an entirely frictional joint, without deterioration or tearing of the graft material. It is contemplated that this method may be used to join any two components where the first-deployed component has a “lasso” mechanism at the distal end and the second component, with a proximal support stent, is deployed within the first component such that the proximal end of the “lasso” is expanded by the stent while the distal end of the “lasso” constricts around the stent. Also, the entire stent could be placed above the distal loop. Although  FIGS. 11A and 11B  depict an internal limb component proximal stent  183 , it is contemplated that the stent may be located external the limb component graft material. 
     Another alternative method of attaching components without hooks or barbs is depicted in  FIGS. 12A and 12B . The main body component  530  is defined by a limb support portion  534  that has a tapered middle portion  78  and a “bell-bottom” distal portion  70 . The limb support portion  534  is further defined by an external support stent  152  located proximal the tapered portion  78  and an external “bell-bottom” stent  171 . The limb component  80  is defined by a self-expanding internal stent  183  at its proximal end  81 . 
     In a preferred embodiment, the contra-lateral limb support portion  534  has a tapered middle portion  78  and “bell-bottom” distal portion  70 . The contra-lateral limb support portion  534  external stent  152  has an axial length of 1 centimeter and the “bell-bottom” portion  70  has an axial length of 2 centimeters with a 0.75 centimeter “bell-bottom” stent  171  at the distal end. Furthermore, the ipsi-lateral limb support portion  533  has an external stent (not shown) with an axial length of 1 to 2 centimeters just proximal a tapered distal end (not shown). Moreover, the contra-lateral limb support portion  534  is at least 1.5 centimeters longer than the ipsi-lateral limb support portion  533 , thereby allowing packing of the main body component  530  without any stents occupying the same axial space. The limb component  80  internal proximal stent  183  has an axial length of 1 to 2 cm. All stents are made of Nitinol. 
       FIG. 12B  depicts the joint formed between the main body component  530  and limb component  80  using this method. The main body component  530  is deployed first. The flow of blood (indicated by the arrow) and the limb support portion  534  stents  152 ,  171  keep a passageway open through which the limb component  80  is inserted. The limb component  80  is delivered in a compressed state and inserted into the limb support portion  534  such that the distal end of the limb component  80  proximal stent  183  is proximal to the limb support portion  534  tapered middle portion  78 . When the limb component  80  is deployed, the radial force of the proximal stent  183  forces the limb component  80  graft material  83  against the limb support portion  534  graft material and the tapered portion  78  prevents distal migration of the limb component  80 . The resulting joint between the components is both mechanical, between the expanded stent  183  and tapered portion  78 , and frictional, between the limb component  80  and limb support component  534  graft materials. Such a joint provides better resistance to distal migration of the limb component  80  than traditional methods, such as an entirely frictional joint, without deterioration or tearing of the graft material. It is contemplated that this method may be used to join any two components where the first-deployed component has a tapered middle portion and “bell-bottom” distal end and the second component, with a proximal support stent, is deployed within the first component such that the distal end of the stent is proximal to the tapered portion. Although  FIGS. 12A and 12B  depict external limb support portion stents  152 ,  171  and an internal limb component proximal stent  183 , it is contemplated that the stents may be located either internal or external the graft material. 
     An alternative method, known within the art, of attaching components without hooks or barbs is engaging a stent attached external the proximal end of the limb component with a main body component limb support portion having an internal cuff or loops sewn inside the graft material near the distal end. Utilizing the stent shown in  FIG. 13  facilitates easier mating of the limb component and limb support portion of the main body component. The stent  284  is defined by cells with separate proximal  103  and distal  104  portions having cell connectors  159  between some of the proximal wishbone areas  58  of the cells. The cell connectors are longer than the compressed length of the proximal cell portions. Therefore, it is possible to partially deploy the proximal portions of the cell while maintaining control of the distal portion of the cell and cell connectors, a process which produces an “umbrella” effect. 
     The stent may be located external the limb component graft material  83 , as shown in  FIG. 14A , or the distal cell portions  104  may be located internal the graft material with the proximal cell portions  103  located beyond the proximal end  81  of the limb, as shown in  FIG. 14B . When the proximal cell portion of the stent is uncovered but the distal cell portion of the stent is still covered, as shown in  FIG. 14C , the proximal cell portion starts to deploy. Since the distal end of the cell connectors  159  are still covered by the catheter jacket  251  and restrain the proximal wishbone area  58  of the proximal cell portions, the deployment is only partial and an “umbrella” or grappling hook shape results. By maneuvering the catheter inner member  216 , the distal wishbone area  105  of the partially deployed proximal cell portion  103  may be mated with a cuff or other attachment mechanism (not shown) of a limb support portion of the main body component. Once proper engagement of the limb component and limb support portion is verified, either visually seeing the limb support component move or feeling a tug once the distal wishbone area  105  engages the attachment mechanism, the catheter jacket  251  is retracted distally to fully deploy the proximal  103  and distal  104  cells portions of the stent. 
     It is contemplated that the “umbrella” stent  284  may be permanently attached to a catheter and utilized as a snare to retrieve clots or pieces of medical devices such as coils, catheter tips, or guidewires. It is also contemplated that an umbrella stent  284  having sharpened distal wishbone areas  105  may be utilized to anchor a graft to the walls of a vessel. 
     The minimum length of the proximal cell portions (indicated as L in  FIG. 15 ) is a function of the catheter inner member  216  outer diameter (indicated as COD in  FIG. 15 ), the limb support portion  34  or lumen  160  inner diameter (indicated as LID in  FIG. 15 ), and angle at which the cell portions expand (indicated as φ in  FIG. 15 ). The relationship is shown by the formula:
 
Δ D=LID−COD  
 
 L =(Δ D/ 2)/SIN φ)
 
     In order to provide the grappling effect in both axis, at least 3 cell connectors are provided. Although the figures show 3 cells between cell connectors, it is contemplated that there may be any number of cells between cell connectors. It is further contemplated that any cell pattern and size, as well as cells with sharp or smooth lower wishbone portions  105  may be used as long as adequate expansion is achieved and the attachment site is adequate to accommodate the cells. 
     Whether the limb attachment methods of the present invention or methods known within the art are utilized, the manner in which the stents are attached to the graft material may effect the strength or fluid seal of the joint between the limb support portion and limb component. By providing additional graft material in areas where the stent-to-graft attachment is prone to leaks or wear as well as enabling the attached stent to move relative to the graft material may result in a better joint. 
       FIGS. 16A and 16B  show a limb component  780  with a self-expanding internal proximal stent  84  attached to the proximal end  81  of the graft material  83  with sutures  88  at only the most proximal and most distal ends of the stent such that an additional layer of graft material is formed where the stent has its widest opening between struts. This is the area most susceptible to the “parachute” effect caused when blood leaks between the joint formed between a proximal limb stent and main body component limb support portion distal stent, whereby the blood collects in the largest graft-to-graft area in the frame stent openings and fills like a parachute. The additional graft material in this area resists the tendency of blood to collect. The additional area of graft material may be formed by attaching the most proximal or most distal end of the stent to the graft material with sutures and pulling the graft material inside itself to form an overlapping area  100  before attaching the other end of the stent to the graft material, thereby forming a fold of graft material around the circumference of the graft material which traverses the widest area between stent struts. It is contemplated that an additional area of graft material may also be utilized for the main body component limb support portion distal stent or for any type of vessel repair that requires an implant seal. 
     Providing a graft pocket within which a self-expanding external stent without attachment hooks or barbs may move is one way to facilitate a better joint between the limb support portion of the main body component and the limb component. The stent, which is not attached to the graft material, moves proximally or distally within the pocket, thereby facilitating self-alignment after deployment. The ability to self-align provides a more secure joint. It is contemplated that a graft pocket may be used for a main body component limb support portion distal stent, limb component proximal stent, or whenever it is desired to attach a self-expanding stent or frame to a graft type material for human vessel repair. 
     A graft pocket may be formed by attaching additional graft material.  FIGS. 17A and 17B  show a limb component  880  with a self-expanding external proximal stent  184  and an additional graft ring patch  249  attached to the proximal end  81  of the graft material  83 , thereby covering the external stent. The graft ring patch, which is attached by sutures  88  at its proximal and distal extremities, forms a pocket within which the stent may move. It is contemplated that the graft ring patch may be attached with a continuous stitching pattern around the entire circumference of the graft, rivets or other methods known within the art rather than with individual sutures. It is also contemplated that a graft ring patch may be attached to the distal end of the main body component limb support portion. 
     Alternately, a graft pocket may be formed without attaching additional graft material.  FIGS. 18A and 18B  show a pocket formed by pulling the proximal end of the limb component  380  graft material  83  distally over the external self-expanding proximal stent  184  and attaching it to the graft material distal the stent. In a preferred process, the proximal stent is covered by the limb component graft material, thereby forming a pocket between an inner graft portion  90  and outer graft portion  91  at the proximal end  81  of the limb component. Attachment of the graft material distal the enclosed stent may be by sutures  88 , a continuous stitch around the graft, rivets or other methods known within the art. It is also contemplated that the graft fold-over may be used at the distal end of the main body component limb support portion. 
     Instead of providing a graft pocket, additional strips of graft material attached to the external surface of the graft material may be utilized to facilitate stent self-alignment without completely enclosing the stent in graft material. It is contemplated that additional strips of graft material that hold self-expanding stents in place may be utilized whether or not the stent has attachment hooks or barbs. It is also contemplated that additional strips of graft material may be used for a main body component limb support portion distal stent, limb component proximal stent, or whenever it is desired to attach a self-expanding stent or frame to a graft type material for human vessel repair. 
     As shown in  FIGS. 19A ,  19 B and  19 C, a single strip of graft material may be used with a stent having no attachment hooks or barbs. The limb component  980  with a self-expanding external proximal stent  184  is held in place by a strip of graft material  101  that traverses the circumference of the proximal end  81  of the graft material  83 . The strip of graft material  101 , which is attached by sutures  88  such that loops  102  are formed within which the stent struts may move, may be thicker or thinner than the limb component graft material  83 . It is contemplated that the strip of graft material  101  may also be attached by rivets or other methods known within the art. 
     Alternately, two strips of graft material may be used with a stent having attachment hooks or barbs.  FIGS. 20A ,  20 B and  20 C show a limb component  980  with a self-expanding external proximal stent  184  having attachment hooks or barbs  86  and two strips of graft material  101  that traverse the circumference of the proximal end  81  of the graft material  83 . The strips of graft material  101 , which are attached by sutures  88  such that loops  102  are formed within which the stent struts may move, may be thicker or thinner than the limb component graft material  83 . The strips of graft material  101  are attached above and below the attachment hooks or barbs  86 , thereby precluding tangling. 
     Providing additional protection at the areas where stents or other metal contact graft material may decrease wear and increase reliability of endovascular graft components. Sites that are susceptible to wear, and hence would benefit from such protection, include frame attachment sites, areas where hooks or barbs penetrate the graft material, and areas of friction or motion between metal features and graft material. 
     One way to reinforce graft material sites susceptible to wear is to reinforce the graft fabric. A coating, such as a thin coat of a biocompatible elastomer can be screen printed or otherwise applied in a band around the graft. 
     Coating the entire surface of the graft material may be preferred, particularly if ultra thin woven PET graft material is used to reduce implant bulk. As the thickness of the graft material is reduced, the permeability increases. Coating the entire surface of the graft material not only increases reliability of the graft but also reduces permeability without increasing bulk. A polyurethane co-polymer coating may be dip-coated onto the woven PET substrate. When the solvent is removed, a biocompatible, non-thrombogenic surface to contact the arterial blood is left bonded to the PET material. The thickness of the coating may vary from a few to many microns. It is contemplated that multiple dipping and drying steps may be performed to produce a thicker coating to meet permeability requirements. 
     Alternately, the weave pattern of the graft material may be altered in certain regions to provide extra strength where needed. A rip stop type graft material weave is one example of a typical graft reinforcement method. 
     An alternate way to reinforce areas of the graft susceptible to wear is to provide an additional layer of graft material.  FIGS. 21A and 21B  show a limb component  380  with the graft material folded over to provide additional reinforcement for the site where a self-expanding external proximal stent  184  is attached to the graft material  83 . In a process similar to that shown in  FIGS. 18A and 18B , a pocket is formed between an inner graft portion  90  and outer graft portion  91  at the proximal end  81  of the limb component into which the proximal eyelets of the stent are placed. The stent is attached using sutures  88  which are sewn through the eyelets and the double layer of graft material, thereby increasing the durability of the joint. Additionally, a running stitch  65  similar to that defined for connection of the main body attachment stent may provide further reinforcement of the suture joint. It is contemplated that the graft fold-over may be used to attach an internal proximal stent by folding the graft material inside rather than outside the original graft material layer. It is further contemplated that the graft fold-over may be used to attach a stent to the distal end of the main body component limb support portion or whenever a stent is attached with sutures to graft material. 
     Although the various attachment mechanisms are depicted with respect to the contra-lateral limb component, it is to be noted that this is done for demonstration purposes only. It is contemplated that the attachment mechanisms depicted may be applied to attach the ipsi-lateral limb component of a bifurcated endovascular graft as well as to attach any two modular endovascular graft components. It is further contemplated that the various attachment mechanisms depicted herein may be swapped. For example, the attachment mechanism depicted as part of the limb component may be provided as part of the main body component and the attachment mechanism depicted as part of the main body component may be provided as part of the limb component. 
     Thus, it will be apparent from the foregoing that, while particular forms of the invention have been illustrated and described, various modifications can be made without the parting from the spirit and scope of the invention. For example, both the main graft component and the limb components can have various configurations including tubular, flared, bifurcated and trifurcated forms. Accordingly, it is not intended that the invention be limited, except as by the appended claims.