Abstract:
A stent system comprising a stent body. At least one barb extends from the stent body and is configured such that a free end thereof is biased to extend radially outward from the stent body. A retaining mechanism is positioned to engage the at least one barb when the stent body is in a compressed state and retain the at least one barb in a tucked position relative to the stent body.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to endoluminal devices, particularly stents and grafts for placement in an area of a body lumen that has been weakened by damage or disease, such as an aneurysm of the abdominal aorta, and more particularly to devices having characteristics that enhance affixation of the devices to the body lumen. 
         [0002]    Medical devices for placement in a human or other animal body are well known in the art. One class of medical devices comprises endoluminal devices such as stents, stent-grafts, filters, coils, occlusion baskets, valves, and the like. A stent typically is an elongated device used to support an intraluminal wall. In the case of a stenosis, for example, a stent provides an unobstructed conduit through a body lumen in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside and/or outside thereof. A covered stent is commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), a stent-graft, or endograft. 
         [0003]    An endograft may be used, for example, to treat a vascular aneurysm by removing or reducing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, an endograft is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the endograft, typically restrained in a radially compressed configuration by a sheath, crocheted or knit web, catheter or other means, is delivered by an endograft delivery system or “introducer” to the site where it is required. The introducer may enter the vessel or lumen from an access location outside the body, such as purcutaneously through the patient&#39;s skin, or by a “cut down” technique in which the entry vessel or lumen is exposed by minor surgical means. The term “proximal” as used herein refers to portions of the endograft, stent or delivery system relatively closer to the end outside of the body, whereas the term “distal” is used to refer to portions relatively closer to the end inside the body. 
         [0004]    After the introducer is advanced into the body lumen to the endograft deployment location, the introducer is manipulated to cause the endograft to be deployed from its constrained configuration, whereupon the stent is expanded to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion typically is effected by spring elasticity, balloon expansion, and/or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration. 
         [0005]    Among the many applications for endografts is that of deployment in lumen for repair of an aneurysm, such as a thorasic aortic aneurysm (TAA) or an abdominal aortic aneurysm (AAA). An AAA is an area of increased aortic diameter that generally extends from just below the renal arteries to the aortic bifurcation and a TAA most often occurs in the descending thoracic aorta. AAA and TAA generally result from deterioration of the arterial wall, causing a decrease in the structural and elastic properties of the artery. In addition to a loss of elasticity, this deterioration also causes a slow and continuous dilation of the lumen. 
         [0006]    The standard surgical repair of AAA or TAA is an extensive and invasive procedure typically requiring a week long hospital stay and an extended recovery period. To avoid the complications of the surgical procedure, practitioners commonly resort to a minimally invasive procedure using an endoluminal endograft to reinforce the weakened vessel wall, as mentioned above. At the site of the aneurysm, the practitioner deploys the endograft, anchoring it above and below the aneurysm to relatively healthy tissue. The anchored endograft diverts blood flow away from the weakened arterial wall, minimizing the exposure of the aneurysm to high pressure. 
         [0007]    Intraluminal stents for repairing a damaged or diseased artery or to be used in conjunction with a graft for delivery to an area of a body lumen that has been weakened by disease or damaged, such as an aneurysm of the thorasic or abdominal aorta, are well established in the art of medical science. Intraluminal stents having barbs, hooks, or other affixation means to secure the stents to the wall of the lumen in which they are to be deployed are also well known in the art. 
         [0008]    While barbed and the like stents are advantageous in anchoring the device, an improved system for retaining and releasing stent barbs is desired. 
       SUMMARY OF THE INVENTION 
       [0009]    In one aspect, the invention provides a stent system comprising a stent body. At least one barb extends from the stent body and is configured such that a free end thereof is biased to extend radially outward from the stent body. A retaining mechanism is positioned to engage the at least one barb when the stent body is in a compressed state and retain the at least one barb in a tucked position relative to the stent body. 
         [0010]    In another aspect, the invention provides a stent delivery system comprising a stent body. At least one barb extends from stent body and is configured such that a free end thereof is biased to extend radially outward from the stent body. A support is positioned at least partially within the stent body, said support including a retaining mechanism positioned to engage the at least one barb when the stent body is in a compressed state and retain the at least one barb in a tucked position relative to the stent body. 
         [0011]    In another aspect, the invention provides a stent a plurality of struts. A barb extends from at least one of the struts and is configured such that a free end thereof is biased to extend radially outward from the strut. A retaining mechanism is positioned to engage the barb when the stent is in a compressed state and retain the barb in a tucked position relative to the stent, wherein the retaining mechanism comprises a shoulder defined between two portions of at least one strut. 
         [0012]    Other aspects and advantages of the present invention will be apparent from the detailed description of the invention provided hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
           [0014]      FIG. 1  is an isometric view of a bushing retainer mechanism in accordance with a first embodiment of the present invention. 
           [0015]      FIG. 2  is a flat pattern of a stent incorporating the bushing retainer mechanism of  FIG. 1 . 
           [0016]      FIG. 3  is an isometric view of a bushing retainer mechanism that is an alternative embodiment of the present invention. 
           [0017]      FIG. 4  is an isometric view of a bushing retainer mechanism that is another alternative embodiment of the present invention. 
           [0018]      FIG. 5  is a top plan view of a stent delivery system incorporating the bushing retainer mechanism of  FIG. 3 . 
           [0019]      FIG. 6  is an expanded view of one of the bushing retainer mechanisms of  FIG. 5 . 
           [0020]      FIG. 7  is a front plan view of a portion of a stent incorporating an alternative retainer mechanism in accordance with the invention. 
           [0021]      FIG. 8  is a rear plan view of a portion of a stent incorporating an alternative retainer mechanism in accordance with the invention. 
           [0022]      FIG. 9  shows a flat pattern of a portion of the stent of  FIG. 7 . 
           [0023]      FIG. 10  is a cross-sectional view along the line  10 - 10  in  FIG. 9 . 
           [0024]      FIG. 11  is a cross-sectional view along the line  11 - 11  in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
         [0026]    Referring to  FIGS. 1-2 , a retainer mechanism  40  that is a first embodiment of the present invention is illustrated. The retainer mechanism  40  includes a generally cylindrical bushing body  42 . While the bushing body  42  is illustrated as cylindrical, it is not limited to such and may have other configurations. The bushing body  42  includes a through bore  44  configured to receive a delivery catheter or guidewire chassis (not shown) of a stent-graft delivery system. The outer surface of the bushing body  42  includes pairs of radially extending pins  46 . Each pair of pins  46  defines a barb receiving space  48  therebetween. The bushing body  42  and the pins  46  may be manufactured from a hard material, for example, polyimide, PEEK or polyurethane, or a softer material, for example, urethanes or silicone, such that the barbs  14  can be compressed within the receiving space  48  and into the surface of the bushing body  42  for increased stability. 
         [0027]      FIG. 2  illustrates an illustrative stent  10 ′ positioned relative to the retainer mechanism  40 . The bushing body  42  is axially positioned along the delivery system such that the barbs  14  align with and are received in the receiving space  48  between a respective pair of pins  46 . The pins  46  are circumferentially aligned with a respective tuck pad  16  or strut  12  such that the barb  14  received in a receiving space  48  is maintained under the tuck pad  16  or strut  12 . Since a pin  46  is provided on each lateral side of the barb  14 , the pins  46  will maintain the barb  14  in proper lateral alignment even if the barb lateral angle α is not maintained to the highest tolerances. 
         [0028]    The pins  46  have a radial height that is approximately one half of the thickness of the struts  12 . As such, the pins  46  do not interfere with the compression of the stent. If the retaining mechanism is manufactured from a softer materials, the bushing body  42  can compress and relieve some of the added thickness of the tucked barb  14 . 
         [0029]    While the preferred retaining mechanism  40  has the pins  46  in pairs, such is not required and the pins  46  can be grouped individually or in groups of more than two. As illustrated in  FIG. 2 , a retaining mechanism  40 ′ with a single pin  46  is provided adjacent an end of the stent  10 ′ to provide a crown  13  locating feature. Additionally, while the bushing body  42  is illustrated as extending a short axial distance adjacent the barb  14 , the body  42  may have a longer axial length. For example, the bushing body  42  may be sufficiently long to extend under one or both belt axial positions such that the belts can be attached to the retaining member  40 . Other shapes and configurations of the bushing body  42  and the pins  46  are within the scope of the present invention. 
         [0030]    Referring to FIGS.  3  and  5 - 6 , a retaining mechanism  50  that is an alternative embodiment of the present invention will be described. The retaining mechanism  50  is similar to the previous embodiment and includes a bushing body  52  with a through bore  54  configured to receive a guidewire chassis  22  of a delivery system as illustrated in  FIGS. 5 and 6 . While the retaining mechanism  50  may be secured to the guidewire chassis  22 , such is not required and freedom of the retaining mechanism  50  may allow for greater flexibility and alignment. The retaining mechanism  50 ′ illustrated in  FIG. 4  is substantially the same as in the present embodiment but includes a secondary through passage  58 . The secondary through passage  58  facilitates passage of additional delivery system items, for example, such as when the retaining mechanism  50 ′ is used with a distal stent. 
         [0031]    Both of the retaining mechanisms  50 ,  50 ′ include a plurality of helical slots  56  formed about the outer surface of the bushing body  52 . Each slot is configured to receive a barb  14  when the stent  10  is compressed via the belts  26 . The helical nature of the slots  56  corresponds with the laying direction of the tucked barbs  14 . The slots  56  may have other configurations to accommodate barbs  14  having different configurations. The slots  56  receive the tucked barbs  14  and retain them in the tucked position, aligned with a corresponding strut or tuck pad. Additionally, since the slots  56  are recessed into the bushing body  52 , the tucked barbs  14  do not add to the radial size of the compressed stent. As seen in  FIG. 5 , multiple retaining mechanisms  50  may be utilized with a delivery system. The direction of the slots  56  for the two retaining mechanisms  50  is opposite such that they accommodate barbs  14  extending in opposite directions. 
         [0032]    Referring to  FIGS. 7-11 , a retaining mechanism  71  that is another alternative embodiment of the present invention is shown. The retaining mechanism  71  is formed integrally with the stent  70 , as opposed to being accommodated on the delivery system as in the previous embodiments. The retaining mechanism  71  is defined by the stent struts  72  and the associated reduced thickness tuck pads  76 . 
         [0033]    Referring to  FIGS. 10 and 11 , each tuck pad  76  has a radial height h that is approximately one-half or less the radial height of the corresponding strut  72 . As such, the retaining mechanism  71  is defined by the shoulder  75  defined between the strut  72  and tuck pad  76 . Referring to  FIGS. 8 and 9 , in the compressed state, the barbs  74  are forced against the shoulder  75  of the retaining mechanism  71 . The risk of the barb  74  overextending past the tuck pad or strut is reduced since the shoulder  75  of the retaining mechanism  71  prevents such. As such, the barb lateral angle α can be increased to ensure that the barbs  74  will not back out while not having to worry about overextension. Additionally, since the tuck pads  76  are approximately one-half or less the height of typical tuck pads, they will have a reduced effect on the radial thickness of the compressed stent  70 .