Abstract:
A stent assembly 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 belt is releasably positioned about the stent body and aligned with the barb to constrain the barb to a position with the free end proximate to the stent body. A method of forming a stent assembly is also provided.

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 assembly 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 belt is releasably positioned about the stent body and aligned with the barb to constrain the barb to a position with the free end proximal to the stent body. 
         [0010]    In another aspect, the invention provides a method of forming a stent assembly, comprising: forming a stent body having at least one barb with a free end extending radially outward from the stent body; and releasably securing a belt about the stent body in alignment with the barb to constrain the barb to a position with the free end proximate to the stent body. 
         [0011]    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 
         [0012]    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: 
           [0013]      FIG. 1  is a side elevation of a compressed stent with belted barbs in accordance with a first embodiment of the present invention. 
           [0014]      FIG. 2  is a side elevation of the compressed stent of  FIG. 1  with the barbs released. 
           [0015]      FIG. 3  shows a flat pattern of the stent of  FIG. 1  illustrating the grinding pattern of the grooves. 
           [0016]      FIG. 4  is a side elevation of a compressed stent with belted barbs in accordance with an alternative embodiment of the present invention. 
           [0017]      FIG. 5  is a side elevation of the compressed stent of  FIG. 4  with the barbs released. 
           [0018]      FIG. 6  shows a flat pattern of the stent of  FIG. 4  illustrating the grinding pattern of the grooves. 
           [0019]      FIG. 7  is a cross-sectional view of a grinding rod of a first method for grinding the stent of  FIG. 4 . 
           [0020]      FIG. 8  is a cross-sectional view similar to  FIG. 7  and illustrating a stent positioned on the grinding rod for grinding. 
           [0021]      FIG. 9  is an isometric view of an alternative grinding rod and associated collar. 
           [0022]      FIG. 10  is a cross-sectional view of the grinding rod of  FIG. 9 . 
           [0023]      FIG. 11  is an end elevation view of the collar of  FIG. 9 . 
           [0024]      FIG. 12  is a cross-sectional view along the line  12 - 12  in  FIG. 11 . 
           [0025]      FIG. 13  is a side elevation of a compressed stent with belted barbs in accordance with another alternative embodiment of the present invention. 
           [0026]      FIG. 14  is a side elevation of the compressed stent of  FIG. 13  with the barbs released. 
           [0027]      FIG. 15  shows a flat pattern of the stent of  FIG. 13  illustrating the grinding pattern of the grooves. 
           [0028]      FIG. 16  shows a flat pattern of another alternative stent illustrating the grinding pattern of the grooves. 
           [0029]      FIG. 17  is a cross-sectional view of a grinding rod of a method for grinding the stent of  FIG. 16 . 
           [0030]      FIG. 18  is a cross-sectional view similar to  FIG. 17  and illustrating a stent positioned on the grinding rod for grinding. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    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. 
         [0032]    Referring to  FIGS. 1-3 , a stent  10  that is a first embodiment of the present invention is illustrated, with  FIGS. 1 and 2  illustrating the stent  10  schematically and  FIG. 3  illustrating a flat pattern of the stent  10 . Stent  10  includes a plurality of struts  12  extending axially between the opposed ends  11 ,  13  thereof. The stent  10  can be oriented in either direction, that is, the end  13  may represent the proximal end or the distal end of the stent  10 , depending on the application. Both ends  11 ,  13  have a plurality of crowns adjoining adjacent struts  12 . The end  13  of stent  10  has a plurality of connecting members  16  configured to connect the stent  10  to a graft or other structure. The illustrated stent  10  structure is merely a representative example, and the invention is not intended to be limited to such. The stent  10  of the present invention can have various structures and is not limited to the strut structure illustrated herein. For example, the stent may have a body defined by a lattice structure or a helical structure. 
         [0033]    Along one or more of the struts  12 , a barb  20  is provided. Referring to  FIG. 3 , the barbs  20  are preferably formed integrally with the struts  12 , but may otherwise be manufactured, for example, as a separate component attached to the struts  12 . Each of the barbs  20  has a pointed tip  21  configured to engage the intended lumen wall. In the present embodiment, each tip  21  slopes outwardly along its outward radial extent. The stent struts  12  and the barbs  20  are preferably self expanding, that is, upon release of a constraining force, the struts  12  will move radially apart and the barbs  20  will extend radially outward. Other configurations, for example, balloon expansion, are also contemplated within the present invention. 
         [0034]    Referring to  FIG. 1 , a belt  24  is compressed about the stent  10  and contacts approximately the tips  21  of the barbs  20  to constrain the barbs  20 . A release wire  25  or the like preferably extends through the ends of the belt  24  to retain the belt  24  in the constraining condition. The release wire  25  may extend through the barb belt  24  alone with a separate wire  17  extending through the main belts  19  retaining the stent  10 , as illustrated. Alternatively, a single wire may pass through all of the belts  19  and  24  and control deployment of the stent  10  and the barbs  20 . The belts  19  and  24  and release wires  17  and  25  can be selected to provide various deployment sequences. For example, the barbs  20  may be deployed first, as illustrated in  FIG. 2 , and thereafter the stent  10  deployed such that the barbs  20  are positioned for engagement as soon as the stent is released. As another example, all of the belts  19  and  24  may be release substantially simultaneously such that the stent  10  opens in a uniform manner. Alternatively, a single belt may be utilized for both maintaining the stent  10  in the compressed configuration and retaining the barbs  20  in the constrained condition. Various belt and release wire configurations and sequences are described in U.S. Patent Application Publication No. US 2004/0138734, which is incorporated herein in its entirety by reference. 
         [0035]    To minimize axial movement of the belt  24 , a circumferential groove  22  is preferably ground, etched (e.g. laser or chemical) or otherwise formed about the stent  10  axially aligned with the barbs  20 . The groove is similar to the circumferential grooves  18  provided for the main belts  19 . In the present embodiment, the groove  22  is substantially aligned with the barb tips  21 , such that the barb tips  21  have a minimal groove  23  therein. The barbs  20  continue to present a sharpened tip and the groove  23  generally does not affect the barb  20  effectiveness. The groove  22  extending across each of the struts  12  and the barb tips  21  can be seen in the schematic drawing in  FIG. 3 . 
         [0036]    As illustrated in  FIG. 1 , the belt  24  retains each of the barbs  20  in a constrained position with the sharpest portion of the tip positioned radially inward from the surface of the stent  10 , thereby providing effective barb  20  constraint. Additionally, since the barbs  20  are not tucked under the struts  12  or tucking pads (which may be used in prior art devices, but not required with the present device), the barbs  20  are free to reliably expand as soon as the belt  24  is removed. As an additional advantage, since the barbs  20  are not tucked under the struts  12 , the stent  10  maintains a slim and more uniform radial profile in the compressed state. In contrast, stents with tucked barbs often have an expanded mid-section, similar to a football shape, due to the double material thickness of the strut and barb tucked underneath. 
         [0037]    Referring to  FIGS. 4-6 , a stent  10 ′ that is an alternative embodiment of the present invention is shown. The stent  10 ′ is similar to that of the previous embodiment, except that a groove  23  is not present on the barb tips  21 ′. This is illustrated more clearly in  FIG. 6 . Referring to  FIG. 5 , the barb  20  includes a full outwardly directed tip  21 ′. In addition to providing more material (since there is no groove  23 ), the belt  24  has the higher radially outward surface of the barb  20  to contact. As such, the belt  24  more effectively depresses the barbs  20  below the outer radial surface of the compressed stent  10 ′. 
         [0038]    Referring to  FIGS. 7 and 8 , a first method of manufacturing the stent  10 ′ of  FIGS. 4-6  will be described. A grinding rod  50  has a generally cylindrical body  52  with a circumferential recess  54  formed adjacent one end of the rod  50 . The circumferential recess  54  is configured to receive the barbs  20  in an inwardly deflected position such that the barb outer surfaces are below the plane of the grinding wheel (not shown). As shown in  FIG. 8 , the stent  10 ′ is positioned on the grinding rod  50  with the barbs  20  axially aligned with the circumferential recess  54 . A deflecting block  60  or the like is attached to the outer surface of each barb  20 . A wire  62  or the like is then tightened about the deflecting blocks  60  such that the blocks  60 , and thereby the barbs  20 , are deflected inward. With the barbs  20  deflected into the circumferential groove  54 , the grinding wheel can be utilized to grind the barb belt groove  22 ′. Upon removal of the stent  10 ′ from the grinding rod  50 , the stent struts  12  include the groove  22 ′, but the barbs  20  do not have the groove  22 ′, as illustrated schematically in  FIG. 6 . The main belt grooves  18  may also be ground prior to removal of the stent  10 ′ from the grinding rod  50 . 
         [0039]    Referring to  FIGS. 9-12 , an alternative method of manufacturing the stent  10 ′ of  FIGS. 4-6  will be described. The method again utilizes a grinding rod  50 ′ having a cylindrical body  52 ′. Instead of providing a full circumferential groove, individual barb slots  54 ′ are provided in the grinding rod  50 ′. As such, the barbs  20  can be deflected into the slots  54 ′ while the struts  12  remain supported along the rod body  52 ′ during grinding of the groove  22 ′. To deflect the barbs  20  into the slots  54 ′, a collar  70  is utilized. The collar  70  includes a cylindrical body  72  with an axial through bore  73  larger than the outer diameter of the stent  10 ′ when it is positioned on the rod  50 ′. The collar  70  includes a plurality of inwardly extending ribs  74  corresponding to the number of barbs  20  and slots  54 ′. The ribs  74  define an inner diameter therebetween which is only slightly larger than the outer diameter of the grinding rod  50 ′. As such, as the collar  70  is moved onto the grinding rod  50 ′, the stent struts  12  fit between the collar body  72  and the grinding rod  50 ′, however, the clearance at the ribs  74  is not sufficient, and the ribs  74  contact the corresponding barbs  20  and deflect the barbs  20  into the corresponding slots  54 ′. Each of the ribs  74  preferably has a tapered forward end  76  to further facilitate passage of the rib  74  onto the respective barb  20 . 
         [0040]    Referring to  FIGS. 13-15 , a stent  10 ″ that is an alternative embodiment of the present invention is shown. The stent  10 ″ is similar to that of the stent  10 ′ of  FIGS. 4-6  and again does not include a groove  22 ″ extending across the barb tips  21 ″, as seen in  FIG. 15 . Referring to  FIG. 14 , the stent  10 ″ differs from the stent  10 ′ in that the barb  20  converges inward to a radially inward tip  21 ″. As such, the barb  21 ″ is yet further recessed from the stent outer surface, as illustrate in  FIG. 13 . In some applications, the inward tip  21 ″ may also prove more effective since the tip  21 ″ will effectively lock against radially inward disengagement once it engages the lumen wall. 
         [0041]    Referring to  FIG. 16 , a flat schematic pattern of another alternative stent  10 ′″ is shown. The current stent  10 ′″ is in opposite to the stent  10 ′ of  FIGS. 4-6  in that the stent  10 ′″ includes a belt groove  22 ′″ extending across the barbs  20 , but no associated belt groove extending across the stent struts  12 . Such a configuration has been found in some applications to provide a better combination of barb recessing and barb constraining effectiveness. 
         [0042]    While various configurations of barb tips are illustrated and described, the invention is not limited to such and other configurations may be utilized. 
         [0043]    Referring to  FIGS. 17 and 18 , a method of manufacturing the stent  10 ′″ of  FIG. 16  will be described. A grinding rod  50 ′″ has a generally cylindrical body  52 ′″ with a circumferential recess  54 ′″ formed at the complete end of the rod  50 ′″. The circumferential recess  54 ′″ is configured to receive the struts  12  and the end  13  of the stent  10 ′″ below the surface of the barbs  20 . To ensure the barbs  20  do not deflect inward, a support wire  64  is positioned between the barbs  20  and the struts  12 . The support wire  64  maintains the barbs  20  in the grinding plane such that belt grooves  22 ′″ may be formed therein. A retaining wire  66  may be provided about the end  13  of the stent  10 ′″ to ensure it is maintained away from the grinding plane.