Abstract:
The present invention provides an apparatus and method for attachment between intersecting stent members and a covering or graft. The attachment fixes the covering relative to selected intersections of the stent members and prevents the covering from wrinkling, crimping, or sliding during radial expansion of the stent. In a preferred embodiment, the attachment comprises a continuous filament passing through the stent covering and looping around stent members between selected intersections and knotted around the intersecting stent members at selected intersections.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to stent-grafts, and more particularly to an apparatus and method for attaching a covering or graft to intersecting stent members.  
         BACKGROUND OF THE INVENTION  
         [0002]    Stent-grafts are used in surgical procedures to treat various vascular defects. Stent-grafts comprise a combination of a graft or covering with a stent or stent frame providing structural support to the graft or covering. The stent in such combinations is generally tubular and typically comprises an open framework or mesh of structural elements such as wires or thin metallic members, which may cross or intersect one another in various ways. In one stent graft configuration, a braided stent is provided where opposing helical stent members overlap one another to form crossing intersections. The braided stent is designed to contract radially for endoluminal placement into a patient and expand radially into a configuration in which it comprises an open lumen. The graft associated with a stent-graft is a covering or liner, disposed inside or outside of the stent and covering the stent framework to define a fluid passageway through the lumen of the stent.  
         SUMMARY OF THE INVENTION  
         [0003]    In accordance with an exemplary embodiment of the present invention, an attachment for securing a stent covering or graft to intersecting stent members includes a continuous filament repeatedly passing through the stent covering and wrapping around a stent member adjacent an intersection of that member with another member. The continuous filament is knotted around the intersection thereof, and then continues repeatedly passing through the covering and wrapping around the intersecting stent member. In an exemplary embodiment, the filament is a suture, the intersecting stent members form the end of a braided stent, and the covering comprises laminated layers of a woven dacron and a thin expanded polytetrafloroethlene.  
           [0004]    The present invention may provide attachment of a vascular graft to a variety of stent configurations, while allowing the stent members to hinge or pivot freely without forming wrinkles and crimps in the graft. According to an exemplary embodiment, the continuous filament is knotted at a plurality of adjacent intersections circumscribing a stent end formed by the intersecting stent members and lashed to a circumferential succession of intersecting stent members. This lashing between the stent members entails the filament repeatedly passing through the covering, and looping around portions of the stent members interconnecting the adjacent intersections. The ends of the covering may follow the contour of the frame members between the selected crossing interactions. Each of the lashing loops may comprise one of several sequential loops on the respective intersecting stent members, with interposed loops of the filament, or optionally some other restraining member, such as a ring or wire loop, surrounding the interposed intersections, preferably longitudinally.  
           [0005]    An attachment may also be provided at an end of a braided stent section comprising alternating crossing and crimped intersections. The lashing is again performed between alternating crossing and crimped intersections. The filament is wrapped around a portion of the stent members and then knotted longitudinally around the intersecting stent members at crossing intersections and horizontally around the intersecting stent members at crimped intersections.  
           [0006]    An attachment may also be provided at an end of a braided section of a stent formed by reversing the axial direction of the stent members. The continuous filament is knotted at a plurality of adjacent intersections circumscribing a stent formed by the stent members. The filament repeatedly passes through the covering and loops around the reversing portions of the stent members (i.e., turns), interconnecting the adjacent intersections. The contour of the frame members may be followed with the ends of the covering between selected crossing intersections. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is an iliac extension of a bifurcate stent-graft;  
         [0008]    [0008]FIG. 2 is a bifurcate section of a bifurcate stent-graft;  
         [0009]    [0009]FIG. 3 shows the proximal end of the iliac extension of FIG. 1 prior to attaching the covering to the intersecting stent members;  
         [0010]    [0010]FIG. 4 shows the proximal end of the iliac extension of FIG. 1 with the covering attached to the intersecting stent members with a continuous filament in accordance with an exemplary embodiment of the present invention;  
         [0011]    [0011]FIG. 5 a  shows a first step of a method for attaching the covering to the intersecting stent members at the proximal end of the iliac extension of FIG. 1 according to an exemplary embodiment of the present invention;  
         [0012]    [0012]FIG. 5 b  shows a second step of a method for attaching the covering to the intersecting stent members at the proximal end of the iliac extension of FIG. 1 according to an exemplary embodiment of the present invention;  
         [0013]    [0013]FIG. 5 c  shows a third step of a method for attaching the covering to the intersecting stent members at the proximal end of the iliac extension of FIG. 1 according to an exemplary embodiment of the present invention;  
         [0014]    [0014]FIG. 5 d  shows a fourth step of a method for attaching the covering to the intersecting stent members at the proximal end of the iliac extension of FIG. 1 according to an exemplary embodiment of the present invention;  
         [0015]    [0015]FIG. 5 e  shows a fifth step of a method for attaching the covering to the intersecting stent members at the proximal end of the iliac extension of FIG. 1 according to an exemplary embodiment of the present invention;  
         [0016]    [0016]FIG. 6 shows, from inside the stent, an attachment at one intersection featuring a knot formed by the continuous filament fixing the covering to the intersecting stent members according to an exemplary embodiment of the present invention;  
         [0017]    [0017]FIG. 7 shows, from outside the stent, an attachment at one intersection featuring the continuous filament with a knot fixing the covering to the intersecting stent members;  
         [0018]    [0018]FIG. 8 shows the distal end of the iliac extension of FIG. 1 with crimped intersections having crimps holding together the intersecting stent members;  
         [0019]    [0019]FIG. 9 shows a continuous lashing, a longitudinal knot at selected crossing intersections, and a lateral knot directly below selected crimped intersections of the stent members;  
         [0020]    [0020]FIG. 10 shows a step in a method for forming an attachment at the proximal end of the bifurcate stent-graft according to an exemplary embodiment of the present invention;  
         [0021]    [0021]FIG. 11 shows a step, subsequent to the step illustrated in FIG. 10, in a method for forming an attachment at the proximal end of the bifurcate stent-graft according to an exemplary embodiment of the present invention;  
         [0022]    [0022]FIG. 12 shows the step illustrated in FIG. 11 from outside the stent;  
         [0023]    [0023]FIG. 13 shows a step in a method for forming an attachment conforming to axially reversing segments of intersecting stent members according to an exemplary embodiment of the present invention;  
         [0024]    [0024]FIG. 14 shows a completed attachment of FIG. 13; and  
         [0025]    [0025]FIG. 15 shows a covering attached to intersecting stent members with a continuous filament and a pivotal restraint in accordance with an alternate exemplary embodiment of the present invention. 
     
    
       [0026]    While the applicant will describe the invention in connection with preferred and alternative embodiments, it should be understand that the invention is not limited to those embodiments. Furthermore, one should understand that the drawings are not necessarily to scale. In certain instances, the applicant may have omitted details, which are not necessary for an understanding of the present invention.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    The invention will next be described with reference to the figures wherein similar numbers indicate the same elements in all figures. Such figures are intended to be illustrative rather than limiting and are included herewith to facilitate the explanation of the apparatus of the present invention.  
         [0028]    [0028]FIGS. 1 and 2 show a modular bifurcate stent graft comprising an iliac extension  2  and a bifurcate section  3 , each having a stent covering  20 , attached to intersecting stent members  12 , which are helically braided to form a tubular stent section. The proximal end  18  of iliac extension  2  attaches to the socket  9  of bifurcate section  3  to form a complete bifurcate stent-graft. FIG. 1 shows an exemplary embodiment, where the iliac extension of a stent-graft comprises a covering  20  attached to intersecting stent members  12  at a distal end  17  of the iliac extension having alternating crossing intersections and crimped intersections. At proximal end  18  of the stent-graft, where covering  20  is attached, adjacent crossing intersections circumscribe the stent-graft. The bifurcated section  3 , shown in FIG. 2, includes a trunk section  8  that bifurcates into a leg  19  adapted to extend into one iliac, and a socket  9  adapted to receive an iliac extension. Iliac extension  2  is a modular piece adapted to be inserted into the socket  9 . The unbifurcated end of trunk  9 , where covering  20  is attached, comprises alternating crossing intersections and crimped intersections. At the end of leg  19 , covering  20  is attached to intersecting stent members at adjacent crossing intersections. At the end of socket  9 , covering  20  is attached to adjacent crossing intersections having reversing portions of stent members or turns therebetween. The unbifurcated end of bifurcate section  3  and the distal end  17  of iliac extension  2  terminate with uncovered end segments  4  comprised of a circumferential series of hexagonal cells.  
         [0029]    As best seen in FIG. 11 intersecting stent members  12  at the distal end  17  of iliac extension  2  (as seen looking radially outwardly) are braided to form a stent segment extending away from uncovered stent segment  4 . The stent segment is formed by at least two continuous members  12  interwoven or braided in a pattern, forming intersections  14 . At each intersection  14 , one member  12  is positioned radially outward relative to the other member  12 . Following each member  12  along its helical path through the series of intersections  14 , that member  12  may be in the radial inward position in one intersection  14  and in the radial outward position in the next intersection  14 , or may be in the inward position for two intersections  14  and in the outward position for the next two, and so on. Exemplary braided stents  10  are disclosed, for example, in U.S. Pat. No. 4,655,771 to Hans I. Wallsten, incorporated herein by reference. The covering  20  attached to stent members  12  seen in FIG. 11 and the attachment between cover  20  and stent members  12  are described in more detail below.  
         [0030]    Bifurcated section  3  (shown in FIG. 2) also comprises a braided construction of stent members  12 . An exemplary braided stent section comprises a first set of stent members wound in a first helical direction and a second set of stent members wound in a second, opposite helical direction, forming a plurality of intersections. The first and second sets of stent members may be continuous stent members reversing axial direction at the ends of leg  19  and socket  9 . Stent members  12  may be wire, such as nitinol or stainless steel, or may comprise polymer or any other stent material known in the art.  
         [0031]    [0031]FIGS. 3 and 4 show an exemplary attachment, such as for the proximal end  18  of the iliac extension  2  (shown in FIG. 1), where the stent members  12  reverse axial direction to form a turn  13  and continue in the opposite direction. Stent members  12  pass over one another to form crossing intersections  14   a.  The covering  20  is trimmed to conform to the stent members  12 , as shown in FIG. 3. When trimming at a first stent member  12   a  is completed, covering  20  may be stitched or lashed with a continuous filament  30  to the stent member. The filament  30  passes through the stent covering  20  and wraps around first stent member  12   a,  lashing covering  20  to first stent member  12   a.  This lashing is repeated until a crossing intersection  14   a  is reached. Then, continuous filament  30  is knotted around intersecting first  12   a  and second  12   b  stent members at a crossing intersection  14   a.  After continuous filament  30  is knotted at intersection  14   a,  it is lashed to second stent member  12   b.  FIG. 3 shows the covering  20  trimmed to follow the contour of the stent members  12 . FIG. 4 shows a finished attachment with the continuous filament  30  knotted around the intersecting stent members  12  at crossing intersections  14   a  circumscribing a section of a stent-graft and lashed to stent members between adjacent crossing intersections. The filament  30  can be a suture or a wire, or other material having sufficient flexibility for lashing and knotting and sufficient strength to attach a covering on a stent.  
         [0032]    [0032]FIGS. 5 a - 5   e  illustrate sequential steps of a method for attaching the covering  20  to a first stent configuration with a continuous lashing and knotting technique according to an exemplary embodiment of the present invention. In the first stent configuration, shown in FIGS. 5 a - 5   e,  stent members  12  have turns  13  where they change axial direction. In the exemplary embodiment of the invention illustrated in FIGS. 5 a - 5   e,  covering  20  does not extend to turns  13 , but is attached at and between adjacent crossing intersections circumscribing the end of the stent-graft section (in FIGS. 5 a - 5   e  the proximal end of the iliac extension from FIG. 1 is illustrated).  
         [0033]    As seen in FIG. 5 a,  the continuous filament  30  lashes covering  20  to a first stent member  12   a  (as shown in FIG. 4). The lashing comprises passing filament  30  through covering  20 , then around first stent member  12   a,  and back through covering  20 . The lashing is repeated to form continuous stitches or lashings until intersection  14   a  is reached.  
         [0034]    Next, as shown in FIG. 5 b,  a first loop  31  is made longitudinally around intersecting stent members  12  at intersection  14   a  with filament  30 . First loop  31  encircles both intersecting stent members  12   a  and  12   b  at intersection  14   a,  allowing the intersecting members  12  to pivot relative to each other while fixing covering  20  at intersection  14   a.  In the exemplary embodiment illustrated in FIG. 5 b,  continuous filament  30  is passed through covering  20  from the inside of stent  10  to the outside of stent  10  at approximately a first apex formed by intersecting stent members  12  and looped around intersection  14   a  at approximately a longitudinally opposite apex formed by intersecting stent members  12 . Then, continuous filament  30  is again passed through covering  20  proximate the first apex. FIG. 5 c  shows a second loop  32  made around the intersection  14   a  with filament  30 . Second loop  32  is formed in the same way as first loop  31 .  
         [0035]    [0035]FIG. 5 d  shows filament  30  passing through the first  31  and second  32  loop. Then, filament  30  is pulled tight to form a longitudinal knot  33  to fix covering  20  to intersecting stent members  12  at intersection  14   a  (shown in FIG. 5 e ).  
         [0036]    Finally, as shown in FIG. 5 e  continuous filament  30  is lashed to second stent member  12   b  (shown in FIG. 4).  
         [0037]    Referring again to FIG. 5 a,  continuous filament  30  is passed through the covering  20 . Prior to beginning the lashing, a knot is made to secure the filament  30  to the covering  20  and stent  10 .  
         [0038]    [0038]FIGS. 6 and 7 show an inside view and outside view, respectively, of the attachment between intersecting stent members  12  and the stent covering  20  at a crossing intersection  14   a.  Covering  20  is attached to intersecting stent members  12  of a stent-graft by consecutive lashings of continuous filament  30  and a longitudinal knot  33 . The attachment is positioned at an end of a braided stent section formed by the stent members  12 .  
         [0039]    [0039]FIGS. 8 and 9 show an exemplary attachment for a stent configuration comprising alternate crossing intersections  14   a  and crimped intersections  14   b,  such as for the distal end  17  of iliac extension  2  (shown in FIG. 1) or the unbifurcated end of bifurcate section  3  (shown in FIG. 2). At crimped intersection  14   b,  stent members  12  meet and are secured together with a crimp  16 . FIG. 8 shows covering  20  trimmed to conform to stent members  12  at an end of a stent section comprising alternate crimped intersections and crossing intersections. FIG. 9 shows the completed attachment of covering  20  to intersecting stent members  12  at an end of a stent section comprising alternate crimped intersections and crossing intersections. The attachment of the present embodiment comprises lashings of a continuous filament  30  onto stent members  12 , longitudinal knot  33  formed in continuous filament  30  at crossing intersections  14   a,  and lateral knot  34  formed in continuous filament  30  directly below crimp  16  at crimped intersections  14   b  of stent members  12 .  
         [0040]    FIGS.  10 - 12  show a method for forming an attachment of covering  20  to intersecting stent members  12 , where intersecting stent members alternately form crossing intersections  14   a  and crimped intersections  14   b  at the end of a braided section of a stent. FIG. 10 shows the proximal end  18  of the bifurcate section  3  (shown in FIG. 2) with crimped intersections  14   b.  As shown in FIG. 10, covering  20  is contoured or trimmed to conform to stent members  12  at the end of a stent section comprising alternate crimped intersections and crossing intersections.  
         [0041]    [0041]FIGS. 11 and 12 shows the completed attachment from inside and outside the stent, respectively. Continuous filament  30  is knotted at a plurality of adjacent intersections  14  circumscribing the stent section formed by stent members  12 . As shown in FIG. 11, continuous filament  30  repeatedly passes through the covering  20  and loops around portions of stent members  12  interconnecting the adjacent intersections  14 . Then, when continuous filament  30  reaches a crossing intersection  14   a,  a longitudinal knot  33  (shown in FIG. 12) is formed as described above. After knot  33  is formed in continuous filament  30 , continuous filament  30  is again repeatedly passed through covering  20  and looped around another portion of a stent member  12  interconnecting the adjacent intersections  14 . Then, when continuous filament  30  reaches a crimped intersection  14   b,  a lateral knot  34  (shown in FIG. 12) is formed. Lateral knot  34  is formed by forming two loops of continuous filament  30  around both stent members at crimped intersection  14   b,  capturing covering  20  in the loops. Continuous filament  30  is then passed through the loops and drawn tight to form knot  34 .  
         [0042]    [0042]FIGS. 13 and 14 show an exemplary attachment, such as for the end of socket  9  of bifurcate section  3  (shown in FIG. 2), where the stent members  12  form turns  13  and covering  20  is attached to the scalloped end of a stent graft section formed by turns  13 . As shown in FIG. 13, covering  20  is contoured or trimmed to match the stent members  12  at turns  13 . As shown in FIG. 13, the contoured ends of covering  20  coincide with the scalloped ends formed by turns  13  in stent members  12 .  
         [0043]    Continuous filament  30  is knotted at a plurality of adjacent crossing intersections  14   a  circumscribing the stent formed by stent members  12 . As shown in FIG. 14, continuous filament  30  repeatedly passes through the covering  20  and loops around turns  13  in stent members  12 . Then, when continuous filament  30  reaches a crossing intersection  14   a,  a longitudinal knot  33  is formed as described above. After knot  33  is formed in continuous filament  30 , continuous filament  30  is again repeatedly passed through covering  20  and looped around another turn  13  formed in stent members  12 .  
         [0044]    An exemplary stent, is configured to treat an abdominal aortic aneurysm (AAA), comprising a bifurcate section  3  with an iliac extension  2  connected to the socket  9  of bifurcate section  3 . Iliac extension  2  and bifurcate section  3  are illustrated in FIGS. 1 and 2, respectively. The exemplary stent comprises various embodiments of the attachment according to the present invention. An attachment comprising lashings, longitudinal knots  33  and lateral knots  34  (as shown in FIG. 12) is provided at the unbifurcated end of trunk  8  of bifurcate section  3  and at the proximal end  17  of iliac extension  2 . An attachment comprising lashings and longitudinal knots  33  (as shown in FIG. 4) is provided at proximal end  18  of iliac extension  2  (shown in FIG. 1) and the distal end of leg  19  of bifurcate section  3  (shown in FIG. 2). An attachment comprising lashings extending around scalloped turns  13  and longitudinal knots  33  (as shown in FIG. 14) is provided at the distal end of socket  9  of bifurcate section  3  (shown in FIG. 2).  
         [0045]    Referring now to FIG. 15, covering  20  may also be attached to stent members  12  using a combination of a continuous filament  30  and a pivotal restraint member  41  according to an alternative exemplary embodiment of the invention. The covering  20  is trimmed to conform to the stent members  12 , as shown in FIG. 3. When trimming at a first stent member  12   a  is completed, covering  20  may be stitched or lashed with a continuous filament  30  to the stent member. The filament  30  passes through the stent covering  20  and wraps around first stent member  12   a,  lashing covering  20  to first stent member  12   a.  This lashing is repeated until a crossing intersection  14   a  is reached. Then, continuous filament  30  is lashed to second stent member  12   b.  The continuous filament  30  lashes cover  20  to the intersecting stent members  12  between crossing intersections  14   a  to circumscribe a section of a stent-graft, preferably at its end. The filament  30  can be a suture or a wire, or other material having sufficient flexibility for lashing and sufficient strength to lash a covering on a stent. At crossing intersections  14   a,  adjacent the lashing, pivotal restraint member  41  is disposed around both stent members forming the intersection and through cover  20 . The pivotal restraint member may be a knot formed in a filament separate from continuous filament  30 . Alternatively, the pivotal restraint may be a ring, staple, or other structure that fixes the filaments at their intersection while allowing them to pivot relative to each other.  
         [0046]    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.