Abstract:
A method for assembling a stent graft onto a balloon delivery catheter is disclosed. The method includes the steps of: assembling a graft over a stent with attached security rings and inserting the ends of the graft between the stent and the rings; placing the assembled stent graft on the delivery balloon of the delivery catheter; and crimping the stent graft onto the balloon. The stent may include a plurality of axially aligned belts that include a plurality of mid belts, and first and second end belts, where each of the mid belts includes a plurality of circumferentially spaced struts having first and second ends adjoining first sinusoidal-shaped elements, and each of the first and second end belts includes at least about twice the number of circumferentially spaced struts adjoining second sinusoidal-shaped elements. Also disclosed is a stent graft for use in practicing the method.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of co-pending U.S. application Ser. No. 10/255,199 filed Sep. 26, 2002 which is a continuation-in-part of U.S. application Ser. No. 09/560,427 filed Apr. 28, 2000 and issued as U.S. Pat. No. 6,520,984 on Feb. 18, 2003 (abandoned), both of which are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a stent graft assembly and method, and more particularly to a stent graft assembly which includes security rings. 
       BACKGROUND OF THE INVENTION 
       [0003]    A composite expandable device with polymeric covering and bioactive coating thereon, delivery apparatus and method are disclosed in U.S. Pat. No. 6,371,980, issued Apr. 16, 2002. In connection with the expandable stent and the polymeric covering forming a graft carried thereby it has been found that it may be possible for the graft to move or become dislodged from its most desirable position on the stent. There is therefore a need for a new and improved stent graft assembly and method which overcomes this possible difficulty. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect, the invention includes a stent graft that includes a stent and a graft in the form of a polymeric sleeve extending over at least a portion of the stent. Security rings are attached on opposite ends of the stent graft to prevent inadvertent displacement of the graft with respect to the stent during deployment of the stent graft into a vessel in a patient. In another embodiment, the security rings can readily accommodate expansion of the stent graft. One or both of the security rings may be attached to the stent with a weld. Preferably, the weld is a laser weld. 
         [0005]    In one embodiment, the stent includes a plurality of axially aligned belts which include a plurality of mid belts, and first and second end belts. Each of the mid belts includes a plurality of circumferentially spaced struts having first and second ends adjoining first sinusoidal-shaped elements. Each of said first and second end belts includes at least about twice the number of circumferentially spaced struts adjoining second sinusoidal-shaped elements compared to the number of the struts in the mid belts. 
         [0006]    In another embodiment, the first and second sinusoidal-shaped elements have hinge points, and the second sinusoidal-shaped elements have narrower hinge points relative to the hinge points of the first sinusoidal-shaped elements. 
         [0007]    The graft may be formed of ePTFE. In one embodiment of the invention, the graft includes a bioactive coating that is disposed on the graft. 
         [0008]    One or more of the security rings of the invention may include a radiopaque marker carried thereon. In one embodiment, one or both of the security rings includes an eyelet and the radiopaque material is disposed in the eyelet. 
         [0009]    Another aspect of the invention includes a method for assembling a stent graft onto a balloon delivery catheter. The method includes the steps of: assembling a graft over a stent with attached security rings and inserting the ends of the graft between the stent and the rings; placing the assembled stent graft on the delivery balloon of the delivery catheter; and crimping the stent graft onto the balloon. One or both of the security rings may be attached to the stent with a weld. Preferably, the weld is a laser weld. 
         [0010]    In one embodiment of the method of the invention, the stent includes a plurality of axially aligned belts which include a plurality of mid belts, and first and second end belts. Each of the mid belts includes a plurality of circumferentially spaced struts having first and second ends adjoining first sinusoidal-shaped elements. Each of said first and second end belts includes at least about twice the number of circumferentially spaced struts adjoining second sinusoidal-shaped elements compared to the number of the struts in the mid belts. 
         [0011]    In another embodiment, the first and second sinusoidal-shaped elements have hinge points, and the second sinusoidal-shaped elements have narrower hinge points relative to the hinge points of the first sinusoidal-shaped elements. 
         [0012]    The graft may be formed of ePTFE. In one embodiment of the invention, the graft includes a bioactive coating that is disposed on the graft. 
         [0013]    One or more of the security rings of the invention may includes a radiopaque marker carried thereon. In one embodiment, one or both of the security rings includes an eyelet and the radiopaque material is disposed in the eyelet. 
         [0014]    Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]      FIG. 1  is a side elevational view of a stent graft assembly incorporating the present invention mounted on the distal extremity of a balloon delivery catheter; 
           [0016]      FIG. 2  is a side elevational view of another embodiment of a stent graft assembly incorporating the present invention also mounted on the distal extremity of a balloon delivery catheter; 
           [0017]      FIG. 3  is a cross-sectional view taken along the line  3 - 3  of  FIG. 2 ; 
           [0018]      FIG. 4  is a view similar to  FIG. 3  showing an alternate embodiment; 
           [0019]      FIG. 5  is a side elevational view of a stent graft assembly with a certain portion of the stent graft being removed and showing the use of different types of security rings; 
           [0020]      FIG. 6  is an enlarged view of one of the security rings shown in  FIG. 5 ; 
           [0021]      FIG. 7  is a view of a balloon with the stent graft with security rings mounted thereon according to one embodiment of the invention; 
           [0022]      FIG. 8  is a detailed view of the stent graft with security rings; 
           [0023]      FIG. 9  is a plan view of a stent which has been split apart longitudinally and spread out to show its construction; and 
           [0024]      FIG. 10  is an enlarged view of a portion of the stent shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    In general, the stent graft assembly incorporating the present invention is for use in placing a stent graft in a vessel of a patient and comprises a balloon delivery catheter having a distal extremity and having an inflatable balloon on the distal extremity. A stent graft is disposed over the inflatable balloon and is comprised of a stent and an outer polymeric sleeve, the sleeve having first and second ends. First and second expandable security rings are disposed over the first and second ends of the graft and serve to secure the first and second ends of the graft to the stent to prevent inadvertent displacement of the sleeve with respect to the stent during deployment of the stent graft into the vessel of the patient. 
         [0026]    More particularly as shown in  FIG. 1  of the drawings, the stent graft assembly includes a stent graft  11  which consists of a stent  12  which is covered by a polymeric sleeve  13 . As shown in  FIG. 1 , the stent graft  11  is disposed over an inflatable balloon  16  on the distal extremity of a balloon delivery catheter  17  of a conventional type and forming a part of the assembly  10 . The balloon delivery catheter  17  includes a multi-lumen shaft  18  which incorporates a balloon inflation lumen (not shown) and may incorporate a guide wire lumen (not shown). 
         [0027]    The balloon delivery catheter  17  and the stent graft  11  consisting of stent  12  and the polymeric sleeve  13  are disclosed in U.S. Pat. No. 6,371,980, issued Apr. 16, 2002, which is incorporated by reference herein in its entirety, and therefore will not be described in detail. As disclosed therein, the stent  12  is in the form of an expandable frame and consists of a plurality of axially spaced-apart circular belts  21  which are interconnected by sinusoidal interconnector  22 . Each belt  21  is comprised of a plurality of circumferentially spaced-apart elongate struts  24 . Sinusoidal-shaped elements  26  and  27  adjoin the ends of the struts  24  and form in conjunction therewith the circular belts  21 . The sinusoidal-shaped interconnectors  22  provided for interconnecting the belts  21  are at circumferentially spaced-apart positions to provide a stent  12  which when expanded is capable of providing circumferential support while at the same time being axially flexible. 
         [0028]    The stent  12  is typically formed of a suitable metal such as stainless steel, titanium and other metals and alloys thereof. It is desirable that the material utilized for the frame be biocompatible with the fluids and tissue of the human body. 
         [0029]    The sleeve  13  is in the form of a tubular member of a size so that it can slip over the stent  12  when it is in an unexpanded condition and preferably has a length so that the extreme ends of the stent  12  extend beyond the sleeve as shown in  FIG. 1 . The sleeve  13  is typically formed of a polymeric material such as ePTFE. 
         [0030]    In order to ensure that the polymeric sleeve  13  remains in the desired position on the stent  12 , security rings  36  and  37  have been positioned over the outer ends of the sleeve  13 . The security rings  36  and  37  typically can be formed of a metal and preferably the same metal which is used for the stent  12 , for example, stainless steel or titanium or alloys thereof. The rings  36  and  37  have sinusoidal-shaped convolutions  38  so that they can be expanded with the stent graft when the stent graft is expanded as hereinafter described. By way of example, the security rings can be formed from laser cut tubing in the same manner as stents having a suitable wall thickness of 0.003″ to 0.006″. The inner surfaces of the security rings can be left unpolished so that they have a rougher inner surface finish to enhance gripping to the outer surface of the sleeve  13 . Alternatively, a texture can be applied to the inner surface to enhance the gripping capabilities of the security ring. 
         [0031]    A radiopaque marker  41  is carried by at least one and, if desired, both of the security rings  36  and  37 , as in  FIGS. 1 and 2 . Thus, as shown, a radiopaque marker  41  is provided on the security ring  37  and can be of a suitable radiopaque material such as gold which has been cold worked or forged into an eyelet receptacle  42  formed as a part of the convolutions  38 . Alternately, as shown in  FIGS. 8 and 9 , the radiopaque marker  148  is provided on either or both ends of the stent  140  in a similar eyelet receptacle  150 . 
         [0032]    In use of the stent graft assembly  10  and the stent graft  11  of the present invention with the method of the present invention, the stent  12  can be placed upon a support mandrel (not shown) after which the sleeve  13  is slipped onto the stent to provide the stent graft  11 . The stent graft  11  is then placed on the balloon  16  of the balloon delivery catheter  17 . The stent graft  11  is then crimped onto the balloon  16  with a crimping tool (not shown). The security rings  36  and  37  are then placed over the sleeve  13  and crimped onto the ends of the sleeve  13  by a crimping tool to ensure that the security rings  36  and  37  remain in place on the ends of the sleeve  13  and also to ensure that the ends of the graft  11  frictionally engage the stent  12  to retain the sleeve  13  in the desired position on the stent  12 . Alternatively, the security rings  36  and  37  and the stent graft  11  can be crimped simultaneously. 
         [0033]    The stent graft assembly  10  shown in  FIG. 1  can now be utilized for positioning the stent graft  11  in a vessel of a patient in a conventional manner as for example by introducing the same through a femoral artery. The advancement of the stent graft  11  can be ascertained by observing the positioning of the radiopaque marker  41  and also by any radiopaque markers on the stent  12  and the balloon catheter  17 . During advancement of the stent graft to the desired site, the security rings  36  and  37  serve to ensure that the sleeve  13  will not accidentally become dislodged or shifted in position on the stent  12 . After the stent graft has been delivered to the desired position in the vessel of the patient, the balloon  16  of the balloon delivery catheter  17  can be expanded to expand the stent  12  and the sleeve  13  carried thereby as well as the security rings  36  and  37 . 
         [0034]    After the stent graft  11  has been delivered and then expanded the desired amount, the balloon  16  of the balloon delivery catheter  17  can be deflated and the balloon delivery catheter  17  removed in a conventional manner. The stent graft  11  will remain in place. Its position can be ascertained by observing the position of the radiopaque marker  41 . 
         [0035]    Another embodiment of a stent graft assembly incorporating the present invention is shown in the stent graft assembly  61  in  FIG. 2 . The balloon delivery catheter  62  shown therein shows the use of radiopaque marker bands  63  and  64  positioned on a shaft  66  on opposite ends of the balloon  67  and held in place by suitable means such as an epoxy  68  and disposed on opposite ends of the stent graft  11  and serve as enlargements to prevent the inadvertent dislodgement of the stent and/or the graft from the balloon during deployment of the stent graft  11 . 
         [0036]    In addition, as in the previous embodiments, security rings  71  and  72  are provided on opposite ends of the stent  12  and the sleeve  13 . Security rings  71  and  72  are each comprised of two elongate elements  76  and  77  in the forms of waves or convolutions which are sinusoidal in shape and which are joined together by circumferentially spaced-apart axially extending struts  78  and eyelets  79 . As with the security rings  36  and  37 , it can be seen that the security rings  71  and  72  can be readily crimped into place and expanded in the same manner as the security rings  36  and  37 . The eyelets  79  carry radiopaque markers  81 . As with the security rings  36  and  37  the inner surfaces of the elements  76  and  77  can be left unpolished or with a textured surface for frictionally engaging the outer surface of the polymeric sleeve  13 . 
         [0037]    In order to further enhance the engagement between the polymeric sleeve  13  on the stent  12 , the radiopaque marker  81  as shown in  FIG. 3  can protrude out of the eyelet  79  so that it can form an indentation  82  with the sleeve  13  which extends into an open. space in the stent  12  to further ensure a good engagement between the sleeve  13  and the stent  12  to prevent dislodgement of the sleeve  13  and ring  71  or  72  from the stent  12 . In a similar manner as shown in  FIG. 4 , an eyelet  86  provided on the stent  12  may also carry a radiopaque marker  87  protruding radially and forming an indentation  88  in the inner surface of the sleeve  13  and to extend into a space in the security ring  72  to further ensure good engagement between the sleeve  13  and the stent  12 . 
         [0038]    Operation and use of the stent graft assembly  61  shown in  FIG. 2  is very similar to that hereinbefore described with respect to  FIG. 1  with the principal difference being that the security rings  71  and  72  have enhanced friction engaging capabilities over the security rings  36  and  37  shown in  FIG. 1 . In addition, the balloon delivery catheter  62 , by providing the marker bands  63  and  64  On Opposite extremities of the stent graft  11  also ensure that the stent graft  11  cannot accidentally become dislodged during deployment of the stent graft  11 . 
         [0039]    Still another embodiment of a stent graft assembly incorporating the present invention is shown in  FIG. 5  in which the balloon delivery catheter  62  as shown therein is similar to the one hereinbefore described. The stent graft  11  is also similar to those hereinbefore described. However, in  FIG. 5  there is shown the use of security rings  91  or  92  (showing two different designs) mounted on opposite ends of the sleeve  13 . The security ring  91  is in the form of a stretchable polymer which can be stretched and fitted over one end of the sleeve  13  to frictionally retain the security ring  91  on the sleeve  13  and similarly to retain the sleeve  13  on the stent  12 . Alternatively, as shown with the security ring  92 , a less stretchable band of polymeric material can be utilized which is provided with circumferentially spaced-apart cutouts  93  therein which as shown in detail in  FIG. 6  are positioned in such a manner so as to provide weakened regions  94  associated with each of the cutouts  93  but being staggered or provided on opposite sides of the security ring  92  so that when the stent graft  11  is expanded, these weakened regions will or can break apart to provide a zig-zag shape or a substantially sinusoidal wave-like shape for the expanded security ring  92 . Thus, it can be seen that a polymeric security ring can be provided which firmly secures the graft to the stent while still permitting expansion of the stent and graft after the stent graft assembly  11  has been deployed to the desired position. 
         [0040]    As shown in  FIG. 7 , the stent graft  100  is shown mounted on a delivery apparatus  102 . The apparatus  102  is provided with a central lumen  103  which is adapted to receive a conventional guide wire. The lumen  103  extends through the apparatus  102  and an opening (not shown) is provided in the apparatus for expanding the apparatus. The apparatus  102  has a substantially continuous diameter and is provided with distal and proximal portions  104  and  106  and an intermediate portion  107  which serves as a working portion of the apparatus, having a length which will accept the length of the stent graft  100 . Radiopaque marker bands  110  and  111  are provided on the portion of the central lumen  103  extending through the apparatus and are mounted in the distal and proximal portions  104  and  106  as shown adjacent to the intermediate portion  102 . 
         [0041]    As illustrated in  FIG. 10 , the stent  160  includes a plurality of serially-connected belts  162  which are axially aligned with each other and are interconnected by sinusoidal interconnector  164 . Each belt  162  includes a plurality of circumferentially spaced-apart elongate struts  166 . Sinusoidal-shaped elements  168  and  169  adjoin the ends of the struts  166  and form in conjunction therewith the circular belts  162 . The sinusoidal-shaped interconnectors  164  provided for interconnecting the belts  162  are at circumferentially spaced-apart positions to provide a stent  160 . Stent  160  is capable of providing circumferential support while, at the same time, being axially flexible. The stent may be formed by forming the desired pattern directly out of a tube, e.g. by laser cutting or chemical etching. Alternatively, the desired pattern may be formed out of a flat sheet, e.g. by laser cutting or chemical etching, and then rolling that flat sheet into a tube and joining the edges, e.g. by welding. Any other suitable manufacturing method known in the art may be employed for manufacturing a stent in accordance with the invention. Furthermore, stents may be formed by etching a pattern into a material or mold and depositing stent material in the pattern, such as by chemical vapor deposition or the like. Such stents may be formed of plastic, metal or other materials and may exhibit a multitude of configurations. The metals from which such stents are formed may include stainless steels, titanium, Nitinol, and tantalum among others. 
         [0042]    In one embodiment, stent  160  includes serially-connected belts  162 , and two end belts  170  and  172 . All belts are connected with serpentine interconnectors  164 . Each end belt  170  and  172  includes a plurality of circumferentially spaced-apart elongate struts  176 . Belts  162  also include spaced-apart elongate struts  166 . Serpentine interconnecting elements  164  are provided for interconnecting the plurality of belts  162  and the end belts  170  and  172  so that the belts  162  and end belts  170  and  172  extend along an axis while permitting axial bending between the belts  162  and the end belts  170  and  172 . Thus, with the construction shown in  FIG. 10  there are provided five belts  162  and two end portions  170  and  172  with six sets of interconnecting elements  164 . The number of belts and interconnecting elements may vary depending on the desired length of the stent graft. 
         [0043]    As described above, a polymer sleeve  142  extends over substantially the entire length of the stent  160 . With reference to  FIG. 10 , there are twice as many struts  176  in end belts  170  and  172  as there are struts  166  in belts  162 . The larger number of struts  176  in end belts  170  and  172  provides more circumferential support for the ends of the polymer sleeve (not shown), without causing unduly high radial strength at the ends of the stent graft. This has the advantage of preventing prolapse of the sleeve into the lumen of the stent graft due to blood flow after the stent graft is implanted into the vessel. 
         [0044]    In addition, security rings  144  and  146  are provided on opposite ends of the stent  160  and the sleeve  142 . The security rings  144  and  146  typically can be formed of a metal and preferably the same metal which is used for the stent  160 , as for example stainless steel or titanium or alloys thereof. The security rings  144  and  146  have sinusoidal-shaped convolutions so that they can be expanded with the stent graft when the stent graft is expanded. A radiopaque marker  148  may be carried by at least one, and if desired both, of the security rings  144  and  146 . Alternatively, as shown in  FIG. 9 , a radiopaque marker  148  is provided on both ends of the stent  160  and is of a suitable radiopaque material which has been cold worked, forged into, or deposited on an eyelet receptacle  150  formed as a part of the convolutions. Examples of materials which can be employed as radiopaque materials include, but are not limited to, iodine and its salts or compounds, barium and its salts or compounds, tungsten, rhenium, osmium, noble metals, palladium, gold, colloidal gold, silver, platinum, tantalum, iridium or their alloys. Preferably, the radiopaque material is gold, platinum, iridium, titanium, tantalum, or alloys. Such materials are highly visible by fluoroscopy even at very minimal thicknesses. 
         [0045]    The security rings  144  and  146  may be attached to the stent  140  by any suitable attachment mechanism to ensure that the security rings  144  and  146  remain in place on the ends of the stent graft. This includes, but is not limited to, suture attachment methods, e.g. where a suture going around one or more struts of the stent is attached to a security ring. Apart from suturing techniques, methods including adhesives also may be used. One can solder or braze the stent and security ring together. Preferably, the security rings  144  and  146  are welded to stent  140  at one or more weld points  152 ,  153 ,  154 . One advantage of welding the security rings to the stent is to improve the mechanical integrity of the stent graft system. The welding connections may be created by welding techniques using welding technologies such as tungsten inert gas (tig) welds, metal inert gas (mig) welds, laser welds, friction welds, and electron beam welds. Other materials known to accelerate the welding process and improve the strength between the welded elements can be added. Electropolishing may be used to remove processing impurities and form a smooth surface following attachment of the stent to the security rings. 
         [0046]    In one embodiment, the stent graft is positioned in a vessel of a patient and the ends of the stent graft are opened first, and then the middle of the stent graft is opened. This method maximizes the ability of the stent graft to capture potential debris material from an underlying stenosis in the vessel. With reference to  FIGS. 10 and 11 , the hinge points  201 ,  202 ,  203  and  204  of end belt  170  are narrower than the hinge points  210 ,  211 , and  212  of belt  162 . This feature provides the advantage of requiring less force to open the end belts  170  and  172  than belts  162 . 
         [0047]    The stent design and functionality in the embodiments described above is not limited to a balloon-expandable stent, but may be employed with the so-called self-expanding stents that are formed for example from shape memory materials such as Nitinol. 
         [0048]    From the foregoing it can be seen that there has been provided a stent graft assembly and method which makes it possible to ensure that the graft is maintained in the desired position on the stent at all times and particularly during deployment of the stent graft while readily accommodating expansion of the stent graft after the stent graft has been deployed into the desired position. It also can be seen that use of the security rings serves to prevent inadvertent movement of the graft with respect to the stent or separation of the graft from the stent.