Abstract:
A covered stent comprises a substrate, a stent adapted to be placed in a lumen of a human body, where the stent has portions interwoven in the substrate, and encapsulation encapsulating the substrate and the portions of the stent interwoven in the substrate and forming a tubular graft member.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to encapsulated stents suitable for placement in a human body lumen such as an artery. 
       BACKGROUND OF THE INVENTION 
       [0002]    Tubular prostheses such as stents, grafts, and stent-grafts (e.g., stents having an inner and/or outer covering comprising graft material and which may be referred to as covered stents) have been used to treat abnormalities in passageways in the human body. In vascular applications, these devices often are used to replace or bypass occluded, diseased or damaged blood vessels such as stenotic or aneurysmal vessels. For example, it is well known to use stent-grafts, which comprise biocompatible graft material (e.g., Dacron® or expanded polytetrafluoroethylene (ePTFE) or some other polymer) supported by a framework (e.g., one or more stent or stent-like structures), to treat or isolate aneurysms. The framework provides mechanical support and the graft material or liner provides a blood barrier. 
         [0003]    Aneurysms are an abnormal widening of a duct or canal such as a blood vessel and generally appear in the form of a sac formed by the abnormal dilation of the duct or vessel wall. The abnormally dilated wall typically is weakened and susceptible to rupture. Aneurysms can occur in blood vessels such as in the abdominal aorta where the aneurysm generally extends from a location below the renal arteries distally to or toward the iliac arteries. 
         [0004]    In treating an aneurysm with a stent-graft, the stent-graft typically is placed so that one end of the stent-graft is situated proximally or upstream of the diseased portion of the vessel and the other end of the stent-graft is situated distally or downstream of the diseased portion of the vessel. In this manner, the stent-graft extends through (spans) the aneurysmal sac and beyond the proximal and distal ends thereof to replace or bypass the weakened portion. The graft material typically forms a blood impervious lumen to facilitate endovascular exclusion of the aneurysm. 
         [0005]    Approaches for making stent-grafts such as abdominal aortic aneurysm stent-grafts have included sewing annular metallic spring elements, which may have a sinusoidal configuration, to woven materials described above such as expanded polytetrafluoroethylene, polytetrafluoroethylene, or Dacron®fabric. Other approaches have included electrospinning the stent structure with a polymer or dip coating the stent structure with a polymer. One example of a known polymeric coated stent-graft is illustrated in  FIG. 1 , where covered stent  100  comprises metallic springs or undulating elements  102   a ,  102   b ,  102   c  and  102   d , which can be referred to as stents or stent elements. In this example, stents or stent elements  102   a ,  102   b ,  102   c  and  102   d  have been treated with an electrospinning or dip coating process to form tubular polymeric graft member  104 , which is adhered thereto. Although electrospinning and dip coating techniques may provide stent-grafts with lower profiles, there is a relatively low contact surface area between the stents and the polymeric material and the line of contact or adhesion between the stent and the polymeric material also may not be uniform throughout the circumference of the stent resulting in non-uniform load distribution when a force is placed on the stent-graft, which can result in delamination. The materials used also can be a factor in creating a tendency for the polymeric membrane and stent to delaminate. An example of separation or detachment between the stent wire and polymeric membrane is diagrammatically depicted and designated with reference character D 1  in  FIG. 1 . Delamination typically is more of a concern in areas of higher stress loading such as the connections between the polymeric graft material and bare spring that extend beyond the edge of the polymeric graft material as shown in  FIG. 2 .  FIG. 2  illustrates a covered stent  110  having a known construction including a plurality of metallic undulating annular stent elements  112   a ,  112   b ,  112   c  . . .  112   n  and annular undulating bare wire spring  116 . A known electrospinning or dip coating process is used to provide the stent elements with a tubular polymeric graft  114  and to secure the apexes at one end of bare spring  116  to the graft. In this example, the apexes, which can be subjected to higher stresses than the stent elements, can detach as diagrammatically shown for example with reference character D 2 . 
         [0006]    There remains a need to develop and/or improve stent-graft constructions. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention involves improvements in covered stent construction. 
         [0008]    In one embodiment according to the invention, a covered stent suitable for placement in a lumen in a human body (e.g., an artery) comprises a substrate; a tubular stent adapted to be placed in a lumen of a human body, the stent having portions interwoven in the substrate; and encapsulation encapsulating the substrate and the portions of the stent interwoven in the and forming tubular graft member. 
         [0009]    In another embodiment according to the invention, a covered stent suitable for placement in a lumen in a human body comprises a substrate; a plurality of stents adapted to be placed in a lumen of a human body, the stents having portions interwoven in the substrate; and a tubular polymeric member covering the stents and extending through at least a portion of the substrate. 
         [0010]    In another embodiment according to the invention, a method of making a covered stent comprises interweaving a wire though a substrate to form a tubular member; and encapsulating the tubular member to form a covered stent having a tubular cover. 
         [0011]    The above is a brief description of some deficiencies in the prior art and advantages of embodiments according to the present invention. Other features, advantages, and embodiments according to the present invention will be apparent to those skilled in the art from the following description and accompanying drawings, wherein, for purposes of illustration only, specific embodiments are set forth in detail. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a known covered stent configuration. 
           [0013]      FIG. 2  illustrates a portion of another known covered stent configuration. 
           [0014]      FIG. 3A  is a cut away view of a covered stent embodiment according to the invention with a portion of the cover removed to show a stent element and a substrate in which it is integrated. 
           [0015]    FIG.  3 B 1  is a sectional view taken along line  3 B 1 - 3 B 1  in  FIG. 3A  and diagrammatically illustrating locations in the tubular substrate where the annular stent is interwoven. 
           [0016]    FIG.  3 B 2  is a sectional view taken through a portion of one of the stents of  FIG. 3A  showing the substrate and cover material 
           [0017]      FIG. 3C  is a close up view illustrating a variation of the substrate-stent configuration shown in  FIG. 3A . 
           [0018]      FIG. 3D  is a close up view illustrating another variation of the substrate-stent configuration shown in  FIG. 3A . 
           [0019]      FIG. 4  is a close up view illustrating a stent-graft substrate and a bare wire spring integrated therein according to another embodiment of the invention. 
           [0020]      FIG. 5A  illustrates a known anchoring mechanism. 
           [0021]      FIG. 5B  illustrates a portion of a covered stent with the anchoring mechanism of  FIG. 5A  integrated therein. 
           [0022]      FIG. 6  is a partial sectional view of a portion of a covered stent with an anchor element secured thereto. 
           [0023]      FIG. 7  is a partial sectional view of a portion of a covered stent with an anchor element secured thereto. 
           [0024]      FIGS. 8A and 8B  illustrate assembly of another covered stent embodiment according to the invention, where  FIG. 8A  illustrates an anchoring attachment component for the covered stent and  FIG. 8B  illustrates the anchoring attachment component integrally formed in a covered stent according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The following description will be made with reference to the drawings where when referring to the various figures, it should be understood that like numerals or characters indicate like elements. Further, when referring to catheters, delivery devices, and loaded fasteners described below, the proximal end is the end nearest the operator and the distal end is farthest from the operator. 
         [0026]    The invention generally involves a method of incorporating one or more stent and/or anchor structures into a polymeric membrane, which can be formed, for example, through known electrospinning or dip coating techniques. The stent or stents or at least a portion thereof are integrally incorporated into a material, which can be referred to as a substrate, and the integrated construction partially or wholly encapsulated (e.g., in a polymer such as polyurethane) by known electrospinning or dip coating techniques. 
         [0027]    According to one embodiment, the substrate material can be loose textile mesh constructed from an open weave, knit, or braid. The textile mesh should be sufficiently open to easily allow the polymer to flow through it during the electrospinning or dip coating process. In the case of wire stents, incorporating or integrating the stent into the substrate material can be accomplished by passing an end of the stent wire back and forth through mesh in an annular direction and then crimping the free ends of the wire together to form an annular stent element. All of the wire need not be weaved in and out of the mesh as will be described in more detail below. Other methods of integrating the stent and mesh material include weaving or knitting the mesh around the entire stent or at least a portion of the stent. The integrated stent-substrate construction is then encapsulated or coated using, for example, a known stent electrospinning or dip coating process, to form the polymeric membrane stent cover. The stent cover provides a fluid barrier that is suitable as for use as a graft in a lumen in a human patient. Typically the cover will provide a continuous blood impervious surface suitable for use in an artery in a human patient. 
         [0028]    One of the many advantages of this construction is that if the stent becomes completely delaminated from the polymeric membrane formed with the foregoing process, it remains attached by the polymer mesh (polymer mesh is a loose weave, braid, or knit. Further, the substrate or mesh can better distribute the load of the stent through the membrane as compared to a stent without such a substrate. The polymeric material also can be selected to improve the bonding or adhesion between the stent-substrate and the polymeric material. 
         [0029]    The mesh substrate has a loose construction suitable for weaving the stent wire in and out of the substrate. It can be a very open weave, knit or braid. Knitted meshes typically offer more flexibility and weaves typically offer more dimensional stability. The substrate mesh can be made from a variety of materials including polyester, UHMWPE, liquid crystal polymers, and Kevlar. 
         [0030]    Referring to  FIG. 3A , a covered stent according to one embodiment of the invention is shown in cut away view so that the substrate can be seen. In the illustrative example, covered stent  200  is shown with three stents  202   a ,  202   b  and  202   c . It should be understood, however, that more or fewer stents can be used. The stents are shown with undulating annular configurations where each undulation has two leg portions which converge at an apex. The number of undulations can vary depending on the size of the stent and the application and in this example there are four undulations where two are hidden from view. In this embodiment, one of each of the two leg portions (of the undulating stent) is interwoven into the material and the other is not woven into the material and is adjacent to the inner surface or outer surface of mesh substrate  206 .  FIG. 3A  depicts descending legs  208   a  and  208   b  interwoven in mesh substrate  206  in which appears as dashed lines, while ascending legs  209   a  and  209   b  are shown positioned along the outer surface of the substrate. The other undulating portions are similarly integrated with mesh substrate  206 , but hidden from view. Thus, every other leg is interwoven into the substrate when moving in an annular or circumferential direction as diagrammatically shown in FIG.  3 B 1 . In the variation shown in  FIG. 3C , an oppositely configured pattern is used. Legs  209   a ,  209   b , and  209   c  are interwoven into mesh substrate  206 , while legs  208   a ,  208   b ,  208   c  are outside the mesh substrate prior to electrospinning or dip coating (the remaining legs forming the annular stent are hidden from view. In the variation shown in  FIG. 3D , all legs of each undulation are interwoven into the mesh substrate before electrospinning or dip coating (five legs are shown in this figure with the remaining legs forming the annular stent being hidden from view). 
         [0031]    Referring to FIG.  3 B 2 , a sectional view of a portion of stent  200  is shown depicting stent wire  202   c  between two layers of polymeric material  204  on opposite sides of the mesh substrate. A noted above, the mesh substrate is sufficiently open so as to allow the polymer to pass therethrough during the electrospinning or dip coating process. 
         [0032]    Referring to  FIG. 4 , another embodiment is shown where undulating bare spring wire  510  is integrated with mesh substrate  506  before electrospinning or dip coating. The apex portions at one end of the bare spring are interwoven in mesh substrate  506 . The apex portions are shown encircled and numbered  512   a ,  512   b , and  512   c . Stent elements can be provided as described in any of the embodiments disclosed herein. 
         [0033]    Referring to  FIGS. 5A and 5B , integration of an anchor into a covered stent will be described.  FIG. 5A  depicts a known stent-graft anchor  600  having a barb support member or cage  602  with a plurality of barbs  604   a,b,c,d  extending from or secured to end portions along one side thereof. Wires or posts  606   a,b,c,d  having eyelets or loops  608   a,b,c,d  at their free ends extend from or are attached to the other side of the cage. Referring to  FIG. 5B , the anchor is secured to covered stent  650  having one or more stents  652  integrated therein using a substrate as described above. The anchor is secured to the substrate with a plurality of high strength filaments  654   a,b . . . n  that are looped through eyelets  608   a,b . . . n . The filaments, each of which can be a high strength fiber, are interwoven in the substrate along a portion of the length of the substrate such as shown in detail in  FIG. 6  before the stent, substrate and eyelets are encapsulated in a polymer by way of, for example, an electrospinning or dip coating process to provide a tubular covered stent that is impervious to blood flow through the tubular cover. The substrate can run the entire length of the covered stent in this embodiment or any other embodiment described herein and the filaments can be interwoven along the entire length of the substrate to maximize filament incorporation or integration with the cover or polymeric membrane  656 , which can comprise, for example, any of the materials described above. However, the substrate need not run the entire length of the covered stent and the filaments need not extend the entire length of the substrate. In another embodiment, the free ends of the filament can be adhered, tied otherwise secured to the substrate. Anchor  600  and the bare springs described below typically are attached to the proximal end of the covered stent, which is the end closest to the heart by reference to blood flow path when the covered stent is positioned in situ. 
         [0034]    Referring to  FIG. 6 , another covered stent embodiment  700  is shown where a bare coil spring  750  with posts  752   a,b,c . . . n  extending therefrom and including eyelets  754   a,b,c . . . n  is secured to the covered stent in the same manner as anchor  600  is secured to covered stent  650 . Each of a plurality of high strength filaments  756   a,b . . . n , each of which can be a high strength fiber, are passed through a respective eyelet and interwoven in the mesh substrate that extends the entire length and the entire circumference of the covered stent. Covered stent  700  is shown in partial section with a portion of polymeric layer or cover  757  removed to show a portion of substrate  758  in an enlarged manner to illustrate filament  756   b  interwoven therein. Substrate  758  has a plurality of interwoven threads that can be interlaced like the warp and weft of a woven fabric. It should be understood that mesh patterns in all of the embodiments described herein are interchangeable and further that other patterns can be used as the illustrative embodiments are provided for the purposes of example and not to limit the scope of possible options. Covered stent  700  also includes one or more stents  780  which can have the same configuration as stents  202   a - c  and can be interwoven into mesh substrate  758  in the same manner as stents  202   a - c  are interwoven into braid-type mesh substrate  206 . 
         [0035]    Referring to  FIG. 7 , another covered embodiment  800 , which is the same as covered stent  700  with the exception that the securing filament pattern differs. Bare spring  850  can have the same construction as bare spring  750  with eyelets  854   a,b,c . . . n  through which high strength filaments  856   a,b,c . . . n  are passed. Filaments  856   a,b,c . . . n  are interwoven in substrate  858 , which can have the same construction as substrate  758  or any other suitable substrate. Covered stent  800  is shown in partial section with a portion of polymeric layer or cover  857  removed to show a portion of substrate  858  in an enlarged manner to illustrate filaments  856   a  and  856   c  interwoven therein. In the illustrative embodiment, each filament has one portion that extends in a clockwise helical direction and another portion that extends in a counterclockwise helical direction. The filaments in this embodiment can improve load distribution from the eyelets. Although not shown, covered stent  800  also includes one or more stents, which can have the same configuration as stents  202   a - c  and can be interwoven into mesh substrate  858  in the same manner as stents  202   a - c  are interwoven into braid-type mesh substrate  206 . 
         [0036]    Referring to  FIGS. 8A and 8B , another covered stent embodiment  900  according to the invention is shown, where  FIG. 8A  illustrates an anchor and attachment component of covered stent  900  and  FIG. 8B  illustrates the anchor and attachment component integrally formed in the covered stent using electrospinning or dip coating techniques. Referring to  FIG. 8A , bare spring  950  has the same construction as bare spring  750  and includes eyelets  954   a,b,c . . . n  through which a single high strength filament  956  is passed. Filament  956 , which can be a high strength fiber, is interwoven in annular substrate  958 , which can have the same construction as substrate  758  or any other suitable substrate. Annular substrate  958  can then be coupled to a tubular substrate such as substrate  206 . Covered stent  800  also includes one or more stents  980 , which can have the same configuration as stents  202   a - c  and can be interwoven into the mesh substrate to which substrate  958  is coupled in the same manner as stents  202   a - c  are interwoven into braid-type mesh substrate  206 . The stent, bare spring, and substrate assembly is then encapsulated with a polymer using any suitable process such as electrospinning or dip coating. 
         [0037]    Although not shown, any of the covered stents described herein can have a bifurcated configuration suitable for treating abdominal aortic aneurysms. 
         [0038]    Any feature described in any one embodiment described herein can be combined with any other feature or features of any of the other embodiments or features described herein. Furthermore, variations and modifications of the devices and methods disclosed herein will be readily apparent to persons skilled in the art.