Abstract:
A removable stent for placement within a lumen is provided. The stent includes a scaffolding of struts configured to define a substantially cylindrical member having a proximal end and a distal end. The stent also includes at least one flexible element spirally wound along at least a portion of a respective strut, wherein the element comprises at least one engageable member such that a force applied to the engageable member does not result in purse-stringing.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to stents, in particular, to a stent removal and repositioning aid that promotes removal or repositioning a stent within a lumen. 
     2) Description of Related Art 
     Stents are devices that are inserted into body lumens such as vessels or passages to keep the lumen open and prevent closure due to a stricture, external compression, or internal obstruction. In particular, stents are commonly used to keep blood vessels open in the coronary arteries and they are frequently inserted into the ureters to maintain drainage from the kidneys, the bile duct for pancreatic cancer or cholangiocarcinoma, or the airways and esophagus for strictures or cancer. Vascular as well as nonvascular stenting has evolved significantly; unfortunately there remain significant limitations with respect to the technology for positioning and removing stents following implantation into various portions of a patient&#39;s anatomy. 
     In various areas of application, e.g., bronchus, biliary, trachea, or esophagus, the stents must be removable from the body or repositionable as a function of the course of the disease or treatment. This can be problematic since newly formed tissue can grow on the support frame of the stent and even grow through it, which can result in complications when removing a stent. In this regard, stents have been developed that include a support frame surrounded on the outside by a thread or wire. The support frame can be radially constricted by pulling on the thread ends that are each provided with a loop or the like, reducing a length of the thread engaged around the stent and creating a “purse-string” effect, which makes it possible for the frame to be removed or repositioned. However, when the wire or thread is guided or braided in multiple windings around the support frame, a high degree of friction results between the two stent components, which has a disadvantageous effect on the explantation process. In addition, stents having eyelets for looping the thread therethrough may have sharp edges that cause the thread to tear or break during the removal process. 
     Alternatively, physicians have grasped the thread ends with forceps or a similar instrument to reposition or remove the stent from within the lumen. However, this can be complex at times when the tissue has grown over the suture thread. Also, the suture may not be strong enough to remove the stent. Grasping may lead to damage to the stent itself, as the forceps may have difficulty accessing or adequately gripping the thread to remove or reposition the stent. Physicians may also use grasping forceps to grab the struts of the stent at a proximal end and remove the stent from the deployment site, but this also risks damage to the lumen or the stent, as the proximal end of the stent may be difficult to access. 
     Thus, there is a need in the industry for a stent that reduces the risk of damage to the stent, thread or suture, and/or the surrounding tissue during removal or repositioning of the stent. In addition, there is a need for a stent that provides for greater accessibility, as well as promotes effective repositioning and/or removal of the stent from a lumen. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  is a plan view of a stent having an interstice geometry, according to one embodiment of the present invention; 
         FIG. 2  is an end view of the stent shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of a stent including a plurality of sutures and illustrating each suture arranged throughout interstices of the stent, according to one embodiment of the present invention; 
         FIG. 4  is a perspective view of a stent including at least one suture and illustrating the suture arranged throughout interstices of the stent, according to another embodiment of the present invention; 
         FIG. 5  an enlarged perspective view of a suture arranged along the interstices of the stent shown in  FIGS. 3-4 , according to one embodiment of the present invention; and 
         FIG. 6  is a partial perspective view of a stent including a plurality of suture loops and a suture extending therethrough, according to yet another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. 
     With reference to  FIGS. 1-2 , a stent  10  is shown having interstice geometry. The stent  10  includes a scaffolding of struts. The struts generally include a plurality of interconnected legs  12  and connectors  14 . As shown in  FIG. 1 , the stent  10  includes a series of legs  12  arranged circumferentially about the stent, as well as arranged in rows along the longitudinal axis of the stent, while a plurality of connectors  14  are arranged parallel to the longitudinal axis of the stent to connect the rows together. The stent  10  is formed of a memory metal that facilitates flexibility of the stent  10  such that the stent may be deformed and return to its original shape. As such, the legs  12  and connectors  14  of the stent  10  are preferably formed from a composite material such as Ni, C, Co, Cu, Cr, H, Fe, Nb, O, Ti and combinations thereof (e.g., Nitinol). The composite material is generally formed into a compressed tube from which the stent is etched and is formed on a suitable shaping device to give the stent the desired external geometry. 
     The stent  10  is generally cylindrical, having openings at the proximal and distal ends. As illustrated in  FIG. 1 , the diameter of the proximal and distal ends is slightly larger than the diameter of longitudinal portion of the stent extending therebetween. In the event the stent is to be shaped to the dimensions of a particular lumen, optical photography and/or optical videography of the target lumen may be conducted prior to stent formation. The interstice geometry of the stent then can be etched and formed in accordance with the requirements of that target lumen. For example, if the stent  10  were designed for the trachea, which has a substantially D shaped lumen and additionally the middle portion of the stent is preferably softer than the proximal or distal ends, the stent could be designed to those specifications. In particular, if the topography of the trachea of a particular patient is captured optically and the appropriate dimension provided, a patient specific prosthesis could be engineered. These techniques can be adapted to other non-vascular lumina but is very well suited for vascular applications where patient specific topography is a function of a variety of factors such as genetics, lifestyle, etc. 
     It should be pointed out that, unlike the use of differing shape memory materials to change regions of a stent  10 , stents in accordance with the present invention can take on an infinite number of characteristic combinations of interstice geometry by changing angles, segment lengths, and segment thicknesses during the etching and forming stages of stent engineering or during post formation processing and polishing steps. Moreover, by modifying the geometry of the connectors  14 , additional functionality may be achieved. 
     The stent could also include a cover, typically a polymer such as polyurethanes (e.g., polycarbonate urethane, or Chronoflex® manufactured by Cardiotech International), that is applied between the legs  12  and connectors  14  to provide a predetermined shape for the stent  10 , as well as graft each of the legs and connectors into a unitary structure. The cover does not inhibit flexing or radial expansion of the stent  10 , although it is possible to design the cover so that it controls the physical properties of the stent. 
     The suture  16  may be any suitable suture material, as known to those skilled in the art, such as polypropylene. However, it is understood that the term “suture” as used herein could be any suitable thread or wire or other material having a preferably flexible, but possibly inflexible, elongate shape, as known to those skilled in the art, capable of transferring force from forceps or a similar instrument to the stent  10  in alternative embodiments of the present invention. 
     Therefore, it is understood that any number of configurations of stents  10  could be incorporated and still be within the present scope of the invention. An exemplary embodiment of the interstice geometry of a stent  10  is disclosed in U.S. Patent Publication No. 20040127973 (application Ser. No. 10/674,972), entitled “Removable Biliary Stent,” which is assigned to the present assignee and is incorporated herein by reference. Thus, the interstice geometry of the stent  10  should not be limited to that depicted in the disclosed Figures, as any number of configurations of interstice geometry could be employed with the present invention to achieve various degrees of rigidity and functionality. U.S. Patent Publication No. 20040122511 (application Ser. No. 10/669,450) entitled “Coated Stent with Geometry Determined Functionality and Method of Making the Same,” which is assigned to the present assignee, is also incorporated herein by reference, and further describes a cover that may be employed with the present invention, including the types of materials and properties suitable for the cover, as well as the process of manufacturing the stent  10 . 
       FIG. 3  illustrates a suture  16  intertwined about the legs  12  and connectors  14  of the stent  10 . The suture  16  preferably defines a plurality of loops  18  located proximate to, and circumferentially about, at least one opening of the stent  10 . However, in alternative embodiments there may be strands of suture  16  extending from the proximal and distal ends instead of loops  18  and, for example, the free end of the suture could have a knot that allows forceps or a similar instrument to grasp the end of the suture. The suture  16  typically extends along the longitudinal axis of the stent  10  from the proximal and/or distal end of the stent and stops three to four leg  12  segments along the connectors  14 . However, the suture  16  could extend along the entire longitudinal axis of the stent  10  from the proximal to distal end or could extend any number or leg  12  segments along a respective connector  14 . Each loop  18  is sized and configured to receive forceps or a similar instrument, and at least a portion of the remaining suture  16  opposite that of the loop is attached to the legs  12  and/or connectors  14  to prevent the suture from coming loose or completely disengaged from the stent  10 . Each loop  18  is attached to the stent  10  such that a force applied through the suture  16  transfers force through the loops and to the stent. The suture  16  could include, for example, a knot that secures the suture to the stent, but an adhesive, a fastener, or similar technique could also be used that is capable of effectively transferring force. In addition, the suture  16  could also be held in place on the stent  10  by a cover and struts on a covered stent. For instance, the suture  16  could be formed integral with the cover and struts of the stent  10  such that knots and the like would not be required. 
     Therefore, when forceps or a similar instrument pulls on one or more of the loops  18  at the proximal end of the stent  10 , the stent is urged in the direction of pulling such that the stent may be repositioned within a lumen or completely removed. Moreover, the forceps could also be positioned through the axis of the stent  10  and through one or more loops to push the stent at the distal end of the stent, such that the stent is pushed to a different position or removed from the lumen. In this regard, pulling or pushing on the loops  18  does not create a purse-string effect and consequently, the expanded diameter of the stent  10  is unlikely to change during repositioning or explantation. Eliminating the purse-string effect reduces the risk of re-expansion failure, such as by plastic deformation of the stent, when the stent  10  is repositioned within the lumen. 
       FIG. 4  illustrates an alternative embodiment, wherein the suture  16  is arranged in a single loop, with the ends of the loop connected with a knot  20 . The loop extends from the proximal and/or distal end of the stent  10 , along one or more connectors  14 , along a series of legs  12 , and along one or more additional connectors. The loop could be arranged about any number of legs  12  and connectors  14 , and even along the entire longitudinal axis from the proximal to the distal end of the stent. In addition, there could be any number of loops about the circumference of the stent in alternative embodiments. The loop of suture  16  is typically intertwined about at least a portion of the legs  12  and connectors  14  and secured with a knot or similar fastening technique such that application of a force on the suture transfers the force to the stent  10 . However, as described above, the suture  16  could also be held in place on the stent  10  by a cover and struts on a covered stent. For instance, the suture  16  could be formed integral with the cover and struts of the stent  10  such that knots and the like would not be required. As before with respect to  FIG. 3 , in alternative embodiments there may be strands of suture  16  extending from the proximal and distal ends instead of forming a loop  18  and, for example, the free ends of the suture could each have a knot that allows forceps or a similar instrument to grasp one or both ends of the suture. 
     Like the stent  10  shown in  FIG. 3 , the stent depicted in  FIG. 4  also does not create a purse-string effect. Thus, when forceps or a similar instrument pulls on one or more of the loops  16  at the proximal end of the stent  10 , the stent is also pulled such that the stent may be repositioned within the lumen or completely removed without changing the expanded diameter of the stent. Similarly, the forceps could be positioned through the longitudinal axis of the stent  10  to engage a loop of suture  16  at the distal end of the stent to push the stent to a different position or to remove the stent from the lumen. 
       FIG. 5  illustrates that the suture  16  is preferably arranged about the connectors  14  in a spiral-like configuration. Arranging the suture  16  in a spiral-like configuration distributes the force along each connector  14  when forceps or a similar instrument pulls upwardly or pushes downwardly on each loop  18  shown in  FIGS. 3 and 4 . Therefore, the spiral-like configuration reduces the risk that the suture  16  will break or become dislodged during repositioning or removal of the stent  10 . It is understood that the suture  16  could be arranged about the legs  12  and/or connectors  14  in the configuration shown in  FIG. 5 , but is not required to have this particular configuration, as there may be alternative configurations in additional embodiments. In addition, the suture  16  in  FIG. 5  is shown as being loosely arranged about the connector  14  for illustrative purposes only, as the suture will typically be in more intimate contact with the scaffolding of the stent  10  or tightly wound about the connector. 
     In an additional embodiment of the present invention,  FIG. 6  depicts a stent  10  having a series of loops  18  arranged about the circumference of the stent at the proximal and/or distal end. The loops  18  are preferably a suture material, and there may be any number of loops about the circumference of the stent  10 . The stent  10  also includes a loop of suture  16  that extends about the circumference of the loop, through the loops  18 , and connects to itself with a knot  20 . The loops  18  could be connected to the stent  10  in the manner described above in conjunction with  FIGS. 3-5 , or the loops could be attached to the outer periphery of the proximal and/or distal end of the stent. Furthermore, the loops  18  could be a single piece of suture circumferentially disposed about the proximal and/or distal end of the stent  10 , or one or more loops could be a single suture. The loops  18  are attached to the stent  10  such that a force applied through the suture  16  transfers force through the loops and to the stent. 
     Unlike the embodiments shown in  FIGS. 3 and 4 , the stent  10  shown in  FIG. 6  creates a purse string effect. As such, pulling or pushing on the suture  16  with forceps or a similar instrument causes the proximal and/or distal end of the stent  10  to purse string. Thus, forceps or a similar instrument could be used to purse string the proximal end of the stent  10  by pulling on the suture  16 , while pushing on the suture at the distal end of the stent will cause the distal end to purse string. Purse stringing the suture  16  crimps the proximal or distal end of the stent  10  to promote repositioning or removal of the stent from the lumen. Once the suture  16  is released, the proximal or distal end of the stent  10  will expand. 
     The present invention provides several advantages. Providing one or more loops from a suture material allows forceps or a similar instrument to engage the loops rather than the stent  10  itself. Therefore, the embodiments of the present invention facilitate easier removal or repositioning of the stent  10  without increasing the likelihood of damage to the stent and/or the lumen. Furthermore, the suture is arranged about the stent  10  to distribute the forces applied during repositioning or removal of the stent, which reduces the risk that the suture and/or stent will be damaged or dislodged. 
     Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.