Abstract:
Methods and devices are disclosed for supporting and holding open a tubular structure in the body of an animal or human. In one form, the device is a manually adjustable variable outside diameter stent that can be repositioned or removed. The stent includes an elastic tubular body and an adjustment mechanism for the moving two ends of the body toward or away from each other. The elastic tubular body comprises a braiding of two groups of spaced apart helically wound elastic strands. The adjustment mechanism includes a bracket, a tension adjustor, and a tensioning wire attached to the bracket and the tension adjuster. The bracket and the tension adjuster are attached to one or more of the elastic strands of the two groups. Using the adjustment mechanism, the distance between the bracket and the tension adjustor can be decreased causing the outside diameter of the body to increase, or vice versa.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application represents the national stage entry of PCT International Application No. PCT/US2011/051733 filed on Sep. 15, 2011, and claims priority from U.S. Provisional Patent Application No. 61/383,587 filed Sep. 16, 2010. The disclosure of each of these applications is hereby incorporated by reference as if set forth in their entirety herein. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to methods and devices for supporting and holding open a tubular structure in the body of an animal or human. In particular, the invention relates to a stent that can be repositioned or removed once deployed. 
     2. Description of the Related Art 
     A stent is a device that can be placed within a body lumen for supporting and holding open a tubular structure in the body of an animal or human. In one common application, a stent is used for holding open a blood vessel. However, a stent can be used inside the lumen of any physiological conduit including arteries, veins, vessels, the biliary tree, the urinary tract, the alimentary tract, the tracheal bronchial tree, the genitourinary system, and the cerebral aqueduct. 
     Stents are generally tubular in structure and are radially expandable between an unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded insertion diameter. A stent is passed through the tubular structure in the body when collapsed, and then the stent will expand or can be expanded to its expanded implantation diameter after the implantation location has been reached. 
     Stents are generally categorized as being self-expanding, i.e., the stent expands by itself, or balloon expandable, i.e., the stent is expanded by a balloon inserted inside the stent. In one method for deploying a self-expanding stent, the stent is restrained within a sheath. After positioning of the self-expanding stent and sheath at the desired location in the lumen, the physician retracts the sheath to expose the stent and allow the stent to self-expand. In one method for deploying a balloon expandable stent, a delivery catheter assembly with an expandable balloon is used to deliver the stent. The stent is mounted on the balloon and the catheter assembly is pushed into the implantation site. Then, the balloon is inflated, radially applying a force inside the stent, and the stent is expanded to its expanded implantation diameter. 
     One problem with known stents is that they can be difficult to reposition or remove once deployed. Once a conventional stent is positioned in a particular tubular structure in the body and expanded in place, the stent cannot be reduced in diameter for repositioning or removal. 
     Thus, there exists a need for an improved stent that has an adjustable outside diameter such that the stent can be repositioned in, or removed from, a tubular structure in the body. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the foregoing needs by providing a stent that has an adjustable outside diameter such that the stent can be repositioned in, or removed from, a tubular structure in the body. The stent includes an elastic tubular body and an adjustment mechanism for the moving the first end of the body toward or away from the second end of the body such that the outside diameter of the body increases when the first end of the body is moved towards the second end of the body, and such that the outside diameter of the body decreases when the first end of the body moves away from the second end of the body. 
     The elastic tubular body comprises a braiding of a first group of spaced apart helically wound first elastic strands and a second group of spaced apart helically wound second elastic strands. The adjustment mechanism includes a bracket, a tension adjustor, and a tensioning wire attached to the bracket and the tension adjustor such that the bracket and the tension adjustor are in spaced apart relationship. The bracket and the tension adjustor are attached to one or more of the first elastic strands and the second elastic strands. Using the adjustment mechanism, the distance between the bracket and the tension adjustor can be decreased causing the outside diameter of the body to increase, or the distance between the bracket and the tension adjustor can be increased causing the outside diameter of the body to decrease. 
     The tension adjustor can include a housing having a hole with internal threads that mate with an external threaded section of the tensioning wire, and the distance between the bracket and the tension adjustor can be varied by rotating the tensioning wire with respect to the hole. A distal end of the tensioning wire can be rotatably attached to the bracket. A proximal end of the tensioning wire can terminate in an enlarged head that is located within an interior space of the housing. The enlarged head of the tensioning wire can be structured to be engageable with a tool. The housing can include an opening, and the stent can further include a movable cover attached to the housing. The cover can include a first position in which the opening is closed off and a second position providing access to the end of the tensioning wire. 
     The stent can include a guide ring surrounding the tensioning wire. The guide ring can be attached to at least one of the first elastic strands and the second elastic strands, and the guide ring can be located between the bracket and the tension adjustor. The tensioning wire and the guide ring can contact at a bearing surface. 
     The bracket can be attached at an intersection of at least one of the first elastic strands and at least one of the second elastic strands, and the tension adjustor can be attached at an intersection of at least one of the first elastic strands and at least one of the second elastic strands. The first end of the body can be circumferential and the bracket can be attached to at least one of the first elastic strands and the second elastic strands comprising the first end of the body. The second end of the body can be circumferential and the tension adjustor can be attached to at least one of the first elastic strands and the second elastic strands comprising the second end of the body. 
     The stent can further include a second adjustment mechanism for the moving a first section of the body toward or away from the second section of the body. The second adjustment mechanism can include a second bracket, a second tension adjustor, and a second tensioning wire attached to the second bracket and the second tension adjustor such that the second bracket and the second tension adjustor are in spaced apart relationship. The second bracket can be attached to at least one of the first elastic strands and the second elastic strands, and the second tension adjustor can be attached to at least one of the first elastic strands and the second elastic strands. A distance between the second bracket and the second tension adjustor can be varied to move the first section of the body towards the second section of the body or to move the first section of the body away from the second section of the body. 
     In one form, the stent is a self-expanding stent. In another form, the stent is a balloon expandable stent. 
     In another aspect, the invention includes a tool for varying the distance between the bracket and the tension adjustor. After a stent is deployed to engage the inner surface of the tubular structure in the animal or human, the tool can be used to operate the tension adjustor to increase the distance between the bracket and the tension adjustor to move the first end of the body away from the second end of the body such that the outside diameter of the body decreases and disengages from the inner surface of the tubular structure in the animal or human. The stent can then be repositioned in a second location in the tubular structure, or removed from the tubular structure. 
     The tension adjustor can include a housing having a hole with internal threads that mate with an external threaded section of the tensioning wire, and the distance between the bracket and the tension adjustor can be varied by engaging the tensioning wire with the tool and rotating the tensioning wire with respect to the hole. A proximal end of the tensioning wire can terminate in an enlarged head that is located within an interior space of the housing, and the enlarged head of the tensioning wire can be structured to be engageable with a distal end of the tool. 
     The tool can include a cable suitable for insertion into the tubular structure in the animal or human, wherein the cable terminates in a tip for engaging the enlarged head of the tensioning wire. The tool can further include a sheath including a passageway having a distal opening, wherein the passageway is dimensioned for insertion of the cable such that the tip of the cable can protrude beyond the distal opening of the passageway. 
     In yet another aspect, the invention provides a method for positioning a stent in a tubular structure in an animal or human. The stent can include an elastic tubular body having a first end and an opposite second end and an outside diameter. The body can include a braiding of a first group of spaced apart helically wound first elastic strands and a second group of spaced apart helically wound second elastic strands such that the outside diameter of the body increases when the first end of the body is moved towards the second end of the body, and such that the outside diameter of the body decreases when the first end of the body moves away from the second end of the body. The stent can further include an adjustment mechanism for the moving the first end of the body toward or away from the second end of the body. The adjustment mechanism can include a bracket, a tension adjustor, and a tensioning wire attached to the bracket and the tension adjustor such that the bracket and the tension adjustor are in spaced apart relationship. The bracket can be attached to at least one of the first elastic strands and the second elastic strands, and the tension adjustor can be attached to at least one of the first elastic strands and the second elastic strands. The stent is positioned in the tubular structure in the animal or human, and the outside diameter of the body is caused to engage an inner surface of the tubular structure in the animal or human. 
     The tension adjustor can be used to decrease a distance between the bracket and the tension adjustor to move the first end of the body towards the second end of the body such that the outside diameter of the body increases and engages the inner surface of the tubular structure in the animal or human. The tension adjustor can be used to increase a distance between the bracket and the tension adjustor to move the first end of the body away from the second end of the body such that the outside diameter of the body decreases and disengages from the inner surface of the tubular structure in the animal or human. The stent can be repositioned in a second location in the tubular structure in the animal or human, and the outside diameter of the body can be caused to engage the inner surface of the tubular structure in the animal or human at the second location. Alternatively, the stent can be removed from the tubular structure in the animal or human after disengaging the stent from the inner surface of the tubular structure in the animal or human. 
     The stent can be caused to engage an inner surface of the tubular structure in the animal or human by restraining a self-expanding stent in a sheath and retracting the sheath such that the outside diameter of the body increases and engages the inner surface of the tubular structure in the animal or human. 
     The stent can be caused to engage an inner surface of the tubular structure in the animal or human by mounting a balloon expandable stent on a balloon and inflating the balloon such that the outside diameter of the body increases and engages the inner surface of the tubular structure in the animal or human. 
     These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings, and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of a stent according to the invention. 
         FIG. 2  is a side view of the stent of  FIG. 1  in one unexpanded state. 
         FIG. 3  is a side view of the stent of  FIG. 1  in one expanded state. 
         FIG. 4  is a side view of an adjustment mechanism of the stent of  FIG. 1  shown partially in cross-section. 
         FIG. 5  is a detailed side view of a tension adjuster of the adjustment mechanism and a complementary tensioning tool of the stent of  FIG. 1  shown partially in cross-section. 
     
    
    
     Like reference numerals will be used to refer to like parts from Figure to Figure in the following description of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Looking first at  FIG. 1 , there is shown an example embodiment of a stent  10  according to the invention. The stent  10  includes an elastic tubular body  12  having a first circumferential end  14  and an opposite second circumferential end  16 . The body is formed from a braiding of (i) a first group of spaced apart helically wound first elastic strands  17   a ,  17   b ,  17   c ,  17   d  to  17   m  where m varies depending on the desired spacing between the first elastic strands and the desired axial length of the body  12  and (ii) a second group of spaced apart helically wound second elastic strands  19   a ,  19   b ,  19   c ,  19   d  to  19   n  where n varies depending on the desired spacing between the second elastic strands and the desired axial length of the body  12 . In the braiding, each strand can pass over one strand and then under the adjacent strand wound in the same direction. 
     The first elastic strands  17   a ,  17   b ,  17   c ,  17   d  to  17   m  and the second elastic strands  19   a ,  19   b ,  19   c ,  19   d  to  19   n  are helically wound with respect to a longitudinal axis defined by the tubular body  12  to create a braided configuration. The first elastic strands  17   a ,  17   b ,  17   c ,  17   d  to  17   m  and the second elastic strands  19   a ,  19   b ,  19   c ,  19   d  to  19   n  are helically wound in opposite directions to create intersections (such as  21   a ,  21   b ,  21   c ,  21   d ,  21   e ) of the first elastic strands  17   a ,  17   b ,  17   c ,  17   d  to  17   m  and the second elastic strands  19   a ,  19   b ,  19   c ,  19   d  to  19   n . One or more of the first elastic strands  17   a ,  17   b ,  17   c ,  17   d  to  17   m  can form the first circumferential end  14  of the body  12 , and one or more of the second elastic strands  19   a ,  19   b ,  19   c ,  19   d  to  19   n  can form the second circumferential end  16  of the body  12 . The first elastic strands  17   a ,  17   b ,  17   c ,  17   d  to  17   m  and the second elastic strands  19   a ,  19   b ,  19   c ,  19   d  to  19   n  can be formed from a metallic material or a polymeric material. Example metallic materials include cobalt and chromium alloys, stainless steel, and nickel-titanium alloys. 
     Referring to  FIGS. 1 ,  4  and  5 , the stent  10  includes an adjustment mechanism  24  for the moving the first end  14  of the body  12  toward or away from the second end  16  of the body  12  of the stent  10 . The adjustment mechanism  24  includes a bracket  26 , a tension adjustor  28  and a tensioning wire  30  that is attached to the bracket  26  and the tension adjustor  28 . Guide rings  32  surround the tensioning wire  30  between the bracket  26  and the tension adjustor  28 . In one embodiment, the bracket  26 , the tension adjustor  28 , the tensioning wire  30 , and the guide rings  32  are formed from the same material as the first elastic strands  17   a ,  17   b ,  17   c ,  17   d  to  17   m  and the second elastic strands  19   a ,  19   b ,  19   c ,  19   d  to  19   n.    
     In the embodiment of  FIGS. 1 to 5 , the bracket  26  is attached to an inner surface of the first circumferential end  14  of the body  12  using a suitable attachment method such as welding, heat sealing or gluing. The tension adjustor  28  is attached to an inner surface of the second circumferential end  16  of the body  12  using a suitable attachment method such as welding, heat sealing or gluing. The guide rings  32  are connected to an inner surface of intersections  21   f ,  21   g ,  21   h ,  21   i ,  21   j  and  21   k  using a suitable attachment method such as welding, heat sealing or gluing. 
     Referring now to  FIGS. 4 and 5 , the construction of the bracket  26 , the tension adjustor  28  and the tensioning wire  30  can be explained in more detail. The tension adjustor  28  includes a housing  34  having a hole  36  with internal threads  38  that mate with an external threaded section  42  of the tensioning wire  30 . The housing  34  includes an opening  44  that can be closed off with a hinged cover  46 . The cover  46  prevents accumulation of debris in the housing  34 . The tensioning wire  30  includes a spherical head  48  that is rotatably mounted in the bracket  26 . A proximal end of the tensioning wire  30  terminates in an enlarged head  50  that is located within an interior space  54  of the housing  34 . The enlarged head  50  of the tensioning wire  30  includes a hexagonal outer surface  52  and a socket  55 . 
     Still referring to  FIGS. 4 and 5 , the stent  10  can be supplied with a tool  56  for varying the distance between the bracket  26  and the tension adjustor  28 . The tool  56  includes a cable  58  suitable for insertion into the tubular structure in the animal or human. The cable  58  terminates in a tip  62  for engaging the enlarged head  50  of the tensioning wire  30 . In the non-limiting example embodiment shown, the tip  62  of the tool  56  has an outer wall  63  for engaging the hexagonal outer surface  52  of the enlarged head  50  of the tensioning wire  30 , and the tip  62  has a central protrusion  64  for engaging the central socket  55  of the enlarged head  50  of the tensioning wire  30 . The tip  62  of the tool  56  and/or the enlarged head  50  of the tensioning wire  30  can be formed of materials that provide magnetic attraction between the tip  62  and the head  50 . The tool  56  can be used with a sheath (not shown) that includes a passageway having a distal opening wherein the passageway is dimensioned for insertion of the cable  58  such that the tip  62  of the cable  58  can protrude beyond the distal opening of the passageway. The sheath is dimensioned for insertion into the tubular structure in the animal or human. 
     Having described the construction of the stent  10  and tool  56 , the use of the stent  10  and tool  56  can be explained. A catheter having a first passageway and a second passageway can be introduced into the tubular structure in the animal or human. The stent  10  can be grasped by an endoscopic forceps, passed through the first passageway and then out of a distal end of the first passageway in the catheter, and positioned at a desired location in the tubular structure in the animal or human. The tool  56  is then passed through the second passageway in the catheter and then out of the distal end of the second passageway in the catheter. After opening the cover  46 , the tip  62  of the tool  56  is then positioned to engage the hexagonal outer surface  52  of the enlarged head  50  of the tensioning wire  30  as shown in  FIG. 5 . In an alternative configuration of the tool, the tool is a multi-functional tool that also grasps the stent  10 . This tool would only require a single passageway in the catheter. 
     When the stent  10  is first passed through the first passageway in the catheter and positioned at a desired location in the tubular structure in the animal or human, the stent  10  can have a configuration as shown in  FIG. 2  in which the stent  10  has an axial length X and an outside diameter Y. With the tip  62  of the tool  56  engaging the hexagonal outer surface  52  of the enlarged head  50  of the tensioning wire  30  as shown in  FIG. 5 , the physician rotates the tool  56  in direction R in  FIG. 5 . Due to the engagement of the internal threads  38  of the housing  34  and the external threaded section  42  of the tensioning wire  30 , rotation in direction R causes the tensioning wire  30  to move toward the opening  44  of the housing  34 . As a result, the bracket  26  moves in direction −A and the tension adjustor  28  moves in direction +A as shown in  FIG. 3 . The guide rings  32  prevent any bowing of the tensioning wire  30  during movement of the tensioning wire  30 . 
     Because the bracket  26  is attached to an inner surface of the first circumferential end  14  of the body  12  and the tension adjustor  28  is attached to an inner surface of the second circumferential end  16  of the body  12 , the first circumferential end  14  and the second circumferential end  16  of the body  12  move toward each other. Due to the helically wound braided configuration of the first elastic strands  17   a  to  17   m  and the second elastic strands  19   a  to  19   n , movement of the first circumferential end  14  and the second circumferential end  16  of the body  12  toward each other causes the stent  10  to move in directions −B and +B into the configuration as shown in  FIG. 3  in which the stent  10  has an axial length X′ and an outside diameter Y′ (which can be compared to the configuration in which the stent  10  has an axial length X and an outside diameter Y as shown in  FIG. 2  and as shown in dashed lines in  FIG. 3 ). Note also how the outside diameter increases because the angle at the intersection of the strands decreases from α 1  in  FIG. 2  to α 2  in  FIG. 3 . The increase in outside diameter from Y to Y′ causes the outside diameter Y′ of the body  12  of the stent  10  to engage the inner surface of the tubular structure in the animal or human. The cover  46  can then be closed. 
     When repositioning or removal of the stent  10  is desired, the catheter having the first passageway and the second passageway can be introduced into the tubular structure in the animal or human. The tool  56  is then passed through the second passageway in the catheter and then out of the distal end of the second passageway in the catheter. After opening the cover  46 , the tip  62  of the tool  56  is then positioned to engage the hexagonal outer surface  52  of the enlarged head  50  of the tensioning wire  30  as shown in  FIG. 5 . With the tip  62  of the tool  56  engaging the hexagonal outer surface  52  of the enlarged head  50  of the tensioning wire  30  as shown in  FIG. 5 , the physician rotates the tool  56  in a direction opposite to direction R in  FIG. 5 . This causes the stent  10  to move back into the configuration as shown in  FIG. 2  in which the stent  10  has an axial length X and an outside diameter Y. An endoscopic forceps is passed through the first passageway and then out of a distal end of the first passageway in the catheter, and the stent can be grasped for repositioning at another desired location, or removal from the tubular structure in the animal or human. After repositioning at another desired location, the outside diameter of the stent  10  can be enlarged for engagement with the inner surface of the tubular structure in the animal or human as described above. 
     When the stent  10  is a self-expanding stent, another method can be used. The stent  10  can be restrained within a sheath, passed through a passageway in a catheter, and positioned at a desired location in the tubular structure in the animal or human. The sheath can be retracted to expose the stent  10  and allow the stent  10  to self-expand to have the configuration as shown in  FIG. 3  in which the stent  10  has an axial length X′ and an outside diameter Y′. This causes the outside diameter of the body  12  of the stent  10  to engage an inner surface of the tubular structure in the animal or human. Thereafter, the stent  10  can be repositioned or removed as desired. Specifically, stent  10  can be caused to move back into the configuration as shown in  FIG. 2  in which the stent  10  has an axial length X and an outside diameter Y and repositioned or removed as explained above. 
     When the stent  10  is a balloon expandable stent, another method can be used. A delivery catheter assembly with an expandable balloon is used. The stent  10  is mounted on the balloon and the catheter assembly is pushed into the implantation site. Then, the balloon is inflated, radially applying a force inside the stent  10 , and the stent  10  is expanded to have the configuration as shown in  FIG. 3  in which the stent  10  has an axial length X′ and an outside diameter Y′. This causes the outside diameter of the body  12  of the stent  10  to engage an inner surface of the tubular structure in the animal or human. Thereafter, the stent  10  can be repositioned or removed as desired. Specifically, stent  10  can be caused to move back into the configuration as shown in  FIG. 2  in which the stent  10  has an axial length X and an outside diameter Y and repositioned or removed as explained above. 
     Other arrangements of the bracket  26 , the tension adjustor  28 , the tensioning wire  30 , and the guide rings  32  of the stent  10  are suitable. For example, the bracket  26  and the tension adjustor  28  can be attached at any of the intersections  21 . The guide rings  32  can be omitted in certain embodiments. Also, more than one adjustment mechanism  24  including the bracket  26 , the tension adjustor  28 , and the tensioning wire  30  can be used. When using different numbers of adjustment mechanisms, one has the ability to manually adjust the outside diameter of either the whole stent or any part(s) of the stent. 
     Thus, the invention provides a manually adjustable variable outside diameter stent. The stent can be repositioned in, or removed from, a tubular structure in the body of an animal or human after being deployed. 
     Although the present invention has been described in detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.