Patent Publication Number: US-2013231752-A1

Title: Endoluminal prosthesis with actuating member

Description:
TECHNICAL FIELD 
     This disclosure relates generally to medical devices. More specifically, this disclosure relates to drainage devices such as ureteral stents useful for urinary drainage. 
     BACKGROUND 
     Indwelling ureteral stents are in common use today. These stents are placed in the ureter, which is the duct between the kidney and the bladder, for establishing and/or maintaining an open, patent passageway for the flow of urine from the kidney to the bladder. The predominate indications for placing a ureteral stent include extrinsic compression, ureteral injury due to trauma, obstructive uropathy, and following surgery in the upper or lower urinary tract. Generally, the stent includes a flexible material having sufficient resiliency to allow the stent to be straightened for insertion into the ureter, while having sufficient memory to return to a predetermined retentive shape when in situ. 
     Indwelling ureteral stents may be positioned in the ureter by one of a variety of procedures including, antegrade (percutaneous) placement, retrograde (cystoscopic) placement through the urethra, placement by open ureterotomy, or surgical placement in the ureter under direct visual placement. Ureteral stent positioning may be accomplished by several methods. In one method, a wire guide is introduced into the ureteral orifice in the bladder via a cystourethroscope under direct vision. The wire guide is advanced up the ureter until the advancing flexible tip of the guide is confirmed by x-ray or fluoroscopy to be in the renal pelvis of the kidney. A tubular stent with both ends open is fed into the exposed external segment of the wire guide and advanced over the wire guide by hand until a short segment of the stent is visible outside the cystourethroscope. A positioner, pusher catheter, or length of tubing is then fed into the exposed external end of the wire guide and advanced over the wire guide by hand until it abuts the stent. With the wire guide held stationary, the positioner is advanced over the wire guide to push the tubular stent up the ureter to the renal pelvis. With the distal end of the stent in the renal pelvis, the positioner is held stationary while the wire guide is gradually extracted from the stent and the positioner. As the wire guide leaves the distal end of the tubular stent, a retentive means at the distal end of the stent is formed to retain the stent in the pelvis of the kidney. As the wire guide is withdrawn past the proximal end of the stent, a retentive hook or curve at the proximal end is formed so that the stent is retained within the bladder. At this point, the positioner and wire guide are completely withdrawn leaving only the stent indwelling in the kidney, the ureter, and the bladder. 
     In another method of ureteral stent placement, a ureteral stent having one tip closed is backloaded into the wire guide. In this “pushup” method, the tip of the wire guide contacts the closed tip of the ureteral stent, which is then introduced into the ureteral orifice in the bladder via a cystourethroscope under direct vision. The stent is advanced up the ureter until the tip of the stent lies within the renal pelvis. A positioner catheter or length of tubing is fed into the external end of the wire guide and advanced over the wire guide by hand until it abuts the open end of the stent. The positioner is held in place while removing the wire guide to leave the stent positioned within the ureter. 
     In some cases, the ureteral stent may be associated with pain or discomfort for the patient. For example, such pain or discomfort may be caused by a failure of the stent to conform to the patient&#39;s ureteral anatomy. This pain or discomfort may be exacerbated by physical movement, respiration, or bladder contractions and expansions of the patient. 
     SUMMARY 
     The present embodiments provide a drainage device such as a ureteral stent useful for urinary drainage. 
     In one example, a non-expandable endoluminal prosthesis for implantation within a body lumen may include an elongate tubular conduit. The tubular conduit may have a first end segment and a second end segment. A drainage lumen may extend longitudinally within the tubular conduit. An actuating lumen may extend longitudinally within the tubular conduit. The prosthesis may include an actuating member received within the actuating lumen. The endoluminal prosthesis may be movable between a delivery configuration in which the tubular conduit is substantially linear and a deployed configuration in which at least one of the first end segment and the second end segment includes a retaining mechanism configured to retain the prosthesis in place relative to the body lumen. The actuating member may be configured to urge the prosthesis toward the deployed configuration. 
     In another example, a system may include a non-expandable endoluminal prosthesis for implantation within a body lumen and a guide wire. The prosthesis may include an elongate tubular conduit. The tubular conduit may have an end segment. A drainage lumen may extend longitudinally within the tubular conduit. An actuating lumen may extend longitudinally within the tubular conduit. The prosthesis may include an actuating member received within the actuating lumen. The actuating member may be movable between a relaxed condition in which a longitudinal axis of the actuating member is substantially non-linear and a strained condition in which the longitudinal axis of the actuating member is substantially linear. The guide wire may be receivable within the drainage lumen of the prosthesis. With the guide wire received within a portion of the drainage lumen corresponding to the end segment of the tubular conduit, the actuating member may be in the strained condition. Upon removal of the guide wire from the portion of the drainage lumen corresponding to the end segment, the actuating member may move to the relaxed condition to form a retaining mechanism in the end segment of the tubular conduit. 
     In another example, a method of implanting an endoluminal prosthesis within a body lumen may include introducing the endoluminal prosthesis in a delivery configuration into the body lumen over a wire guide. The endoluminal prosthesis may include an elongate tubular conduit having a first end segment and a second end segment. A drainage lumen may extend longitudinally within the tubular conduit. An actuating lumen may extend longitudinally within the tubular conduit. An actuating member may be received within the actuating lumen. The method may include removing the wire guide from the first end segment of the tubular conduit to enable at least a first portion of the actuating member corresponding to the first end segment to move to a relaxed configuration to form a first retaining mechanism in the first end segment of the tubular conduit. The method may include removing the wire guide from the second end segment of the tubular conduit to enable at least a second portion of the actuating member corresponding to the second end segment to move to the relaxed configuration to form a second retaining mechanism in the second end segment of the tubular conduit. 
     Other systems, methods, features, and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems; methods, features, and advantages be within the scope of the invention, and be encompassed by the following claims. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1  illustrates one embodiment of a drainage device configured as a ureteral stent. 
         FIG. 1A  is a close-up view of a distal end segment of the drainage device of  FIG. 1 . 
         FIG. 1C  is a transverse cross sectional view of a distal end segment of the drainage device of  FIG. 1 . 
         FIG. 2  illustrates another embodiment of a drainage device configured as a ureteral stent. 
         FIG. 2B  is a close-up view of a distal end segment of the drainage device of  FIG. 2 . 
         FIG. 3  illustrates a drainage device in a delivery configuration on a wire guide. 
         FIG. 4A  illustrates a illustrates the introduction of a drainage device into a ureter of a patient. 
         FIG. 4B  illustrates a drainage device indwelling within a ureter of a patient. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED EMBODIMENTS 
     Detailed embodiments of the present invention are disclosed herein. It is understood, however, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various and alternative forms. The figures are not necessarily to scale, and some figures may be configured to show the details of a particular component. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for the claims and for teaching one skilled in the art to practice the present invention. 
     In the present disclosure, the term “proximal” refers to a direction that is generally toward a physician during a medical procedure, while the term “distal” refers to a direction that is generally toward a target site within a patient&#39;s anatomy during a medical procedure. 
     Various medical devices for implantation in a body vessel are disclosed herein. Preferred embodiments relate to a medical drainage device including one or more actuating members configured to move at least a portion of the drainage device from a delivery configuration to a deployed configuration. The medical drainage devices are described with respect to an exemplary ureteral stent embodiment including a tubular conduit. However, this disclosure is not so limited, and may be applicable to other medical drainage devices such as biliary stents, esophageal stents, or other types of drainage devices. For example, a drainage stent may be configured for use within a biliary, pancreatic, urethral, esophageal, or blood vessel. In any of the embodiments described herein, the medical drainage device may be configured as an expandable or a non-expandable endoluminal prosthesis. 
       FIG. 1  shows one embodiment of a medical drainage device  100  configured as a ureteral stent. The drainage device  100  may include a tubular conduit  110 . The tubular conduit  110  may be configured as an elongate tubular member having an inlet  112  and an outlet  114 . A drainage lumen  116  may extend longitudinally within the tubular conduit  110  between the inlet  112  and the outlet  114 . The drainage lumen  116  may be in fluid communication with the inlet  112  and the outlet  114  to provide a continuous passageway for fluid to flow through the drainage device  100 . In any of the embodiments described herein, the tubular conduit  110  may include one or more drainage holes  117 . Each drainage hole  117  may extend through a wall of the tubular conduit  110 , and the drainage lumen  116  may be in fluid communication with a point external of the tubular conduit through the drainage hole. Fluid may be allowed to flow through the drainage holes  117  to enhance the flow of fluid through the drainage device  100 . In other embodiments, the inlet  112  and/or the outlet  114  may be omitted, and fluid may enter or exit the drainage lumen  116  through the drainage holes  117 . 
     The tubular conduit  110  may be formed from any suitable material known in the art. For example, the tubular conduit  110  may be formed from silicone, polyurethane, polyamide, polyvinyl chloride, or any other suitable polymer or metal. The tubular conduit  110  may be a solid structure or a porous structure. In one preferred embodiment, the tubular conduit  110  may be formed from expanded polytetrafluoroethylene (ePTFE) tubing. Such an ePTFE material may be highly flexible and lubricious. When fabricated in an appropriate porosity range, the ePTFE tubing also may exhibit sufficient column strength to withstand introduction within a body vessel and sufficient radial compression strength to maintain an open lumen (e.g., the drainage lumen  116 ) upon implantation within the body vessel. In one example, the porosity of the ePTFE tubing may range from about 5 to about 60 microns. Additionally, the ability of the ePTFE tubing to conform to the patient&#39;s anatomy may make the drainage device  100  having the tubular conduit  110  formed from ePTFE particularly comfortable for the patient when implanted within the body lumen. 
     The drainage device  100  may include a distal end segment  120 , a proximal end segment  140 , and an intermediate segment  130  adjoining the distal end segment and the proximal end segment to one another. The distal end segment  120  and/or the proximal end segment  140  may be configured as a retaining mechanism for retaining the drainage device  100  in a desired location within a body lumen (e.g., the ureter). To that end, the distal end segment  120  and/or the proximal end segment  140  of the drainage device  100  may include one or more loops  118  formed in the tubular conduit  110 . For example, each of the distal end segment  120  and the proximal end segment  140  may include one loop  118  formed in the tubular conduit  110  as shown in  FIGS. 1-1A . This may be referred to as a double-J pigtail configuration. In another example, each of the distal end segment  120  and the proximal end segment  140  may include two loops  118  formed in the tubular conduit  110  as shown in  FIGS. 2-2B . This may be referred to as a multi-length configuration. In other examples, the distal end segment  120  and the proximal end segment  140  may include any number of loops  118 . The distal end segment  120  may include the same or a different number of loops  118  as the proximal end segment  140 . The loops  118  may be configured to retain the corresponding end segment of the drainage device  100  in a desired location within the body (e.g., a kidney or a bladder) as further described below. In other examples, the retaining mechanism of the distal end segment  120  and/or the proximal end segment  140  may be J shaped, helical shaped, zig-zag shaped, or any other shape configured to retain the drainage device  100  in a desired location within a body lumen. Additionally, or alternatively, the distal end segment  120  and/or the proximal end segment  140  may include a barb, a malecot, a balloon, or any other suitable mechanism configured to retain the drainage device  100  in a desired location within a body lumen. In any of the examples described herein, a retaining mechanism having any known configuration may be substituted for the loops  118  without departing from the scope of this disclosure. 
       FIG. 1C  shows a transverse cross sectional view of the distal end segment  120  of the drainage device  100 . The tubular conduit  110  of the drainage device  100  may include an actuating lumen  119 . The actuating lumen  119  may extend longitudinally within the tubular conduit  110 . In one example, the actuating lumen  119  may extend along substantially an entire length of the tubular conduit  110  between the inlet  112  and the outlet  114 . In another example, the actuating lumen  119  may extend along a portion of the length of the tubular conduit  110  corresponding to the distal end segment  120  or the proximal end segment  140 . In yet another example, the actuating lumen  119  may be configured as two actuating lumens: a distal actuating lumen extending along a portion of the length of the tubular conduit  110  corresponding to the distal end segment  120  and a proximal actuating lumen extending along a portion of the length of the tubular conduit corresponding to the proximal end segment  140 . The actuating lumen  119  may be configured to receive an actuating member as further described below to form the loops  118  in the tubular conduit  110 . 
     The tubular conduit  110  may be configured as a length of dual lumen tubing. The dual lumen tubing may be formed using any process known in the art including, for example, extrusion. The actuating lumen  119  may be positioned adjacent to the drainage lumen  116  within the tubular conduit  110 . To that end, the drainage lumen  116  may be offset from the longitudinal axis of the tubular conduit  110 . In other words, the tubular conduit  110  and the drainage lumen  116  may not be coaxial with one another. For example, the drainage lumen  116  may be offset within the tubular conduit  110  so that the tubular conduit includes a thin walled section  111  and a thick walled section  113 . The thickness of the wall of the tubular conduit  110  may taper circumferentially around the tubular conduit from a minimum thickness at the thin walled section  111  to a maximum thickness at the thick walled section  113  as shown in  FIG. 1C . The actuating lumen  119  may be positioned within the thick walled section  114  of the tubular conduit  110 . In other examples, the drainage lumen  116  may be coaxial with the tubular conduit  110 , and the actuating lumen  119  may be positioned adjacent to the drainage lumen  116  within the tubular conduit. 
     The actuating lumen  119  may have any suitable cross sectional shape. The cross sectional shape of the actuating lumen  119  may be configured to correspond to a cross sectional shape of an actuating member  150  which may be received in the actuating lumen as further described below. For example, the actuating lumen  119  may have a rectangular cross sectional shape as shown in  FIG. 1C . Such a rectangular actuating lumen  119  may be configured to receive an actuating member also having a rectangular cross sectional shape. In other examples, the actuating lumen  119  may have a circular, elliptical, triangular, arcuate, or any other polygonal or non-polygonal shaped cross section. 
     The drainage device  100  also may include at least one actuating member  150 . The actuating member  150  may be received within the actuating lumen  119  as shown in  FIG. 1C . The actuating member  150  may extend along substantially an entire length of the tubular conduit  110  between the inlet  112  and the outlet  114  of the drainage device  100 . In other examples, the drainage device may include one actuating member received in a portion of the actuating lumen  119  corresponding to the distal end segment  120  of the drainage device  100  and another actuating member received in a portion of the actuating lumen  119  corresponding to the proximal end segment  140  of the drainage device. In still other examples, the drainage device may include multiple actuating members received in multiple actuating lumens as described above. 
     The actuating member  150  may be configured to form the loops  118 , or a retaining mechanism having any other shape, in the tubular conduit  110  as described above. To that end, the actuating member  150  may include a shape memory material or a superelastic material. The actuating member  150  may include any shape memory or superelastic material including, for example, a shape memory or superelastic metal such as nitinol (i.e. a nickel-titanium alloy), stainless steel, copper-zinc-aluminum-nickel alloy, copper-aluminum-nickel alloy, or any other alloy which may include zinc, copper, gold, and/or iron. The actuating member  150  may include any shape memory polymer such as, for example, polyurethane, polyether ether ketone (PEEK), polyethylene terephthalate (PET), polyethylene oxide (PEO), polystyrene, or copolymers thereof. In one example, the actuating member  150  may be configured as a length of wire formed of a superelastic metal. In this example, the wire may be formed from a superelastic nitinol alloy, which may exhibit stress induced martensite at a body temperature. In other examples, the wire may be formed from a shape memory nitinol alloy, which may exhibit temperature induced martensite at a body temperature. The wire may have a rectangular cross sectional shape as shown in  FIG. 1C . In other words, the wire may have a conventional flat wire configuration. Such a flat wire configuration may reduce the required profile, or height, of the actuating lumen  119 . In other examples, the wire may have an arcuate cross-sectional shape. The arcuate cross-sectional shape may have a curvature similar to a curvature of the outer wall of the tubular conduit  110 . In other examples, the wire may have a circular elliptical, triangular, or any other polygonal or non-polygonal shaped cross section. 
     The nitinol alloys described herein may exhibit superelastic or shape memory behavior. That is, the nitinol alloy may undergo a reversible phase transformation that allows it to “remember” and return to a previous shape or configuration. The nitinol alloy may transform between a lower temperature phase (martensite) and a higher temperature phase (austenite). Austenite is characteristically the stronger phase, and martensite may be deformed up to a recoverable strain of about 8%. Strain introduced in the alloy in the martensitic phase to achieve a shape change may be substantially recovered upon completion of a reverse phase transformation to austenite, allowing the alloy to return to a previous shape. The strain recovery may be driven by the application and removal of stress (superelastic effect) and/or by a change in temperature (shape memory effect). 
     The actuating member  150  also may enhance the structural stability of the drainage device  100 . For example, the actuating member  150  may be substantially inflexible in the direction of the longitudinal axis of the tubular conduit  110 . Upon application of a force to the drainage device  100  in the direction of the longitudinal axis of the tubular conduit  110 , the actuating member  150  may not bend or flex to a substantial degree. This longitudinal rigidity may help to prevent buckling or folding (e.g., like an accordion) of the tubular conduit  110  of the drainage device  100  upon implantation in the patient&#39;s body. 
     The actuating member  150  may be retained within the actuating lumen  119  by a friction or interference fit. In one example, one or both ends of the actuating lumen  119  may be closed (e.g., using a tipping operation) to retain the actuating member  150  within the actuating lumen. In other words, the actuating lumen  119  may be configured as a chamber within the drainage device  100  and sealed on either end. In this example, the drainage device  100  may include a cap which may be bonded to the end of the drainage device to close the lumen  119 . Alternatively, or additionally, the drainage device  100  may include an adhesive  115  disposed between an inner surface of the actuating lumen  119  and the actuating member  150 . The adhesive  115  may be disposed between one surface of the actuating member  150  and the inner surface of the actuating lumen  119  as shown in  FIG. 1C . In other examples, the adhesive  115  may substantially surround the actuating member  150  to fill a gap which may be formed between the actuating member and the inner surface of the actuating lumen  119 . The adhesive  115  may include any biocompatible adhesive material known in the art. For example, the adhesive  115  may include a cyanoacrylate (e.g., ethyl cyanoacrylate, butyl cyanoacrylate, octyl cyanoacrylate, and hexyl cyanoacrylate), an epoxy, a silicone, or any combination thereof. Additionally, or alternatively, the tubular conduit  110  and/or the actuating member  150  may be crimped using any suitable crimping technique to retain the actuating member within the actuating lumen  119 . 
     The actuating member  150  may be configured such that, in a relaxed condition, the actuating member takes on the desired shape of the retaining mechanism (e.g., the loops  118 ). The actuating member  150  may be formed into the desired shape by any means known in the art. For example, the loops  118  may be formed in the actuating member  150  using a shape setting process such as heating in a media bath (e.g., a salt bath or a sand bath), heating in an oven (e.g., an air furnace or a vacuum furnace), heating on a heated die, cold working, stamping, injection molding, exposure to infrared (IR) radiation, or exposure to radio frequency (RF) energy. The actuating member  150 , received within the actuating lumen  119 , may cause the distal end segment  120  and/or the proximal end segment  140  of the tubular conduit  110  to take on the shape of the actuating member. In this manner, the actuating member  150  may form the loops  118  in the tubular conduit  110 . 
     The tubular conduit  110  of the drainage device  100  may be formed from an ePTFE material as described above. This ePTFE may exhibit desirable column strength and radial compression strength. However, the ePTFE may not exhibit shape memory or superelastic properties. In other words, ePTFE may be substantially unable to return to a predefined shape following deformation. The presence of the actuating member  150  within the actuating lumen  119  of the drainage device  100  may enable the tubular conduit  110  formed from ePTFE to exhibit the desired shape memory or superelastic properties. In other words, including the actuating member  150  within the actuating lumen  119  may provide the tubular conduit  110  with the desired shape memory or superelastic properties (due to the superelasticity or shape memory properties of the actuating member  150 ) so that the loops  118  may be formed in the distal end segment  120  and/or the proximal end segment  140  of the tubular conduit even though the ePTFE material itself may not exhibit such shape memory or superelastic properties. Because the ePTFE itself may not be required to exhibit shape memory or superelastic properties, the durometer, or hardness, of the tubular conduit  110  may be reduced relative to conventional drainage devices. In one example, the durometer of the tubular conduit  110  may range from about 15 to about 90 measured on a type A scale. In other words, the presence of the actuating member  150  may enable a softer tubular conduit  110  to be used. This softer tubular conduit  110  may be more comfortable for the patient upon implantation of the drainage device  100  including ePTFE. 
     The tubular conduit  110  may be configured as a length of dual lumen tubing as described above. The tubular conduit  110  may be sized and shaped for implantation within a body lumen. Exemplary dimensions of the tubular conduit  110  are described below with reference to  FIG. 1C . The dimensions are merely exemplary and not limiting. The tubular conduit  110  may have any dimensions suitable for the intended use of the drainage device  100 . In one example, the tubular conduit  110  may be formed from a length of 4.7 Fr dual lumen tubing. In this example, the tubular conduit  110  may have an outer diameter A of about 0.062 inches. The thin walled section  111  of the tubular conduit  110  may have a thickness B of about 0.005 inches, and the thick walled section  113  may have a thickness C of about 0.014 inches. The drainage lumen  116  may have a diameter D of about 0.043 inches. The actuating lumen  119  may have a rectangular cross section, as described above, having a width E of about 0.012 inches and a height F of about 0.004 inches. In another example, the tubular conduit  110  may be formed from a length of 6 Fr dual lumen tubing. In this example, the outer diameter A of the tubular conduit  110  may be about 0.079 inches. The thickness B of the thin walled section  111  may be about 0.009 inches, and the thickness of the thick walled section  113  may be about 0.023 inches. The diameter D of the drainage lumen  116  may be about 0.047 inches. In yet another example, the tubular conduit  110  may be formed from a length of 7 Fr dual lumen tubing. In this example, the outer diameter A of the tubular conduit  110  may be about 0.092 inches. The thickness B of the thin walled section  111  may be about 0.010 inches, and the thickness of the thick walled section  113  may be about 0.026 inches. The diameter D of the drainage lumen  116  may be about 0.056 inches. In still another example, the tubular conduit  110  may be formed from a length of 8 Fr dual lumen tubing. In this example, the outer diameter A of the tubular conduit  110  may be about 0.105 inches. The thickness B of the thin walled section  111  may be about 0.012 inches, and the thickness of the thick walled section  113  may be about 0.038 inches. The diameter D of the drainage lumen  116  may be about 0.055 inches. In other examples, the tubular conduit  110  may be formed from a length of dual lumen tubing having any size such as, for example, about 2 to about 26 Fr. The dual lumen tubing may be sized for placement at a particular location within a patient&#39;s body. 
     The drainage device  100  may be movable between a delivery configuration and a deployed configuration.  FIG. 3  shows the drainage device  100  in the delivery configuration. In the delivery configuration, the tubular conduit  110  of the drainage device  100  may be substantially linear. In other words, the loops  118  of the distal end segment  120  and the proximal end segment  140  may be unrolled or straightened so that the tubular conduit is substantially linear as shown in  FIG. 3 . A wire guide  160  may be received within the drainage lumen  116  of the drainage device  100 . The wire guide  160  may restrain the tubular conduit  110  of the drainage device in the delivery configuration. In other words, the wire guide  160  received within the drainage lumen  116  may counteract the force of the actuating member  150  received within the actuating lumen  119  to prevent the loops  118  from being formed in the distal end segment  120  and the proximal end segment  140 . Upon removal of the wire guide  160  from the drainage lumen  116 , the actuating member  150  may cause the drainage device  100  to return to the deployed configuration as shown in  FIG. 1 . 
     Implantation of the drainage device will be described in further detail below. Although the description will generally refer to the implantation of a ureteral stent within a ureter, a similar method may be used to implant a drainage device in any other body lumen. 
     The wire guide  160  may be introduced into a urethra  480  of a patient as shown in  FIG. 4A . The wire guide  160  may be advanced through the urethra  480  and into the bladder  482 . The wire guide  160  then may be advanced into a ureter  484  and to a kidney  486 . A cytoscope or other visualization device may be used to aid in positioning the wire guide  160 . The position of the distal end of the wire guide  160  in the kidney  486  may be confirmed by x-ray, fluoroscopy, ultrasound, or any other suitable visualization technique. 
     The drainage device  100  may be advanced over the proximal end of the wire guide  160  remaining outside of the patient&#39;s body. The wire guide  160  may be received within the drainage lumen  116  of the drainage device  100  to restrain the drainage device in the delivery configuration as described above. The drainage device  100  may be advanced over the wire guide  160  and through the urethra  480 , the bladder  482 , and the ureter  484 . The drainage device  100  may be advanced until the distal end segment  120  of the drainage device is positioned within the kidney  486 . The drainage device  100  may be advanced by hand (i.e., by pushing the drainage device along the wire guide  160 ) until the proximal end segment  140  of the drainage device is near the end of the urethra. Then, the drainage device  100  may be advanced using a positioner. For example, the positioner may be advanced over the wire guide  160  until the distal end of the positioner contacts the proximal end segment  140  of the drainage device  100 . The positioner may be further advanced to push the drainage device  100  along the wire guide  160 . When the drainage device  100  is in the desired position within the ureter  484 , the positioner may be retracted from the patient&#39;s body. 
     With the distal end segment  120  of the drainage device  100  positioned within the kidney  486 , the wire guide  160  may be retracted proximally relative to the drainage device. Upon removal of the wire guide  160  from the portion of the drainage lumen  116  corresponding to the distal end segment  120  of the drainage device  100 , the actuating member  150  may cause the loop  118 , or other retention mechanism, to be formed in the distal end segment as described above. The loop  118  may have a diameter that is larger than a diameter of the ureter  484 . In this manner, the loop  118  may retain the distal end segment  120  of the drainage device  100  within the kidney  486 . In other words, the loop  118  may prevent the drainage device from moving within the ureter  484  away from the kidney  486  and toward the bladder  482 . Additionally, or alternatively, a change in the temperature of the actuating member  150  may cause the loop  118  to be formed in the distal end segment  120  of the drainage device  100 . In other words, the loops  118  may be formed in response to exposure to a body temperature within the patient&#39;s body (e.g., for shape memory alloys or polymers). The wire guide  160  may be further retracted to remove the wire guide from the drainage device. Upon removal of the wire guide  160  from the portion of the drainage lumen  116  corresponding to the proximal end segment  140  of the drainage device  100 , the actuating member  150  may cause the loop  118 , or other retention mechanism, to be formed in the proximal end segment as described above. The loop  118  may have a diameter that is larger than a diameter of the ureter  484 . In this manner, the loop  118  may retain the proximal end segment  140  of the drainage device  100  within the bladder  482 . In other words, the loop  118  may prevent the drainage device from moving within the ureter  484  away from the bladder  482  and toward the kidney  486 .  FIG. 4B  shows the drainage device  100  in the deployed configuration (i.e., with the retaining mechanisms formed at the distal end segment  120  and the proximal end segment  140  of the drainage device) implanted within the ureter  484 . The drainage device  100  may enable a fluid such as urine to flow through the drainage lumen  116  from the kidney  486  to the bladder  482 . The intermediate segment  140  of the drainage device  100  may aid in maintaining the patency of the ureter  484 . 
     Forming the tubular conduit  110  of the drainage device  100  from ePTFE, as described above, may enhance the conformance of the drainage device to the patient&#39;s ureteral anatomy. This enhanced conformance may be enabled by the highly flexible nature of the ePTFE. The ePTFE also may exhibit superior lubricity relative to other polymers. For example, the drainage device  100  including ePTFE may have a lower coefficient of friction against the wire guide  116  compared to conventional drainage devices including polyurethane. In one example, the coefficient of friction for ePTFE may range from about 0.02 to about 0.2. The coefficient of friction for polyurethane may range from about 0.2 to about 3.0. The coefficient of friction for nitinol may range from about 0.02 to about 0.06. This relatively low coefficient of friction may enable the drainage device  100  including ePTFE to be advanced more easily over the wire guide  160  as described above. This may make implantation of the drainage device  100  including ePTFE easier for the physician which also may reduce the time required for an implantation procedure. 
     While various embodiments of the invention have been described, the invention is not to be restricted except in light of the attached claims and their equivalents. Moreover, the advantages described herein are not necessarily the only advantages of the invention and it is not necessarily expected that every embodiment of the invention will achieve all of the advantages described.