Abstract:
The multi-material stent includes a renal portion and a bladder portion with respective, different hardness. A valve is disposed within the stent to guide liquid from the renal portion of the stent to the bladder portion of the stent. The present invention relates towards systems and method for stents. More particularly, the invention relates to a stent designed to increase patient comfort by minimizing irritation and reflux through the use of a stent that incorporates one or more flexible elements, which may involve materials with varying degrees of hardness, and a valve disposed therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on, claims priority to, and incorporates herein by reference in its entirety U.S. Provisional Application Ser. No. 61/782,272, filed Mar. 14, 2013, and entitled, “FLEXIBLE ANTI-REFLUX URETERAL STENT.” 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    N/A 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates towards systems and method for stents. More particularly, the invention relates to a stent designed to increase patient comfort by minimizing irritation and reflux through the use of a stent that incorporates one or more flexible elements, which may involve materials with varying degrees of hardness, and a valve disposed therein. 
         [0004]    Stents are thin, hollow tubes inserted into a conduit in a patient to assist in opening a passageway that has been obstructed, or to assist in maintaining a passageway between two localized areas in the patient. Stents may be used to prevent flow constriction and to allow access for surgical procedures. One specific type of stent, a ureteral stent, is used to maintain a passageway between a patient&#39;s kidneys and bladder due to complications from infection, tumors, kidney stones, or other conditions that impact the urinary tract. In particular, a ureteral stent is inserted into the ureter to assist in draining urine from the patient&#39;s kidney to the patient&#39;s bladder if there is a blockage or other condition that does not allow for normal urine flow. Stents are also routinely inserted into a patient&#39;s ureter for several days after ureteroscopic kidney stone surgery to remove kidney or ureteral stones. Stents are designed to be positioned within a patient for days or weeks until the blockage is removed or normal urine flow is otherwise restored. 
         [0005]    There are numerous problems and side effects associated with existing ureteral stents, however. One such problem is migration of the stent after insertion such that the stent does not remain in the specified location over the duration that the stent is disposed within the patient. To combat migration issues in stents, typical ureteral stent designs (e.g., double J) utilize coils at opposing proximal and distal ends of the stent to anchor the stent in the patient&#39;s kidney and bladder, respectively. Stents utilizing a double J design are more successful in retaining the ureteral stent in the desired location in the patient, but cause various other undesirable side effects due to the lower coil being disposed adjacent to and aggravating the patient&#39;s bladder. For example, the lower coil frequently causes the patient to suffer from bleeding, urges to pass urine frequently, and burning while passing urine due to the coil scratching the bladder. 
         [0006]    An additional consideration for a ureteral stent is the desirability to control urine reflux that occurs during urination while using a stent. Stents frequently include at least one hollow tube (e.g., a lumen) so typically some amount of urine refluxes back into the patient&#39;s kidneys during and after urination as opposed to exiting from the body. Existing ureteral stents have insufficient mechanisms to control reflux that also allow for urine flow to pass from the patient. Reflux may cause pain (sometimes severe) in some patients and may lead to serious health conditions including urinary tract infections and even renal failure in extreme cases. 
         [0007]    Attempts have been made to modify ureteral stent design to overcome the aforementioned problems to prohibit migration of the stent while minimizing patient discomfort. For example, one such stent incorporates a coiled end portion designed to reside in the patient&#39;s kidney and terminates at one or more flexible loops. The stent is substantially rigid throughout the length thereof until terminating at the loops. However, significant drawbacks exist with this stent design. For example, the stent includes a significant portion of rigid material that irritates the patient&#39;s urinary tract and results in patient discomfort. Further, this stent design does not include a mechanism to control reflux. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention overcomes the aforementioned drawbacks by providing a stent including one or more flexible elements which may be achieved by materials having different hardness properties or by a single material with different types of reinforcement and/or thicknesses, and whereby the stent incorporates a self-retaining securement mechanism to assist in preventing migration. The self-retaining securement mechanism is substantially more rigid than a majority of the rest of the stent and the softer material enhances patient comfort and minimizes patient irritation. The stent may further incorporate a valve therein to address reflux problems. 
         [0009]    In one non-limiting configuration, a stent comprises a renal portion having a hardness characterized between about 20 Shore A to about 90 Shore A. A bladder portion has a hardness characterized between about 5 Shore A to about 60 Shore A. A valve is disposed within the stent to guide liquid from the renal portion of the stent to the bladder portion of the stent. 
         [0010]    In a different configuration, a stent includes an elongate conduit defined by a renal portion and a bladder portion. A valve is disposed within the conduit, and between about 75% to about 99% of the conduit is characterized by a hardness of less than about 80 Shore A. The valve facilitates fluid flow only in one direction through the conduit. 
         [0011]    In a further configuration, a stent includes a self-retaining securement mechanism having a first hardness value. A flexible tube defining a bladder portion has a second hardness value, wherein the first hardness value is greater than that of the second hardness value. A valve is disposed in the stent. 
         [0012]    The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a partial schematic view depicting a possible installation of a ureteral stent in a urinary tract of a patient; 
           [0014]      FIG. 2  is an isometric view of one type of a stent; 
           [0015]      FIG. 3  is a portion of a self-retaining securement mechanism of the stent of  FIG. 2  enlarged for magnification purposes; 
           [0016]      FIG. 4  is a portion of the self-retaining securement mechanism of  FIG. 3  and a connector portion of the stent of  FIG. 2  enlarged for magnification purposes; 
           [0017]      FIG. 5  is a side elevational view of a different embodiment of a stent; 
           [0018]      FIG. 6  is a portion of a connector portion of the stent of  FIG. 5  enlarged for magnification purposes; 
           [0019]      FIG. 7  is a portion of a tip of the stent of  FIG. 5  enlarged for magnification purposes; 
           [0020]      FIG. 8  is a cross-sectional view of an end of the stent of  FIG. 5  adjacent a self-retaining securement mechanism taken generally along the lines  8 - 8  of  FIG. 5 ; 
           [0021]      FIG. 9  is a front axial view of the stent of  FIG. 5 ; 
           [0022]      FIG. 10  is a top plan view of another embodiment of a stent; 
           [0023]      FIG. 11  is a cross-sectional view of an end of the stent of  FIG. 10  taken generally along the lines  11 - 11  of  FIG. 10 ; 
           [0024]      FIG. 12  is a cross-sectional view of an opposing end of the stent of  FIG. 10  taken generally along the lines  12 - 12  of  FIG. 10 ; 
           [0025]      FIG. 13  is a cross-sectional side view of the stent of  FIG. 10  having a valve therein taken generally along the lines  13 - 13  of  FIG. 10 ; and 
           [0026]      FIG. 14  is a front axial view of the stent of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    As best seen generally in  FIGS. 1-14 , a stent  100  includes an elongate conduit  102  having a renal portion  104  and a bladder portion  106 . The elongate conduit  102  defines at least one lumen, which allows fluid communication therethrough. The stent  100  is designed to be placed or otherwise positioned in a passageway of a patient (e.g., urinary tract), and in particular, into a patient&#39;s ureter  108 . The renal portion  104  of the stent  100  is designed to be positioned proximate the patient&#39;s kidney  110  and the bladder portion  106  is designed to be positioned proximate the patient&#39;s bladder  112 . The stent  100  provides a passageway from the kidney  110  to the bladder  112  through the ureter  108  to allow urine to flow unimpeded and exit from the patient through the urethra (not shown). 
         [0028]    In one embodiment, the stent  100  is defined by at least two separate materials having a different hardness parameter as discussed herein. In a different embodiment, the stent  100  is defined by the same material over the length thereof that have varying diameters to provide different hardness characteristics along the length thereof. For example, in one embodiment, the renal portion  104  and the bladder portion  106  include different materials, wherein the bladder portion  106  is defined by a hardness characteristic less than that of the renal portion  104 . In a different embodiment, the renal portion  104  and the bladder portion  106  are characterized by the same material. In this embodiment, portions (or all) of the bladder portion  106  are defined by a diameter parameter smaller than that of the renal portion  104  such that the bladder portion  106  is more flexible due to the smaller size. In still a further embodiment, the renal portion  104  and the bladder portion  106  each include a different material and are characterized by a different diameter parameter with respect to each other. 
         [0029]    The total length of the stent  100  may be selected with respect to numerous factors including the size of the patient. In one embodiment, the stent  100  is defined by a length dimension of between about 15 cm to about 40 cm as measured from a first end  114  of the renal portion  104  to a second end  116  at the bladder portion  106 . The length dimension may be more preferably between about 18 cm to about 35 cm, and most preferably between about 22 cm to about 28 cm. Although it should be appreciated that the length of the stent  100  may be adjusted as desired. 
         [0030]    As best seen in  FIG. 3 , the stent  100  includes a self-retaining securement mechanism  120  disposed on the renal portion  104  thereof. The self-retaining securement mechanism  120  includes a rounded J-shaped coil  122  that terminates at a straightened portion  124 . The self-retaining securement mechanism  120  is designed to be located adjacent the kidney  110  and to securely anchor the stent  100  thereto. In one embodiment, the self-retaining securement mechanism  120  is defined by the single J-shaped coil  122  extending therefrom (see  FIG. 3 ). In a different embodiment, the self-retaining securement mechanism  120  includes other types of pigtail or spiral coils (not shown) as known in the art. In another embodiment, the self-retaining securement mechanism  120  may be substantially straight (see  FIGS. 5 and 10 ). In a further embodiment, the self-retaining securement mechanism  120  includes other structures and/or shapes that assist in retaining the stent  100  in the kidney  110 . 
         [0031]    In one embodiment, the self-retaining securement mechanism  120  includes a rigid material as compared to the other portions of the stent  100  or the same material, but applied in way that results in greater rigidity, such as through layering the material or adding additional support to the material, such as through a wire or other reinforcement addition. For example, suitable materials for use as the self-retaining securement mechanism  120  include any biocompatible materials having the hardness defined herein. Examples of suitable materials for the self-retaining securement mechanism  120  include polymers and copolymers such as polyurethane, polyamides, and various ethylene copolymers and block copolymers (e.g., ethyl vinyl acetate (EVA)). Other useful materials include biocompatible plastics, e.g., polyester, nylon based biocompatible polymers, polytetrafluoroethylene polymers, silicone polymers, polyurethane polymers, polyethylene polymers, and thermoplastic polymers. 
         [0032]    The self-retaining securement mechanism  120  is preferably defined by hardness parameter of about 30 Shore A to about 80 Shore A as determined by the ASTM D-2240 method. In other embodiments, the self-retaining securement mechanism  120  includes a hardness parameter between about 20 Shore A to about 90 Shore A. In still other embodiments, the self-retaining securement mechanism  120  includes a material having other rigidity properties. 
         [0033]    The self-retaining securement mechanism  120  is also defined by an outer diameter of between about 2 Fr. to about 12 Fr. and more preferably between about 4 Fr. to about 8 Fr. In one embodiment, the outer diameter of the self-retaining securement mechanism  120  is about 5 Fr. In a different embodiment, the outer diameter of the self-retaining securement mechanism  120  is about 6 Fr. In still a different embodiment, the outer diameter of the self-retaining securement mechanism  120  is about 7 Fr. Further, the self-retaining securement mechanism  120  includes an interior diameter of between about 0.01 Fr. to about 3 Fr. and more preferably between about 1 Fr. to about 2 Fr. In one embodiment, the interior diameter of the self-retaining securement mechanism  120  is about 2 Fr. In a different embodiment, the interior diameter of the self-retaining securement mechanism  120  is about 3 Fr. In still a different embodiment, the interior diameter of the self-retaining securement mechanism  120  is about 4 Fr. It should be recognized that a self-retaining securement mechanism  120  including a larger diameter may assist in preventing migration of the stent  100  from the kidney  110 , however the increased thickness may also increase patient discomfort. 
         [0034]    The self-retaining securement mechanism  120 , which includes the J-shaped coil  122  and the straightened portion  124 , preferably includes a length dimension from about 5 cm to about 20 cm as measured from the first end  114  of the J-shaped coil  122  to an end  126  of the straightened portion  124  (as measured when the coil is unwound and straightened). The length dimension of the self-retaining securement mechanism  120  is more preferably between about 8 cm to about 18 cm, and most preferably between about 12 cm to about 14 cm. Although it should be appreciated that the length of the self-retaining securement mechanism  120  may be adjusted as desired. 
         [0035]    As best seen in  FIG. 6 , the straightened portion  124  of the self-retaining securement mechanism  120  is integral with a tapered connector conduit  130 , and together collectively form the renal portion  104  of the stent  100 . The tapered connector conduit  130  is defined by a truncated cone having a diameter at a proximal end  132  that is substantially similar to the outer diameter of the self-retaining securement mechanism  120 . The connector conduit  130  tapers inwardly until terminating at a distal end  134  that includes an outer diameter that is substantially similar to an outer diameter of the bladder portion  106 , discussed in more detail hereinbelow. 
         [0036]    The connector conduit  130  includes a length dimension of between about 0.01 cm to about 6 cm, and more preferably between about 1 cm to about 2 cm. In one embodiment, the length dimension is about 0.5 cm. In a different embodiment, the length dimension is about 1 cm. In still a different embodiment, the length dimension is about 2 cm. 
         [0037]    The connector conduit  130  includes an outer diameter of between about 2 Fr. to about 12 Fr., and more preferably between about 4 Fr. to about 8 Fr. at the proximal end  132  thereof. In one embodiment, the outer diameter of the connector conduit  130  is about 5 Fr. adjacent the proximal end  132 . In a different embodiment, the outer diameter of the connector conduit  130  is about 6 Fr. at the proximal end  132 . In still a different embodiment, the outer diameter of the connector conduit  130  is about 7 Fr. at the proximal end  132 . 
         [0038]    The connector conduit  130  tapers inwardly until having an outer diameter of between about 2 Fr. to about 6 Fr., and more preferably between about 3 Fr. to about 5 Fr. at the distal end  134  thereof. In one embodiment, the outer diameter of the connector conduit  130  is about 5 Fr. adjacent the distal end  134 . In a different embodiment, the outer diameter of the connector conduit  130  is about 4 Fr. at the distal end  134 . In still a different embodiment, the outer diameter of the connector conduit  130  is about 3 Fr. at the distal end  134 . 
         [0039]    The ratio of the diameter of the connector conduit  130  with respect to the outer diameter dimension measured at the proximal end  132  as compared to the distal end  134  is about 2 to about 1. In a different embodiment, the ratio of the connector conduit  130  with respect to the outer diameter dimension measured at the proximal end  132  as compared to the distal end  134  is about 3 to about 1. In still a different embodiment, the ratio of the connector conduit  130  with respect to the outer diameter dimension measured at the proximal end  132  as compared to the distal end  134  is about 3 to about 2. In a different embodiment, the ratio of the connector conduit  130  with respect to the outer diameter dimension measured at the proximal end  132  as compared to the distal end  134  is about 4 to about 3. Although it is contemplated that the connector conduit  130  may include a substantially uniform diameter over the length thereof, the narrowing of the connector conduit  130  assists in preventing urine reflux. 
         [0040]    As best seen in  FIG. 6 , the connector conduit  130  tapers inwardly in substantially the same manner throughout the circumference thereof. In particular, angles A and A′ are formed by an exterior surface of the connector conduit  130  as defined by a longitudinal axis L and an axis formed by the slope of the surface of the connector conduit  130 . In one embodiment, the angles A and A′ are between about 90 degrees to about 45 degrees, in a different embodiment, the angles A and A′ are between about 60 degrees to about 88 degrees. In a further embodiment, the angles A and A′ are between about 75 degrees to about 85 degrees. In one specific embodiment, the angles A and A′ are about 85 degrees. 
         [0041]    In one embodiment, the connector conduit  130  includes the same material as other portions of the self-retaining securement mechanism  120  (i.e., the coil  122  and/or the straightened portion  124 ). In a different embodiment, the connector conduit  130  includes a material similar to the material of the bladder portion  106  of the stent  100 . In still a different embodiment, the connector conduit  130  includes a plurality of materials such that the hardness of the material of the connector conduit  130  lessens moving from the proximal end  132  to the distal end  134 . 
         [0042]    As best seen in  FIG. 2 , the distal end  134  of the connector conduit  130  is integral with and terminates at the bladder portion  106  of the stent  100 . The bladder portion  106  includes a flexible tube  140  that defines a lumen including a relatively soft material as compared to the other portions of the stent  100 . In particular, in one embodiment, the flexible tube  140  is defined by hardness of about 5 Shore A to about 60 Shore A. In other embodiments, the flexible tube  140  includes a hardness between about 10 Shore A to about 30 Shore A. In another embodiment, the tube  140  includes the same material as one or more other portions of the stent  100  (e.g., the renal portion  104 ). In still other embodiments, the flexible tube  140  may include a material having other rigidity properties. 
         [0043]    Suitable materials for use as the flexible tube  140  include any biocompatible materials having the hardness defined herein. For example, in some embodiments, the flexible tube  140  of the stent  100  is constructed of a thermoplastic elastomer, or a natural or synthetic polymer such as silicone. It should be recognized that other materials may be utilized as desired, but that the hardness of the material(s) used for the flexible tube  140  is typically less than the hardness of the materials used for the self-retaining securement mechanism  120  and/or the connector conduit  130 . The flexible tube  140  preferably includes a material that has a binding energy greater than about 400 kJ/mol. 
         [0044]    The flexible tube  140  is defined by an outer diameter of between about 2 Fr. to about 6 Fr. and more preferably between about 3 Fr. to about 5 Fr. In one embodiment, the outer diameter of the flexible tube  140  is about 5 Fr. In a different embodiment, the outer diameter of the flexible tube  140  is about 4 Fr. In still a different embodiment, the outer diameter of the flexible tube  140  is about 3 Fr. Further, the flexible tube  140  includes an interior diameter of between about 0.01 Fr. to about 3 Fr. and more preferably between about 1 Fr. to about 2 Fr. In one embodiment, the interior diameter of the flexible tube  140  is about 1 Fr. In a different embodiment, the interior diameter of the flexible tube  140  is about 2 Fr. In still a different embodiment, the interior diameter of the flexible tube  140  is about 1.5 Fr. 
         [0045]    Now turning to  FIG. 7 , the flexible tube  140  terminates at a tip  150  at the second end  116  of the stent  100 . In one embodiment, the tip  150  includes the same material as the flexible tube  140 . In a different embodiment, the tip  150  includes other materials discussed herein in connection with any portion of the stent  100 . In still a different embodiment, the tip  150  may be made of a different material. The tip  150  is designed to be positioned adjacent the patient&#39;s bladder  112  and is shaped to facilitate removal therefrom. In contrast to many prior art stents, the tip  150  is designed to conform to the shape of the patient&#39;s passageway (e.g., ureter) and does not have a preformed coil, spiral, or loop shape. 
         [0046]    In the embodiment depicted in  FIG. 7 , the tip  150  is provided in the form of a truncated triangle and includes two opposing sloped walls  152  that taper inwardly toward one another until terminating at a small opening  154 . The tip  150  preferably has a smaller profile than the outer diameter of the flexible tube  140 . Although depicted as a truncated triangle, the tip  150  may be other shapes and sizes as desired. Alternatively, the tip  150  may be omitted all together such that the flexible tube  140  is the end of the stent  100 . 
         [0047]    The use of one or more materials in the stent  100  having different hardness properties is important to realizing the advantages described herein. In one embodiment, the stent  100  is formed entirely of materials characterized by a hardness of less than about 40 Shore A. In a different embodiment, between about 75% to about 99% of the materials of the stent  100  are characterized by a hardness of less than about 40 Shore A. In another embodiment, between about 50% to about 75% of the stent  100  is characterized by a hardness of less than about 40 Shore A. In yet another embodiment, greater than about 70% of the stent  100  is characterized by a hardness of less than about 40 Shore A (all as determined using the ASTM D-2240 method). 
         [0048]    In another embodiment, the stent  100  is formed entirely of materials characterized by a hardness of less than about 80 Shore A, or less than about 60 Shore A. In a different embodiment, between about 75% to about 99% of the stent  100  is characterized by a hardness of less than about 80 Shore A. In another embodiment, between about 50% to about 75% of the stent  100  is characterized by a hardness of less than about 80 Shore A. In yet another embodiment, greater than about 70% of the stent  100  is characterized by a hardness of less than about 80 Shore A (all as determined using the ASTM D-2240 method). 
         [0049]    It should be recognized that the hardness of one or more portions of the stent  100  may be impacted by various factors. In one embodiment, the stent  100  includes a single material, whereby hardness of one portion of the stent  100  (e.g., the renal portion  104 ) is higher (i.e., more stiff) than that of one or more other portions of the stent  100  (e.g., the bladder portion  106 ). The perceived hardness may be caused by various factors including the specific material used, the diameter of the stent  100  over the length thereof, and/or the inclusion of wire or other reinforcement mechanisms within the stent  100 . In one particular embodiment, the stent  100  includes a single material with a reinforcement mechanism (e.g., wire) disposed in a portion thereof to provide rigidity over a discrete length. Other portions of the stent  100  may not include the reinforcement mechanism, and thus, have a hardness parameter less than that of the portion having the reinforcement mechanism. In a different embodiment, the diameter of the stent  100  tapers from about 6 Fr. to about 4.5 Fr. The tapering of the stent  100  causes the portion having the larger diameter to be more stiff than the portion having the smaller diameter. 
         [0050]    The hardness of the stent  100  may also be characterized in other ways. For example, in one embodiment, portions of the stent  100  include one or more materials defined by a hardness of less than about 100 Shore D. In another embodiment, one portion of the stent  100  is defined by a hardness of less than about 60 Shore A and a second portion of the stent  100  is defined by a hardness of less than about 75 Shore D. Although hardness parameters are discussed herein, the hardness or softness of portions of the stent  100  may include other parameters and characteristics, and the stent  100  herein is not limited thereby. 
         [0051]    As best seen in  FIGS. 5 and 10 , other embodiments of a stent are depicted. The stents  200 ,  300  are similar to the stent  100  described herein except for the below noted differences. In particular, the stents  200 ,  300  include a substantially straightened self-retaining securement mechanism  220 ,  320  disposed on a renal portion thereof. The self-retaining securement mechanisms  220 ,  320  each include a straightened portion  224 ,  324  as opposed to the J-shaped coil  122  of the stent  100 . The self-retaining securement mechanisms  220 ,  320  are designed to be located adjacent the patient&#39;s kidney and to securely anchor the stent  200 ,  300  thereto. 
         [0052]    Similar to the stent  100 , the self-retaining securement mechanisms  220 ,  320  include a rigid material as compared to the other portions of the stents  200 ,  300 . For example, suitable materials for use as the self-retaining securement mechanisms  220 ,  320  include any biocompatible materials having the hardness defined herein. Examples of suitable materials for the self-retaining securement mechanisms  220 ,  320  include polymers and copolymers such as polyurethane, polyamides, and various ethylene copolymers and block copolymers (e.g., ethyl vinyl acetate (EVA)). Other useful materials include biocompatible plastics, e.g., polyester, nylon based biocompatible polymers, polytetrafluoroethylene polymers, silicone polymers, polyurethane polymers, polyethylene polymers, and thermoplastic polymers. 
         [0053]    The stents  200 ,  300  each include a tapered connector conduit  230 ,  330  that extends between the self-retaining securement mechanisms  220 ,  320  and tubular members  240 ,  340 . Tips  250 ,  350  are optionally provided at ends of the stents  200 ,  300 . 
         [0054]    Now turning to  FIG. 13 , a valve  400  is disclosed for use with any of the stents  100 ,  200 ,  300  described herein. The valve  400  may be any number of valves including a one-way valve having a single leaflet, a single flap valve, or a ball valve. In a different embodiment, the valve  400  may include a bi-leaflet or tri-leaflet valve. In still a further embodiment, the valve  400  includes a valve with a spherical flap. In one embodiment, the valve  400  is preferably a one-way valve such that the valve  400  is designed to allow liquid to pass therethrough in a single direction (i.e., away from the patient&#39;s kidneys toward the patient&#39;s bladder). In a different embodiment, the valve  400  inhibits fluid flow in a direction longitudinally toward the renal portion  104  of the stent  100 . In other embodiments, the valve  400  may be omitted all together. The valve  400  may be other types of valves that operate in the manner described herein. 
         [0055]    The valve  400  may be positioned in the stent  100  in any suitable location. For example, in one embodiment, the valve  400  is positioned adjacent the connector conduit  130  (as shown in  FIG. 13 ). In a further embodiment, the valve  400  is disposed adjacent the renal portion  104  (i.e., the rounded J-shaped coil  122  or straightened portion  124 ). In a further embodiment, the valve  400  is positioned adjacent the tip  150 . It should be recognized that although the valve  400  is discussed in connection with the stent  100  of  FIGS. 1-4 , the valve  400  may be utilized with stents  200 ,  300  of the other embodiments. 
         [0056]    One or more portions of the stent  100  may include a coating and/or may include a hydrophilic or hydrophobic material. In some embodiments, the stent is coated with a lubricious hydrophilic coating. Such a coating can be applied to any portion of the stent  100  to reduce irritation caused by contact with the surrounding tissue in the urinary tract and/or bladder. The coating is preferably compatible with the materials used. In one particular embodiment, the preferred coating is heparin, which is known to reduce infection, anti-calcification, and/or encrustation. In another embodiment, the stent  100  is coated with a coating intended to prevent calcification. In a different embodiment, the stent  100  is coated with a coating intended to prevent inflammation, and in a further embodiment, the stent  100  is coated with a coating intended to prevent infection. 
         [0057]    One or more portions of the stent  100  may further include one or more radio opaque markers (not shown) to assist in inserting, positioning, and/or removing the stent  100 . In one embodiment, one or more portions of the stent  100  are made of a radio opaque material. In a different embodiment, one or more radio opaque markers may be added to portions of the stent  100 . For example, a radio opaque marker may be disposed adjacent the self-retaining securement mechanism  120  disposed on the renal portion  104  of the stent  100 . The marker may be visible to a physician under X-ray, flouroscopy, or other visual aids. The stent  100  may include one or more radio opaque markers on other portions thereof, including on the connector conduit  130 , flexible conduit  140 , and/or the tip  150 . In use, the physician may use the mark(s) to facilitate placement of the stent  100  in the patient and more particularly, to assist in guiding the self retaining securement mechanism  120  into the patient&#39;s kidney  110 . 
         [0058]    One or more portions of the stent  100  may include a catch (not shown) or other mechanism to facilitate insertion of the stent  100  into the patient. The catch is designed to interact with a deployment mechanism such as a guidewire (not shown) to assist in positioning the stent  100 . In one embodiment, the self-retaining securement mechanism  120  of the stent  100  is inserted into a patient by using a guidewire that extends from the bladder  112 , through the ureter  108 , and into the kidney  110 . The guidewire may extend substantially along the length of the self-retaining securement mechanism  120 , which causes the J-shaped coil  122  to temporarily deform into a substantially linear shape. A pusher or other similar tool may be placed over the guidewire adjacent to a portion of the stent  100 . In one embodiment, the pusher exerts a force on a portion of the coil  122  (e.g., the end  114 ) to appropriately locate the stent  100  proximate to the kidney. It is contemplated that the pusher may be substantially longer than a standard pusher. Typical pushers push end-to-end whereas the pusher may be designed to fit over the distal portion of the stent and go into the ureter. In a different embodiment, the pusher is positioned adjacent the valve  400  to assist in the positioning thereof. In a further embodiment, the pusher may contact or otherwise move other portions of the stent  100  to assist in the positioning thereof. After the stent  100  is positioned, the guidewire and pusher are removed, which causes the J-shaped coil  122  to bend into a shape similar to the shape depicted in  FIG. 3  or any other shape designed to self retain and secure the placement of the stent  100  in the kidney. 
         [0059]    The stent  100  may be positioned in the patient using a variety of other methods, techniques, and/or tools. For example, the stent  100  may be utilized in conjunction with the guidewire described in U.S. patent application Ser. No. 12/660,891, filed on Mar. 5, 2010, and incorporated by reference in its entirety. That is, the stent can be placed through a sheath, even without a guidewire. 
         [0060]    The present invention has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside From those expressly stated, are possible and within the scope of the invention. Any of the embodiments described herein may be modified to include any of the structures or methodologies disclosed in connection with different embodiments.