Patent Publication Number: US-2022218461-A1

Title: Stent with atraumatic spacer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/169,370, filed Oct. 24, 2018, which claims priority to U.S. Provisional Application Ser. No. 62/576,890, filed Oct. 25, 2017, the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to devices, methods and systems for implanting stents. More particularly, the present invention relates to implantable stents having atraumatic spacer members. 
     BACKGROUND 
     An intraluminal prosthesis is a medical device used in the treatment of bodily lumens. One type of intraluminal prosthesis used in the repair and/or treatment of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract, gastrointestinal tract, esophageal tract, tracheal/bronchial tubes and bile duct, as well as in a variety of other applications in the body. 
     Lumen apposing metal stents are also used to drain pancreatic fluid collections and to provide direct biliary and gallbladder drainage. The positioning of the metal stent adjacent a cyst wall may result in post acute bleeding as the distal surface of the stent and the cyst wall come in contact as the cyst volume reduces due to drainage. Repetitive interaction between the end of the stent, such as a multi-terminal pointed stent end, with the cyst wall may be involved. Accordingly, there is an ongoing need to mitigate or remove this tissue interaction and negate the bleeding when an intraluminal prosthesis, such as a stent, is used for drainage. 
     SUMMARY 
     The present disclosure is directed to various embodiments of a stent, for example a braided stent, having an integral spacer mechanism. 
     A first example stent includes a tubular body formed of one or more interwoven wires, the tubular body having first and second opposing open ends and a lumen extending therebetween, the tubular body defining a longitudinal axis extending between the first and second open ends, a first anchor member disposed adjacent the first open end and a second anchor member disposed adjacent the second open end, the first and second anchor members each extending radially outward from the tubular body, the first and second anchor members each having an outer diameter larger than an outer diameter of the tubular body disposed between the first and second anchor members, and a plurality of spacer members disposed around the first open end and extending longitudinally beyond the first open end, wherein when a pulling force is applied to the spacer members, the outer diameter of the tubular body is not reduced. 
     Alternatively or additionally to any of the above examples, each spacer member has first and second legs extending along a portion of the tubular body toward the second open end. 
     Alternatively or additionally to any of the above examples, the spacer members extend radially outward beyond the outer diameter of the tubular body. 
     Alternatively or additionally to any of the above examples, each spacer member is formed from a single wire loop. 
     Alternatively or additionally to any of the above examples, the spacer members are formed separately from the tubular body and attached to an inner wall of the tubular body. 
     Alternatively or additionally to any of the above examples, the spacer members are interwoven with the tubular body. 
     Alternatively or additionally to any of the above examples, the spacer members are less flexible than the tubular body. 
     Alternatively or additionally to any of the above examples, the plurality of spacer members includes a first group of spacer members with a first length and a second group of spacer members having a second length shorter than the first length. 
     Alternatively or additionally to any of the above examples, the first group of spacer members are more flexible than the second group of spacer members. 
     Alternatively or additionally to any of the above examples, the stent may further include a covering extending over an entirety of the tubular body, first and second anchor members, and the plurality of spacer members. 
     Alternatively or additionally to any of the above examples, at least one spacer member has a variable flexibility along its length. 
     Alternatively or additionally to any of the above examples, the at least one spacer member is formed from a tapered wire having a first thickness in a first region adjacent the tubular body, and a second thickness in a second region disposed furthest away from the tubular body. 
     Alternatively or additionally to any of the above examples, the second thickness is smaller than the first thickness, resulting in a greater flexibility in the second region. 
     Alternatively or additionally to any of the above examples, the first and second anchor members extend perpendicular to the longitudinal axis. 
     Alternatively or additionally to any of the above examples, the stent may further include a retrieval element disposed at the second open end. 
     Another example stent includes a tubular body formed of one or more interwoven wires, the tubular body having first and second opposing open ends and a lumen extending therebetween, the tubular body defining a longitudinal axis extending between the first and second open ends, a first group of spacer members disposed around the first open end and extending longitudinally beyond the first open end and extending radially outward beyond an outer diameter of the tubular body, the first group of spacer members having a first length, a second group of spacer members disposed around the first open end and extending longitudinally beyond the first open end and extending radially outward beyond an outer diameter of the tubular body, the second group of spacer members having a second length shorter than the first length, and wherein when a pulling force is applied to the first and/or second group of spacer members, the outer diameter of the tubular body is not reduced. 
     Alternatively or additionally to any of the above examples, a first anchor member disposed adjacent the first open end and a second anchor member disposed adjacent the second open end, the first and second anchor members each extending radially outward from the tubular body, the first and second anchor members each having an outer diameter larger than the outer diameter of the tubular body disposed between the first and second anchor members. 
     Alternatively or additionally to any of the above examples, the first group of spacer members are more flexible than the second group of spacer members. 
     Alternatively or additionally to any of the above examples, at least one spacer member in the first or second group of spacer members is formed from a tapered wire having a first thickness in a first region adjacent the tubular body, and a second thickness in a second region disposed furthest away from the tubular body, wherein the second thickness is smaller than the first thickness, resulting in a greater flexibility in the second region. 
     Another example is a method of draining a cyst comprising implanting a stent through a tissue wall with a first open end of the stent disposed within the cyst and a second open end of the stent disposed outside the cyst, the stent including a tubular body formed of one or more interwoven wires, the tubular body defining a lumen extending between the first and second open ends, the stent including a plurality of spacer members disposed around the first open end and extending longitudinally beyond the first open end, and draining fluid from the cyst through the lumen of the stent, wherein as the cyst drains, a wall of the cyst comes into contact with one or more of the plurality of spacer members, wherein the plurality of spacer members prevents the wall of the cyst from contacting the first open end of the stent. 
     The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, and Detailed Description, which follow, more particularly exemplify some of these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
         FIG. 1  is a side view of a prior art stent disposed adjacent a cyst wall; 
         FIG. 2  is a side view of a hollow, tubular stent in accordance with an embodiment of the disclosure, adjacent a cyst wall; 
         FIG. 3  is an end view of the stent of  FIG. 2 ; 
         FIG. 4  is an end view of a stent in accordance with another embodiment of the disclosure; 
         FIG. 5  is a perspective view of the end of the stent of  FIG. 2  positioned in a tissue structure; 
         FIGS. 6A and 6B  are side partial cross-sectional views of a stent in accordance with another embodiment of the disclosure implanted in a target tissue structure; 
         FIG. 7  is a side view of a stent in accordance with a further embodiment of the disclosure; 
         FIG. 8  is a perspective view of the end of the stent of  FIG. 7  in a tissue structure; and 
         FIG. 9  is a side view of a stent in accordance with another embodiment of the disclosure. 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
     DETAILED DESCRIPTION 
     For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification. 
     All numeric values are herein assumed to be modified by the term “about,” whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. 
     The recitation of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     It is noted that references in the specification to “an embodiment”, “some embodiments”, “other embodiments”, etc., indicate that the embodiment described may include one or more particular features, structures, and/or characteristics. However, such recitations do not necessarily mean that all embodiments include the particular features, structures, and/or characteristics. Additionally, when particular features, structures, and/or characteristics are described in connection with one embodiment, it should be understood that such features, structures, and/or characteristics may also be used connection with other embodiments whether or not explicitly described unless clearly stated to the contrary. 
     The following detailed description should be read with reference to the drawings in which similar structures in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the disclosure. 
       FIG. 1  depicts a prior art woven stent  5  positioned adjacent a tissue wall such as a cyst wall  40 . As the cyst volume reduces due to drainage through the stent lumen, the terminal end  7  of the stent  5  may come in contact with the cyst wall  40 , and may result in tissue irritation with resultant bleeding and/or vessel infection. Additionally the premature contact of the device end and tissue wall may leave residual pockets of cystic fluid unable to effectively drain due to the device lumen being blocked off. 
       FIG. 2  shows a stent  10  including a tubular body  20  and multiple atraumatic spacer members  30  extending beyond the end of the tubular body  20 . The tubular body  20  is a hollow tubular structure having an open first end  22 , an open second end  24 , and a lumen extending therebetween. The tubular body  20  may be formed from one or more, or a plurality of wires  15 . The wires  15  may be woven, braided, wound, knitted, and combinations thereof, to form the tubular body  20 . 
     The stent  10  may include multiple wires  15  of a metal material, such as nitinol or nitinol-containing material, or other nickel-titanium alloy, for example. In some instances, the wires  15  may have a diameter of about 0.011 inches, for example. The number of wires  15  and the diameters of the wires  15 , which may be the same or different, depicted in  FIG. 2  are not limiting, and other numbers of wires  15  and other wire diameters may suitably be used. Desirably, an even number of wires  15  may be used, for example, from about 10 to about 36 wires  15 . 
     Desirably, the wires  15  are made from any suitable implantable material, including without limitation nitinol, stainless steel, cobalt-based alloy such as Elgiloy®, platinum, gold, titanium, tantalum, niobium, polymeric materials and combinations thereof. Useful and nonlimiting examples of polymeric stent materials include poly(L-lactide) (PLLA), poly(D,L-lactide) (PLA), poly(glycolide) (PGA), poly(L-lactide-co-D,L-lactide) (PLLA/PLA), poly(L-lactide-co-glycolide) (PLLA/PGA), poly(D,L-lactide-co-glycolide) (PLA/PGA), poly(glycolide-co-trimethylene carbonate) (PGA/PTMC), polydioxanone (PDS), Polycaprolactone (PCL), polyhydroxybutyrate (PHBT), poly(phosphazene) poly(D,L-lactide-co-caprolactone) PLA/PCL), poly(glycolide-co-caprolactone) (PGA/PCL), poly(phosphate ester) and the like. Wires made from polymeric materials may also include radiopaque materials, such as metallic-based powders, particulates or pastes which may be incorporated into the polymeric material. For example the radiopaque material may be blended with the polymer composition from which the polymeric wire is formed, and subsequently fashioned into the stent  10  as described herein. Alternatively, the radiopaque material may be applied to the surface of the metal or polymer wire  15  of the stent  10 . In either embodiment, various radiopaque materials and their salts and derivatives may be used including, without limitation, bismuth, barium and its salts such as barium sulphate, tantalum, tungsten, gold, platinum and titanium, to name a few. Additional useful radiopaque materials may be found in U.S. Pat. No. 6,626,936, the contents of which are incorporated herein by reference. Metallic complexes useful as radiopaque materials are also contemplated. The stent may be selectively made radiopaque at desired areas along the wire or may be fully radiopaque. 
     In some instances, the wires  15  may have a composite construction having an inner core of tantalum, gold, platinum, tungsten, iridium or combination thereof and an outer member or layer of nitinol to provide a composite wire for improved radiopacity or visibility. In one example, the inner core may be platinum and the outer layer may be nitinol. The inner core of platinum may represent about at least 10% of the wire  15  based on the overall cross-sectional percentage. Moreover, nitinol that has not been treated for shape memory such as by heating, shaping and cooling the nitinol at its martensitic and austenitic phases, is also useful as the outer layer. Further details of such composite wires may be found in U.S. Pat. No. 7,101,392, the contents of which is incorporated herein by reference. The wires  15  may be made from nitinol, or a composite wire having a central core of platinum and an outer layer of nitinol. Further, the filling weld material, if required by welding processes such as MIG, may also be made from nitinol, stainless steel, cobalt-based alloy such as Elgiloy, platinum, gold, titanium, tantalum, niobium, and combinations thereof. 
     The tubular body  20  may have one or more anchor members  26 ,  28  adjacent the first and second ends, respectively. The anchor members  26 ,  28  may be regions that extend radially outward from the tubular body  20 , forming flanges. In the example shown in  FIG. 2 , the anchor members  26 ,  28  extend circumferentially and radially outward from the tubular body  20 , substantially perpendicular to the longitudinal axis X of the stent  10 . The anchor members  26 ,  28  may have an outer diameter larger than the outer diameter of the stent body portion disposed between the anchor members  26 ,  28 . 
     The stent  10  may include a plurality of atraumatic spacer members  30  disposed around the first end  22  of the tubular body, as shown in  FIG. 2 . In other examples, a plurality of spacer members  30  may be disposed around both the first end  22  and the second end  24 . The spacer members  30  are configured to hold the first end  22  of the stent away from the cyst wall  40  as the cyst is drained and the cyst wall  40  advances toward the first end  22 . The spacer members  30  prevent the cyst wall  40  of the cyst from contacting the first end  22  of the tubular body  20  of the stent  10 . Even when the cyst has fully drained, the spacer members  30  may prevent contact between the cyst wall and the first end  22  of the tubular body  20 , thus preventing damage to the tissue wall by contacting the bare first end  22  of the stent. In some instances, the spacer members  30  may be formed from the wires  15  defining the tubular body  20 . For example, the spacer members  30  may be formed by extending one or more wires  15  from the first end  22  of the tubular body  20  and then weaving that wire back into the tubular body  20 . In other examples, the spacer members  30  may be formed from additional wires added to a previously formed tubular body  20 . The spacer members  30  may have a first region  36  disposed adjacent the first end  22  of the tubular body  20 , and a terminal end  38  which is the point of the spacer member  30  furthest away from the first end  22  of the tubular body  20  measured along the length of the spacer member  30 . The spacer members  30  may be formed from a biocompatible material such as the metallic and polymeric materials listed above for the wires  15  of the tubular body  20 . The spacer members  30  may be self-supporting, such that the spacer members  30  may be cantilevered and/or extend from the first end  22  of the tubular body  20  while retaining their shape. However, when the spacer members  30  engage a lumen wall, the spacer members  30  may provide insufficient radial resistance to anchor the stent  10 . 
     In the example shown in  FIG. 2 , the spacer members  30  are each formed from a single wire  35  formed in a loop and attached to the previously formed tubular body  20 , with ends of the wire loop defining legs  32 ,  34  attached to an inner surface of the tubular body  20 . In other examples, multiple spacer members  30  may be formed from a single wire. The legs  32 ,  34  may be welded onto the inside of the tubular body  20 . Alternatively, the legs  32 ,  34  may be attached with adhesive, wire wrapping, or other suitable permanent connection. In some instances, the legs  32 ,  34  may be woven into the wires  15  of the tubular body  20 . The legs  32 ,  34  may extend over 25% or more, 50% or more, or 75% or more of the length of the tubular body  20 , from the first end  22  toward the second end  24 . In some examples, the legs  32 ,  34  extend over the entire length of the tubular body  20  from the first end  22  to the second end  24 . The legs  32 ,  34  may extend along the inner surface of the tubular body  20  substantially parallel to the longitudinal axis or at an oblique angle to the longitudinal axis, and thus in a helical direction. In some examples, the legs  32 ,  34  may follow the path of and be juxtaposed along the wires  15  in the braiding pattern of the stent  10 . 
     The legs  32 ,  34  from one spacer member  30  may overlap the legs  32 ,  34  of another spacer member  30  in some instances. For example, in some embodiments, the legs  32 ,  34  of a first spacer member  30  may extend in a first helical direction along the inner surface of the tubular body  20  while the legs  32 ,  34  of a second spacer member  30  may extend in an opposite second helical direction along the inner surface of the tubular body  20  and intersect the legs  32 ,  34  of the first spacer member  30 . In other examples, all of the legs  32 ,  34  of all spacer members  30  extend along the interior of the tubular body  20  without contacting legs  32 ,  34  of another spacer member  30 . For example, the legs  32 ,  34  of each spacer member  30  may extend in the same helical direction along the interior of the tubular body  20 . 
     The spacer members  30  may be arranged uniformly around the circumference of the first end  22  and radiate outward in a radial direction. The spacer members  30  may be spaced apart, as shown in  FIG. 3 . In other examples, spacer members  30  may overlap with an adjacent spacer member  30  around the circumference of the first end  22 . For instance, each spacer member  30  may overlap with the adjacent spacer member  30  on each side thereof. As depicted in  FIG. 3  the stent  10  includes three spacer members  30 . In other embodiments, the stent  10  may have two opposing spacer members  30 , or four, five, six, or more spacer members  30  evenly or unevenly spaced around the circumference of the stent  10 . 
     The wire  35  forming the spacer members  30  may have the same or different properties than the wires  15  which form the tubular body  20 . For example, the wires  35  may be of the same or different stiffness or flexibility, all of which may be tailored for a particular application. In some embodiments, the wire  35  forming spacer members  30  may be stiffer than the stent wires  15  forming the tubular body  20  of the stent  10 . In some instances, the wire  35  forming the spacer members  30  may be formed of a different material and/or may have a different diameter than the stent wires  15 . In some instances, the wire  35  forming the spacer members  30  may be stainless steel while the stent wires  15  may be formed of a nickel-titanium alloy, such as nitinol. The material forming the spacer member wires  35  may have a stiffness greater than, equal to, or less than the material forming the wires  15  of the tubular body  20  and/or the material forming the spacer member wires  35  may have a modulus of elasticity (Young&#39;s modulus) greater than, equal to, or less than the material forming the wires  15  of the tubular body  20 . The choice of material, wire diameter and pre-treatment of the wires  35 ,  15  and stent configuration are some of the factors which may be varied to achieve particular stent properties. Additionally, at least one of the spacer members  30  may also be made radiopaque by various methods, for example with a coating or finish, with a band or as part of the stent material. Color or different finishes may also be added to the spacer members  30  to visually differentiate them from the rest of the stent wires  15 . 
     The spacer members  30  are configured such that applying a pulling or squeezing force on the spacer members  30  does not reduce the outer diameter of the tubular body  20 . 
     In examples in which spacer members  30  are formed from additional wires attached to the previously formed tubular body  20 , the attachment is such that pulling on the spacer members  30  does not reduce the outer diameter of the tubular body  20 . For example, welding the spacer members  30  or using adhesive to attach the spacer members  30  to one or more wire cross-over points on the inner surface of the tubular body  20  may prevent the spacer members  30  from interacting with the weave or braided structure of the tubular body  20  to reduce its diameter when the spacer members  30  are pulled or squeezed. In examples where the spacer members  30  are formed from one or more wires used in forming the tubular body  20 , the portion of the wire(s) forming the spacer members  30  may be stabilized relative to the tubular body  20  such that pulling on the spacer members  30  does not reduce the outer diameter of the tubular body  20 . In one example, stabilizing may include welding one or more of the last wire cross-over points at the first end  22  of the tubular body where the wire forming the spacer member  30  exits the tubular body  20 . In other examples, adhesive or additional wire wrapping may be used to stabilize the spacer members  30  relative to the tubular body  20 . The spacer members  30  thus do not function as retrieval elements to reduce the diameter of the stent  10  for removal. In some examples, a separate retrieval element  80  may be disposed on the second end  24  and/or the first end  22  of the tubular body  20 . In the example shown in  FIG. 2 , the stent  10  includes a retrieval element  80  attached to the second end  24  of the tubular body  20 . In some instances, the retrieval element  80  may be a wire or suture woven through loops of the wires  15  of the tubular body  20  at the second end  24  of the tubular body  20 . 
     The spacer members  30  extend longitudinally beyond the first end  22  of the tubular body  20 . The spacer members  30  may extend beyond the first end  22  of the tubular body  20  for a distance D. In some instances, distance D may be 5% to 50%, 10% to 50%, 10% to 30%, or 5% to 30% of the total length of the tubular body  20 , for example. In some examples, the spacer members  30  may extend 8 mm to 15 mm beyond the first end  22 . The spacer members  30  may also extend radially away from the tubular body  20 , beyond the outer diameter of the tubular body  20  as measured at the first end  22 . In the example shown in  FIGS. 2 and 3 , the spacer members  30  also extend radially beyond the outer diameter of the anchor members  26 ,  28 . For example, the spacer members  30  may extend radially outward at an angle of between about 20 degrees to about 85 degrees, between about 25 degrees to about 75 degrees, about 30 degrees to about 60 degrees, or about 45 degrees to about 75 degrees from the longitudinal axis X of the stent  10 . The angle of the spacer members  30  relative to the longitudinal axis X may be, for example, 25 degrees or more, 30 degrees or more, 35 degrees or more, 40 degrees or more, 45 degrees or more, 50 degrees or more, 55 degrees or more, 60 degrees or more, 65 degrees or more, 70 degrees or more, 75 degrees or more, 80 degrees or more, or 85 degrees or more degrees, or other desired angle. The spacer members  30  illustrated in the figures are shaped as elongated loops. In other examples, the spacer members  30  may be any shape desired, including circular, elliptical, teardrop, etc. The terminal end  38  of the spacer members  30  may be rounded, as shown in  FIG. 3 , to provide an atraumatic end that engages the cyst wall  40 . 
     The spacer members  30  may provide a structure which has the required stiffness to maintain the stent  10  in a spaced orientation away from the cyst wall  40 , thus preventing damage to the tissue wall from contact with the first end  22  of the tubular body  20 . In some examples, the flexibility of the spacer members  30  varies along their length. The spacer members  30  may be formed from a wire having a variable thickness along its length. In one example, as shown in  FIG. 4 , the stent  100  includes at least one spacer member  130  formed from a wire having a first thickness in the first region  136  adjacent the tubular body  120 , tapering down and/or transitioning to a second thickness at the terminal end  138 . As illustrated in  FIG. 4 , the second thickness may be smaller than the first thickness to achieve a spacer member  130  that is more flexible at the terminal end  138 . The more flexible terminal end  138  may allow the spacer member  130  to bend slightly at the terminal end  138  as it contacts the cyst wall  40 , reducing the potential for tissue injury. 
     In some embodiments the stent  10 ,  100  may include a covering  70 ,  170  disposed over at least a portion of the tubular body  20 ,  120  of the stent  10 ,  100 . For example, the covering  70 ,  170  may fully cover the entire length of the tubular body  20 ,  120  of the stent  10 ,  100 , forming a fully covered stent in which all of the interstices defined in the braided or woven pattern are covered with the covering  70 ,  170  to prevent tissue in-growth and fluid leakage into the lumen of the tubular body  20 ,  120 . In other examples, the covering  70 ,  170  may cover only a portion of the length of the tubular body  20 ,  120  of the stent  10 ,  100 , forming a partially covered stent in which a portion of the interstices defined in the braided or woven pattern remain uncovered, allowing tissue in-growth. In some instances, the spacer members  30 ,  130  may be covered by the covering  70 ,  170 , thus the entire stent  10 ,  100 , including both the entire tubular body  20 ,  120  and the spacer members  30 ,  130  may be covered by the covering  70 ,  170 . For instance, the covering  70 ,  170  may extend across and fill the space between adjacent sides of the loop formed by the wire(s) forming the spacer members  30 ,  130  while the gap between adjacent spacer members  30 ,  130  may be devoid of any covering material, permitting fluid to flow between the spacer members  30 ,  130  around the end of the stent  10 ,  100  and into the lumen of the stent  10 ,  100 . In some instances, the stent  10 ,  100  may be dipped into a solution of silicone or other polymer to form the covering  70 ,  170 . In other instances, a polymer sheet or tube may be placed around the tubular body  20 ,  120  and/or within the tubular body  20 ,  120  to form the covering  70 ,  170 . The covering  70 ,  170  may be disposed on external or internal surfaces of the tubular body  20 ,  120 , or on both the internal and external surfaces of the tubular body  20 ,  120 , thereby embedding the stent  10 ,  100  in the polymeric material. The coating or covering may be a polymer covering, such as a polytetrafluoroethylene (PTFE) or silicone covering, however other coverings, particularly elastomeric polymers, may be used. Non-limiting examples of useful polymeric materials include polyesters, polypropylenes, polyethylenes, polyurethanes, polynaphthalenes, polytetrafluoroethylenes, expanded polytetrafluoroethylene, silicone, and combinations and copolymers thereof. 
       FIG. 5  shows one end of the stent  10  of  FIG. 2  implanted in a tissue site represented as a cyst. In a method of draining a cyst, the first end portion of the stent  10  may be implanted through an opening in a tissue wall with the first anchor member  26 , first end  22  of the tubular body  20 , and three spacer members  30  all protruding through the tissue wall  46  into a cavity representing the cyst. The second anchor member  28  may be disposed on the other side of the tissue wall to secure the stent  10  across the tissue wall  46 . The larger diameter of the first anchor member  26  holds the stent  10  in place and the spacer members  30  are disposed within the cyst. As the cyst volume decreases due to drainage through the lumen of the stent  10 , the lower cyst wall (see  FIG. 2 ) will contact the spacer members  30 , instead of the first end  22  of tubular body  20 . The spacer members  30  prevent the wall of the cyst from contacting the first end  22  of the tubular body  20 . The spacer members  30  hold the first end  22  of the tubular body  20  away from the cyst wall and permit fluid to pass around the first end  22  of the tubular body  20  between adjacent spacer member  30  and into the lumen of the tubular body  20  to drain the fluid from the cyst. Even when all fluid has been drained from the cyst, the cyst wall is spaced away from the first end  22  of the tubular body  20  by the spacer members  30 . This spacing may reduce or eliminate tissue irritation and/or resultant bleeding. 
       FIGS. 6A and 6B  illustrate another example of a stent  200  disposed through a tissue wall  46  with the first end  222  of the stent  200  disposed in the cavity of a cyst  242 . The stent  200  includes a tubular body  220 , a first group of spacer members  230  having a first length extending from the first region  236  adjacent the first end  222  of the tubular body  220  to the terminal end  238  of spacer members  230 . The stent  200  includes a second group of spacer members  231  extending from the first region  237  adjacent the first end  222  of the tubular body  220  to the terminal end  239  of spacer members  231 . The second group of spacer members  231  have a second length that is shorter than the first length of the first group of spacer members  230 , positioning the terminal ends  239  of the second group of spacer members  231  closer to the first end  222  of the tubular body  220  than the terminal ends  238  of the first group of spacer members  230 . As the fluid in the cyst  242  is drained through the lumen of the stent  200 , in direction of arrow  260 , the cyst wall  40  collapses and engages the terminal ends  238  of the first group of spacer members  230 , as shown in  FIG. 6A . Then, as the cyst continues to drain and the cyst wall  40  advances toward the first end  222  of the tubular body  220 , the first group of spacer members  230  may flex or bend back toward the second end  224  of the tubular body  220 , in the direction of arrow  250 , permitting the terminal ends  239  of the second group of spacer members  231  to engage the cyst wall  40 , as shown in  FIG. 6B . 
     The first group of spacer members  230  may be more flexible than the second group of spacer members  231 , allowing the first group of spacer members  230  to flex, bend or partially collapse as the cyst wall  40  advances towards the first end  222  of the tubular body  220 . As with the spacer members  30  described above, the first and second groups of spacer members  230 ,  231  may have a variable flexibility along their length. In particular, one or both of the first and second groups of spacer members  230 ,  231  may have terminal ends  238  that are more flexible than first regions  236  adjacent the tubular body  320 . As with the stent  10  described above, when the first and second groups of spacer members  230 ,  231  engage a lumen wall, the spacer members  230 ,  231  provide insufficient radial resistance to anchor the stent  200 . Similar to the spacer members  30  discussed above, the spacer members  230 ,  231  are configured such that applying a pulling or squeezing force on the spacer members  230 ,  231  does not reduce the outer diameter of the tubular body  220 . 
     A further example of a stent  300  with a tubular body  320  and a plurality of spacer members  330  is shown in  FIG. 7 . In this example, the tubular body  320  is formed from one or more stent wires  315  and has a substantially uniform diameter along its length, without anchor members. The plurality of spacer members  330  may be attached to the first end  322  of the tubular body  320 , the second end  324  of the tubular body  320 , or both. The spacer members  330  may be formed from wires  315  forming the tubular body  320 , or from wires  335  attached to the tubular body  320  after the tubular body  320  has been formed. As with the stent  10  discussed above, the wires  335  may be attached to the tubular body  320  by welding, adhesive, wire wrapping or other suitable permanent connection. Also as with the stent  10  discussed above, the spacer members  330  are configured such that applying a pulling or squeezing force on the spacer members  330  does not reduce the outer diameter of the tubular body  320 . 
     The wires  335  may be tapered to provide a variable flexibility along the spacer member  330 . For example, the wires  335  may have a first thickness in the first region  336  adjacent the tubular body  320  and taper down to a second, smaller thickness in the region of the terminal end  338  of the spacer member  330 , resulting in the terminal end  338  being more flexible than the first region  336 . This allows the terminal end  338  of the spacer members  330  to flex or bend back toward the opposite end of the tubular body  320  upon contact with a tissue wall. The stiffer first region  336  holds the end of the tubular body  320  away from the tissue wall allowing fluid drainage around the first end  322  of the tubular body  320  into the lumen of the stent  300 . The flexibility of the terminal end  338  of the spacer members  330  allows the spacer members  330  to gently engage the tissue wall below the stent  300 , but the spacer members  330  provide insufficient radial resistance to anchor the stent  300  against lumen walls extending substantially parallel to the longitudinal axis. The stiffer first region  336  may provide sufficient resistance in a longitudinal direction to anchor the stent  300  disposed perpendicular to a tissue wall.  FIG. 8  shows the first end  322  of the tubular body  320  extending through an opening in a tissue wall  46 . In this example of the stent  300 , the spacer members  330  have the dual function of holding the stent  300  in place within the opening in the tissue wall, and spacing the first end  322  of the tubular body  320  of the stent  300  from the tissue wall as the cyst drains. 
       FIG. 9  shows another example of a stent  400  with a tubular body  420  formed from one or more wires  415  woven, braided, knitted, or wound into the tubular body  420 . The stent  400  includes a first group of spacer members  430  having a first length extending from the first region  436  adjacent the first end  422  of the tubular body  420  to the terminal end  438  of the spacer members  430 . The stent  400  includes a second group of spacer members  431  extending from the first region  437  adjacent the first end  422  of the tubular body  420  to the terminal end  439  of the spacer members  431 . The second group of spacer members  431  have a second length that is shorter than the first length of the first group of spacer members  430 , positioning the terminal ends  439  of the second group of spacer members  431  closer to the first end  422  of the tubular body  420  than the terminal ends  438  of the first group of spacer members  430 . The first group of spacer members  430  may be more flexible than the second group of spacer members  431 , allowing the first group of spacer members  430  to flex, bend or partially collapse as the cyst drains and the tissue wall advances towards the first end  422  of the tubular body  420 . In this example, the tubular body  420  has a substantially uniform diameter along its length, without anchor members. The first and second groups of spacer members  430 ,  431  may be attached to the first end  422  of the tubular body  420 , the second end  424  of the tubular body  420 , or both. The spacer members  430 ,  431  may be formed from wires  415  forming the tubular body  420  or wires  435  attached to the tubular body  420  after the tubular body  420  has been formed. As with the stent  10  discussed above, the spacer members  430 ,  431  are configured such that applying a pulling or squeezing force on the spacer members  430 ,  431  does not reduce the outer diameter of the tubular body  420 . The wires  435  may be tapered to provide a variable flexibility along the spacer members  430 ,  431 . For example, the wires  435  may have a first thickness in the first region  436 ,  437  adjacent the tubular body  420  and taper down or transition to a second, smaller thickness in the region of the terminal end  438 ,  439 , resulting in the terminal end  438 ,  439  being more flexible than the first region  436 ,  437 . This allows the terminal end  438 ,  439  of the spacer members  430 ,  431  to bend back toward the second end  424  of the tubular body  420  upon contact with a tissue wall. The stiffer first region  436 ,  437  holds the end of the tubular body  420  away from the tissue wall. The flexibility of the terminal end  438 ,  439  of the spacer members  430 ,  431  allows the spacer members  430 ,  431  to gently engage the tissue wall below the stent  400 , but provide insufficient radial resistance to anchor the stent  400  against lumen walls extending substantially parallel to the longitudinal axis. The stiffer first region  436 ,  437  may provide sufficient resistance in a longitudinal direction to anchor the stent  400  disposed perpendicular to a tissue wall. 
     As with the stent  10 , stents  100 ,  200 ,  300  and  400  may include a covering, similar to covering  70 ,  170  described above, disposed over at least a portion of the tubular body of the stent  100 ,  200 ,  300 ,  400 . For example, the covering may fully cover the entire length of the tubular body of the stent  100 ,  200 ,  300 ,  400 , forming a fully covered stent in which all of the interstices defined in the braided or woven pattern are covered with the covering to prevent tissue in-growth and fluid leakage into the lumen of the tubular body. In other examples, the covering may cover only a portion of the length of the tubular body of the stent  100 ,  200 ,  300 ,  400 , forming a partially covered stent in which a portion of the interstices defined in the braided or woven pattern remain uncovered, allowing tissue in-growth. In some instances, the spacer members  130 ,  230 ,  330 ,  430  may be covered by the covering, thus the entire stent  100 ,  200 ,  300 ,  400 , including both the entire tubular body and the spacer members  130 ,  230 ,  330 ,  430  may be covered by the covering. For instance, the covering may extend across and fill the space between adjacent sides of the loop formed by the wire(s) forming the spacer members  130 ,  230 ,  330 ,  430 , while the gap between adjacent spacer members  130 ,  230 ,  330 ,  430  may be devoid of any covering material, permitting fluid to flow between the spacer members  130 ,  230 ,  330 ,  430  around the end of the stent  100 ,  200 ,  300 ,  400  and into the lumen of the stent  100 ,  200 ,  300 ,  400 . 
     Various stent types and stent constructions may be employed for the stent  10 ,  100 ,  200 ,  300 ,  400 . For example, the stent  10 ,  100 ,  200 ,  300 ,  400  may be a self-expanding stent or a balloon expandable stent. The stent  10 ,  100 ,  200 ,  300 ,  400  may be capable of radially contracting to a compressed or collapsed configuration for delivery, and then expandable to an expanded configuration during deployment in the body lumen. Thus, the stent  10 ,  100 ,  200 ,  300 ,  400  may be described as radially distensible or deformable. Self-expanding stents include those that have a spring-like action which causes the stent to radially expand, or stents which expand due to the memory properties of the stent material for a particular configuration at a certain temperature. The configuration of the stent may also be chosen from a host of geometries. For example, wire stents can be fastened into a continuous helical pattern, with or without a wave-like or zig-zag in the wire, to form a radially deformable stent. Individual rings or circular members can be linked together such as by struts, sutures, welding or interlacing or locking of the rings to form a tubular stent. In other embodiments, the stent  10 ,  100 ,  200 ,  300 ,  400  may be formed as a monolithic tubular member by etching or cutting a pattern of interconnected struts from a tube. 
     It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the disclosure. This may include, to the extent that it is appropriate, the use of any of the features of one example embodiment being used in other embodiments. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.