Patent Publication Number: US-2021186723-A1

Title: Esophageal stent including a valve member

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. application Ser. No. 16/176,451, filed Oct. 31, 2018, which application claims priority under 35 U.S.C. § 119 to U.S. Provisional Application Ser. No. 62/579,990, filed Nov. 1, 2017, the entirety of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains to medical devices, methods for manufacturing medical devices, and uses thereof. More particularly, the present disclosure pertains to stents including a valve, such as an anti-reflux valve, and methods for manufacturing and using such stents. 
     BACKGROUND 
     The lower esophageal sphincter is a muscle located between the esophagus and the stomach. The sphincter normally functions as a one-way valve, allowing material (e.g., food) that travels downward through the esophagus to enter the stomach while preventing the backflow (reflux) of hydrochloric acid and other gastric contents into the esophagus. However, in some cases the lower esophageal sphincter does not close adequately, and therefore, permits stomach acid to reflux into the esophagus, causing heartburn. A weak or inoperable lower esophageal sphincter is a major cause of gastroesophageal reflux disease (GERD). 
     Therefore, a variety of intracorporeal medical devices have been developed to treat gastroesophageal disease caused by a malfunctioning lower esophageal sphincter. For example, elongated stents incorporating flexible valves have been developed to allow material (e.g., food) to travel through the esophagus and enter the stomach while also preventing stomach acid to reflux into the esophagus. However, there is an ongoing need to provide alternative configurations of and/or methods of forming stents including a two-way valve to treat gastroesophageal disease, as well as other medical conditions. 
     BRIEF SUMMARY 
     This disclosure provides design, material, manufacturing method, and use alternatives for medical devices. An example medical device includes an expandable stent. The stent includes a tubular scaffold formed of one or more interwoven filament. The tubular scaffold includes an inner surface and a flexible valve extending radially inward from the inner surface of the scaffold. Further, the valve is configured to shift between a closed configuration and an open configuration and the one or more filaments of the scaffold bias the valve to the closed configuration while in a nominally deployed state. 
     Alternatively or additionally to any of the embodiments above, wherein the valve shifts from the closed configuration to the open configuration due to a peristaltic force applied to the tubular scaffold. 
     Alternatively or additionally to any of the embodiments above, wherein the valve includes a valve opening extending therethrough, and wherein the valve opening is ovular-shaped in the open configuration. 
     Alternatively or additionally to any of the embodiments above, wherein the tubular scaffold includes a first tapered region and a second tapered region, and wherein the valve is positioned between the first tapered region and the second tapered region. 
     Alternatively or additionally to any of the embodiments above, wherein the first tapered region is configured to funnel material toward the valve. 
     Alternatively or additionally to any of the embodiments above, wherein the one or more filaments of the scaffold are configured to radially expand to shift the valve from the closed configuration to the open configuration when subjected to a radial expansion force of 0.800 N/cm 2  or greater. 
     Alternatively or additionally to any of the embodiments above, further comprising a coating disposed along the one or more filaments, and wherein the valve is formed from a portion of the coating. 
     Alternatively or additionally to any of the embodiments above, the valve is a two-way valve configured to permit material to pass through the valve in a first direction and a second direction, and wherein the first direction is opposite the second direction. 
     An example method of manufacturing a stent includes forming a tubular scaffold, wherein the tubular scaffold includes a first end, a second end and a narrowed region positioned between the first end and the second end. The tubular scaffold is positioned on a coating mandrel such that the coating mandrel radially expands the narrowed region such that the tubular scaffold is spaced away from the coating mandrel at the narrowed region. A coating is applied to the tubular scaffold while the tubular scaffold is positioned on the coating mandrel. Applying the coating to the tubular scaffold includes forming a valve within the narrowed region of the tubular scaffold. Thereafter, the tubular scaffold is removed from the coating mandrel and the tubular scaffold radially collapses at the narrowed region to bias the valve in a closed configuration after being removed from the coating mandrel. 
     Alternatively or additionally to any of the embodiments above, wherein forming the tubular scaffold comprises braiding at least two or more stent filaments together. 
     Alternatively or additionally to any of the embodiments above, wherein forming the tubular scaffold further comprises positioning the tubular scaffold on a shaping mandrel, and wherein the shaping mandrel is configured to radially pinch the one or more filaments to create the narrowed region. 
     Alternatively or additionally to any of the embodiments above, wherein forming the tubular scaffold further comprises heat treating the tubular scaffold while the tubular scaffold is positioned on the shaping mandrel. 
     Alternatively or additionally to any of the embodiments above, wherein applying the coating to the tubular scaffold further includes spraying the coating on the tubular scaffold. 
     Alternatively or additionally to any of the embodiments above, wherein the valve has an ovular-shaped opening in an open configuration. 
     Another example expandable stent includes a braided tubular scaffold formed of a plurality of interwoven filaments. The tubular scaffold includes a first end, a second end and a lumen extending therethrough. The tubular scaffold further includes a narrowed region positioned between the first end and the second end. A flexible valve is positioned within the lumen at the narrowed region. The plurality of interwoven filaments apply a radially compressive force on the valve to bias the valve to a closed configuration while the stent is in a nominally deployed state. 
     Alternatively or additionally to any of the embodiments above, wherein the radially compressive force is less than or equal to 0.800 N/cm 2 . 
     Alternatively or additionally to any of the embodiments above, wherein the narrowed region includes a first diameter while in the nominally deployed state, and wherein the narrowed region is configured to radially expand to open the valve when subjected to a radially expanding force of 0.800 N/cm 2  or greater. 
     Alternatively or additionally to any of the embodiments above, wherein the valve shifts from the closed configuration to an open configuration due to a peristaltic force applied to the plurality of interwoven filaments. 
     Alternatively or additionally to any of the embodiments above, wherein the valve includes a valve opening extending therethrough, and wherein the valve opening is ovular-shaped in the open configuration. 
     Alternatively or additionally to any of the embodiments above, further comprising a coating disposed along the plurality of filaments, and wherein the valve is formed from a portion of the coating. 
     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 these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which: 
         FIG. 1  is an example stent; 
         FIG. 2  is a cross-sectional view of the stent of  FIG. 1  including a valve; 
         FIGS. 3 and 4  are cross-sectional views of the stent of  FIG. 1  illustrating material passing through the valve; 
         FIG. 5  is an enlarged cross-sectional view of a portion of the stent of  FIG. 1  including the valve in a closed configuration; 
         FIG. 6  is a cross-sectional view of the stent and valve of  FIG. 5  taken along line  6 - 6  of  FIG. 5 ; 
         FIG. 7  is an enlarged cross-sectional view of a portion of the stent of  FIG. 1  including the valve in an open configuration; 
         FIG. 8  is a cross-sectional view of the stent and valve of  FIG. 7  taken along line  8 - 8  of  FIG. 7 ; 
         FIG. 9  is a cross-sectional perspective view of an example shaping mandrel and fixture device; 
         FIG. 10  is another cross-sectional view of the shaping mandrel and fixture device shown in  FIG. 9 ; 
         FIG. 11  is a cross-sectional view of the shaping mandrel and fixture device shown in  FIG. 9  with a stent positioned thereon; 
         FIGS. 12-13  illustrate an example manufacturing method for forming a valve within an example stent; and 
         FIG. 14  is an example stent delivery system; 
         FIG. 15  is a plan view of the stent delivery system shown in  FIG. 14  with the outer member retracted; 
         FIG. 16  is a cross-sectional view of the stent and valve of  FIG. 15  taken along line  16 - 16  of  FIG. 15 ; 
         FIG. 17  illustrates an example test fixture; 
         FIG. 18  illustrates an example testing step of the example test fixture shown in  FIG. 17 ; 
         FIG. 19  illustrates another example testing step of the example test fixture shown in  FIG. 17 . 
     
    
    
     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 disclosure 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 (e.g., 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 elements 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. 
     Gastroesophageal reflux disease (GERD) is a medical condition whereby stomach acids enter the lower portion of the esophagus because the lower esophageal sphincter (positioned at the entrance of the stomach) fails to close properly. In some instances, the lower esophageal sphincter&#39;s inability to close is due to disease or general atrophy. When left open, the sphincter may permit reflux of stomach acids into the esophagus, causing severe heartburn and potentially contributing to the onset of other diseases. 
     One method of treating GERD is to place an anti-reflux stent into the entrance of the stomach. An anti-reflux stent may include an expandable two-way valve which allows food and liquid to enter the stomach but limits liquids (stomach acids) from passing back through the valve under normal digestive conditions (e.g., the valve may permit liquids to pass back through the valve during periods then the stomach contracts to permit vomiting). In general, there is an ongoing need for an anti-reflux stent to provide a smooth lumen opening into the stomach while limiting stomach acids from passing back through the valve and into the esophagus. 
       FIG. 1  shows an example stent  10 . Stent  10  may include a tubular scaffold  22  having a first end, which may extend to the first end of the stent  10 , a second end, which may extend to the second end of the stent  10 , and a lumen extending therethrough. The tubular scaffold  22  may be configured to provide the support structure for stent  10 . The tubular scaffold  22  may be formed of one or more stent filaments  14 , or a plurality of stent filaments  14 . Filaments  14  may extend longitudinally along stent  10 . In some instances, filaments  14  may extend longitudinally along stent  10  in a helical fashion. While  FIG. 1  shows filaments  14  extending along the entire length of stent  10  between first and second ends of stent  10 , in other examples, the filaments  14  may extend only along a portion of the length of stent  10 . 
     Additionally,  FIG. 1  shows example stent  10  including one or more enlarged portions (e.g., flanges)  12  proximate the first end  21  and second end  23  of the stent  10 . In some instances, enlarged portions  12  may be defined as an increase in the outer diameter, the inner diameter or both the inner and outer diameter of stent  10  relative to a medial region of the stent  10 . The enlarged portions  12  may be beneficial to anchor the stent within the esophagus and/or the opening to the stomach. Additionally, as will be described in greater detail below,  FIG. 1  illustrates stent  10  including a first tapered portion  17 , a second tapered portion  19  and a narrowed region  11  positioned between the first tapered portion  17  and the second tapered portion  19 . First tapered portion  17  may taper toward the narrowed region (i.e., neck)  11  from a larger diameter to a smaller diameter, while second tapered portion  19  may taper toward the narrowed region (i.e., neck)  11  from a larger diameter to a smaller diameter. 
     In some instances, stent  10  may be a self-expanding stent. Self-expanding stent examples may include stents having one or more interwoven filaments  14  to form a tubular scaffold  22 , having openings defined between adjacent filaments  14 . For example, stent filaments  14  may be wires braided, knitted or otherwise interwoven to form the tubular scaffold  22 . Openings or interstices through the wall of the tubular scaffold  22  may be defined between adjacent stent filaments  14 . Alternatively, tubular scaffold  22  of stent  10  may be a monolithic structure formed from a cylindrical tubular member, such as a single, cylindrical tubular laser-cut Nitinol tubular member, in which the remaining portions of the tubular member form the stent filaments  14  with openings defined therebetween. 
     Stent  10 , or components thereof, (including tubular scaffold  22  and/or stent filaments  14 ) disclosed herein may be constructed from a variety of materials. For example, stent  10  (e.g., self-expanding or balloon expandable), or components thereof, may be constructed from a metal (e.g., Nitinol). In other instances, stent  10  or components thereof may be constructed from a polymeric material (e.g., PET). In yet other instances, stent  10 , or components thereof, may be constructed from a combination of metallic and polymeric materials. Additionally, stent  10 , or components thereof, may include a bioabsorbable and/or biodegradable material. 
     Additionally, stent  10  may include one or more coating layers disposed on tubular scaffold  22 , such as positioned on and/or adjacent to the inner surface and/or outer surface thereof. The coating layer may be positioned on a portion of filaments  14  forming tubular scaffold  22  and extend across openings or cells between adjacent filaments  14 . For example,  FIG. 2  shows stent  10  including a coating layer  20  disposed along the inner surface of tubular scaffold  22 . In some instances, coating layer  20  may be an elastomeric or non-elastomeric material. For example, coating layer  20  may be a polymeric material, such as silicone, polyurethane, or the like. Further, the coating layer  20  may span the spaces (e.g., openings, cells, interstices) in the wall of tubular scaffold  22  defined between adjacent filaments  14 . For example, the coating layer  20  may extend along and cover the inner surface and/or outer surface of tubular scaffold  22  such that the coating layer  20  spans one or more of spaces (e.g., openings, cells, interstices) between filaments  14  in the wall of tubular scaffold  22 . 
     As described above, stent  10  may have a first end  21  and a second end  23 . When positioned in a body lumen (e.g., esophagus) first end  21  may be defined as the proximal end of stent  10  and oriented as the end of stent  10  closest to a patient&#39;s mouth and second end  23  may be defined as the distal end of stent  10  and oriented as the end of stent  10  closest to a patient&#39;s stomach. In some examples, a first end region of stent  10  extending proximal of a proximal most flange  12  may be longer than a second end region of stent  10  extending distal of a distal most flange  12 . The additional length of first end region may extend into and cover the lower esophagus in the event a small amount of stomach acid were to leak through the valve  16  (shown in  FIG. 2 ). 
     As shown in  FIG. 2 , coating layer  20  may extend along the length of tubular scaffold  22  from first end  21  to second end  23 . In other words, in some instances coating layer  20  may be defined as a continuous layer that extends from first end  21  to second end  23  of stent  10  and fully extends across and fills cells or interstices defined between filaments  14  of tubular scaffold  22 . However, in other instances coating layer  20  may extend less than the entire length of stent  10 , if desired, leaving a portion of cells or interstices defined between filaments  14  of tubular scaffold  22  unfilled or open. 
     Additionally,  FIG. 2  shows a valve  16  positioned within the lumen of stent  10 . As will be discussed in greater detail below, valve  16  may be formed as a portion of coating layer  20 . In other words, valve  16  may be a unitary or monolithic structure formed in conjunction with forming coating layer  20  on tubular scaffold  22 . For example,  FIG. 2  illustrates that valve  16  may be an inwardly extending portion of coating layer  20  extending radially inward of tubular scaffold  22  at narrowed or necked region  11 . In other words, valve  16  may be defined as a unitary or monolithic portion of coating layer  20  that extends radially inward from an inner surface of tubular scaffold  22  toward the central longitudinal axis  25  of stent  10 . 
     Further, in some examples, valve  16  may be defined as a monolithic portion of coating layer  20  that extends circumferentially within the lumen of stent member  10 . In other words, it can be appreciated that valve  16  may be defined as an annular member that extends continuously around the lumen of stent  10  positioned radially inward of tubular scaffold  22  in the narrowed or necked region  11 . Further, valve  16  may be defined as an uninterrupted extension of coating layer  20  projecting toward central longitudinal axis  25 , forming an annular rim of polymeric material radially inward of tubular scaffold  22  in the narrowed or necked region  11 . 
     As described above,  FIG. 2  illustrates that stent  10  may include a first tapered (e.g., conical) region  17  and a second tapered (e.g., conical) region  19  with the narrowed or necked region  11  positioned therebetween. Both first conical region  17  and second conical region  19  may generally be shaped to taper radially inwardly in opposite directions toward the longitudinal axis  25  providing the stent  10  with an hourglass shape. For example, first conical region  17  may taper radially inward from a first transition point  13  along stent  10  to valve  16  while second conical region  19  may taper radially outward from valve  16  to a second transition point  15  along stent  10 . For example, the first conical region  17  (including the stent filaments  14  and coating layer  20 ) may bear some resemblance to a cone-shaped funnel tapering from a wide portion nearest a patient&#39;s mouth to valve  16 . Further, second conical region  19  (including the stent filaments  14  and coating layer  20 ) may bear some resemblance to a cone-shaped funnel tapering from valve  16  to a wide portion closer to a patient&#39;s stomach. Further, as illustrated in  FIG. 2 , in a closed configuration, valve  16  may taper inwardly toward central longitudinal axis  25  and close (e.g., contact, seal, etc.) onto itself such that it stops flow of material (e.g., stomach acid) from flowing through the lumen of stent  10 . As discussed above, it may be desirable for valve  16  to prevent stomach acids from flowing from a patient&#39;s stomach toward the patient&#39;s mouth.  FIG. 2  shows valve  16  in a closed configuration. The stent  10  may be configured to bias valve  16  to the closed configuration in a nominally deployed state. 
     As described above, in some instances it may be desirable for valve  16  to expand radially outward to permit nutritional material (e.g., food, water, etc.) to pass through the lumen of stent  10 . For example, in some examples it is desirable for valve  16  to radially expand to permit a bolus of food or liquid to pass from a patient&#39;s mouth, through the valve  16 , to the stomach. As will be described in greater detail below, at least some stent and valve examples disclosed herein may include stent filaments of tubular scaffold  22  which impart a radially compressive force inward on valve  16  to maintain the valve  16  in a closed configured while in a “nominally-deployed” state (e.g., a state in which no outside forces are acting on the stent  10  to move the valve  16  to an open configuration). 
     Further, the compressive force exerted by filaments  14  of tubular scaffold  22  on valve  16  must be low enough such that normal, peristaltic contractions associated with normal digestive processing (e.g., normal eating and digesting of food) will open valve  16 , thereby permitting the bolus of nutritional material to pass through valve  16  and into the stomach (while also permit vomiting contractions to expel food back through valve  16 ). However, this compressive force must also be large enough to ensure the valve  16  reverts to the closed configuration when in the nominally deployed state such that stomach acids will not leak through the valve  16  from the stomach, causing symptoms of acid reflux. 
     Therefore, in at least some examples a threshold radially inward compressive force may be imparted by the filaments  14  onto the valve  16  in the nominally deployed state to hold the valve  16  in the closed configuration. In other words, stent  10  (including the radial compression of filaments  14 ) must be designed such that valve  16  remains closed in a nominally deployed state, yet opens when peristatic forces greater than the threshold inward compressive force are imparted onto the valve  16  (e.g., when peristaltic forces push a bolus of food or liquid through the valve aperture  124 , thereby causing radially outward expansion forces of greater than the threshold inward compressive force to be imparted to the scaffold  22 ) to overcome the radially inwardly compressive forces biasing the valve  16  to the closed configuration. In some instances, the threshold inward compressive force may be less than 0.900 N/cm 2 , less than 0.800 N/cm 2 , less than 0.700 N/cm 2 , less than 0.600 N/cm 2 , less than 0.500 N/cm 2 , or less than 0.400 N/cm 2 . Furthermore, forces less than the threshold inward compressive force (such as those imparted onto the valve  16  via acid reflux) will not cause valve  16  to open, thereby preventing stomach acids from flowing from the stomach into the esophagus. In some instances, the threshold inward compressive force may be at least 0.200 N/cm 2 , at least 0.300 N/cm 2 , at least 0.400 N/cm 2 , at least 0.500 N/cm 2 , at least 0.600 N/cm 2 , at least 0.700 N/cm 2 , or at least 0.800 N/cm 2 . In some instances, the threshold inward compressive force may be in the range of between 0.200 N/cm 2  to 0.900 N/cm 2 , in the range of between 0.200 N/cm 2  to 0.800 N/cm 2 , in the range of between 0.300 N/cm 2  to 0.900 N/cm 2 , in the range of between 0.300 N/cm 2  to 0.800 N/cm 2 , in the range of between 0.400 N/cm 2  to 0.800 N/cm 2 , in the range of 0.400 N/cm 2  to 0.700 N/cm 2 , for example. 
       FIG. 3  and  FIG. 4  illustrate valve  16  expanding radially outward to allow a bolus of nutritional material (e.g., food)  18  to pass through the lumen of stent  10  and through valve  16 . As shown by the arrow in  FIG. 3 , and, in general, bolus of nutritional material  18  may flow through stent  10  from a first end  21  (e.g., the end closest to a patient&#39;s mouth) to a second end  23  (e.g., the end closest to a patient&#39;s stomach).  FIG. 4  illustrates that valve  16  may permit the material  18  to pass through the lumen of the stent  10  by expanding radially outward as the material  18  passes through valve  16 . While not shown in  FIG. 4 , it is contemplated that in some examples valve  16  may conform to the shape of material  18  as it passes through valve  16 . 
       FIG. 5  illustrates an enlarged and detailed view of example stent  10  including tubular scaffold  22  and valve  16 . As described above, stent  10  may include a coating layer  20  covering tubular scaffold  22  and forming valve  16 . For example,  FIG. 5  illustrates that coating layer  20  may include a thickness depicted as “X” extending along a substantial portion and covering filaments  14 , such as covering an inner surface and/or outer surface of filaments  14 . For illustrative purposes, coating layer  20  is shown extending along inner surface of tubular scaffold  22 , however, it is noted that additionally or alternatively coating layer  20  may extend along outer surface of tubular scaffold in some embodiments. In some examples, the coating layer  20  may be formed from a silicone material or a polyurethane material, for instance. 
     Further, as shown in  FIG. 5  (and illustrated further in  FIG. 6 ), the coating layer  20  may extend radially inward from the inner surface of tubular scaffold  22  to form the valve  16  at narrowed or necked region  11  of stent  10 . As will be further illustrated in  FIG. 6 , valve  16  may have an annular shape and include a circumferential, curvilinear surface extending around the longitudinal axis  25  of stent  10  whereby the coating layer  20  extends away from the inner surface of the wall of the tubular scaffold  22  (e.g., radially inward toward the longitudinal axis  25 ) to form valve  16 . As illustrated in  FIG. 5 , valve  16  may include a thickness depicted as “Y” in  FIG. 5 . 
       FIG. 5  illustrates that in some instances the thickness “Y” of valve  16  may be substantially equal to the thickness “X” of coating layer  20 . In other words, coating layer  20  may maintain a substantially uniform thickness “X” along the length of scaffold  22  which extends uniformly to form the thickness “Y” of valve  16 . However, in other embodiments the wall thickness “X” of coating layer  20  and/or the thickness “Y” defining valve  16  may be different. For example, some portions of coating layer  20  and/or the thickness defining valve  16  may be thinner or thicker than other portions along stent  10 . 
     Similar to that shown in  FIG. 2 ,  FIG. 5  illustrates the first tapered region  17  and the second tapered region  19 , both of which may bear some resemblance to a cone-shaped funnel and together form an hourglass shape. For example, stent  10  (including tubular scaffold  22  and coating layer  20 ) may taper radially inward from a first transition point  13  toward valve  16 . Valve  16  includes a valve aperture  24 . Valve aperture  24  may be defined as the “opening” of valve  16  (e.g., the opening of valve  16  through which nutritional material may flow). As illustrated in  FIG. 5 , valve aperture  24  may be aligned with the central longitudinal axis  25 . 
       FIG. 5  further illustrates stent  10  (including scaffold  22  and coating layer  20 ) tapering radially inward from a second transition point  15  toward valve  16 . Further, both the first tapered region  17  and the second tapered region  19  may include a wide portion having an inner diameter (depicted in  FIG. 5  as dimension “W”) tapering to a narrower portion having an inner diameter (depicted in  FIG. 5  as dimension “Z”) less than the inner diameter of the wide portion. As shown in  FIG. 5 , the wide portion of each of the first tapered region  17  and the second tapered region  19  may be positioned adjacent to first transition point  13  and second transition point  15 , respectively. Further, the narrower portion may be positioned closer to valve  16 . 
       FIG. 6  shows a cross-sectional view of stent  10  through narrowed region  11  and valve  16  taken along line  6 - 6  of  FIG. 5 . In particular, line  6 - 6  of  FIG. 5  intersects valve aperture  24  of valve  16  described above. As shown in  FIG. 6 , valve aperture  24  may intersect the longitudinal axis  25  of stent  10 . As described above,  FIG. 6  depicts valve  16  in a closed configuration whereby filaments  14  (defining scaffold  22  described above) are imparting a radial inward compressive force onto valve  16 , thereby maintaining valve aperture  24  in a closed configuration.  FIG. 6  illustrates that narrowed region  11  of stent  10  may include an outer diameter which is depicted as “Dc” in  FIG. 6  in the closed configuration. The closed configuration of valve  16  may be defined as a configuration which the valve aperture  24  is closed and prevents material from flowing through the valve aperture  24 . As described above,  FIG. 6  shows the shape of valve  16  as substantially circular and extending circumferentially around the longitudinal axis  25  of the stent  10 . 
       FIG. 7  shows an enlarged view of stent  10  described above with valve  16  in an open configuration. For example,  FIG. 7  shows valve aperture  24  opened to a width depicted as dimension “V” in  FIG. 7 . As discussed above, it can be appreciated that valve aperture  24  may open via a force being imparted radially outward (e.g., a force generated via nutritional material being driven through the valve  16  via peristalsis) which is large enough to overcome the radially inward compressive force (described above) imparted by filaments  14  of tubular scaffold  22  described above. 
       FIG. 8  shows a cross-sectional view of the stent  10  through narrowed region  11  and valve  16  taken along line  8 - 8  of  FIG. 7 .  FIG. 8  further illustrates the valve  16  in an open configuration. In other words,  FIG. 8  shows narrowed region  11  of stent  10  being expanded to an outer diameter depicted as “D O ” in  FIG. 8 . Diameter D O  may be greater than diameter D C  described above with respect to  FIG. 6 . It can be appreciated that as narrowed region  11  of stent  10  expands due to peristaltic forces acting thereupon, the outer diameter of narrowed region of stent  10  may increase from diameter D C  depicted in  FIG. 6  to diameter D O  depicted in  FIG. 8 . Accordingly, as the outer diameter of narrowed region of stent  10  increases from diameter Dc depicted in  FIG. 6  to diameter D O  depicted in  FIG. 8 , valve  16  (including valve aperture  24 ) may shift from a closed configuration to an open configuration. Likewise, tubular scaffold  22  radially expands in narrowed region  11  between the closed configuration to the opened configuration. 
     Additionally, line  8 - 8  of  FIG. 7  transects the valve aperture  24  described above.  FIG. 8  illustrates the valve  16  extending radially inward from stent filaments  14  (defining scaffold  22  described above). As shown in  FIG. 8 , valve aperture  24  may be an opening centered about the central longitudinal axis  25  of the lumen of stent  10 . However, while the figures described herein depict example valves and related elements centered about the central longitudinal axis  25 , it is contemplated that any of the examples described herein may be designed such that the structural elements defining any portion of stent  10  and/or valve  16  may be off-center. In other words, valve  16  may be asymmetrical about the central longitudinal axis  25  in one or more examples described herein. 
     Additionally,  FIG. 8  shows that valve aperture  24  may be substantially ovular (e.g., elliptically) shaped in the open configuration. The ovular shape of the valve aperture  24  may reduce the force required to maintain valve  16  in closed configuration while also permitting valve  16  to open via peristaltic forces acting upon valve  16  as described above. While the example shown in  FIG. 8  illustrates an ovular-shaped valve aperture  24 , other examples are contemplated in which the shape of valve aperture  24  may be circular, triangular, star-shaped, square, rectangular, etc. Additionally, in some examples the valve aperture  24  may include one or more structures including flaps, leaflets, channels, slits, cuts, grooves, etc. Further, valve aperture  24  designs which combine the various geometric shapes, orientations and structures are contemplated. 
       FIGS. 9-11  illustrates an example device and method for forming (e.g., heat setting) the stent structure including stent scaffold  22  formed from filaments  14  as shown and described above. For example,  FIG. 9  illustrates an example stent shaping mandrel  44  which is mounted on (e.g., engaged with) an external stent fixture device  42 . As illustrated in  FIG. 9 , stent shaping mandrel  44  may include a first mandrel segment  41  and a second mandrel segment  43 . External stent fixture  42  may hold first mandrel segment  41  in a fixed position relative to second mandrel segment  43  with a gap between first mandrel segment  41  and second mandrel segment  43  such that first mandrel segment  41  is spaced away from second mandrel segment  43  and not directly contacting one another. Additionally, shaping mandrel  44  may further include a compressive member  45 . Compressive member  45  may be positioned in the gap between the first mandrel segment  41  and the second mandrel segment  43 . Compressive member  45  may include a narrowed aperture (e.g., opening, pinch point, etc.)  52 . In some instances, compressive member  45  may comprise a plurality of circumferentially arranged dies circumferentially arranged about a central longitudinal axis extending through first and second mandrel segments  41 ,  43 . The plurality of dies may be radially movable toward and away from central longitudinal axis to adjust the size of the narrowed aperture  52 . 
     As will be illustrated and described below, stent shaping mandrel  44  may be utilized to change the shape (e.g., form) of a straight, cylindrical tubular, braided stent scaffold into a more complex-shaped stent scaffold such as stent scaffold  22  shown in  FIG. 1  (which includes enlarged portions  12 , tapered portions  17 / 19  and narrowed region  11 ). In order to form the complex scaffold  22  shape illustrated in  FIG. 1 , it may be desirable to utilize a stent fixture device  42  to manipulate the various components of the shaping mandrel  44  shown in  FIG. 9 . For example, the fixture device  42  may include a frame  46  attached between first mandrel segment  41  and second mandrel segment  43  and maintain first and second mandrel segments  41 ,  43  a fixed distance apart. In some instances, frame  46  may include an adjustment mechanism (e.g., an adjustment screw) which may allow a user to adjust the distance between the first mandrel segment  41  and the second mandrel segment  43  to a desired fixed distance. Additionally, adjusting the distance between the first mandrel segment  41  and the second mandrel segment  43  may also alter their distance from the compressive member  45 . The distance between the first mandrel segment  41  and the second mandrel segment  43  may control the shape of the first tapered region  17  and the second tapered region  19  described above with respect to  FIG. 2 . 
       FIG. 10  illustrates a cross-sectional view of the shaping mandrel  44  shown in  FIG. 9 .  FIG. 10  shows shaping mandrel  44  removed from the fixture device  42  described above. As described above,  FIG. 10  shows shaping mandrel  44  including first mandrel segment  41 , second mandrel segment  43  and compressive member  45  (positioned between first mandrel segment  41  and second mandrel segment  43 ). As described above,  FIG. 10  shows that the compressive member  45  may include a narrowed aperture  52  (e.g., opening, pinch point, etc.). It can be appreciated that the narrowed aperture  52  of compressive member  45  may be utilized to form the narrowed region  11  of the tubular scaffold  22  shown in  FIG. 1 . The narrowed region  11  of tubular scaffold  22  of  FIG. 1  may be referred to as a “necked” region. Additionally,  FIG. 10  illustrates that shaping mandrel  44  may include a first raised annular rim  48  and a second raised annular rim  48 . First annular rim  48  may be provided with first mandrel segment  41  and second annular rim  48  may be provided with second mandrel segment  43 . As will be shown and described below with respect to  FIG. 11 , first and second raised annular rims  48  may be utilized to form the enlarged portions  12  or flanges of the tubular scaffold  22  shown in  FIG. 1 . Furthermore, fixture device may include a first saddle  47  and a second saddle  49  configured to be placed around the first mandrel segment  41  and the second mandrel segment  43 , respectively, to clamp a braided tubular scaffold to the shaping mandrel  44 . For instance, a first end region of the braided tubular scaffold can be clamped between the first saddle  47  and the first mandrel segment  41  and a second end region of the braided tubular scaffold can be clamped between the second saddle  49  and the second mandrel segment  43 . 
     An example method to form tubular scaffold  22  may include positioning a straight, cylindrical tubular braided scaffold around shaping mandrel  44  (shown in  FIG. 11 ) followed by the application of a heat treatment to anneal the stent filaments  14  (shown in  FIG. 11 ) in a preferred shape (e.g., the shape dictated by the shaping mandrel  44 ). For example,  FIG. 11  illustrates an example cylindrical tubular braided scaffold  56  which has been positioned (e.g., disposed) around first mandrel segment  41  and second mandrel segment  43 , having first and second end regions clamped to the first and second mandrel segments  41 ,  43  with first and second saddles  47  and  49 , respectively. Braided tubular scaffold  56  may be formed from one or more interwoven filaments  14  formed into a cylindrical structure.  FIG. 11  further illustrates braided scaffold  56  disposed along first mandrel segment  41  and second mandrel segment  43 , with raised annular rims  48  positioned in the lumen of the braided scaffold  56  such that filaments  14  of braided scaffold  56  conform to the curvature/shape of the raised annular rims  48 . It can be appreciated that first saddle or clamp  47  and second saddle or clamp  49  may be designed to grasp and hold the braided scaffold  56  along the outer surface of both first mandrel segment  41  and second mandrel segment  43 , respectively. Additionally, first saddle or clamp  47  may be positioned proximate the first raised annular rim  48  to instill a first ridge portion  57  in the braided scaffold  56  and second saddle or clamp  49  may be positioned proximate the second raised annular rim  48  to instill a second ridge portion  59  in the braided scaffold  56 . Both first ridge portion  57  and second ridge portion  59  may extend radially away from other portions of braided scaffold  56 . Additionally, both first ridge portion  57  and second ridge portion  59  may extend circumferentially around the outer surface of braided segment  56 . 
     It can be appreciated from  FIG. 11  that the shape of each of first ridge portion  57  and second ridge portion  59  may define a particular shape of the tubular scaffold  22  after a heat treatment is applied to the braided cylindrical scaffold  56 . For example, after heat treating the braided scaffold  56  shown in  FIG. 11 , the first ridge portion  57  and second ridge portion  59  may correspond to the enlarged portions or flanges  12  of the tubular scaffold  22  shown in  FIGS. 1 and 2 . Similarly, it can be appreciated that the outer diameter of first end portion  21  and second end portion  23  of the tubular scaffold  22  shown in FIGS.  1  and  2  may correspond to the outer diameter of first mandrel segment  41  and second mandrel segment  43  shown in  FIG. 11 . 
       FIG. 11  further illustrates that shaping mandrel  44  may form a narrowed (e.g., necked) region in braided scaffold  56  by passing stent filaments  14  through the narrowed aperture  52  of the compressive member  45 . For example,  FIG. 11  illustrates filaments  14  tapering radially inward from first mandrel segment  41  to the narrowed aperture  52  and tapering radially inward from second mandrel segment  43  to the narrowed aperture  52 , with filaments of braided scaffold  56  extending through narrowed aperture  52 . In some instances, one or more dies of compressive member  45  may be actuated radially inward to radially constrain filaments  14  of braided scaffold  56  at narrowed aperture  52  to a reduced diameter, with tapered portions  60  and  62  on either side of compressive member  45 . The compressive member  45  may restrain the diameter of the braided scaffold  56  at the necked region to a diameter of D c  or less of the finished stent  10 , as described above. Additionally, it can be appreciated that first tapered portion  60  of braided scaffold  56  and second tapered portion  62  of the braided scaffold  56  may correspond to first tapered region  17  and second tapered region  19  of the tubular scaffold  22  of stent  10  shown in  FIG. 1 . 
     With the filaments  14  of the tubular braid scaffold  56  held in a desired configuration with the shaping mandrel  44 , the tubular braid scaffold  56  can be subjected to a heat treatment process to anneal the stent filaments  14  in a preferred formed shape. Thereafter, the braided scaffold  56  may be removed from the shaping mandrel  44 , while retaining its formed shape to be used as the tubular scaffold  22  of the stent  10 . 
     It can further be appreciated that the configuration that braided scaffold  22  embodies after being removed from the shaping mandrel  44  may be considered its “nominally deployed” configuration. In other words, the heat treatment process applied to the braided scaffold  56  during the forming process described above may impart a shape-memory configuration in which the scaffold  22  will revert to when unconstrained by an external force. This shaped memory configuration may be referred to as the stent&#39;s “nominally deployed” configuration. For example, if scaffold  22  is radially expanded to a diameter greater than its “nominally deployed” diameter, it will return to its “nominally deployed” diameter once the force which is maintaining the scaffold in the radially expanded configuration is removed. The nominally deployed configuration is important because it may define the threshold radial force imparted by the stent filaments  14  to maintain valve  16  in a closed configuration. As discussed above, this threshold force is the force for which the peristaltic contractions must overcome in order to open the valve  16 . Correspondingly, it provides the force imparted onto the valve  16  to bias the valve in the closed configuration to ensure stomach acids cannot leak back through the valve from the stomach (while a patient is lying down at rest, for example). 
       FIG. 12  shows method further process for constructing coating layer  20  and valve  16  within braided scaffold  22  (after braided scaffold  56  has been removed from shaping mandrel  44  as described above). As shown in  FIG. 12 , after being removed from the shaping mandrel  44 , braided scaffold  22  may be positioned on a coating mandrel  61 . The coating mandrel  61  may be constructed of multiple components to facilitate inserting the coating mandrel  61  into the lumen of the tubular scaffold  22  and through the narrowed region. For example, a first member of the mandrel  61  may be inserted into the lumen of the tubular scaffold  22  from a first end of the tubular scaffold  22  and a second member of the mandrel  61  may be inserted into the lumen of the tubular scaffold  22  from a second end of the tubular scaffold  22 . For instance, coating mandrel  61  may include a female member  66  coupled to a male member  64 . The male member  64  may include a screw member  74  that may be threaded into a female threaded recess  75  located in female member  66 , for example. It can be appreciated that this male-female connection may allow coating mandrel  61  to be easily separated and removed after coating material  65  is applied to braided scaffold  22 . 
     In some instances, the outer diameter of coating mandrel  61  may be larger than the inner diameter of braided scaffold  22  being positioned thereon. It can be appreciated that designing coating mandrel  61  to have a larger outer diameter versus inner diameter of scaffold  22  may result in the scaffold  22  being positioned snug against the outer surface of coating mandrel  61  ( FIG. 12  shows scaffold  22  being positioning snug on the outer surface of coating mandrel  61 ). Further, the larger outer diameter of coating mandrel  61  (as compared to the inner diameter of scaffold  22 ) may “radially expand” the scaffold  22  as compared to its “nominally deployed” configuration (e.g., nominally deployed diameter) as discussed above. Namely, the coating mandrel  61 , extending through the narrowed region  11 , radially expands the tubular scaffold  22  at the narrowed region to a diameter greater than its diameter Dc in the nominally deployed configuration in which the valve  16  is in the closed configuration. As will be discussed further with respect to  FIG. 13 , it can be appreciated that after coating mandrel  61  is removed from the scaffold  22  (after applying the coating layer to the scaffold  22 ), scaffold  22  may radially compress to its “nominally deployed” configuration (determined via the heat treatment process described above with respect to  FIG. 11 ) to bias the valve  16  to the closed configuration. 
     Further, it can be appreciated that coating mandrel  61  may be a variety of shapes and/or configurations. For example, coating mandrel  61  may have a profile which substantially matches the profile of the tubular scaffold  22  being positioned thereon.  FIG. 12  shows coating mandrel  61  including a profile which substantially matches the profile of the scaffold  22 . 
       FIG. 12  shows spraying element  63  applying a spray coating  65  to scaffold  22  with coating mandrel  61  extending within lumen of scaffold  22 . The layer of material applied to scaffold  22  may correspond to coating layer  20  described in the examples above. Further, as shown in  FIG. 12 , spraying element  63  may translate the full length of scaffold  22  while rotating tubular scaffold  22  and coating mandrel  61  together, depositing material corresponding to coating layer  20  accordingly. 
     It can further be appreciated that the shape of coating mandrel  61  may define the shape of valve  16 . For example, it can be appreciated that spray  65  may pass through the cells of scaffold  22 , forming a layer of material on the inner surface of scaffold  22  at locations where scaffold  22  is spaced away from coating mandrel  61 . For instance, the detailed view of  FIG. 12  shows coating mandrel  61  including a recessed portion  67  spacing the surface of coating mandrel  61  away from tubular scaffold  22  at narrowed region  11 . Recessed portion  67  may also be referred to as a “reservoir.” Further, recessed portion  67  may extend circumferentially around the entire circumference of coating mandrel  61 . Recessed portion  67  may facilitate the formation of a portion of coating layer  20  that extends radially inward from the inner surface of tubular scaffold  22 . Accordingly, the shape/contour of coating layer  20  forming the valve  16  may be determined by the profile of recessed portion  67 . For example, the cross-sectional shape of recessed portion  67  may be substantially ovular. It can be appreciated that the ovular shape created by recessed portion  67  may correspond to the ovular valve aperture  24  described above. Thus, valve  16  may be formed in the open configuration during the coating process. 
       FIG. 12  shows that in some instances, the outer surface of coating mandrel  61  will be positioned and/or aligned substantially “flush” with the inner surface of scaffold  22 . Depositing coating layer  65  along portions of coating mandrel  61  which are substantially flush with the interior surface of scaffold  56  may cause coating layer  20  to adhere to and/or form an integral interface with the inner surface of tubular scaffold  22  with the coating layer  20  filling open cells or interstices of tubular scaffold  22 . As discussed above, applying spray  65  along portions of coating mandrel  61  which are not substantially flush with the interior surface of scaffold  22  (e.g., recessed portion  67 ) may result in spray  65  passing through the cell openings of scaffold  22  and being deposited along the surfaces coating mandrel  61 . It can be appreciated that the recessed portions  67  of coating mandrel  61  may allow space for spray  65  to extend radially inward beyond the inner surface of scaffold  22  such that the coating layer  20  is molded according to the shape of the recessed portion  67 . It can be further appreciated from  FIG. 12  that coating layer  20  applied along surface of recessed portion  67  may, therefore, form the radially inward extending portions of valve  16  (including ovular aperture  24 ) described above. 
       FIG. 13  shows scaffold  22  after coating mandrel  61  (e.g., coating mandrel  61  described with respect to  FIG. 12 ) has been removed. As discussed above, components of mandrel  61  (i.e., first and second members  64 ,  66 ) may be separated to remove coating mandrel  61  from lumen of tubular scaffold  22  to provide stent  10  including scaffold  22  and coating layer  20 . For instance, male member  64  may be unscrewed from the female member  66  and separated therefrom. 
     As described above, after stent  10  is removed from coating mandrel  61 , tubular scaffold  22  may radially compress and return to its “nominally deployed” configuration. In other words, filaments  14  may radially compress narrowed region  11  inward to return the scaffold  22  to its nominally deployed configuration described above and collapse the valve  16  to its closed configuration. Valve  16  may be formed from a deflectable and/or compressible material which would deform as coating mandrel  61  is removed from scaffold  22 . For example, after valve  16  has been constructed according to the method described with respect to  FIG. 12 , its flexibility may permit the valve aperture  24  (described above but not shown in  FIG. 12 ) to close in response to scaffold  22  radially compressing and returning to its nominally deployed configuration. 
       FIG. 14  illustrates an example stent delivery system  80 . Stent delivery system may be utilized to advance and position the stent  10  described above. Accordingly, stent delivery system may include a handle member  81  coupled to an outer tubular member  82  and/or an inner member  83 . The inner member  83  may extend through the lumen of outer tubular member  82  and is depicted as a dotted line extending through a lumen of outer tubular member  82 ). The inner member  83  may be coupled to a tip member  84 . 
       FIG. 15  illustrates stent  10  positioned over (e.g., surrounding) the inner member  83  (it is noted that the outer tubular member  82  may surround a portion of stent  10  and is shown in a partially retracted configuration for simplicity). As will be described in greater detail below, the inner member  83  may extend through the lumen of stent  10  (including the valve aperture  24  described above). It can further be appreciated that the handle member  81  may be utilized to retract the outer tubular member  82  relative to stent  10 , inner member  83  and tip member  84  to deploy the stent  10 . 
     As shown in  FIG. 15 , the tip member  84  may include one or more tapered portions  85  designed to allow the tip to be easily retracted back through the lumen of stent  10  after stent  10  has been deployed at a target site. This feature is important because valve  16  of stent  10  may be radially compressed on inner member  83  when loaded on the inner member  83  with the inner member  83  extending through valve  16 . Therefore, tapered portions  85  are designed to minimize chance that tip member  84  may engage and interfere with the positioning of stent  10  as tip member  84  is retracted through the lumen of stent  10 , and through valve  16 . 
       FIG. 16  is a cross-sectional view taken along line  16 - 16  of  FIG. 15 . As described above,  FIG. 16  shows stent  10  including filaments  14  encircling valve  16 . Valve  16  may extend radially inward from the inner surface of the filaments  14  and includes an ovular valve aperture  24  through which the inner member  83  extends. As described above, valve  16  of stent  10  may be radially compressed on the inner member  83  in its “nominally deployed” configuration. In this configuration, the valve  16  (via the filaments  14 ) may exert a radially compressive force onto the surface of the inner member  83 . 
     As discussed above with respect to  FIG. 1 ,  FIG. 3  and  FIG. 4 , valve  16  may expand radially outward to allow a bolus of nutritional material (e.g., food)  18  to pass through the lumen of stent  10  and through valve  16 . Further, as discussed with respect to  FIG. 2 , in some instances it may be desirable for the valve  16  to expand radially outward to permit nutritional material (e.g., food, water, etc.) to pass through the lumen of stent  10 . For example, the stent filaments of tubular scaffold  22  which impart a radially compressive force inward on valve  16  may maintain the valve  16  in a closed configured while in a “nominally-deployed” state (e.g., a state in which no outside forces are acting on the stent  10  to move the valve  16  to an open configuration). However, the compressive force exerted by filaments  14  of tubular scaffold  22  on valve  16  must be low enough such that normal, peristaltic contractions associated with normal digestive processing (e.g., normal eating and digesting of food) will open valve  16 , thereby permitting the bolus of nutritional material to pass through valve  16  and into the stomach (while also permit vomiting contractions to expel food back through valve  16 . 
     To that end, when designing stent  10  (shown in  FIG. 1 ), it may be beneficial to understand the radially outward forces generated by a bolus of nutritional material passing through portions of stent  10 . For example, it may be beneficial to understand the minimum radially outward forces generated by a bolus of nutritional material passing through the narrowed region  11  of the stent  10 . It can be appreciated from the above discussion that the minimum radially outward forces generated by the bolus of material passing through the narrowed region  11  of the stent  10  may correspond to the maximum compressive forces exerted by filaments  14  of the tubular scaffold  22  on the valve  16 . For example, in some instances that stent  10  may be designed such that the maximum compressive forces exerted by filaments  14  of tubular scaffold  22  on valve  16  must be low enough to permit the minimum radially outward force generated by bolus of material to pass through the stent  10 . For instance, the stent  10  may be designed such that the maximum radially compressive force exerted by the filaments  14  of tubular scaffold  22  on valve  16  to close the valve  16  in a nominally-deployed state are less than the minimum radially outward force generated by a bolus of material passing through the stent  10 , in order to ensure the valve  16  opens sufficiently to allow the bolus of material to pass through the stent  10 . 
       FIG. 17  illustrates an example bolus force test fixture  90 . The test fixture  90  may be utilized to determine the radially outward forces generated by a representative bolus of material passing through the stent  10 . As shown in  FIG. 17 , the test fixture  90  may include a first stent engagement member  94   a  and a second stent engagement member  94   b , each of which are secured to a base  92 . The first stent engagement member  94   a  and the second stent engagement member  94   b  may be aligned with one another along a longitudinal axis  93 . As illustrated in  FIG. 17 , each of the first stent engagement member  94   a  and the second stent engagement member  94   b  may be secured to the base  92  via a first engagement mount or strap  97   a  (utilized to secure the first stent engagement member  94   a  to the base  92 ) and a second engagement mount or strap  97   b  (utilized to secure the second stent engagement member  94   b  to the base  92 ). 
     Each of the first and the second stent engagement members  94   a ,  94   b  may be shaped such that they are designed to engage the first end  21  and the second end  23  of the stent  10  (not shown in  FIG. 17 , but shown in  FIG. 1 ). For example, each of the first and the second stent engagement members  94   a ,  94   b  may include a first protrusion  95   a  (extending radially outward from the outer surface of the stent engagement member  94   a ) and a second protrusion  95   b  (extending radially outward from the outer surface of the stent engagement member  94   a ). It can be appreciated that the shape of each of the first engagement member  94   a  and the second engagement member  94   b  may be designed to mate with the first end  21  and the second end  23  of the stent  10  (not shown in  FIG. 17 , but shown in  FIG. 1 ). For example, the first protrusion  95   a  and the second protrusion  95   b  may each be designed to mate with the enlarged portions  12  of the stent  10 . 
     Additionally,  FIG. 17  illustrates that each of the first stent engagement member  94   a  and the second stent engagement member  94   b  may include a first lumen  92   a  and a second lumen  92   b , respectively. It can be appreciated that each of the first lumen  92   a  and the second lumen  92   b  may be designed (e.g., sized) such that a bolus member  96  may pass therethrough. The bolus member  96  may resemble a spherically shaped ball designed to mimic (e.g., resemble, etc.) a bolus of nutritional material which may pass through the stent  10  (shown in  FIG. 1 ). While  FIG. 17  illustrates that bolus member  96  spherically-shaped, other shapes are contemplated to mimic various types of nutritional material passing through the stent  10 . 
     Further,  FIG. 17  illustrates that the bolus member  96  may be attached to a pull member  98  which may be designed to pass through the first lumen  92   a  and the second lumen  92   b  of the first stent engagement member  94   a  and the second stent engagement member  94   b , respectively. In other words, it can be appreciated that the pull member  98  may be utilized to pull the bolus member  96  along the axis  93  through each of the first stent engagement member  94   a  and the second stent engagement member  94   b , and thus through the valve  16  of a stent  10  mounted to the fixture  90 . 
       FIG. 18  and  FIG. 19  illustrate the example bolus member  96  being pulled through the stent  10  described above. In particular,  FIG. 18  illustrates the first end  21  of the stent  10  mounted to the first engagement member  94   a  and the second end  23  of the stent  10  mounted to the second engagement member  94   b . Further, as described above,  FIG. 18  illustrates each of the first engagement strap  97   a  and a second engagement strap  97   b  securing the first engagement member  94   a  and the second engagement member  94   b  to the base  92 . 
     Additionally,  FIG. 18  illustrates the bolus member  96  aligned with the first lumen  94   a  along the axis  93 . Further, the pull member  98  is attached to the bolus member  96  while also extending through the first lumen  92   a  of the first engagement member  94   a , the stent  10  (including the narrowed region  11 ) and through the second lumen  92   b  of the second engagement member  94   b.    
       FIG. 19  illustrates the bolus member  96  being pulled through the stent  10 . In particular,  FIG. 19  illustrates bolus member  96  being pulled through the narrowed region  11  of stent  10 . It can be appreciated that to measure the radially outward forces generated by the bolus member  96  as the bolus member  96  is pulled through the stent  10 , one or more components of the testing fixture  90  may be attached (e.g., gripped, clamped, supported, etc.) to a force measurement machine (e.g., a tensile testing machine, Instron® machine, etc. It is noted that, for simplicity, the force testing machine is not shown in  FIG. 18  or  FIG. 19 ). For example, in some instances, the base  92  may be secured to one portion of the force testing machine while the pull member  98  may be attached to another portion of the force testing machine. 
     Further, the force testing machine may be designed to “pull” the pull member  98  (which is attached to the bolus member  96 ) through the stent  10 , as indicated by the arrow  99  in  FIG. 19 . As the pull member  98  pulls the bolus member  96  through the stent  10  (e.g., through the narrowed region  11  of stent  10  as shown in  FIG. 19 ), the force testing machine may continuously record the radially outward forces generated by the bolus member  96  as it advances through the stent  10 , as a function of the axial force measured. It can be appreciated that the speed with which the bolus member  96  is pulled through the stent  10  may be varied to better understand how the stent reacts (e.g., the force variations placed upon the stent  10 ) as the bolus member  96  passes through the stent  10  at varying speeds. 
     In some instances, the test methodology described above has shown that the radially outward forces generated by the bolus member  96  having a diameter of 15 mm may be in the range of between 2.40 N to 4.70 N as the bolus member  96  is pulled through the stent  10  at a speed of 5 mm/s, in the range of between 2.20 N to 3.40 N as the bolus member  96  is pulled through the stent  10  at a speed of 7 mm/s, in the range of between 2.20 N to 3.30 N as the bolus member  96  is pulled through the stent  10  at a speed of 10 mm/s, in the range of between 2.00 N to 3.30 N as the bolus member  96  is pulled through the stent  10  at a speed of 12 mm/s, and in the range of between 2.0 N to 3.30 N as the bolus member  96  is pulled through the stent  10  at a speed of 15 mm/s, for example. Thus, in such an instance, the filaments  14  should exert a radially inward compressive force of less than 2.0 N, less than 1.5 N, or less than 1.0 N in a nominally deployed state to ensure that the valve  16  will open sufficiently to permit a bolus of material to pass through the valve  16 . 
     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 disclosure&#39;s scope is, of course, defined in the language in which the appended claims are expressed.