Patent Publication Number: US-2021186720-A1

Title: Stents with improved fixation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/859,440 filed on Dec. 30, 2017, and claims benefit of U.S. Provisional Application No. 62/441,087 filed on Dec. 30, 2016, which are hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure provides stents, particularly esophageal stents, comprising a micro-textured surface, and a method of manufacturing thereof. The micro-textured surface advantageously contacts esophageal surfaces and reduces or prevents stent migration. 
     BACKGROUND OF THE INVENTION 
     The present disclosure relates to implantable treatment devices, and more particularly to stents and other prostheses intended for fixation in body lumens especially including the esophagus 
     Stents are generally employed to open or keep open a body lumen. For example, carcinomas in the esophagus lead to progressive dysphagia, i.e. difficulty in swallowing, and the inability to swallow liquids in the most severe cases. While surgical removal is sometimes effective, the majority of patients have tumors that cannot be surgically removed. Repeated dilations of the body lumen of the esophagus provide only temporary relief. 
     Difficult or refractory cases often are treated by intubation using open wire weave prostheses or stents. An example of an open wire weave stent is provided in U.S. Pat. No. 4,800,882 (Gianturco), wherein is described such a device employed as an endovascular stent. These prostheses are frequently subject to migration. Self-expanding mesh stents also have been considered for use as esophageal prostheses. U.S. Pat. No. 4,655,771 (Wallsten) discloses a mesh stent as a flexible tubular braided structure formed of helically wound thread elements. Mesh stents appear unlikely to lead to pressure necrosis of the esophageal wall. The inherent scalability of mesh stents, as compared to a rigid plastic stents, makes them more easily inserted and the subsequent implantation causes much less trauma to the patient. 
     A difficulty with self-expanding stents concerns their accurate placement and deployment. Typically a tube surrounds the self-expanding stent and radially compresses the stent into a reduced-radius delivery configuration. With the stent positioned at a treatment site, the outer tube is axially withdrawn, permitting the stent to radially self-expand. However, the larger size of an esophageal stent (as compared to biliary and vascular applications, for example) gives rise to substantial friction at the stent/outer tubing interface. As a result, it is difficult to precisely maintain the position of the stent during deployment, and practically impossible to retract the stent after partial deployment. 
     Migration resistant stent designs include the addition of a mechanically lumen-bonding surface to the outer surface of a stent. U.S. Pat. No. 8,435,283 (Jordan et al) describes the addition of a cross hatch pattern of pyramids to the outer surface of a stent. The texture is intended to mechanically grasp tissue, and thereby anchor the stent. Such stents suffer from the disadvantage that dislocation by peristaltic motion causes inflammation of the inner lining of the body lumen, leading to infection, necrosis and possibly perforation. 
     Stenting of the esophagus has proven to be a particularly challenging stent application. The esophagus is a muscular lumen that is about ten inches long and extends from the hypopharynx to the stomach. The esophageal lumen is subject to wavelike contractions known as peristalsis, which pushes food down through the esophagus to the stomach. 
     Conventional stents utilized for the esophagus have significant drawbacks. Because the esophagus is very soft and flexible compared to other lumina, preventing migration of the stent is problematic. In particular, the esophagus frequently changes size and position, which causes complications for typical stents. For instance, a stent having a constant diameter along its entire axial length will have a tendency to migrate as the esophagus expands. The stricture is narrower than the lumen located proximally and distally of the stricture, and the stent is longer than the length of the stricture such that the portions of the stent proximately and distally of the stricture do not help prevent the stent from migrating. Therefore, there is an increased possibility that the stent will migrate within the lumen. 
     Moreover, the esophageal lumen is muscular and its wavelike contractions generally travel from its proximal end to its distal end resulting from an impulse applied at one side of the lumen wall. Due to the actions of the lumen, flexible stents have been designed to mimic the movement of the lumen. However, flexible stents may be prone to infolding or kinking, effectively occluding one or both of the openings of the stent. Furthermore, providing more rigid stents increases the risk of damage to the lumen of the esophagus, such as by damaging the blood vessels lining the lumen. Rigid stents are also typically more prone to migration. 
     A further difficulty with self-expanding esophageal stents is that they can cause gastrointestinal reflux. To place the self-expandable esophageal stent at a lesioned part of the stenosed gullet, an operator primarily shrinks the stent so as to reduce the cross section of the stent, installs the shrunken stent in a stent insertion device, and inserts the stent into the stenosed part of the gullet using the insertion device. After the stent reaches the stenosed part of the gullet, the stent is pushed so that the stent, usually fabricated from shape-memory alloy wires, is separated from the insertion device and elastically expands and restores its original shape, thus pushing the wall of the stenosed part outwards in radial directions and thereby enlarging the size of the passage of the stenosed part, making swallowing easier. 
     However, when the esophagus is stenosed near the stomach, where the esophageal sphincter is located, the esophageal stent must be placed in the lower end of the esophagus. Low end esophageal placement can open the esophageal sphincter causing gastrointestinal reflux. The presence of stomach acid in the esophagus can significantly complicate an already pathologic condition. 
     Accordingly, there is a need in the industry for a stent that is capable of conforming to a lumen and maintaining the opening through a stricture. In addition, there is a need for a stent that reduces migration and the possibility of obstruction of the stent openings. 
     BRIEF SUMMARY OF THE INVENTION 
     With these considerations in mind, the present disclosure provides a stent device possessing an exterior (body lumen contacting) textured surface to prevent stent migration. A further object of the disclosure is to provide a radially self-expanding stent including a freely radially self-expanding fixation region in combination with a barrier region to inhibit tumor ingrowth. 
     Yet another object of the disclosure is to provide a stent that is in a reduced cross section state prior to implantation, and expands in the body to achieve a therapeutic state possessing larger cross section. 
     Yet another object is to provide an esophageal prosthesis deployable with reduced trauma to the patient, having more resistance to migration, and providing a barrier to tumor ingrowth. 
     Yet another object is to provide an esophageal prosthesis with controllable expansion regarding both rate and final cross section. 
     Yet another object is to provide an esophageal prosthesis with the proximal end of minimal diameter, and not engaged in preventing stent migration, so as not to affect the esophageal sphincter. 
     Yet another object is to provide an esophageal stent wherein the fixation region is detachable from the stent. 
     Yet another object is to provide a stent fixation region that does not rely on mechanical bonding to the inner lumen wall. 
     In particular, it is an object of the present application to provide a luminal stent that is resistant to migration, minimally damaging to the lumen lining, the contact with the lumen lining is adjustable, and the contact with the lumen lining follows any variations in the geometry or kinetics of the lumen lining. 
     The present invention is specifically directed to fixing or preventing the migration of a stent once it has been placed in a body lumen. And more specifically, to fixing region that employ a Wenzel-Cassie effect to provide a shear force in opposition to axial displacement of a stent. 
     The present disclosure the above needs and achieves other advantages which can be understood by the example of providing a stent for a lumen of the esophagus. The stent includes a tubular member and fixation regions located on or in contact with the tubular member. The fixation regions are configured to reduce migration and infolding of the stent during changes in geometry of the body lumen; for example, peristalsis. 
     Accordingly, the stent is capable of not only maintaining or even expanding a target area within a lumen but also mimicking the size and movement of the lumen. The present invention in some embodiments utilizes a modification of the stent&#39;s outer surface with microtextured features such as sinusoids, cylinders, ridges and other surfaces geometries to provide a non-mechanical bonding surface. 
     One embodiment of the present invention therefore relates to a radially-expandable implant for implantation in a bodily passageway, being at least partially expandable from an initial unexpanded state to an expanded state, having an outer surface with a geometric pattern covering said outer surface to minimize migration after implantation. It should be appreciated this pattern is extremely small in size, and in most cases undetectable by touch. However, the pattern presents a surface of microscopically and hierarchically arranged regions of varying hydrophilicity which has the unexpected effect of fixing a prosthetic within the aqueous and lubricious environment characteristic of most body lumens. 
     The stent is useable in various bodily passageways for implanting a stent, including the gastrointestinal tract (e.g., bile ducts, colon, duodenum), esophagus, trachea, urinary tract (e.g., urethra, prostate) and vasculature (e.g., aorta, coronary blood vessels, peripheral blood vessels, intracranial blood vessels). 
     According to one aspect of the present invention, the expandable cylindrical body of the stent may comprise more than one distal cuff in order to address the occurrence of a branch in the body vessel. The expandable cylindrical body being either modular or unibody in nature. 
     These and other features will be better understood through a study of the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1A -ID is a schematic diagram of an exemplary textured surface useful in the stents of the present disclosure. 
         FIG. 2A  depicts an exemplary stent having a microtextured surface region, and  FIG. 2B  depicts the stent of  FIG. 2A  further comprising a delivery sleeve. 
         FIG. 3  is alternative embodiment of a stent having a microtextured surface region. 
         FIG. 4  is a schematic of an embodiment where the textured regions are provided as bands. 
         FIG. 5  depicts a stent having a hydrogel coating disposed on a cuffed or flared end of the stent. 
         FIG. 6  depicts a two-part stent comprising a stent and a fixation sleeve. 
         FIG. 7  depicts a stent having a fixation region woven into the stent. 
         FIG. 8  depicts a stent having a fixation region disposed on flared regions, and further having a lubricious region on the stent body. In this embodiment, the spring constant of the stent body may be selected to match the spring constant of the esophagus in which it is inserted. 
         FIG. 9  depicts a stent having a plurality of surface textures regions disposed annularly about the stent body with a selected spatial periodicity alternating with slip regions. 
         FIG. 10  depicts an embodiment of a stent wherein a first end comprises a cuffed or flared region comprising a surface texture and second end that is free floating within a body lumen. The free end may comprises lubricious ribs axially oriented. 
         FIG. 11  depicts an esophageal stent comprising a surface textured region. The stent body advantageously dilates in response to a peristaltic wave from a body lumen. 
         FIG. 12  depicts a stent comprising dilated or flared regions that are displaced with respect to the stent body centerline. 
         FIG. 13  depicts a stent comprising slip ribs and a surface texture region. The surface texture region in this embodiment is capable of engaging with an esophageal growth in the esophagus. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is an exemplification of the principles of the present disclosure and is not intended to limit the disclosure to the particular embodiments illustrated herein. 
     Stents perform three functions: 1) stent or hold open a body lumen, 2) prevent ingrowth into a body lumen, and 3) anchor or fix functions 1 and 2 at a specific site within the body lumen. 
     Generally, there is no clinical requirement that the stent part responsible for the anti-migration or fixation feature should be fixed permanently to the stent part responsible for the radial force component. In other words, the anti-migration function and the stent function can be completely decoupled structurally. In this disclosure, the stent is considered to be all components of a lumen opening device implanted in a body. 
     Accordingly, the embodiments can be divided into three categories: 1) fixation regions integral to the stent, 2) fixation regions separable from the stent, and 3) fixation regions that are both separable and integral to the stent. In the third category, the fixation region provides the dual role of providing fixation and blocking ingrowth. 
     Textured Surface Fixation 
     The textured surfaces responsible for the fixation or gripping features of the stents of the present invention comprise textures that initially create Cassie and Wenzel states when exposed to a liquid environment in a mammalian body. These states evolve in situ, and their evolution analogues differ from typical Wenzel and Cassie states in that they involve a solid hydrophilic phase, a liquid hydrophobic phase, and a liquid hydrophilic phase or a solid hydrophobic phase, a liquid hydrophilic phase, and a liquid hydrophobic phase. In these modified Wenzel and Cassie states, the trapped phase analogous to the classical gaseous phase is the liquid hydrophobic phase. Alternatively, a trapped gaseous phase is preferentially replaced by a liquid hydrophobic phase. 
     The Cassie and Wenzel phenomena, occur when three phases are in contact with one another. In the body, the respective states lead to the formation and retention of an implant of a liquid hydrophobic film in the Cassie state and retention of tissue (containing lipids) in the Wenzel state. In a hybrid Cassie-Wenzel state, where one texture scale is Wenzel and the other is Cassie, the implant can be localizing to a tissue surface. 
     A scale of interaction is defined by the surface texture of the present stent surfaces, and is typically hierarchical, and characterized by at least two spatial scales, one on the order of micrometers (microns) and another on the order of 10 to 100 microns. The surface texture may induce one state with a large difference between preceding and receding contact angles (contact angle hysteresis), or alternatively another state with a small contact angle hysteresis. States of interest are known respectively as Wenzel and Cassie states. Each of the hierarchical spatial scales may induce separately a Wenzel or Cassie state, such that combinations are possible on a multiplicity of spatial scales. It is this combination of states that results in the surprising non-traumatic gripping feature of the present stents. 
     Examples of geometrical structures having scales of interaction include pillars, cubes, pyramids, or any feature with a typical overall size. For example, in the case of a cube, the scale of interaction would be the length of the cube. These surface structures, characterized by a scale of interaction are typically spaced apart, distance center to center, by a spatial frequency known as pitch. For example 4 micron squares with pitch 8 microns would mean the squares are separated on their surfaces by 4 microns. Typically the pitch is 1 to 10 times the scale of interaction. Also typically regarding hierarchical arrangement of different scales of interaction, the different scales of interaction and the pitch are 1 to 10 times smaller than the next hierarchical level. In many cases, one size of interaction is located on a large size of interaction. For example 1 micron pillars placed on the top surface of 10 micron pillars, with pitch 1 and 10 microns respectively. 
     These textures develop phenomena between hydrophobic and hydrophilic components of a mixture disposed on a surface interface. For example, the smaller interaction scales are hydrophobic and the larger interaction scales are hydrophilic. A hydrophobic surface attracts hydrophobic components in a interfacial mixture, and repels hydrophilic components, and conversely for hydrophilic surfaces. 
     The interaction of a solid textured surface with water in a gaseous environment is described by the Cassie-Baxter model. In this model, air is trapped in the microgrooves of a textured surface and water droplets rest on a compound surface comprising air and the tops of micro-protrusions. The importance of a fractal dimension between multiple scales of texture is well recognized and many approaches have been based on the fractal contribution, i.e., the dimensional relationship between different scales of texture. However, regardless of the material (organic or inorganic) used and geometric structure of the surface texture (particles, rod arrays, or pores), multiple scales of texture in combination with low surface energy has been required to obtain the so called superhydrophobic surfaces. 
     Superhydrophobicity is variously reported as a material exhibiting a contact angle with water that is greater than contact angles achievable with smooth but strongly hydrophobic materials. The consensus for the minimum contact angle for a superhydrophobic substance is 150 degrees, so in this context most of the embodiments of the present invention are not strictly superhydrophobic, although this option is not excluded. The reason for this is that a Wenzel-Cassie state lies in its hydrophobicity between non-textured surfaces and surface that generate a Cassie-Baxter interface. In optimizing the fixation of the stents of the present invention superhydrophobicity is just one aspect of a number of interesting texture controlled mechanisms, and in this context the contact angle is less important than the contact angle hysteresis. 
     A hydrophobic surface repels water. The hydrophobicity of a surface can be measured, for example, by determining the contact angle of a drop of water on a surface. The contact angle can be measured in a static state or in a dynamic state. A dynamic contact angle measurement can include determining an advancing contact angle or a receding contact angle with respect to an adherent species such as a water drop. A hydrophobic surface having a small difference between advancing and receding contact angles (i.e., low contact angle hysteresis) results in surfaces with low resistance to in plane translation (low adherence). Water can travel across a surface having low contact angle hysteresis more readily than across a surface having a high contact angle hysteresis, thus the magnitude of the contact angle hysteresis can be equated with the amount of energy needed to move a substance. 
     A high surface area is achieved by superimposing multiple structures one on top of the other in superposition. When these multiple structures are sufficiently different in dimension then the superposition of these structures is referred to as a hierarchical structure or pattern. A subset of surfaces useful in the present invention are characterized as superhydrophobic. 
     Surface textures useful in the stents disclosed herein provide a gripping or fixation region when in contact with a body lumen, such as a lumen of an esophagus. The surface texture can comprise at least one class of hydrophobic regions on at least one spatial interaction dimension, and at least one class of hydrophilic regions on one or more other spatial interaction dimensions, wherein the ratio of any two spatial dimensions is greater than 2. 
     One embodiment of a surface texture useful in the present stents is a biomimetic of the natural rose pattern. Referring to  FIG. 1 , the pattern  100  comprises three structures: 1) a two-dimensional sinusoidal pattern  102 , 2) a first column pattern  104 , and 3) a second column pattern  106  combined with a flute pattern  108  disposed on second column  106 . These structures have characteristic dimensions. For example the amplitude  110  and pitch  112  of the sinusoidal pattern  102  is in the range of 50 to 500 microns or larger. The height  114 , diameter  116  and pitch  118  of the first column pattern is in the range 20-50 microns. The height  120 , diameter  122  and pitch  124  of the second column pattern as well as the height  126  and pitch  128  of the flutes are in the range of 5-20 microns. 
     Fixation Integral to the Stent 
     In accordance with one embodiment of the present invention, the stent can be manufactured by utilizing an injection molding process. By utilizing this process, a particular surface texture of the stent can be controlled by cutting the inverse surface texture pattern into the inner diameter of the mold. The inner surface of the mold can contain any of various geometrical patterns arranged hierarchically and possessing different spatial dimensions such as sinusoids, columns, pyramids or flutes, as shown in  FIG. 1 . 
     In some embodiments, low profile geometries on the exterior wall of the stent will minimize migration while preventing tissue damage in situ or upon removal. Additionally, these structures, since they are arranged hierarchically allow fluids to flow between the stent and body lumen. For example, fluids from either the pancreatic duct or cystic duct can pass between the wall of the bile duct and the outer surface of the stent, should the stent pass over these ducts. 
     In one embodiment, the invention comprises a stent and, more preferably, a stent suited for placement within the gastrointestinal (GI) tract of an animal or a human. In a further embodiment, the GI tract comprises the esophagus, the pancreatic duct, cystic duct or common bile duct. In yet a further embodiment, the outer surface of the implant comprises at least one surface texture that provides a fixation region to assist in limiting the potential migration of the implant within the body lumen. In addition to its use as an esophageal prosthetic, the present invention may be used in any bodily vessel, such as in the coronary or peripheral vasculature, esophagus, trachea, bronchi, colon, biliary tract, urinary tract, prostate, brain, as well as in a variety of other applications in the body. 
       FIG. 2A  depicts stent  200  of the present invention. In one embodiment, stent  200  includes a stent body  202  having an axial length  224 . The stent  200  assumes the normal or relaxed configuration, as depicted in  FIG. 2 , when it is not subject to any external load or stress. The stent body  200  may be partly or fully covered with an elastomeric membrane or film  204 . The elastomeric film  204  is defined by an exterior surface  206  and an inner surface  208 . The film may be disposed axially along the stent to cover substantially the entirety of the axial length of the stent. Stent  200  comprises an open weave construction of mesh segments  210 . Mesh segments  210  may be metal wire or a polymeric mesh, and provide a flexible stent structure in some embodiments. Wires or segments  210  may be paired and helically wound. 
     Stent  200  includes several regions, including an intermediate region  212 , a distal end cuff region  214  and a proximal end cuff region  216 . The distal end cuff region  214  and the proximal end cuff region  216  may be shaped so as to have a wider cross-section than intermediate region  212 , for example, which may be useful as an esophageal prosthetic device. Distal end cuff region  214  and proximal end cuff region  216  may include flares or dilated regions having cross sections  218  and  220 . The cuff region and/or the flares have a diameter that is larger than the diameter of the intermediate region and aid in fixation of the stent when inserted in a body lumen. 
     The stent  200  further includes a surface texture disposed on a portion thereof, the surface texture providing a fixation region of the stent. As depicted in  FIG. 2A , the surface texture  222  may be disposed on the flare regions  218  and  220  in some embodiments. The surface texture  222  can be a three dimensional geometric structure depicted in  FIG. 1 , and may be integrally formed with the elastomeric film  204 . The surface texture  222  provides an anti-migration effect to the prosthesis  200 . 
     This embodiment provides improved stent fixation and is particularly effective in resisting either proximal or distal migration of the stent  200  upon insertion into a body lumen. Flared cuffs  218 ,  220  may be designed with flexibility to readily conform to changes in the body lumen wall during the transmittal of bodily fluid or food. Alternatively, the present invention also envisions a stent body having no flared end, or including one flared end. 
     In some embodiments, each end of the stent comprises a fixation region. In some embodiments, the fixation region comprises an inflatable annulus. In other embodiments, the textured region comprises an elastic polymeric torus. 
       FIG. 2B  depicts an embodiment of stent  200  having a delivery sleeve  223  disposed around the exterior of stent body  200 . The delivery sleeve may be disposed around any area of the stent  200 , including at least one of the intermediate region  212 , distal end cuff region  214  and proximal end cuff region  216 . The delivery sleeve advantageously aids in the positioning and deployment of the stent within the body lumen. 
     Generally, the exterior surface  206  of the stent  200  may be designed to be fairly smooth. A surface texture  222 , such as a three dimensional geometric structure depicted in  FIG. 1  may be integrally formed with the elastomeric film  204 . The surface texture  222  provides an anti-migration effect to the prosthesis  200 . 
     As depicted in  FIG. 1 , surface texture  222  may be a three-dimensional geometric structure containing a relief feature such as columns, sinusoids, or flutes. However, the surface texture  222  may encompass any projection or indents of shapes or other complex geometries which comprise hierarchical and alternating regions of differing hydrophilicity over the exterior surface  206 . When formed with the surface texture  222  disposed over the exterior surface  206 , the stent body  200  is given a wet surface gripping functionality over all or a portion of the surface  206 , which act as fixation regions between the stent body  200  and the body lumen into which the stent body  200  is disposed. 
     The surface texture  222  may be configured to accommodate various tolerances in delivery systems which in some embodiments are to be used with the stent body  200 . For instance, a stent body  200  is depicted in its relaxed or normal configuration in  FIG. 2 . As depicted, the intermediate region  212  may have a diameter of about 15-20 mm, and the cuff of the proximal region  214  and/or the cuff of the distal end region  216  may have a diameter of about 25-28 mm. In this particular embodiment, the wires  210  may have a diameter of about 0.22 mm or less. The three-dimensional structure  222  may preferably have a cross section of less than approximately 1 mm. This tolerance ensures that the overall diameter increase of the delivery device is kept, for instance, less than 2 mm (assuming one three-dimensional structure  222  wraps around the stent). However, the present invention is not limited by the exemplary dimension tolerance. The total diameter may vary according to usage of the particular delivery device in a particular vessel. For instance, the dimensional tolerance for esophageal stent may be different from a coronary stent. 
       FIG. 3  depicts yet another embodiment of the present invention in which the surface texture layer  322  is not integrally formed with the elastomeric membrane  304 . As depicted in  FIG. 3 , a thin discrete layer may be disposed on the exterior surface  306 . In one particular embodiment, the anti-migration structure layer  322  forms a pattern helically expanded about the exterior surface  304  of the intraluminal prosthesis  300 . According to one embodiment of the invention, the surface texture  322  may be formed from the same material from the elastomeric membrane  304  is formed. In some embodiments, the surface texture  322  may be in the form of bands that span across a common longitudinal axis of the stent body  300 . 
     In another embodiment, the stent body  300  may be provided with the first set of anti-migration bands comprising surface texture  322  having a common direction of winding but circumferentially displaced relative to each other. In this embodiment, the first set of anti-migration bands comprising surface texture  322  may be configured to cross a second set of anti-migration bands also circumferentially displaced relative to each other but winding in substantially opposite direction. In this embodiment, the stent body  300  is sufficiently configured to have anti-migration properties, as provided by the anti-migration bands. The directions of the bands for the present invention are not limited by the above examples, and also may extend lengthwise or perpendicular to the longitudinal axis. Further, the bands may change direction at random locations, for example, they may be curved or wavy at random locations along stent  300 . 
     The device  300  of the present invention may include surface textures  322  provided as bands configured to flex along certain selective dimensions. For instance, the surface texture band  322  may include an anti-migration structure that is flexible in a radially outward direction of the stent body  300 . In addition, the surface texture  322  may be rigid in the longitudinal direction at certain locations. 
     Various methods of forming the stents are provided herein. In one embodiment, during the fabrication process of the stent body  200 , surface texture  222  may be added to the wires  210  after the outer surface  206  is disposed on the wires  210 . In an alternate embodiment, the surface texture  222  may be provided as a layer formed integrally with the wires  210 . Instead of the layer completely wrapping over exterior surface  206 , bands of the surface texture  222  may be interwoven with the wires  210 . In this embodiment, the surface texture  222  may partially or wholly substitute the elastic membrane  204 . 
       FIG. 4  depicts a portion of a stent body  200 . The surface texture  422  may be provided as anti migration bands  430  having smaller width  432  than the distance  434  between wires  410 . In an alternate embodiment, the bands  436  may along exposed portions  438  have a width  440  larger than the distance  434  between wires  410 . Further, the stent  400  may be configured with a variety of bands  422  of different widths. 
     Yet another advantage of the surface texture being provided as anti-migration bands  430  disposed on the elastomeric membrane is that it may provide structural reinforcement along the stent body. This reinforcement may enable the wires  410  to be constructed with a reduced angle. As used herein, the angles between the wires  410  is measured based on their incline deviation from the axis  440  of the stent. 
     In prior stents, an angle  436  of 45 degrees from the axis  440  may have been considered a lower practical limit for the angle of a mesh or open weave wire stent  200 . Employing the present invention, however, may enable a reduction of the braid angle to as low as 20 degrees from the axis  440 . The advantage of a lower angle for the wires  410  follows from the fact that the angle may contribute to the ratio of stent axial shortening to its radial increase structure. As the stent expands, either through use of self-expanding materials or through the assistance of a balloon, a lower angle facilitates greater radial expansion of the stent body  200 . With a reduced braid angle, upon expansion, there may be less axial shortening for a given radial expansion. Due to the reduced axial shortening, the stent body  200  may be more accurately positioned within the body lumens during its deployment. Thus, the profile of a surface texture  422 , in combination with the stent  200 , may resist the extraneous stretching and assist in the precise positioning of the stent inside a body lumen. 
     There are a multiplicity of arrangements of the anti-migration layer that are clinically preferred, depending upon the application. The possibilities are: full coverage of the stent, spiral patterns formed using strips, checkerboard pattern of squares or circles located on the crossing points of the wires, and mainly on the end regions (flared) and in segments or a continuous band. 
     In general, coating of the device with an elastomeric membrane is designed to enhance lumen patency. In addition, the tubular coating may resist tumor ingrowth. The thickness of the elastomeric membrane may be in the range of 0.075-0.25 mm. However, such elastomeric membrane may also be up to a range of 0.75-1.00 mm. In some embodiments, the elastomeric membrane may include a silicone film layer. The elastomeric membrane  204  may be disposed onto the outer surface of the stent body  200  by any desired means, including by placing the elastomeric membrane onto the surface, by extruding the elastomeric membrane onto the outer surface, or by dipping or spraying the elastomeric membrane onto the outer surface. 
     The elastomeric membrane of the prosthesis may also be formed of polytetrafluoroethylene (PTFE/ePTFE). Considered alone, the coating should provide an effective barrier to tissue ingrowth. In addition, the elastomeric membrane may be elastic, and thus may radially expand like the remainder of stent body. Thus, silicone construction, in general, may be engineered to exert constant, gentle pressure to help adapt to normal luminal patency, for instance of esophageal peristalsis as its smooth inner surface helps facilitate passage of fluid. Optionally, the ends of the prosthesis may also be reinforced by continuous polymeric film to help resist hyperplasia. 
     All of the components of the intraluminal device should be made of biocompatible materials, including metals or polymeric materials. Any materials may be used in the forming of these elements. In one embodiment, the elastomeric membrane preferably includes silicone, but other materials having elastomeric and biocompatible characteristics are also envisioned by the present invention. By way of example and not limiting the invention in any manner, other materials for any or all of the components of the device may include polyurethane, polyethylene, polytetrafluoroethylene, or expanded polytetrafluoroethylene, polyolefins such as high density polyethylene and polypropylene, polyolefin copolymers and terpolymers, polyethylene terephthalate, polyesters, polyamides, polyurethaneureas and polycarbonates, polyvinyl acetate, thermoplastic elastomers including polyether-polyester block copolymers, polyvinyl chloride, polystyrene, polyacrylate, polymethacrylate, polyacrylonitrile, polyacrylamide, silicone resins, combinations and copolymers thereof, and the like. 
     Other useful coating materials include any suitable biocompatible coating. Non-limiting examples of suitable coatings include hydrophilic materials, hydrogels, and the like. Useful hydrophilic coating materials include, but are not limited to, alkylene glycols, alkoxy polyalkylene glycols such as methoxypolvethylene oxide, polyoxyalkylene glycols such as polyethylene oxide and its copolymers, polyethylene oxide/polypropylene oxide copolymers, polvalkylene oxide-modified polydimethylsiloxanes, polyphosphazenes, poly(2-ethyl-2-oxazoline), homopolymers and copolymers of (meth) acrylic acid, poly(acrylic acid), copolymers of maleic anhydride including copolymers of methylvinyl ether and maleic acid, pyrrolidones including poly(vinylpyrrolidone) and its derivatives, homopolymers and copolymers of vinyl pyrrolidone, poly(vinylsulfonic acid), acryl amides including poly(N-alkyl acrylamide), poly(vinyl alcohol), poly(ethyleneimine), poly(carboxylic acids), methyl cellulose, carboxymethylcellulose, hydroxypropyl cellulose, polyvinyl sulfonic acid, water soluble nylons, heparin, dextran, modified dextran, hydroxylated chitin, chondroitin sulphate, lecithin, hyaluronan, combinations and copolymers thereof, and the like. 
     Other non-limiting examples of suitable hydrogels include hydroxyethyl acrylate or hydroxyethyl(meth)acrylates; polyethylene maleic anhydride, combinations and copolymers thereof, and the like. 
     Other useful synthetic biocompatible polymeric materials include, but are not limited to, polyesters, including poly methyl acetates, naphthalene dicarboxylate derivatives, and silks. The polymeric materials may further include a metallic, a glass, ceramic or carbon constituent or fiber. Useful and non limiting examples of bioabsorbable or biodegradable polymeric materials include poly(L-lactide), poly(D,L-lactide), poly(glycolide), poly(L-lactide-co-D,L-lactide), poly(L-lactide-co-glycolide), poly(D,L-lactide-co-glycolide) (PLA/PGA), poly(glycolide-co-trimethylene carbonate) (PGA/PTMC), polydioxanone, Polycaprolactone, polyhydroxybutyrate, poly(phosphazene) poly(D,L-lactide-co-caprolactone), poly(glycolide-co-caprolactone), poly(phosphate ester) and the like. Some other materials which may be used as the filament include, but are not limited to polyether ether ketone, fluorinated ethylene propylene, and polyimide, polybutylene terephthalate, polyurethane rubber, and silicone rubber. 
     Any component of the prosthetic device, and particularly the anti-migration structure layer, may also include a therapeutic agent that may be released into the body. Useful therapeutic agents or drugs include but not limited to, anti-platelets, anti-thrombins, anti-tumor drugs, anti-hyperplasia agents, anti-plaque building agents, cytostatic agents, and anti-proliferative agents, or other drugs for a specific purpose. This may also include agents for gene therapy. The therapeutic agent or drug is preferably selected from the group of therapeutic agents or drugs consisting of urokinase, dextro phenylalanine proline arginine chloromethylketone, enoxaparin, angiopeptin, acetylsalicylic acid, paclitaxel, 5-fluorouracil, cisplatin, vinblastine, vincristine, sulfasalazine, mesalamine, sodium heparin, low molecular weight heparin, hirudin, prostacyclin and prostacyclin analogues, dextran, glycoprotein Ib/IIIa platelet membrane receptor antibody, recombinant hirudin, thrombin inhibitor, calcium channel blockers, colchicine, fibroblast growth factor antagonists, fish oil, omega 3-fatty acid, histamine antagonists, HMG-CoA reductase inhibitor, methotrexate, monoclonal antibodies, nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitor, suramin, serotonin blockers, steroids, thiol protease inhibitors, triazolopyrimidine and other PDGF antagonists, alpha-interferon and genetically engineered epithelial cells, and combinations thereof. The foregoing list of therapeutic agents is provided by way of example and is not meant to be limiting, as other therapeutic agents and drugs may be developed which are equally applicable for use with the present invention. 
     Stents of the present disclosure may be manufactured from a mold comprising a top portion and a bottom portion. The top portion may comprise an inner and outer surface, wherein the inner surface may be adapted to receiving material for the manufacture of the stent according to the present invention. The stent may be formed as a hollow structure, which may be etched, or may be formed as a coiled structure resembling a coil spring. U.S. patent application Ser. No. 10/683,314, filed Oct. 10, 2003, disclose suitable materials and geometries for stents. 
     In another alternate method of manufacture, the stent may be formed by molding the exterior surface modification onto a separate layer of material, such as for example a non-textile material. As used herein, the term “non-textile” and its variants refer to a material formed by casting, molding, spinning or extruding techniques to the exclusion of typical textile forming techniques, such as braiding, weaving, knitting and the like. Non limiting examples of useful polymeric materials for the non-textile polymeric graft portions include polyesters, polypropylenes, polyethylenes, polyurethanes, polynaphthalenes, polytetrafluoroethylenes, expanded polytetrafluoroethylene, silicone, and combinations and copolymers thereof. Desirably, the polymeric material polytetrafluoroethylene, including expanded polytetrafluoroethylene. 
     A stent can be formed in a variety of configurations and of a variety materials known to one skilled in the art. In particular, conventional esophageal stents can be used or readily modified for use in the present invention. Such stents can be of the non-expanding or expanding variety, including those typically used in addressing problems of progressive dysphagia associated with esophageal cancer. Expanding stents include those that are deformable and that are typically expanded using, e.g., a balloon catheter, as well as those that are resilient in nature and that can be delivered in a compressed state and which can self-expand to their original state. Preferably, the stents are of the radially self-expanding variety for ease of deployment in the esophagus. Typically, such stents are made of stainless steel or nitinol (nickel-titanium alloy) and formed into e.g. knitted wire tube, tubular mesh, coiled spring, and like configurations. Suitable self-expanding esophageal metal stents include those sold under the brand names Esophacoil™ (Medtronic/Instent, Eden Prairie, Minn.). Ultraflex™ (Boston Scientific/Microvasive, Natick, Mass.), Wallstent™ (Boston Scientific/Microvasive, Natick, Mass.), and Z-stent™ (Wilson-Cook, Winston-Salem, N.C.). Additional examples of such stents include those described in U.S. Pat. Nos. 5,876,448 and 6,248,058, each of which is incorporated herein by reference in its entirety. Length and diameter of the stent can usually range from 6-15 cm (length) and 16-22 mm (diameter) for most applications. The stents may further be coated, either partially or completely, with e.g. a polymeric film such as silicone. 
     Any stent can have a covering and the coverings are thus not limited to nitinol stents. Moreover, the stent need not be covered whatsoever, may be partially covered or may be fully covered. The stent may also have a covering on the inside, the outside or both. 
     Other suitable covering materials can be employed as well. Examples of other suitable covering materials include, but are not limited to, polyethylene, polypropylene, polyvinyl chloride, polytetrafluoroethylene, including expanded polytetrafluoroethylene, fluorinated ethylene propylene, fluorinated ethylene propylene, polyvinyl acetate, polystyrene, poly(ethylene terephthalate), naphthalene, dicarboxylate derivatives, such as polyethylene naphthalate, polybutylene naphthalate, polytrimethylene naphthalate and trimethylenediol naphthalate, polyurethane, polyurea, polyamides, polyimides, polycarbonates, polyaldehydes, polyether ether ketone, natural rubbers, polyester copolymers, styrene-butadiene copolymers, polyethers, such as fully or partially halogenated polyethers, and copolymers and combinations thereof. 
     Alternatively, the stent may have a braided construction with a flared proximal end. In this embodiment, the stent is an esophageal stent. A stent may be formed of any suitable stent material including metallic and non-metallic materials as well as shape memory materials. Examples of suitable materials include, but are not limited to, shape memory alloys such as Nitinol, other metallic materials such as stainless steel, tantalum, titanium, nickel-chrome, or cobalt-chromium alloys such as those sold under the tradename of Elgiloy®. A stent may have a flared distal end or flared proximal and distal ends as well. 
     Hydrogel Cushioned Stents 
     In  FIG. 5 , a hydrogel coated stent  500  is shown in its expanded form. The hydrogel coated stent  510  comprises a proximal cuff or flare  525 , a main elongated body  520 , a distal cuff or flare  530 . A hydrophilic polyurethane hydrogel  535  is disposed about at least one of the proximal  525  and distal cuffs  530  of the stent  510 . Preferably, the proximal cuff  525  includes a hydrophilic polyurethane hydrogel. According to another aspect of the present disclosure, both cuffs  525  and  530  comprise the polyurethane hydrogel. 
     When initially inserted into the body vessel, each of the cuffs  525 ,  530  and the elongated body  520  are similar in diameter and allow for continued fluid flow around the exterior of the stent  510 . However, upon exposure to an aqueous environment (i.e., bodily fluids) the polyurethane hydrogel expands so that the outer diameter of the cuffs  525 ,  530  increases. This increase in diameter causes the cuffs  525 ,  530  to exert a sealing force against the wall of the body vessel. This sealing force stops the bodily fluid from flowing between the cuffs  525 ,  530  and the vessel wall, thereby, forcing all of the fluid flow to enter and exit through the stent  510 . 
     The use of a hydrophilic polyurethane hydrogel can potentially reduce the incidence of encrustation and the occurrence of a complicating infection. However, if this polymer layer is a polyurethane hydrogel, the polymer layer will enlarge or swell when exposed to an aqueous environment, thereby, allowing the struts of the stent-graft to bend more freely without kinking. 
     The polyurethane hydrogel layer represents a 3-dimensional network of cross-linked hydrophilic macromolecules that can swell and absorb about 20 to 90 percent by weight of water. The hydrogel layer may be applied as or onto the cuff of a stent-graft by coating, adhesive bonding, lamination, extrusion, or molding. The application method used is selected to provide a layer of the hydrogel having a substantially uniform thickness. 
     The stent may comprise an expandable or inflatable structure embedded within a polymeric matrix or a solid polymeric matrix. In both cases, the polyurethane hydrogel may be applied as a strip or band disposed around the outer surface of the cuff, such as a torus shape or an annulus. 
     After the hydrogel is disposed around the cuff of a stent, it may be dried by any method known in the art, including but not limited to conduction drying, convection drying, hot air impingement, steam treatment, infrared irradiation, ultraviolet irradiation, and microwave irradiation. Preferably, the hydrogel coating is dried by the application of thermal energy. 
     Drying the hydrogel causes it to dimensionally shrink. A stent whose hydrogel cuff is dried can be made to shrink to a cross section ready for insertion into a body vessel. In this condition, the hydrogel cuff can take about the same diameter as the elongated body  520  of the stent  510 . In some cases the act of drying the polyurethane gel will cause the stent to be in collapsed state. If the hydrogel is formed around a mesh, the gel will expand only in the direction perpendicular to the mesh. The shape and ratio of polyurethane to water is predetermined at the moment of polymerization. 
     The migration resistant surface texture can be applied to the hydrogel or elsewhere on the stent. If applied to the hydrogel, the surface texture can be applied either in the hydrogel dry state or wet state. In either case, the surface texture can be applied as an elastomeric layer or a segmented layer, or formed in the hydrogel itself. 
     Fixation Separate from the Stent 
     In some cases, once the stent is deployed, the position of the stent may shift relative to its position in the body lumen prior to deployment. After the stent is deployed, it can be difficult to reposition the stent. In some cases, re-positioning of the stent can be facilitated by decoupling the stenting function from the fixation function. 
     Referring to  FIG. 6 , a two-part stent  610  comprises a conventional wire stent  612  and fixation sleeve  614 . Stent  610  is shown in its deployed state. To deliver the stent, stent  610  is collapsed. Once deployed, outer sleeve surface  616  with surface texture  618  engages the inner wall of the body lumen. On initial deployment, wire stent  612  can easily be relocated within sleeve  614  without moving the sleeve  614  relative to the body lumen. 
     Wire stent  612  comprises outer surface  620  and optionally a fixation region  624 . Alternatively, in the case where fixation region  624  is absent, wire stent  612  can be fixed to sleeve  614  via suture, staple or the like. 
     Preferably, fixation region  624  is a surface texture  622  coated with a water soluble material such that initially surface texture  622  is smooth. Optionally, a second coated surface texture may be placed on the inner surface  626  of sleeve  614 . The coating may be any material used in the pharmaceutical industry to delay release of a drug. 
     After a predetermined time, the coating dissolves either through irrigation or due to body fluids present in the body lumen. Upon dissolution of the coating, wire stent  612  fixes to sleeve  614 , and sleeve  614  is fixed to the inner wall of the body lumen, thus fixing stent  610  within the body lumen. 
     Fixation both Separate and Integral to the Stent 
     In yet another embodiment, the fixation region can be woven into the stent in a relatively loose configuration, which allows repositioning of the stent without repositioning the fixation region. After deployment, the loose configuration can be tightened or fixed. 
     In one particular embodiment shown in  FIG. 7 , stent  700  comprises stenting body  710  and movable anchoring element  720  is in the form of a strip of patterned silicone. Stent  710  may be coiled or patterned as a braided or woven open network of wires, fibers or filaments interwoven in a braided pattern to form a tubular stent  700 , 
     In this embodiment, the movable anchoring element  720  may extend in the direction of the longitudinal axis of the stent and can be interwoven in the braided construction of the stent  710 . The anchoring elements  720  may be fixed at one end, both ends, or at some point in between the distal and proximal portions of the stent. The anchoring element may comprise a surface texture as described herein. 
     Any number of strips can be employed. Suitably, a minimum of two strips are positioned symmetrically about the circumference of the stent  700  to provide uniform anchoring in a body lumen. 
     Additionally, a single circumferential ring of anchoring elements may be positioned in the middle of the stent to prevent stent “walking” which may occur if anchoring elements are positioned at both ends of the stent. 
     With reference to  FIG. 8 , an esophageal stent  800  comprises stent body  802  and dilated regions  804  where a surface texture  806  is disposed thereon, thereby providing a fixation region. A lubricious region  808  is disposed on the middle of the stent body  802 . The spring constant of the stent body  802  may be designed to match the spring constant of a target esophagus. 
     With reference to  FIG. 9 , an esophageal stent  900  comprises stent body  902  and dilated regions  904  where a surface texture  906  is provided as an annular band and disposed over the stent body  902  with a particular spatial periodicity. In this embodiment, the wavelength of the target esophageal peristaltic motion is known. For example, for the adult human esophagus the peristaltic wavelength is approximately 5 cm. When stent  900  is placed in a human esophagus, the surface texture  906  is placed at ½ wavelength intervals  908 , such that esophageal peristaltic wave  910  is alternatingly slipping in regions  912  and gripping the esophageal wall in regions  914 . This arrangement of grip surfaces allows the passage of the esophageal peristaltic wave without displacement of esophageal stent  900  relative to the esophagus  916 . Alternatively, the spacing  908  may be one wavelength. Alternatively, surface textures  918  may be disposed on cuff or flared regions  904 . 
     The slip regions of  FIGS. 8 and 9  may comprise a lubricious membrane, such as silicone, or a gel, such as a hydrogel. 
     With reference to  FIG. 10 , an esophageal stent  1000  comprises a stent body  1002  and one flared or cuff region  1004  where surface texture  1006  is disposed over the stent body  1002 . In this embodiment, one end  1008  is free floating within an esophagus. Optionally, end  1008  may be configured with lubricious ribs  1010  oriented axially, such that the esophagus is induced to slip axially without stent end  1008  displacement. Ribs  1010  may be of sufficient height to prevent rotational displacement of stent end  1008 . Optionally, hydrogels may be disposed on ribs  1010 . 
     With reference to  FIG. 11 , an esophageal stent  1100  comprises a stent body  1102  and cuff or flare regions  1104  where surface texture  1106  is disposed over the stent body  1102 . Stent body  1102  when compressed in direction  1108  by peristaltic wave  1110 , stent body  1102  dilates in direction  1112 , such that stent body  1102  stays in contact and follows peristaltic wave  1110 . Optionally, stent body  1102  may be disposed with grip regions  1106  with peristaltic wave periodicity as illustrated in  FIG. 9 . 
     With reference to  FIG. 12 , an esophageal stent  1200  comprises a stent body  1202  and dilated regions  1204  where surface texture  1206  is disposed over the stent body  1202 . Cuff or flare regions  1204  are displaced with respect to stent body centerline  1208 . The displacements of the two cuff or flare regions  1204  are ideally 180 degrees out of phase, such that one end is displaced “up” and the other end is displaced “down”. This configuration induces the middle part of stent body  1202  to deflect in direction  1212  with respect to peristaltic wave  1210 . Accordingly, stent body  1202  follows peristaltic wave  1210 . 
     With reference to  FIG. 13 , an esophageal stent  1300  comprises a stent body  1302  and cuff or flare regions  1304  where slip ribs  1306  are disposed over the stent body  1302 . The primary fixation region  1308  is designed to engage an esophageal growth  1310  on esophagus  1312 . Optionally, region  1308  may be radially reinforced, or stiffer than dilated regions  1304 . Optionally one cuff or flare region  1304  may be gripping, rather than slipping. 
     Alternatively, some of the wires through which the strips are woven can be separate from the stent construction, such that when they are removed, the interwoven pattern is undone, and the textured strips are released from the stent. 
     The description provided herein is not to be limited in scope by the specific embodiments described which are intended as single illustrations of individual aspects of certain embodiments. The methods, compositions and devices described herein can comprise any feature described herein either alone or in combination with any other feature(s) described herein. Indeed, various modifications, in addition to those shown and described herein, will become apparent to those skilled in the art from the foregoing description and accompanying drawings using no more than routine experimentation. Such modifications and equivalents are intended to fall within the scope of the appended claims. 
     All publications, patents and patent applications mentioned in this specification are herein incorporated by reference in their entirety into the specification to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. Citation or discussion of a reference herein shall not be construed as an admission that such is prior art. 
     Thus, although there have been described particular embodiments of the present invention of a new and useful Stents with Improved Fixation it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.