Stent with Anti-Migration Features

Abstract

An exemplary stent may include an elongate tubular member having a first end and a second end and an intermediate region disposed therebetween. The elongate tubular member is configured to transition between a collapsed configuration and an expanded configuration. The elongate tubular member may include at least one twisted filament, such as a knit filament having a plurality of twisted knit stitches with intermediate rung portions extending between adjacent twisted knit stitches and one or more anti-migration features formed in one or more intermediate rung portions.

Description

[Technical field]

[0001] The present disclosure relates to medical devices, methods for manufacturing medical devices, and uses thereof. More particularly, the present disclosure relates to stents for implantation in a body lumen, and related methods. [Background technology]

[0002] A wide variety of intracorporeal medical devices have been developed for medical applications, such as surgical and / or intravascular applications. Some of these devices include guidewires, catheters, medical device delivery systems, and the like (e.g., stents, grafts, replacement valves, and the like). These devices may be manufactured by any one of a variety of different manufacturing methods and used according to any one of a variety of methods. Summary of the Invention

[0003] The present disclosure provides design, materials, manufacturing methods, and use alternatives for medical devices. An exemplary medical device may include a stent.

[0004] In a first example, a stent may include an elongate tubular member comprising at least one knit filament with a plurality of twisted knit stitches having intermediate rung portions extending between adjacent twisted knit stitches. The elongate tubular member may be configured to transition between a collapsed configuration and an expanded configuration. The elongate tubular member may further include one or more anti-migration features formed in one or more of the intermediate rung portions. When the elongate tubular member is in the expanded configuration, the one or more anti-migration features may extend radially therefrom.

[0005] Alternatively, or in addition to any of the above examples, in another example, the one or more anti-migration features can extend radially beyond the base diameter of the elongated tubular member in the expanded configuration in a range of 1 to 4 millimeters.

[0006] Alternatively or in addition to any of the above examples, in another example, when the elongate tubular member is in the expanded configuration, the one or more anti-migration features can extend at a non-parallel angle relative to the longitudinal axis of the elongate tubular body.

[0007] Alternatively or in addition to any of the above examples, in another example, the one or more anti-migration features can include a distally oriented apex when the elongate tubular member is in the expanded configuration.

[0008] Alternatively or in addition to any of the above examples, in another example, the one or more anti-migration features can bend back onto themselves when the elongate tubular member is in the expanded configuration.

[0009] Alternatively or in addition to any of the above examples, in another example, each of the one or more anti-migration features may include a first bonding curved portion adjacent to a first twisted knit stitch and a second bonding curved portion adjacent to a second twisted knit stitch.

[0010] Alternatively or in addition to any of the above examples, in another example, the first coupling curved portion and the second coupling curved portion can be configured such that an anti-migration loop flattens when the elongated tubular body transitions from the expanded configuration to the collapsed configuration.

[0011] Alternatively or in addition to any of the above examples, in another example, when the elongate tubular member is in the collapsed configuration, at least a portion of the one or more anti-migration features can be included in one or more adjacent twisted knit stitches.

[0012] Alternatively or in addition to any of the above examples, in another example, a length of the middle rung portion in the collapsed configuration may be less than a length of the middle rung portion in the expanded configuration.

[0013] Alternatively or in addition to any of the above examples, in another example, at least some of the plurality of twisted knit stitches are suspended from a twisted knit stitch of a preceding row.

[0014] Alternatively or in addition to any of the above examples, in another example, the diameter of the elongated tubular member in the collapsed configuration can be in the range of approximately 60% to 80% smaller than the diameter of the elongated tubular member in the expanded configuration.

[0015] In another example, a method of manufacturing a stent having an anti-migration feature may include knitting a stent blank, where the knitted stent blank may include at least one knit filament with a plurality of twisted knit stitches having intermediate rung portions extending between adjacent twisted knit stitches; placing the knitted stent blank in position on a mandrel, where the mandrel includes one or more anti-migration feature forming elements; engaging one or more intermediate rung portions of the knitted stent with the one or more anti-migration feature forming elements to form an anti-migration feature having a first bend point and a second bend point; annealing the woven stent blank while positioned on the mandrel to form a shaped stent having the anti-migration feature; and disengaging the one or more anti-migration feature forming elements to remove the shaped stent from the mandrel.

[0016] Alternatively or in addition to any of the above examples, in another example, the one or more anti-movement feature forming elements may comprise a pin configured to be driven radially outward relative to a central longitudinal axis of the mandrel, and engaging the wire with the one or more anti-movement feature forming elements may include driving the pin in the radially outward direction relative to the central longitudinal axis of the mandrel.

[0017] Alternatively or in addition to any of the above examples, in another example, disengaging the one or more anti-movement feature forming elements may comprise allowing the pin to move radially inward relative to the central longitudinal axis of the mandrel.

[0018] Alternatively or in addition to any of the above examples, in another example, positioning the knitted stent blank into position on the mandrel may include stretching the knitted stent blank over the mandrel and conforming the knitted stent blank to an outer surface of the mandrel.

[0019] In another example, a stent may comprise an elongate tubular member comprising at least one knit filament having a plurality of twisted knit stitches with intermediate rung portions extending between adjacent twisted knit stitches, the elongate tubular member may be configured to transition between a collapsed configuration and an expanded configuration, and one or more anti-migration features may be formed in one or more of the intermediate rung portions, and when the elongate tubular member is in the expanded configuration, the one or more anti-migration features may extend radially therefrom.

[0020] Alternatively, or in addition to any of the above examples, in another example, the one or more anti-migration features can extend radially beyond the base diameter of the elongate tubular member in the expanded configuration by a range of 1 to 4 millimeters.

[0021] Alternatively or in addition to any of the above examples, in another example, when the elongate tubular member is in the expanded configuration, the one or more anti-migration features can extend at a non-parallel angle relative to the longitudinal axis of the elongate tubular body.

[0022] Alternatively or in addition to any of the above examples, in another example, the one or more anti-migration features can include a distally oriented apex when the elongate tubular member is in the expanded configuration.

[0023] Alternatively or in addition to any of the above examples, in another example, the one or more anti-migration features can bend back onto themselves when the elongate tubular member is in the expanded configuration.

[0024] Alternatively or in addition to any of the above examples, in another example, each of the one or more anti-migration features may include a first bonding curved portion adjacent to a first twisted knit stitch and a second bonding curved portion adjacent to a second twisted knit stitch.

[0025] Alternatively or in addition to any of the above examples, in another example, the first coupling curved portion and the second coupling curved portion can be configured such that an anti-migration loop flattens when the elongated tubular body transitions from the expanded configuration to the collapsed configuration.

[0026] Alternatively or in addition to any of the above examples, in another example, when the elongate tubular member is in the collapsed configuration, at least a portion of the one or more anti-migration features can be included in one or more adjacent twisted knit stitches.

[0027] Alternatively or in addition to any of the above examples, in another example, a length of the middle rung portion in the collapsed configuration may be less than a length of the middle rung portion in the expanded configuration.

[0028] Alternatively or in addition to any of the above examples, in another example, the diameter of the elongated tubular member in the collapsed configuration can be in the range of approximately 60% to 80% smaller than the diameter of the elongated tubular member in the expanded configuration.

[0029] In another example, a stent may comprise an elongate tubular member comprising at least one knit filament with a plurality of twisted knit stitches each including an overlapping base region with a loop portion and an intermediate rung portion extending between adjacent twisted knit stitches, at least some of the plurality of twisted knit stitches being suspended from an intermediate rung portion of a preceding row, the elongate tubular member configured to transition between a collapsed configuration and an expanded configuration, and one or more anti-migration features formed in one or more of the intermediate rung portions, the one or more anti-migration features may extend radially therefrom when the elongate tubular member is in the expanded configuration.

[0030] Alternatively, or in addition to any of the above examples, in another example, the one or more anti-migration features may be disposed at similar longitudinal positions around the circumference of the elongate tubular member.

[0031] Alternatively, or in addition to any of the above examples, in another example, the one or more anti-migration features can extend radially beyond the base diameter of the elongate tubular member in the expanded configuration by a range of 1 to 4 millimeters.

[0032] Alternatively or in addition to any of the above examples, in another example, when the elongate tubular member is in the expanded configuration, the one or more anti-migration features can extend at a non-parallel angle relative to the longitudinal axis of the elongate tubular body.

[0033] Alternatively or in addition to any of the above examples, in another example, the one or more anti-migration features can bend back onto themselves when the elongate tubular member is in the expanded configuration.

[0034] Alternatively or in addition to any of the above examples, in another example, the one or more anti-migration features may each include a first binding curved portion adjacent to the overlapping base region of the first twisted knit stitch and a second binding curved portion adjacent to the overlapping base region of the second twisted knit stitch.

[0035] In another example, a method of manufacturing a stent having an anti-migration feature may include knitting a stent blank, the knitted stent blank including at least one knit filament with a plurality of twisted knit stitches having intermediate rung portions extending between adjacent twisted knit stitches; placing the knitted stent blank in position on a mandrel, the mandrel including one or more anti-migration feature forming elements; engaging one or more intermediate rung portions of the knitted stent with the one or more anti-migration feature forming elements to form an anti-migration feature having a first bend point and a second bend point; annealing the woven stent blank while positioned on the mandrel to form a shaped stent having the anti-migration feature; and disengaging the one or more anti-migration feature forming elements to remove the shaped stent from the mandrel.

[0036] Alternatively or in addition to any of the above examples, in another example, the one or more anti-movement feature forming elements may comprise a pin configured to be driven radially outward relative to a central longitudinal axis of the mandrel, and engaging the wire with the one or more anti-movement feature forming elements comprises driving the pin in the radially outward direction relative to the central longitudinal axis of the mandrel.

[0037] Alternatively or in addition to any of the above examples, in another example, disengaging the one or more anti-movement feature forming elements may comprise allowing the pin to move radially inward relative to the central longitudinal axis of the mandrel.

[0038] Alternatively or in addition to any of the above examples, in another example, positioning the knitted stent blank into position on the mandrel may include stretching the knitted stent blank over the mandrel and conforming the knitted stent blank to an outer surface of the mandrel.

[0039] The above summary of some embodiments is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The following figures and detailed description more particularly exemplify these embodiments. [Brief description of the drawings]

[0040] The present invention may be more fully understood from the following detailed description of various embodiments considered in conjunction with the accompanying drawings.

[0041] [Figure 1] FIG. 1 is a side view of an exemplary stent. [Diagram 2] 2 is an enlarged side view of a portion of the exemplary stent of FIG. 1. [Diagram 3] 2 is a partial side view of the exemplary stent of FIG. 1 in an elongated configuration. [Figure 4] 1 is an exemplary method of forming a stent. [Diagram 5] FIG. 1 is a perspective view of an adjustable mandrel. [Figure 6] FIG. 6 is an exploded perspective view of the adjustable mandrel of FIG. [Figure 7] FIG. 6 is a cross-sectional view of the adjustable mandrel of FIG. 5 with the anti-movement feature forming pins shown in a fully extended position. [Figure 8] FIG. 6 is a cross-sectional view of the adjustable mandrel of FIG. 5 with the anti-movement feature forming pins shown in a partially extended position. [Figure 9] FIG. 6 is a perspective view of an anti-movement feature forming pin forming part of the adjustable mandrel of FIG. [Figure 10] 6 is a side view of a portion of the adjustable mandrel of FIG. 5 showing a portion of a knitted stent disposed about the adjustable mandrel. [Figure 11A] FIG. 11 is a side view of the exemplary knitted stent of FIG. 10 removed from the adjustable mandrel. [Figure 11B] FIG. 13 is a side view of another exemplary knitted stent removed from an adjustable mandrel. [Figure 11C]FIG. 13 is a side view of another exemplary knitted stent removed from an adjustable mandrel. [Figure 12A] 1A-1C are schematic diagrams of anti-migration features that a knitted stent may include. [Figure 12B] 1A-1C are schematic diagrams of anti-migration features that a knitted stent may include. [Figure 12C] 1A-1C are schematic diagrams of anti-migration features that a knitted stent may include. [Figure 12D] 1A-1C are schematic diagrams of anti-migration features that a knitted stent may include. [Figure 13] FIG. 13 is a partial side view of another exemplary knitted stent having one or more anti-migration features. [Figure 14] FIG. 14 is a side view of region A of the stent of FIG. [Figure 15] FIG. 15 is a side view of the stent of FIG. 14 in a second configuration. [Figure 16] FIG. 1 is a side view of an exemplary delivery system for delivering a stent. [Figure 17] 17 is a side view of the exemplary delivery system of FIG. 16 having a stent in a partially deployed configuration.

[0042] While the disclosure is susceptible to various modifications and alternative forms, details of which 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 aspects of the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The following defined terms shall have these definitions applied, unless a different definition is given in the claims or elsewhere in this specification.

[0044] All numerical values, whether expressly indicated or not, are assumed to be modified herein by the term "about." The term "about" generally refers to a range of numbers that one of ordinary skill in the art would consider equivalent to the recited value (i.e., having the same form or result). In many cases, the term "about" may be expressed as including numbers that are rounded to the nearest significant figure.

[0045] The recitation of numerical ranges by endpoints includes all numbers within that range (eg, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5).

[0046] Although certain preferred dimension ranges and / or values ​​for various components, features and / or specifications are disclosed, those skilled in the art stimulated by this disclosure will understand that the desired dimensions, ranges and / or values ​​may deviate from those expressly disclosed.

[0047] 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 used in its sense to include "and / or" unless the content clearly dictates otherwise.

[0048] The following detailed description should be read with reference to the drawings, in which similar elements in different drawings are numbered the same. The detailed description and drawings, which are not necessarily to scale, depict exemplary embodiments and are not intended to limit the scope of the invention. The illustrated exemplary embodiments are intended as examples only. Selected features of any exemplary embodiment may be incorporated in additional embodiments, unless expressly indicated to the contrary.

[0049] In some cases, it may be desirable to provide patients with esophageal strictures or other pathologies with an intraluminal implant or stent capable of achieving luminal patency. Such stents may sometimes be used in patients experiencing dysphagia due to esophageal cancer. Esophageal stents may allow patients to maintain nutritional intake via oral intake during cancer treatment or palliative periods. Current gastrointestinal (GI) stenting therapies for the treatment of vascular stenosis may rely on self-expanding stents (SES) to resolve the underlying stricture while remaining in place. However, this type of stenting may have a high incidence of migration, especially in fully covered designs. Some stents may include protrusions (e.g., loops, quills, etc.) that protrude radially outward from the stent body. These raised features may interact with the conduit to reduce device migration. However, these devices may be difficult to remove or reposition because they may be difficult to reduce to a smaller diameter. Furthermore, devices with these types of protrusions (or anti-migration features) may be indicated for permanent implantation. If it is desired that these devices be removable, removal or repositioning of the device may be limited since corners of the protrusions may cause ductal injury along with stent migration. What may be desired is an intraluminal implant or stent that includes anti-migration features and that may also be easily retracted for repositioning and / or removal. Although the embodiments disclosed herein are discussed with reference to esophageal stents, it is envisioned that the stents described herein may be used and sized for use in other locations, such as, but not limited to, body tissues, body organs, ductal lumens, non-ductal lumens, and combinations thereof (such as, but not limited to, the coronary or peripheral vasculature, trachea, bronchi, colon, small intestine, bile duct, urinary tract, prostate, brain, and stomach).

[0050] FIG. 1 illustrates a side view of an exemplary intraluminal implant 10, such as, for example, but not limited to, a stent. In some cases, the stent 10 may be formed from an elongated tubular member 12. Although the stent 10 is described as being generally tubular, it is envisioned that the stent 10 may assume any cross-sectional shape desired. The stent 10 may have a first or proximal end 14, a second or distal end 16, and an intermediate region 18 disposed between the first and second ends 14, 16. The stent 10 may include a lumen 20 extending from a first opening adjacent the first end 14 to a second opening adjacent the second end 16 to allow the passage of food, fluids, and the like.

[0051] The stent 10 is expandable from a first radially crimped configuration (not explicitly shown) to a second radially expanded configuration. In some cases, the stent 10 may be deployed to a configuration between the crimped configuration and the fully expanded configuration. The stent 10 may be configured to extend across a stenosis and exert radially outward pressure on the stenosis in the lumen to open the lumen and allow the passage of food, fluid, air, etc. When the stent 10 is in the radially crimped configuration, the outer diameter of the stent 10 is reduced to a fully or partially expanded configuration. In some cases, the stent 10 is stretched or lengthened to reduce the diameter of the stent 10 for delivery to a target location. As the stent 10 is deployed (transitioning from a delivery configuration to an expanded configuration), the length of the stent 10 decreases and the diameter increases. In some cases, the stent 10 may be reduced (e.g., the percent that the length of the stent decreases from its delivery configuration to its expanded configuration) in the range of about 20% to about 40%. It is envisioned that the change in length and / or change in diameter of the stent 10 may depend at least in part on the size (e.g., diameter) of the stent. In some cases, a biliary stent may have a deployed diameter in the range of about 8 millimeters to about 10 millimeters and a constrained diameter of about 2.5 millimeters to about 3 millimeters. This may correspond to a reduction in diameter of about 60% to about 80% from the expanded configuration to the delivery configuration. This is by way of example only. The reduction in diameter may be less than 60% or more than 80%, as desired. In another embodiment, an endoscopic stent may have a deployed diameter in the range of about 18 millimeters to about 23 millimeters and a constrained diameter of about 6 millimeters to about 6.5 millimeters. This may correspond to a reduction in diameter of about 60% to about 80% from the expanded configuration to the delivery configuration. This is by way of example only. The reduction in diameter may be less than 60% or more than 80%, as desired.

[0052] The proximal end 14 of the stent 10 may include a plurality of loops 22. The loops 22 may be configured to receive a retrieval tether or suture that is braided therethrough or passed through one or more of the loops 22. The retrieval suture may be used to collapse and retrieve the stent 10, if desired. For example, the retrieval suture may be pulled like a drawstring to radially collapse the proximal end 14 of the stent 10 to facilitate removal of the stent 10 from the body lumen.

[0053] The stent 10 may have a knit structure made from a single filament 24 that is woven with itself and defines open cells 25. In some cases, the filament 24 may be a monofilament, and in other cases, the filament 24 may be two or more filaments wound, braided, or woven together. In some cases, the interior and / or exterior surfaces of the stent 10 may be entirely, substantially, or partially covered with a polymeric covering or coating. The covering or coating may extend over and / or occlude one or more or a plurality of cells 25 defined by the struts or filaments 24. The covering or coating may help reduce food impaction and / or tumor or tissue ingrowth.

[0054] It is envisioned that the stent 10 can be made from a number of different materials, such as, but not limited to, metals, metal alloys, shape memory alloys, and / or polymers, as desired, allowing the stent 10 to expand and shape when correctly positioned within the body. In some cases, the material may be selected to also allow the stent 10 to be relatively easily removed. For example, the stent 10 may be formed from alloys, such as, but not limited to, Nitinol and Elgiloy®. Depending on the materials selected for construction, the stent 10 may be self-expanding (i.e., configured to automatically radially expand when unconstrained). In some embodiments, a fiber may be used to make the stent 10, which may be, for example, a composite fiber with an outer shell made of Nitinol with a platinum core. It is further envisioned that the stent 10 may be formed from a polymer, including, but not limited to, polyethylene terephthalate (PET). In some embodiments, stent 10 may be self-expanding, while in other embodiments, stent 10 may be expanded by an expansion device, such as, but not limited to, a balloon inserted within lumen 20 of stent 10. As used herein, the term "self-expanding" refers to the tendency of a stent to return to a preprogrammed diameter when not restrained by an external biasing force, such as, but not limited to, a delivery catheter or sheath. Stent 10 may include a one-way valve, such as an elastomeric slit valve or duckbill valve, disposed within its lumen 20 to prevent the backflow of gastrointestinal fluids.

[0055] In some cases, in the radially expanded configuration, the stent 10 may include a first end region 26 proximate the proximal end 14 and a second end region 28 proximate the second end 16. In some embodiments, the first end region 26 and the second end region 28 may include a retention feature or anti-migration flared region (not explicitly shown) having an enlarged diameter relative to the intermediate portion 18. The anti-migration flared region, which may be disposed adjacent the first end 14 and the second end 16 of the stent 10, may be configured to engage an inner portion of the wall of the esophagus or other body lumen. In some embodiments, the retention feature or flared region may have a larger diameter than the cylindrical intermediate region 18 of the stent 10 to prevent the stent 10 from migrating after being placed in the esophagus or other body lumen. It is contemplated that the transition from the cross-sectional area of ​​the intermediate region 18 to the retention feature or flared region may be gradual, sloped, or occur in a steep step manner, as desired.

[0056] In some embodiments, the first anti-migration flare region may have a first outer diameter and the second anti-migration flare region may have a second outer diameter. In some cases, the first and second outer diameters may be nearly the same, while in other cases, the first and second outer diameters may be different. In some embodiments, the stent 10 may include only one of the anti-migration flare regions, or may not include any anti-migration flare regions at all. For example, the first end region 26 may include an anti-migration flare and the second end region 28 may have a similar outer diameter as the mid-region 18. It is further contemplated that the second end region 28 may include an anti-migration flare and the first end region 26 may have a similar outer diameter as the mid-region 18. In some embodiments, the stent 10 may have a uniform outer diameter from the first end 14 to the second end 16. In some embodiments, the outer diameter of the mid-region 18 may be in the range of 15 to 25 millimeters. The outer diameter of the anti-migration flare may be in the range of 20 to 30 millimeters. It is envisioned that the outer diameter of the stent 10 may be varied to suit a desired application.

[0057] The stent 10 may further include one or more radially extending anti-migration features 30. As described in more detail herein, the anti-migration features 30 may be portions or loops of filaments 24 and extend radially from the stent body 12. For example, the anti-migration features 30 may have an outer diameter that is greater than the intermediate region 18 and / or greater than the anti-migration flared region (if so provided). In some cases, the anti-migration features 30 may extend beyond a base diameter of the stent 10 in a range of about 1 millimeter to about 4 millimeters. The base diameter may be a nominal (e.g., substantially constant) outer diameter of the body 12 of the stent 10 taken at the same longitudinal position as the anti-migration feature 30. When the stent 10 is in an expanded configuration, the anti-migration features 30 may extend at a non-parallel angle relative to the longitudinal axis of the stent 10. It is envisioned that the angle of the anti-migration features 30 may be determined, at least in part, by the length of the anti-migration features 30. For example, to reduce the risk of puncture, longer anti-migration features 30 may be oriented at a smaller angle relative to the longitudinal axis of the stent 10 than shorter anti-migration features. This is by way of example only. In some cases, when the stent 10 is covered or partially covered with a covering or coating, the anti-migration features 30 may remain bare or uncovered (e.g., without a covering or coating) to allow tissue ingrowth to further reduce migration of the stent 10. However, this is not required. In some cases, the anti-migration features 30 may include a covering or coating.

[0058] In some cases, the anti-migration features 30 may be disposed circumferentially around the circumference of the stent 10 at similar longitudinal locations. However, it is envisioned that the anti-migration features 30 may be disposed at one or more different locations along the length of the stent 10, if desired. It is further envisioned that the anti-migration features 30 may be provided in circumferential rows or as another configuration (e.g., not necessarily extending around the circumference of the stent 10) as desired. When provided as another configuration, the anti-migration features 30 may be positioned or disposed asymmetrically or randomly in a pattern that does not necessarily include full circumferential rows. For example, the pattern may include, but is not limited to, staggered or alternating anti-migration features 30.

[0059] In some cases, the anti-migration feature 30 may be formed such that the apexes 32 of the anti-migration feature 30 are angled in a generally distal direction. Such an orientation may help limit distal migration of the stent 10 when implanted. However, other configurations may be used as desired. In some cases, the anti-migration feature 30 may be formed such that the apexes 32 are angled in a proximal direction. In yet other cases, the stent 10 may include a combination of anti-migration features 30 angled in a distal direction and anti-migration features 30 angled in a proximal direction. As described in more detail herein, it is envisioned that the apexes 32 of the anti-migration feature 30 may be curved or bent back over the length of the anti-migration feature 30 such that the apexes 32 do not contact tissue (e.g., to form a more atraumatic anti-migration feature).

[0060] It is envisioned that the stent 10 can be made from a number of different materials, such as, but not limited to, metals, metal alloys, shape memory alloys, and / or polymers, as desired, allowing the stent 10 to expand and shape when correctly positioned within the body. In some cases, the material may be selected to also allow the stent 10 to be relatively easily removed. For example, the stent 10 may be formed from alloys such as, but not limited to, Nitinol and Elgiloy®. Depending on the materials selected for construction, the stent 10 may be self-expanding or may require an external force to expand the stent 10. In some embodiments, composite filaments may be used to make the stent 10, and may include, for example, an outer shell or metal coating made from Nitinol and a core made from platinum or other radiopaque material. It is further envisioned that the stent 10 may be formed from a polymer, including, but not limited to, polyethylene terephthalate (PET). In some cases, the filaments of stent 10, or portions thereof, may be bioabsorbable or biodegradable, and in other cases, the filaments of stent 10, or portions thereof, may be biostable.

[0061] FIG. 2 shows a partial enlarged side view of the knitted configuration of stent 10. Stent 10 may include multiple rows 50a, 50b, 50c, 50d (collectively, 50) extending circumferentially around stent 10. Stent 10 may include any number of rows 50 as desired. For example, the number of rows 50 may be selected to achieve a desired length of stent 10. The top or first row 50a may be non-fixed and active. In some examples, first row 50a may include multiple loops 60a, 60b, 60c (collectively, 60). Loops 60 may each include loop portions 62a, 62b, 62c (collectively, 62) and overlapping base portions 64a, 64b, 64c (collectively, 64). An overlapping base portion 64a, 64b, 64c is understood as a portion of a loop 60 where one portion of the filament overlaps or crosses a second portion of the filament, forming a loop portion 62a, 62b, 62c extending therebetween. Adjacent loops 60 may be interconnected by rung portions 66a, 66b (collectively, 66). For example, a first rung portion 66a may extend between a base portion 64a of a first loop 60a and a base portion 64b of a second loop 60b. A next row 50b may be suspended from the loops 60 of the first row 50a. For example, the second row 50b may include a plurality of loops 70a, 70b, 70c (collectively, 70), each loop including a loop portion 72a, 72b, 72c (collectively, 72) and a base portion 74a, 74b, 74c (collectively, 74). Adjacent loops 70 may be interconnected by rung portions 76a, 76b (collectively, 76). When the stent 10 is braided, the loop portion 72 may be wrapped around the base portion 64 of the preceding row 50a.

[0062] It is contemplated that a single row 50 may be formed at a time. For example, rows may be formed in succession, such that a subsequent row (e.g., row 50b) is formed after a preceding row (e.g., row 50a) has formed sufficient circulation. Although not explicitly shown, the loops 60 of the first row 50a may be wrapped around a portion of the filament 24 that is not looped. As described herein, the loops 70 of the second row 50b may be wrapped around the base portion 64 of the loops 60 of the preceding row 50a. For example, the filament 24 may be braided to extend from a first rung portion 76a, wrap around the base portion 64b of the preceding row 50a, cross back over itself to form the base portion 74b, and continue to the next rung portion 76b. It is contemplated that the loop portion 70 may be disposed on a first side of the rungs 66a, 66b, and on a second, opposite side of the loop portion 62b. In other words, the filament 24 may be wound such that it extends over the second rung portion 66b, behind the base portion 64b, and over the first rung portion 66a before crossing over itself to form the base portion 74b of the loop 70b of the second row 50b. The reverse configuration is also envisioned in which the filament 24 may be wound such that it extends behind the second rung portion 66b, above or over the apex of the base portion 64b, and behind the first rung portion 66a before crossing over itself to form the base portion 74b of the loop 70b of the second row 50b.

[0063] In the knitted structure of the stent 10, the cells 25 and / or loop portions 62, 72 may allow the loop portions 62, 72 to be lengthened or shortened such that the stent 10 has a first profile when the stent 10 is in an expanded configuration and a second profile different from the first profile when the stent 10 is in a collapsed delivery configuration. Lengthening the loop portions 62, 72 allows the cross-sectional diameter of the stent 10 to be reduced for delivery. To lengthen, the loops 60, 70 are stretched using a portion of the length of the filament 24 from the rungs 66, 76. FIG. 3 shows a portion of the stent 10 in an extended configuration. As can be seen, when the loops 60, 70 are stretched, the rung members 66, 76 are retracted into the loop portions 62, 72 to allow the loops to be stretched (e.g., in a direction along the longitudinal axis 80) and the intermediate rung portions 66, 76 are shortened. The rung material 66, 76 is accessible and can be easily incorporated into the loop portions 62, 72 due to the twisted regions 64, 74. Similarly, the anti-migration features 30 are easily incorporated into the loop portions. This allows the stent 10 to be restrained with less force and loaded into a coaxial delivery system. It is envisioned that the knit structure of the stent 10 may be less susceptible to wire breakage due to fatigue caused by peristalsis compared to previous stent knits. The softer curvature of the current knit pattern allows the loops 60, 70 to be easily puckered by external forces that may be applied to the stent 10 by the anatomy. It is envisioned that the stent 10 may be heat treated or annealed in the expanded configuration such that when the external forces are released, the diameter of the stent 10 expands but the anti-migration features 30 may easily resume their radially outward extending configuration.

[0064] Once the stent 10 is deployed, the stent 10 may be stretched (thus reducing the diameter) to remove or reposition the stent 10. To collapse the stent 10 for repositioning or removal, the stent 10 may be actuated from either or both of the proximal end 14 or distal end 16 of the stent 10. In some cases, pull wires may be used to facilitate collapsing the stent 10. However, other actuation mechanisms may be used as desired. For example, a physician may use one or more forceps to grasp one or both ends of the stent 10. It is anticipated that the stent 10 may reduce in diameter in the range of about 60% to about 80% of its length before it can be easily moved within the body lumen. Because the diameter of the stent 10 may be reduced first at the end that receives the actuation force, a clinician may select the end of the stent 10 to be actuated based on the desired movement of the stent 10.

[0065] Returning to FIG. 2, the anti-migration feature 30 may be formed in one of the interconnected rung portions 96a, 96b (collectively, 96) of the row 50d. Although FIG. 2 shows the anti-migration feature 30 in a single row 50d, it is contemplated that any number of rows 50 at any longitudinal location may include the anti-migration feature 30. It is further contemplated that not all rungs 96 may be formed in the anti-migration feature 30. For example, in some cases, every other rung 96 may be formed in the anti-migration feature. Other patterned, asymmetric, and / or random configurations for the anti-migration feature 30 may be used as desired. The anti-migration feature 30 may extend radially outward from the body 12 of the stent 10 at a generally non-parallel angle relative to the longitudinal axis 80. In some cases, the apex 32 of the anti-migration feature 30 may be oriented in a generally distal direction. In other cases, the apexes 32 of the anti-migration features 30 may be generally oriented in a proximal direction (see, e.g., FIG. 11B). In still other cases, the stent 10 may include one or more anti-migration features 30 that face in a distal direction and one or more anti-migration features 30 that face in a proximal direction. It is further contemplated that one or more of the apexes 32 may be unwound upon themselves such that the apexes 32 are generally oriented in a different direction than the general direction of the anti-migration features 30 (see, e.g., FIG. 11C). In some cases, the stent 10 may be formed by first forming a constant diameter blank and then stretching the constant diameter stent blank over a mandrel prior to the forming and / or annealing process. However, this is not required. In some cases, the stent 10 may be formed by braiding the stent 10 directly over the shaped mandrel. The formation of the anti-migration features 30 is described in more detail herein.

[0066] FIG. 4 shows a side view of an exemplary stent 100 being formed around a constant diameter mandrel 110. The stent 100 may be similar in form and configuration to the stent 10 described above. The stent 100 may be formed from a single knit strand or filament 120. Generally, the stent 100 is formed by braiding in a single direction. For example, in the embodiment shown in FIG. 4, the strand 120 is braided in a counterclockwise direction as indicated by the arrow 160. However, it should be understood that the stent 100 may be formed by braiding in a clockwise direction if desired. The strand 120 may follow a looped path around the mandrel 110 configured to form a plurality of interconnected loops.

[0067] The strand 120 may be manipulated (e.g., braided) into a plurality of rows 130, 132, 134, 136, 138, with each row having a plurality of interconnected or interlocking loops 140a-c, 142a-c, 144a-c, 146a-c, 148d-e. The stent 100 may include as many rows as necessary to form a stent 100 having a desired length. As mentioned above, the loops may be loosely braided and may include interconnecting intermediate rung portions, such as rung portions 152a and 152b, which interconnect three loops 146d, 146c, 146b in one of the rows 136. It should be understood that because the stent 100 is formed from a single strand 120, the rows 130, 132, 134, 136, 138 may not be separate, separate rows, but may instead form continuous connections with preceding and / or succeeding rows. It is further envisioned that the stent 100 need not be formed from a single strand 120, but rather may include two or more strands braided together. In some instances, the loops may be generally aligned with or suspended from the loops of a preceding row in a direction generally parallel to the longitudinal axis of the stent 100 (e.g., circumferentially aligned along the length of the stent 100). As can be seen, the loops 146b of one row 136 are suspended from the loops 144b of the row 134 above them. Thus, the loops may form axially extending columns or ridges 150a-e, although this is not required.

[0068] To form the stent 100, the end region 154 of the strand 120 is passed over the intermediate rung portion 152b of the preceding row 136, as indicated by arrow 156. The end region 154 of the strand 120 may then be wrapped behind the loop 146c in a direction opposite to the general direction 160 of the overall knit. The end region 154 of the strand 120 may then be passed over the rung portion 152a opposite the loop 146c (relative to rung portion 152b) before being crossed over itself to complete the loop. The reverse configuration is also envisioned, where the loop passes behind rung portions 152b, 152a and over loop 146c. The loops 140a-c, 142a-c, 144a-c, 146a-c, 148d-e may generally take the form of a twisted knit stitch, with each individual loop twisted. It is envisioned that the twisted nature of the loops may form ridges on the exterior surface of the stent 100. These ridges may help anchor the stent 100 in the body lumen.

[0069] FIG. 5 is a perspective view of a mandrel 200 for forming a stent having anti-migration features, such as the stent 10 described herein. Some exemplary mandrels are described in commonly assigned U.S. Patent Application Publication No. 2019 / 0029850, entitled "ADJUSTABLE MANDREL FOR FORMING STENT WITH ANTI-MIGRATION FEATURES," the disclosure of which is incorporated herein by reference. As discussed above, in some instances, the stent may further include a tapered outer profile region having one or more flared end regions as well as an anti-migration feature. In some cases, the stent may be considered to have, for example, an hourglass profile. However, in other instances, the stent may have a generally constant outer diameter with one or more anti-migration features extending radially outward therefrom.

[0070] As can be seen, the mandrel 200 can include a mandrel body 202, a mandrel cap 204, an actuation element 206, and a number of anti-migration feature forming pins 208. FIG. 6 is an exploded perspective view of the mandrel 200, with the anti-migration feature forming pins removed for clarity. In some cases, the mandrel cap 204 can be removably secured to the mandrel body 202 via a bolt 218, a bayonet connection, or other fastening mechanism. In some instances, the mandrel cap 204 is removable from the mandrel body 202 to facilitate removal of the stent from the mandrel 200. In other embodiments, the mandrel body 202 and the mandrel cap 204 can be formed as a unitary or monolithic structure, particularly where the mandrel cap 204 has an outer diameter approximately the same as the outer diameter of the mandrel body 202. In some examples, the mandrel body 202 may include a cylindrical portion having an outer diameter, and the mandrel cap 204 may have an outer diameter that is larger than the cylindrical portion of the mandrel body 202.

[0071] The mandrel body 202 shown in Figures 5 and 6 can include a first stent forming portion 210 and a second stent forming portion 212. In some cases, the mandrel cap 204 can be a third stent forming portion 211. The first stent forming portion 210 can be a cylindrical portion of the mandrel body 202 having a first diameter, the second stent forming portion 212 can be a cylindrical portion of the mandrel body having a second diameter, and the third stent forming portion 211 can be a cylindrical portion of the mandrel cap having a third diameter. In some cases, the first stent forming portion 210, the second stent forming portion 212, and / or the third stent forming portion 211 can have a non-cylindrical profile. For example, the first stent forming portion 210, the second stent forming portion 212, and / or the third stent forming portion 211 may instead have a polygonal cross-sectional profile, such as an octagonal cross-sectional profile. This is merely an example. The first, second, and third diameters may be selected based on the desired shape of the stent in the expanded configuration. For example, the mandrel 200 shown in FIG. 5 may produce a stent having a generally hourglass shape. The first diameter may be different from the second diameter and / or the third diameter. For example, the first diameter may be larger than the second diameter. However, this is not required. In some cases, the first diameter and the second and / or third diameters may be the same or substantially the same. When the first and second diameters are different, the tapered portion 214 extends between the first stent forming portion 210 and the second stent forming portion 212 and defines a tapered surface 216 extending from the outer cylindrical surface of the first stent forming portion 210 to the outer cylindrical surface of the second stent forming portion 212. A similar tapered portion may extend between the second and third diameters. The tapered portion 214 includes a plurality of openings 220 extending through a peripheral wall of the tapered portion from the tapered surface 216 to an axially extending internal bore 228 (see, e.g., FIGS. 7 and 8) within the mandrel body 202 for receiving the anti-migration feature forming pins 208.It will be appreciated that the angle of tapered surface 216 relative to first stent forming portion 210 and / or second stent forming portion 212 may affect the relative angle at which anti-migration feature forming pins 208 extend outward from tapered surface 216. In some cases, particularly where first stent forming portion 210, second stent forming portion 212, and / or third stent forming portion 211 have similar or identical outer diameters, tapered surface 216 itself may not be tapered, but may instead have a constant outer diameter.

[0072] In some instances, at least some of the plurality of openings 220 may have a major dimension that is orthogonal to the tapered surface 216. In some cases, at least some of the plurality of openings 220 may have a major dimension that extends at an acute angle relative to the tapered surface 216. It will be appreciated that in some cases, some of the plurality of openings 220 may extend at different angles relative to the tapered surface 216. As shown, the plurality of openings 220 may be considered to be radially aligned in a ring that extends around the tapered portion 214. It will be appreciated that in some cases, some of the plurality of openings 220 may be axially offset relative to others of the plurality of openings 220. In other words, some of the plurality of openings 220 may form a first ring around the tapered portion 214 and others of the plurality of openings 220 may form a second ring around the tapered portion 214 that is axially offset from the first ring around the tapered portion 214.

[0073] In some cases, at least some of the plurality of openings 220 may extend linearly through the tapered portion 214 such that each corresponding pin 208 extends through the opening 220 perpendicular to the tapered surface 216. In some cases, at least some of the openings 220 may have a curved or helical shape such that when a corresponding pin 208, which may have a complementary curved or helical shape, extends out of the opening 220, the pin 208 is pivotable such that the distal end of the pin 208 is movable radially as well as axially.

[0074] The actuating element 206 can be configured to extend from one end of the mandrel body 202 (e.g., the end of the mandrel body opposite the mandrel cap 204) into a bore 228 of the mandrel body 202 to selectively engage and actuate the pin 208 in the opening 220. For example, the actuating element 206 shown in FIG. 6 includes a tapered end 222 that can be configured to engage the anti-migration feature forming pin 208 and a threaded body 224 configured to threadably mate with a threaded opening extending into the first stent forming portion 210 of the mandrel body 202. In some examples, the tapered end 222 can be a conical, frustoconical, convex, or concave taper. The actuating element 206 may include a handle 226 that may be used to rotate the actuating element 206, either by an individual or a machine, and advance the actuating element 206 into the bore of the mandrel body 202 by rotating in a first direction, or withdraw the actuating element 206 from the bore of the mandrel body 202 by rotating in a second, opposite direction. Thus, the threaded body 224 may be threadably engaged with a threaded region of the bore of the mandrel body 202 such that rotating the actuating element 206 in a first rotational direction threadably advances the actuating element 206 into the bore (e.g., toward the mandrel cap 204) and rotating the actuating element 206 in a second, opposite rotational direction withdraws the actuating element 206 from the bore (e.g., away from the mandrel cap 204). This is shown, for example, in connection with Figures 7 and 8, which are cross-sectional views taken along line 7-7 of Figure 5 showing the actuating element 206 fully (Figure 7) or partially (Figure 8) extended into the bore 228 of the mandrel body 202. It is contemplated that in other cases, rather than the actuating element 206 itself including a threaded region, a threaded fastener may be configured to engage the threaded bore 228 of the mandrel body 202 to actuate the actuating element 206 relative to the mandrel body 202.

[0075] 7 shows the actuating element 206 extended fully into the bore 228 of the mandrel body 202, with the threaded body 224 threadably engaged with the threaded region of the bore of the mandrel body 202. In particular, the bore of the mandrel body 202 includes a first threaded region 230 extending from a first end of the mandrel body 202 into the first stent forming portion 210 of the mandrel body 202, which is configured in diameter, depth, and thread pitch to threadably engage the threaded body 224 of the actuating element 206. In some examples, as shown, the mandrel body 202 also includes a second threaded bore or region 232 extending from a second opposite end of the mandrel body into the second stent forming portion 212 of the mandrel body 202, which is configured to threadably engage, in diameter depth and thread pitch, threads on a threaded fastener (e.g., bolt or screw) 218 ​​to releasably secure the mandrel cap 204 in place relative to the mandrel body 202 at the second end of the mandrel body 202. It is envisioned that in some cases, rather than utilizing a separate threaded fastener 218, the mandrel cap 204 itself may include a threaded protrusion configured to engage the second threaded bore 232. It is also envisioned that the second end of the mandrel body 202 may instead include a threaded projection and the mandrel cap 204 may include a threaded bore or opening for engaging the threaded projection of the mandrel body 202 or a through hole for passing the threaded projection to be threadably engaged with a mating threaded fastener (e.g., a nut) on the opposite side of the mandrel cap 204. In either case, the mandrel cap 204 may be secured to or removed from the mandrel body 202, particularly to aid in removing the formed stent from the mandrel 200. In some cases, the mandrel cap 204 may be permanently secured to the mandrel body 202, particularly when the mandrel 200 has an outer configuration in which the outer diameter of each successive stent forming portion is equal to or less than the outer diameter of the preceding stent forming portion and the formed stent may simply be slid off the mandrel 200 without removing the mandrel cap 204.In some cases, the mandrel body 202 may include a positioning or centering opening 234 configured to receive a positioning or centering feature 236 extending from the mandrel cap 204, although this is not required in all cases. In some cases, rather than using fasteners 218 to secure the mandrel cap 204 to the mandrel body 202, the positioning or centering feature 236 itself may be threadably engaged with the positioning or centering opening 234.

[0076] As shown in FIG. 7, the actuating elements 206 are fully extended into the first threaded region 230 of the bore of the mandrel body 202. As a result, the anti-migration feature forming pins 208 are seen to extend radially outward through the corresponding openings 220. In some cases, depending on the particular dimensions of the various components forming the mandrel 200, the anti-migration feature forming pins 208 may be considered to extend radially outward as far as the actuating elements 206 can go before the actuating elements 206 are fully extended into the first threaded region 230 of the bore of the mandrel body 202. The base 238 of each pin 208 may be seen to engage the tapered end 222 of the actuating elements 206. This can be contrasted with FIG. 8, in which the actuating elements 206 extend only partially into the first threaded region 230 of the bore of the mandrel body 202. Thus, it can be seen that while the base 238 of each pin 208 (only two pins are shown for clarity) is still engaged with the tapered end 222 of the actuation element 206, the pins 208 do not extend radially outward through the corresponding opening 220 as far as the pins 208 extend in FIG. 7. In some cases, as shown in FIGS. 7 and 8, the base 238 of each pin 208 may be larger in at least one dimension than the diameter of the corresponding opening 220. Thus, the extent to which the pins 208 can extend radially outward through the opening 220 may be limited when the base 238 of the pin 208 abuts the periphery of the opening 220. As a result, the pins 208 are retained within the opening 220 and do not fall out. The pin 208 may, in some cases, be sufficiently removed by withdrawing the actuating element 206 from the bore of the mandrel body 202, allowing the pin 208 to move radially inward of the opening 220 and then drop into the bore 228 of the mandrel body 202.

[0077] FIG. 9 is a perspective view of an example of an anti-migration feature forming pin 208. In some cases, the pin 208 may include a pin body 240 extending between a base 238 (which may have an enlarged cross-section relative to the pin body 240) and a pin end 242 opposite the base 238. As discussed above, the base 238 may be larger in diameter than the pin body 240, but this is not required in all cases. It is contemplated that the number of anti-migration forming pins 208, as well as their size, shape, and / or orientation (e.g., angle) may be varied to achieve an anti-migration feature having a desired shape and orientation. In some cases, the pin end 242 may be curved to facilitate forming a portion of the wires of the stent into a curved shape. In some cases, the curved shape may be a single curve. In some examples, the curved shape may be a compound curve, such as an undulating or wavy shape. In some examples, the pin end 242 may include a recessed slot 244 that may be configured to accommodate one or more wires of a stent to be formed on the mandrel 200. In some cases, the concave slots 244 may themselves have a single or compound curve shape such that the stent wires extending through the concave slots 244 assume a corresponding single or compound curve shape. For example, in some embodiments, the concave slots 244 may be curved slots 244, providing a curved region for the wires disposed therein. In some cases, the concave slots 244 may include two converging portions that converge to a point at the pin ends 242, providing the wires with a sharp bend for the anti-migration features. In some cases, the stent being formed is a knitted stent, and a knitted stent blank of constant diameter, such as stents 10 or 100, may be stretched over the mandrel 200 with certain wires of the knitted stent blank disposed within the concave curved slots 244 to form the anti-migration features extending radially outward from the knitted tubular wall of the stent. In other cases, the stent may be knitted directly onto the mandrel 200.

[0078] Although the pin ends 242 are shown as curved profiles and are not larger in dimension than the pin body 240, it is envisioned that in some cases the pin ends 242 may extend laterally beyond the pin body 240 to form an arcuate surface. In some cases, for example, the arcuate surfaces of each of the pin ends 242 may align end-to-end and essentially form a raised ring extending around the mandrel 200. The individual arcuate surfaces of each of the pin ends 242 may be driven outwardly by rotating the actuating element 206 in a first rotational direction, causing the actuating element 206 to extend into the mandrel body 202 to form a raised ring of anti-migration features on the stent. Rotating the actuating element 206 in a second, opposite rotational direction may cause the pin 208 to be withdrawn and the stent to be removed from the mandrel 200.

[0079] 10 shows a portion of a knitted stent 300 disposed on a mandrel 200, while FIG. 11A shows the knitted stent 300 removed from the mandrel 200. The stent 300 may be similar in form and configuration to the stents 10, 100 described above. The stent 300 may have a first or proximal end 320, a second or distal end 322, and an intermediate region 324 disposed between the first end 320 and the second end 322. Generally, the stent 300 may be formed from a single knitted strand or filament 302, as described above with respect to the stents 10, 100. The stent 300 includes a plurality of loops 304, each loop having an overlapping base portion 305 and a plurality of interconnecting rung portions 306. 10, one of the rung portions 306 of the knitted stent 300 may extend radially outward from the knitted tubular wall of the stent 300 along the recessed slots 244 of the pins 208 to form one or more of the anti-migration features 308 of the stent 300. Thus, the outwardly extending rung portion 306 that forms the anti-migration feature 308 may extend radially outward relative to a longitudinally and / or circumferentially adjacent rung portion 306. In some cases, a knitted stent such as the knitted stent 300 may be formed by first knitting a constant diameter stent blank (not shown) and then stretching the constant diameter stent blank over the mandrel 200 prior to the forming and / or annealing process. The knitted stent 300 can be seen to have a first enlarged diameter portion 310 adjacent a first end of the knitted stent 300 corresponding to the first stent shaping portion 210, a second enlarged diameter portion 314 adjacent a second end of the knitted stent 300 corresponding to the third stent shaping portion 211, and a (relatively) reduced diameter portion 312 (e.g., a cylindrical body region intermediate the first and second enlarged diameter portions 310, 314) corresponding to the second stent shaping portion 212.

[0080] The knitted stent 300 includes anti-migration features 308 corresponding to the pins 208 disposed circumferentially around the knitted stent 300 in the transition region between the first enlarged diameter portion 310 and the reduced diameter portion 312. However, it is envisioned that the anti-migration features 308 may be disposed at different locations along the length of the knitted stent 300, if desired. The pins 208 may be actuated radially outwardly with the wire disposed within the recessed slots 244 after the knitted stent black is placed on the mandrel 200, such that the portion of the wire engaged with the pins 208 is forced radially outwardly from the knitted tubular wall of the stent to form the anti-migration features 308. The anti-migration features 308 may extend generally in a distal direction. However, this is not required. It is envisioned that the general orientation of the anti-migration features 308 may be altered as desired by changing the orientation or shape of the pins 208. For example, Figure 11B illustrates a perspective view of an exemplary stent 300b having an alternative configuration for anti-migration features 308b. In the exemplary embodiment of Figure 11B, the anti-migration features 308b are oriented in a generally proximal direction. Figure 11C illustrates a perspective view of an exemplary stent 300c having yet another alternative configuration for the anti-migration features 308c. In the exemplary embodiment of Figure 11C, the anti-migration features 308c extend first in a generally distal direction and then fold back on themselves such that the apex of the anti-migration features 308c is oriented in a more proximal direction. Other orientations or combinations of orientations may be used as desired.

[0081] 12A is an end view of knitted stent 300 showing anti-migration features 308 extending radially outward from the knitted tubular wall of knitted stent 300. As shown, each of anti-migration features 308 is a loop of the filaments or wires forming knitted stent 300 that extends between adjacent overlapping base portions 305, each loop being approximately equal in shape and size. As discussed above, overlapping base portions 305 may be where a portion of the filaments or wires crosses or loops around another portion of the filaments or wires. In other cases, some of the anti-migration features 308 may vary in shape and / or size, for example, or may not be equally spaced. Although anti-migration features 308 are shown as curved, in some cases anti-migration features 308 may be pointed or include flat regions, for example.

[0082] For example, FIG. 12B shows a knitted stent 300d including several anti-migration features 308d. Each of the anti-migration features 308d extends between adjacent overlapping base portions 305, and each is approximately equal in shape and size. However, by comparing FIG. 12B with FIG. 12A, the anti-migration feature 308 shown in FIG. 12A can be seen to extend radially outward further than the anti-migration feature 308d shown in FIG. 12B. The anti-migration feature 308d can be formed, for example, by using an anti-migration feature forming pin 208 with a shorter length, or by not advancing the actuation element 206 farther into the mandrel body 202, and thus not advancing the pin 208 radially outwardly farther from the surface of the tapered portion 214 of the mandrel body 202. The anti-migration feature 308d can be, for example, pointed, or have other shapes.

[0083] It will be appreciated that the relative size of anti-migration feature 308 and anti-migration feature 308d may be a function of the ultimate end use of knitted stent 300 (or 300d). Relatively larger anti-migration features 308, 308d may be useful in situations where knitted stent 300 (or 300d) is placed in an anatomical location where knitted stent 300 (or 300d) may be subject to relatively strong migration forces and / or where the patient's anatomy is more likely to change in dimensions. Relatively smaller anti-migration features 308, 308d may be useful in situations where knitted stent 300 (or 300d) may be subject to relatively weak migration forces and / or where the patient's anatomy is less likely to change in dimensions. In some cases, the overall size of knitted stent 300 (or 300d) may play a role as well. In some cases, for example, a larger diameter knitted stent 300 (or 300d) may have relatively larger anti-migration features 308, 308d, while a smaller diameter knitted stent 300 (or 300d) may have relatively smaller anti-migration features 308, 308d.

[0084] FIG. 12C illustrates a knitted stent 300e including several anti-migration features 308e. In contrast to the knitted stents 300 and 300d illustrated in FIGS. 12A and 12B, the anti-migration features 308e do not extend between the respective adjacent overlapping base portions 305 around the circumference of the knitted stent 308b. Each of the anti-migration features 308e extends between the adjacent overlapping base portions 305, but some of the overlapping base portions 305 are not attached to the anti-migration features 308e. The anti-migration features 308e illustrated in FIG. 12C may have an alternating pattern (e.g., alternating between the anti-migration features 308e and the rung portions 306). Other patterns or asymmetric arrangements may be used as desired. As illustrated, each of the anti-migration features 308e is approximately equal in shape and size. The anti-migration features 308e may be formed, for example, by only placing the anti-migration feature forming pins 208 in some of the openings 220. It is contemplated that in some cases, some of the anti-movement features 308e may be smaller or larger in size and / or may be different in shape relative to other anti-movement features 308e.

[0085] 12D illustrates a knitted stent 300f that includes several anti-migration features 308f and several anti-migration features 308g, each extending between adjacent overlapping base portions 305. As shown, each of the anti-migration features 308f is approximately equal in shape and size, and each of the anti-migration features 308g is approximately equal in shape and size, but it will be understood that they do not extend radially outward to anti-migration features 308g. Anti-migration features 308f and 308g may be formed, for example, by using a longer length pin 208 to form each of the anti-migration features 308f and a shorter length pin 208 to form each of the anti-migration features 308g. It will be understood that the particular anti-migration features 308, 308b, 308c, 308d, 308e, 308f, and 308g shown in Figures 11A-11C and 12A-12D are merely illustrative and may be mixed or matched in any desired pattern.

[0086] FIG. 13 is a partial side view of another knitted stent 400 having one or more anti-migration features 408. The stent 400 may be similar in form and configuration to any of the stents described herein. For example, the stent 400 may have a generally constant diameter from the proximal end to the distal end, similar to the stents 10, 100 described above. Alternatively, the stent 400 may include one or more regions having an increased diameter, similar to the stent 300 described above. The stent 400 may be formed from a single knitted strand or filament 402. The strand 402 may be manipulated (e.g., knitted) into multiple rows, each having multiple interconnected or interlocking loops 404a-f (collectively, 404), each having an overlapping base portion 405. The stent 400 may include as many rows as necessary to form a stent 400 having a desired length. As described above, the loops 404 may be loosely knitted and may include intermediate rung portions 406 interconnecting between the loops 404. It is further envisioned that the stent 400 need not be formed from a single strand 402, but rather may include two or more strands braided together. In some instances, the loops may be generally aligned with or suspended from the loops of a preceding row in a direction generally parallel to the longitudinal axis of the stent 400 (e.g., circumferentially aligned along the length of the stent 100). Thus, the loops 404 may form axially extending columns or ridges, although this is not required.

[0087] As discussed above, some (or all) of the intermediate rung portions 406 may be molded into the anti-migration features 408. For example, one or more rung portions 406 may be biased to extend radially from the body of the stent 400 using a mandrel, such as the mandrel 200 described herein. It is envisioned that inflection points 410a, 410b (collectively, 410) may be formed in one or more of the anti-migration features 408 while the anti-migration features 408 are being formed. The inflection points 410 may be pinch points or areas where the anti-migration feature 408 undergoes a direct, abrupt change, as opposed to being a smooth curve. The inflection points 410 may be formed near or at the intersection of the anti-migration feature 408 and the adjacent loops 404a, 404b when the stent is in a radially expanded configuration. Along with forming the anti-migration feature 408, the portion of the strand 402 including the bend point 410 may pass under adjacent loops 404a, 404b to tie the anti-migration feature 408 back to the stent 400. It is envisioned that the angle of the bend point 410 may be selected to provide a desired angle or orientation of the anti-migration feature 408. The bend point 410 may be formed using an anti-migration feature forming pin 208. For example, the pin 208 may include a recess along its lower edge that forms the bend point. The stent 400 may be annealed or heat treated after the formation of the anti-migration feature 408 and / or the bend point 410.

[0088] When the stent 400 is deployed, the anti-migration features 408 protrude radially from the stent 400 as shown in FIG. 14, which shows a side view of region A of the stent 400 of FIG. 13. As seen in FIG. 14, the inflection point 410 may be located under or adjacent to the loops 404a, 404b in the radially expanded configuration. Although the anti-migration features 408 are shown extending generally perpendicular to the longitudinal axis of the stent 400, the anti-migration features 408 may extend at an angle between about 0° and 180° relative to the longitudinal axis of the stent 400. The inflection point 410 may be formed between a first portion or arm 414a, 414b (collectively, 414) and a second portion or arm 416a, 416b (collectively, 416) of the filament. The first arm 414 may be a portion of a filament that exits from an adjacent loop 404, while the second arm 416 may together form the anti-migration feature 408. The bend point 410 may be formed such that the second portion 416 extends at an angle 412a, 412b (collectively, 412) relative to the first portion 414. The angle 412 may determine the angle and / or direction in which the anti-migration feature 408 is oriented. For example, in the illustrated example, the angle 412 is approximately 90°, and thus the anti-migration feature 408 extends at an angle of approximately 90° relative to the longitudinal axis of the stent 400. If the bend point 410 is formed such that the angle 412 is an obtuse angle, the anti-migration feature 408 may be generally oriented in a distal direction 418. For example, in some instances, angle 412 can be greater than 90° but less than 155°, greater than 90° but less than 145°, greater than 90° but less than 135°, greater than 90° but less than 120°, greater than 100° but less than 155°, greater than 100° but less than 145°, greater than 100° but less than 135°, or greater than 100° but less than 120°. If inflection point 410 is formed such that angle 412 is acute, anti-migration feature 408 can be oriented generally in proximal direction 420.For example, in some instances, angle 412 may be less than 90° but greater than 25°, less than 90° but greater than 35°, less than 90° but greater than 45°, less than 90° but greater than 55°, less than 80° but greater than 25°, less than 80° but greater than 35°, less than 80° but greater than 45°, or less than 80° but greater than 55°.

[0089] It is envisioned that the angle 410 may be determined by the radius of curvature of the inflection point 410. A smaller radius of curvature may result in a sharper angle 412, while a larger radius of curvature may result in a more obtuse angle 412. In some cases, the radius of curvature of the angle 412 may be less than four times the diameter of the strand or filament, may be less than three times the diameter of the strand or filament, may be less than two times the diameter of the strand or filament, or the radius of curvature of the angle 412 may be equal to or less than the diameter of the strand or filament. In some embodiments, the inflection points 410 may be formed to have similar angles 412 (and / or radii of curvature). In other embodiments, some anti-migration features 408 may be formed with a first angle 412 and other anti-migration features 408 may be formed with a second angle that is different from the first angle 412. This allows the anti-migration features 408 to have different radial profiles (as shown in FIG. 12D). It is envisioned that any number of angles 412 may be combined in various patterns to achieve a desired effect.

[0090] 15, which illustrates the stent 400 of FIG. 14 with a force 450 applied, when a removal force is applied to the stent 400 for repositioning or removal of the stent 400, the stent 400 begins to elongate (similar to that shown in FIG. 3). As the stent 400 elongates, the inflection points 410 are pulled through adjacent loops 404a, 404b. As the inflection points 410 pass the loops 404, the anti-migration features 408 are deflected radially inward, as indicated by arrows 452, and flatten along the body of the stent 400. Thus, a portion of the anti-migration features 408 (the portion of the strand or filament that forms the anti-migration feature 408 between adjacent inflection points 410) may also be pulled through adjacent loops 404a, 404b. In some examples, as the stent 400 stretches, the angle 412 at the bend point 410 may increase as the anti-migration feature 408 is deflected radially inward toward the outer diameter of the body of the stent 400. It is envisioned that each anti-migration feature 408 located at a similar longitudinal position along the stent 10 may be deflected downward at the same point of the stent 10's stretch. These features may reduce the force required to move or remove the stent 400 from the body or tissue. It is envisioned that the direction of the applied force may vary based on the direction the anti-migration feature 408 is oriented and / or the angle of the bend point 410. For example, an anti-migration feature 408 oriented in a distal direction may be more easily disengaged from tissue by a force applied in a proximal direction, while an anti-migration feature 408 oriented in a proximal direction may be more easily disengaged from tissue by a force applied in a distal direction.

[0091] To form a knitted stent, such as stents 10, 100, 300, 300b-f, 400 described herein, having a non-uniform profile and one or more anti-migration features, a knitted stent blank of constant diameter (as shown in FIG. 4) may be positioned on a mandrel (such as mandrel 200) having a tapered outer surface and one or more anti-migration feature forming elements. It should be noted that a knitted stent having a generally uniform diameter and one or more anti-migration features may be formed by placing a knitted stent blank of constant diameter on a generally uniform mandrel having one or more anti-migration feature forming elements. In other embodiments, a knitted stent having a non-uniform or uniform profile may be knitted directly onto a mandrel having one or more anti-migration feature forming elements. In some cases, positioning the constant diameter knitted stent blank into position on the mandrel includes stretching the constant diameter knitted stent blank over the mandrel and allowing the constant diameter knitted stent blank to conform to the varying diameter outer surface of the mandrel (e.g., to conform to various constant diameter and / or tapered diameter regions of the mandrel).

[0092] One or more anti-migration feature forming elements (such as, but not limited to, pin 208) may be engaged by a portion of the stent to provide a desired shape prior to annealing. In some cases, the one or more anti-migration feature forming elements are pins configured to be driven radially outward relative to an outer surface of the mandrel. Engaging the one or more anti-migration feature forming elements with the stent may include driving the pins radially outward relative to the mandrel to engage respective ends of the pins and the wire(s) or filament(s) radially outward relative to the knitted tubular structure of the stent. The mandrel with the anti-migration features formed thereon and the stent thereon may then undergo an annealing or shape-setting process. After the annealing or shape-setting process, the one or more anti-migration feature forming elements may be disengaged to remove the shaped stent from the mandrel. In some cases, disengaging the one or more anti-migration feature forming elements comprises allowing the pins to move inward relative to the mandrel.

[0093] In some cases, it may be desirable to form a knitted stent having one or more anti-migration features from metallic and non-metallic or further biodegradable components. In such cases, the metallic and non-metallic components may be molded separately and then combined to form the stent. In some cases, each of the metallic and non-metallic or further biodegradable components may each include an anti-migration feature, with the anti-migration feature of the non-metallic or further biodegradable component complementing the anti-migration feature of the metallic component. If the non-metallic component is biodegradable, the biodegradable anti-migration feature may provide additional resistance to migration upon initial implantation of the stent, but may degrade over time.

[0094] To form a two (or more) component stent, in some cases, a constant diameter knitted metallic stent blank may be placed onto a mandrel having a tapered outer surface and one or more anti-migration feature forming elements. The mandrel may be, for example, mandrel 200. However, it is not required that the mandrel have a tapered surface or a variable diameter. In some cases, placing the constant diameter knitted metallic stent blank into position on the mandrel includes stretching the constant diameter knitted metallic stent blank over the mandrel and allowing the constant diameter knitted metallic stent blank to conform to the varying diameter outer surface of the mandrel (e.g., to various constant diameter and / or tapered diameter regions of the mandrel).

[0095] One or more anti-migration feature forming elements (such as, but not limited to, pin 208) may be engaged with a portion of the metallic knitted stent to provide a desired shape prior to annealing. In some cases, the one or more anti-migration feature forming elements are pins configured to be driven radially outward relative to an outer surface of the mandrel. For example, to engage a portion of the stent, the pins are driven radially outward relative to the mandrel, engaging respective ends of the pins and the wire(s) or filament(s) radially outwardly relative to the knitted tubular structure of the stent. The mandrel and the stent thereon with the anti-migration features formed thereon may then undergo an annealing or shape-setting process. After the annealing or shape-setting process, the one or more anti-migration feature forming elements may be disengaged to remove the shaped stent from the mandrel. In some cases, disengaging the one or more anti-migration feature forming elements comprises allowing the pins to move inward relative to the mandrel.

[0096] In some cases, once the shaped metallic stent is removed from the mandrel, a constant diameter biodegradable knitted stent blank may be placed onto the mandrel having a tapered outer surface and one or more anti-migration feature forming elements. In some cases, placing the constant diameter biodegradable knitted stent blank into position on the mandrel includes stretching the constant diameter biodegradable knitted stent blank onto the mandrel and conforming the constant diameter biodegradable knitted stent blank to the varying diameter outer surface of the mandrel. The one or more anti-migration feature forming elements may be engaged to provide a desired shape prior to annealing.

[0097] In some cases, the annealing process for the biodegradable knitted stent blank may require a lower temperature than that used for the metallic knitted stent blank. The mandrel with the anti-migration features formed thereon and the stent thereon may then undergo an annealing or shape-setting process. After the annealing or shape-setting process, the one or more anti-migration feature forming elements may be disengaged to remove the shaped biodegradable stent from the mandrel. In some cases, disengaging the one or more anti-migration feature forming elements comprises allowing a pin to move inwardly relative to the mandrel. In some cases, although not shown, the shaped biodegradable stent may be disposed around or within the shaped metallic stent.

[0098] 16 is a side view of an exemplary delivery system 500 for delivering a stent, such as stents 10, 100, 300, 300b-f, 400 described herein, to a target region. The delivery system 500 may include an outer or external elongate shaft or tubular member 502 and an inner elongate shaft or tubular member 504. The inner tubular member 504 may be slidably disposed within the lumen of the outer tubular member 502. The outer tubular member 502 may extend proximally from a distal end region 506 to a proximal end region 508 configured to remain outside the patient's body. A first hub or handle 510 may be coupled to the proximal end region 508 of the outer tubular member 502. The inner tubular member 504 may extend proximally from a distal end region 512 to a proximal end region 514 configured to remain outside the patient's body. A second hub or handle 516 may be coupled to the proximal end region 514 of the inner tubular member 504. In some cases, the distal end region 506 of the outer tubular member 502 may be configured to be atraumatic.

[0099] The outer tubular member 502 may include a lumen 518 extending from the distal end region 506 to the proximal end region 508. The lumen 518 may also extend through the first handle 510. The lumen 518 of the outer shaft 502 and the first handle 510 may be configured to slidably receive the inner shaft 504. The inner tubular member 504 may include a lumen 520 extending from the distal end region 512 to the proximal end region 514. The lumen 520 of the inner tubular shaft 504 may also extend through the second handle 516. The lumen 520 of the inner shaft 504 may be configured to receive a guidewire 522, if desired.

[0100] The stent 10 may be disposed around a portion of the inner tubular member 504 at or adjacent its distal end region 512. When the stent 10 is disposed over the inner tubular member 504 and in a collapsed and extended delivery configuration, the stent 10 may be restrained in a collapsed reduced diameter or delivery configuration by the outer tubular member 502, which surrounds the stent 10. In the collapsed configuration, the stent 10 may have a smaller diameter and a longer length than in the expanded deployed configuration. The distal end region 506 of the outer tubular member 502 may be disposed such that the outer tubular member 502 surrounds and covers the length of the stent 10 during delivery. The outer tubular member 502 may have sufficient hoop strength to hold the stent 10 in its collapsed state.

[0101] 17 shows a side view of the delivery system 500 with the stent 10 in a partially deployed configuration. The delivery system 500 may be advanced through the gastrointestinal tract (or other body lumen) as desired. The delivery system 500 may be advanced with or without the use of a guidewire 522. Once the stent 10 is positioned adjacent to the target area, the restraining forces maintaining the stent 10 in the radially collapsed configuration may be removed to deploy the stent 10.

[0102] The stent 10 may be released by actuating the first handle 510 proximally relative to the second handle 516, for example by pulling the first handle 510 proximally 524 while maintaining the second handle 516 in a fixed position. Thus, the outer tubular shaft 502 may be retracted proximally relative to the inner tubular shaft 504. In other words, the outer tubular shaft 502 may be retracted proximally while the inner tubular shaft 504 is held stationary. As the outer tubular shaft 502 is retracted proximally 524 to expose the stent 10, as shown in FIG. 17, the biasing force is removed from the exterior of the stent 10, and the stent 10 assumes a radially expanded, unbiased, deployed configuration. When the outer tubular member 502 no longer covers the proximal end 14 of the stent 10, the stent 10 may assume a fully deployed configuration, as shown in FIG. 1. The delivery system 500 may then be removed from the body lumen.

[0103] The stents, delivery systems, and various components thereof may be made from metals, metal alloys, polymers (some examples of which are disclosed below), metal-polymer composites, ceramics, combinations thereof, and the like, or other suitable materials. Some examples of suitable metals and metal alloys include stainless steels, such as 304V, 304L, and 316LV stainless steels, mild steels, nickel-titanium alloys, such as linear elastic and / or superelastic Nitinol, nickel-chromium-molybdenum alloys, nickel-copper alloys, nickel-cobalt-chromium-molybdenum alloys, nickel-molybdenum alloys, other nickel-chromium alloys, other nickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-iron alloys, other nickel-copper alloys, other nickel-tungsten or other nickel alloys, such as tungsten alloys, cobalt-chromium alloys, cobalt-chromium-molybdenum alloys, platinum-strengthened stainless steels, titanium, combinations thereof, and the like, or any other suitable materials.

[0104] Some examples of polymers suitable for stents or delivery systems include polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP), polyoxymethylene (POM, e.g., DELRIN® available from DuPont), polyether block esters, polyurethanes (e.g., Polyurethane 85A), polypropylene (PP), polyvinyl chloride (PVC), polyetheresters (e.g., ARNITEL® available from DSM Engineering Plastics), ether or ester based copolymers (e.g., butylene / poly(alkylene ether) phthalates and / or other polyester elastomers such as HYTREL® available from DuPont), polyamides (e.g., DURETHAN® or Elf® available from Bayer), and the like. Atochem's CRISTAMID®), elastomeric polyamides, block polyamide / ethers, polyether block amides (PEBA, available, for example, under the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA), silicones, polyethylene (PE), MARLEX® high density polyethylene, MARLEX® low density polyethylene, linear low density polyethylene (e.g., REXELL®), polyester, polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polytrimethylene terephthalate, polyethylene naphthalate (PEN), polyether ether ketone (PEEK), polyimide (PI), polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polyparaphenylene terephthalamide (e.g., KEVLAR®), polysulfone, nylon, nylon-12 (e.g., EMS American GRILAMID® available from Grillon), perfluoro(propyl vinyl ether) (PFA), ethylene vinyl alcohol, polyolefins, polystyrene, epoxies, polyvinylidene chloride (PVdC), poly(styrene-b-isobutylene-b-styrene) (e.g., SIBS and / or SIBS50A), polycarbonates, ionomers, biocompatible polymers, other suitable materials, or mixtures, combinations, copolymers, polymer / metal composites, and the like.

[0105] In at least some embodiments, parts or all of the stent or delivery system may also be coated with, made from, or otherwise include radiopaque materials. Radiopaque materials are generally understood to be materials that are opaque (at a thickness of <0.005 inches (0.127 mm)) to RF energy in the wavelength range from x-rays to gamma rays. These materials can produce a relatively dark image on a fluoroscopy screen versus the bright image produced by non-radiopaque materials such as tissue. This relatively bright image aids the user of the stent or delivery system in determining its location. Some examples of radiopaque materials may include, but are not limited to, gold, platinum, palladium, tantalum, tungsten alloys, polymeric materials filled with radiopaque fillers, and the like. Additionally, other radiopaque marker bands and / or coils may also be incorporated into the design of the stent or delivery system to achieve the same results.

[0106] It should be understood that the present disclosure is in many respects merely illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps, without departing from the scope of the present disclosure. This may include, to the extent appropriate, the use of any of the features of one illustrative embodiment used in another embodiment. The scope of the invention is, of course, defined in the language in which the appended claims are expressed.

Claims

1. an elongate tubular member comprising at least one knit filament having a plurality of twisted knit stitches having intermediate rung portions extending between adjacent twisted knit stitches, the elongate tubular member being configured to transition between a collapsed configuration and an expanded configuration, the plurality of twisted knit stitches including a first twisted knit stitch and a second twisted knit stitch; one or more anti-migration features formed on one or more of the intermediate rung portions, each of the one or more anti-migration features including a first inflection point adjacent a loop of the first twisted knit stitch and a second inflection point adjacent a loop of the second twisted knit stitch; the one or more anti-migration features extend radially from the elongate tubular member when the elongate tubular member is in the expanded configuration; a stent, wherein the first bend point and the second bend point are configured to cause the anti-migration feature to pass flattened through the loops of the first twisted knit stitch and / or the loops of the second twisted knit stitch when the elongated tubular member transitions from the expanded configuration to the collapsed configuration.

2. The stent of claim 1, wherein the one or more anti-migration features extend radially beyond a base diameter of the elongate tubular member in the expanded configuration in a range of 1 to 4 millimeters.

3. 3. The stent of claim 1 or 2, wherein the one or more anti-migration features extend at a non-parallel angle to a longitudinal axis of the elongated tubular member when the elongated tubular member is in the expanded configuration.

4. The stent of any one of claims 1 to 3, wherein the one or more anti-migration features include distally oriented apexes when the elongate tubular member is in the expanded configuration.

5. The stent of any one of claims 1 to 3, wherein the one or more anti-migration features bend back onto themselves when the elongate tubular member is in the expanded configuration.

6. The stent of any one of claims 1 to 5, wherein when the elongate tubular member is in the collapsed configuration, at least a portion of the one or more anti-migration features are contained within one or more adjacent twisted knit stitches.

7. The stent of any one of claims 1 to 6, wherein a length of the intermediate rung portion in the collapsed configuration is shorter than a length of the intermediate rung portion in the expanded configuration.

8. The stent of any one of claims 1 to 7, wherein at least some of the plurality of twisted knit stitches are suspended from a twisted knit stitch of a preceding row.

9. The stent of any one of claims 1 to 8, wherein the diameter of the elongated tubular member in the collapsed configuration is in the range of 60% to 80% smaller than the diameter of the elongated tubular member in the expanded configuration.

10. knitting a stent blank, the knit stent blank including at least one knit filament with a plurality of twisted knit stitches having intermediate rung portions extending between adjacent twisted knit stitches, the plurality of twisted knit stitches including a first twisted knit stitch and a second twisted knit stitch; placing the knitted stent blank in position over a mandrel, the mandrel including one or more anti-migration feature forming elements; engaging one or more intermediate rung portions of the knitted stent blank with one or more anti-migration feature forming elements to form an anti-migration feature having a first inflection point adjacent a loop of the first twisted knit stitch and a second inflection point adjacent a loop of the second twisted knit stitch, wherein when the stent is deployed, the anti-migration feature protrudes radially from the stent and when the stent is elongated, the first inflection point and the second inflection point flatten the anti-migration feature through the loop of the first twisted knit stitch and / or the loop of the second twisted knit stitch; annealing the knitted stent blank while disposed on the mandrel to form a shaped stent having the anti-migration features; and disengaging the one or more anti-migration feature forming elements to remove the shaped stent from the mandrel.

11. 11. The method of claim 10, wherein the one or more anti-movement feature forming elements comprise pins configured to be driven radially outward relative to a central longitudinal axis of the mandrel, and engaging a wire with the one or more anti-movement feature forming elements comprises driving the pins radially outward relative to the central longitudinal axis of the mandrel.

12. The method of claim 11 , wherein disengaging the one or more anti-movement feature forming elements comprises allowing the pins to move radially inward relative to the central longitudinal axis of the mandrel.

13. 13. The method of claim 12, wherein placing the knitted stent blank into position on the mandrel comprises stretching the knitted stent blank over the mandrel and conforming the knitted stent blank to an outer surface of the mandrel.

Images