stents

Abstract

The stent comprises a series of longitudinally circumferentially oriented tubular segments separated and alternating by gaps along the length of the stent between a series of opposing end segments. Each segment in the series comprises struts arranged in a circumferentially extending undulating array. Successive segments in the series are interconnected by connectors that bridge the respective gaps. Each segment in the series arranged between the end segments comprises at least one anchor segment preformed in a radially expanded configuration relative to at least one interconnected adjacent body segment having a smaller radius. In use, the anchor segment, aided by the serrations defined by the struts in the undulating array, engages the surrounding vessel wall to resist stent migration. The anchor segment is connected to the body segment by a connector that extends between opposing valleys in the undulating array of these successive segments.

Description

[Technical Field]

[0001] The present invention relates to stents, particularly stents for treating blockages in blood vessels, and more particularly to stents having a skeletal framework resulting from a pattern of slits cut or otherwise formed in a tube prior to expanding the tube to open up the structure.

[0002] Stents are typically inserted into a blood vessel in an initially narrowed state and then radially expand to support the surrounding vessel wall and restore or maintain vascular patency. Some stents self-expand elastically when released from within a sleeve or catheter. Other stents expand plastically when activated, for example, by the application of heat to a shape-memory alloy, or by being pushed radially outward from the inside using an instrument such as a balloon catheter. [Background technology]

[0003] The origins of the present invention relate to the need to treat occluded iliac and femoral veins using stents to establish patency and adequate blood flow, and to prevent stent migration along the vein in which it is placed. The present invention has particular advantages in that context, and more generally in the context of venous applications. However, the inventive concept also encompasses other stent applications where longitudinal migration may be an issue, including arterial applications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2007 / 0142907 [Patent Document 2] International Publication No. 2018 / 110999 Summary of the Invention [Problem to be solved by the invention]

[0005] FIG. 1 shows the human common iliac veins 10, shown in solid lines, as they converge at the lower end of the inferior vena cava 12. The iliac veins 10 drain blood from the lower abdomen and legs into the inferior vena cava 12, which carries blood to the heart. The inferior vena cava 12 extends to the heart alongside the abdominal aorta 14, shown in dotted lines, which carries blood back and forth from the heart to the lower abdomen and legs. The abdominal aorta 14 branches at its lower end to join the common iliac arteries 16.

[0006] The inferior vena cava 12 and abdominal aorta 14 lie alongside each other in front of the spinal column 18, the outline of which is shown schematically in FIG. 1 by parallel dashed lines. The bifurcation of the abdominal aorta 14 coincides with the fourth lumbar vertebra, typically known as L4. Because FIG. 1 is a frontal view, the abdominal aorta 14, shown on the right, is to the left of the inferior vena cava 12 from the individual's perspective. Similarly, the individual's left common iliac vein 10 is shown on the right, and so on.

[0007] It is clear from Figure 1 that the right common iliac artery 16 crosses over and overlies the left common iliac vein 10. The positional relationship between the common iliac vein 10 and the common iliac artery 16 is also clear from the cross-sectional views of Figures 2a and 2b.

[0008] 2a and 2b show that the common iliac vein 10 and common iliac artery 16 also lie in front of the spinal column 18, typically in front of the lowest lumbar vertebra, known as L5. As a result, the left common iliac vein 10 is positioned between the spinal column 18 and the overlying right common iliac artery 16, which in turn crosses the left common iliac vein 10. Therefore, the left common iliac vein 10 is susceptible to compression by the right common iliac artery 16, which can significantly reduce the patency of this region, as shown in FIG. 2b, in contrast to the uncompressed state in FIG. 2a.

[0009] Luminal compression of the left common iliac vein is common throughout the population, occurring in approximately one-quarter of healthy individuals. While the condition is largely asymptomatic, in some cases, loss of patency can become clinically significant and result in May-Turner syndrome, also known as iliac vein compression syndrome. May-Turner syndrome is characterized by swelling, pain, deep vein thrombosis, skin discoloration, ulcers, and / or collateral vessel formation, all of which are caused by alterations in venous flow or venous pressure resulting from restricted blood flow from the affected leg. Its symptoms can severely impact an individual's quality of life.

[0010] When properly diagnosed, luminal compression of the common iliac vein is called a non-thrombotic iliac vein lesion (NIVL) 20 and typically occurs at or just upstream of the junction between the left common iliac vein 10 and the inferior vena cava 12, as shown in Figure 1.

[0011] Venous stenting has become a standard technique for treating obstructive blockages in the iliac and femoral veins. In particular, patency of the common iliac vein can be successfully restored by placing a stent device across the obstructed segment of the NIVL. The stent pushes the vein wall back against the overlying artery, restoring normal blood flow and thereby allowing venous drainage.

[0012] Various commercially available stents are currently used to treat NIVL. While braided stents have been used, they are largely ineffective for this purpose due to their insufficient radial strength and crush resistance. Therefore, laser-cut nitinol straight tubular stents are preferred for treating NIVL. These stents are cut in various patterns to form a skeletal framework when expanded or deployed, which has led to various claimed functional benefits.

[0013] In some cases, venous stents may dislodge and migrate downstream through the vasculature. Retrieving the dislocated stent may require another surgical or endoscopic procedure, which increases risk and inconvenience for the patient. When a stent is used to treat NIVL, migration can be particularly serious because the dislodged stent often migrates into the inferior vena cava and from there to the heart, potentially threatening the patient's life. In this regard, the cross-sectional lumen area of ​​the inferior vena cava increases downstream from the common iliac vein toward the heart, thus offering little resistance to the continued migration of a dislodged stent from the NIVL.

[0014] Stent migration is a particular problem with laser-cut stents placed in patients with NIVL. Numerous cases of venous stent migration have occurred in recent years. In these cases, the stent has been observed to migrate within hours of the procedure, but in other cases, migration can occur up to six months after the procedure.

[0015] In this regard, stents are most susceptible to dislodgement when they are too small for the lumen, or inner diameter, of the vessel into which they are to be placed. Therefore, before a stent is placed in a venous lesion such as NIVL, the diameter of the vein must be carefully measured to ensure that a stent of the appropriate diameter is selected. However, sizing a vessel is a difficult and imprecise technique. Veins, especially those deformed by luminal compression, are difficult to measure accurately, and vein diameter can vary due to various factors, such as the patient's hydration level, the patient's position (whether supine or upright), respiratory movements during measurement, and the Valsalva maneuver. As a result, a stent that is too small may be placed in the vein, posing a risk of migration and ultimately becoming lodged in the heart.

[0016] Figure 3 shows an example of a "Venovo" stent offered by Becton, Dickinson and Company (BD). These trademarks are acknowledged. The Venovo device is a laser-cut nitinol stent 22 comprising a series of circumferential crowns or segments 24, each containing a zigzag arrangement of struts 26 defining peaks and valleys. Successive segments 24 are joined by short longitudinal connectors 28 extending from the peak of one segment 24 to the peak of the next. Unlike the substantially uniform cross-sectional diameter of other commercially available stents, the ends 30 of the stent 22 are flared outward. Thus, the ends 30 defined by the terminal segments 24 of the stent 22 are approximately frustoconical in shape, increasing in diameter outward in opposite longitudinal directions.

[0017] While the flared ends 30 of the Venovo stent 22 are intended to reduce the risk of migration, migration of this stent type is still observed in the NIVL patient population. To understand why this is the case, refer to FIG. 4, which shows the Venovo stent 22 in situ. Here, the stent 22 is deployed to treat an NIVL 20 located at or near the junction between the common iliac vein 10 and the inferior vena cava 12.

[0018] The proximal end of the stent 22 is located at or slightly downstream of the junction between the common iliac vein 10 and the inferior vena cava 12, while the distal end of the stent 22 is located entirely upstream within the iliac vein 10. Indeed, in this example, the distal end of the stent is within the external iliac vein 32 upstream of its junction with the internal iliac vein 34.

[0019] The flared end 30 functions optimally to resist movement only in the outward flared direction. In this regard, the proximal end of the stent 22 is distal relative to the direction of blood flow. The flared proximal end 30 engages the vessel wall and, with continued downstream or proximal longitudinal movement, tends to flare or stretch, thus more firmly gripping or mechanically engaging the vessel wall.

[0020] Conversely, the trailing distal end 30 of the stent 22 lacks the same advantage because it tapers rather than widens in the direction of movement. As a result, the trailing end of the stent tends to narrow and therefore disengage from the vessel wall as longitudinal movement continues, providing little resistance to that movement. In that situation, only minimal friction can result from the radially outward force exerted by the distal edge of the trailing end against the vessel wall.

[0021] Thus, the location of the stent 22 relative to migration depends primarily on the flared proximal end 30 of the stent 22. As discussed above, the proximal end 30 is located downstream or distal to the stent 22 relative to blood flow, and therefore is located at or near the bifurcation or carina 36 of the bifurcation between the inferior vena cava 12 and the left and right common iliac veins 10.

[0022] The flared end 30 functions optimally to limit longitudinal movement of the stent 22 when contacting the peripheral wall of a blood vessel having a circular or elliptical luminal cross-section. In this case, the distal edge of the flared end 30 can consistently and firmly contact the vessel wall along the entire circumference. However, in the bifurcation region of the inferior vena cava 12, the vessel cross-section is noncircular, and the cross-sectional area increases as one moves proximally, i.e., downstream. In fact, the shape of the vessel wall constantly changes in multiple directions, particularly around the carina 36 located between the left and right common iliac veins 10. Around the carina 36, ​​in particular, the proximal edge of the distal end of the flared end 30 may not optimally contact the vessel wall along its entire circumference. In this case, the flared end 30 at the distal or proximal end of the stent 22 may provide insufficient resistance to downstream axial movement.

[0023] U.S. Patent Application Publication No. 2007 / 0142907 describes a prosthetic implant for treating a diseased aortic valve. The implant includes an adjustable ring to accommodate different sized valves. The diameter of the adjustable ring is expanded postoperatively by the surgeon placing the implant. Therefore, the expansion of the ring is dependent on the surgeon's skill. Furthermore, the described adjustable ring is susceptible to unintended diameter changes during installation, for example, due to magnetism during an MRI procedure.

[0024] WO 2018 / 110999 discloses a pancreatic stent having a body and a bent portion. During implantation, the stent is axially compressed, and the bent portion radially expands, forming a flange feature that extends around the entire circumference of the stent body. Such a stent is not suitable for venous or arterial applications. [Means for solving the problem]

[0025] It is against this background that the present invention has been devised. In one aspect, the present invention relates to a stent comprising a tubular body extending longitudinally between a proximal open end and a distal open end, the tubular body having an enlarged portion extending longitudinally between the proximal open end and the distal open end. The enlarged portion is disposed between longitudinally adjacent portions of the tubular body and has a radially enlarged configuration relative to at least both of the longitudinally adjacent portions. The enlarged portion may be preformed in a radially enlarged configuration relative to the proximal open end and the distal open end.

[0026] The present invention also relates to a stent comprising a series of longitudinally oriented tubular segments separated by and alternating with gaps between opposing end segments along the length of the stent. Each segment in the series comprises struts arranged in a circumferentially extending wave-like arrangement. Successive segments in the series are interconnected by connectors that bridge the respective gaps. Each segment in the series disposed between the end segments comprises at least one anchor segment preformed in a radially expanded configuration relative to at least one interconnected adjacent body segment having a smaller radius.

[0027] At least one anchor segment may be of substantially constant diameter along its longitudinal length or may be flared along its longitudinal length, in which case the or each flared anchor segment may extend longitudinally toward one of the end segments, or at least two anchor segments may flare in opposing longitudinal directions.

[0028] The connectors suitably extend between the peaks of each of the undulations of successive segments, for example, a valley connector may extend between opposing valleys of the undulations of successive segments.

[0029] In this case, a valley connector can connect at least one anchor segment to a series of at least one body segment. Conversely, a vertex-to-vertex connector can extend between opposing vertices of a wave-like arrangement of consecutive segments. Such a vertex-to-vertex connector can connect a series of consecutive anchor segments and / or consecutive body segments. The connector can have consecutive opposing bends or inflections along its length.

[0030] At least two of the anchor segments may be grouped in longitudinal succession, and at least one anchor segment may extend longitudinally to a substantially different extent than at least one other segment in the series.

[0031] A stepped exterior shape can be defined between at least one anchor segment and the series of interconnected segments. The stepped exterior shape can include, for example, a radially extending circumferential shoulder or can be circumferentially serrated. The serrations of the stepped exterior shape can be gracefully defined by a wavy arrangement of struts of the anchor segments.

[0032] The stent may include a group of anchor segments, the radii of which increase and / or decrease along the group. At least two anchor segments may be longitudinally spaced along the group and separated by at least one body segment. The or each body segment may be substantially the same diameter as the end segments.

[0033] The inventive concept also includes a method of manufacturing a stent, the method comprising inserting a cylindrical mandrel having at least one radially protruding circumferential band into a lumen of the stent; longitudinally aligning at least a portion of the stent with the or each band of the mandrel, wherein the or each aligned portion of the stent is inward of an opposing end of the stent; and effecting relative radial movement between the stent and the mandrel to form the stent about the mandrel such that the or each portion longitudinally aligned with the or each band is radially expanded relative to other portions not longitudinally aligned with the or each band.

[0034] In the case of a segmented stent, the manufacturing method may include inserting a cylindrical mandrel having at least one radially protruding circumferential band into the lumen of a stent having a series of interconnected circumferential tubular segments in the longitudinal direction; longitudinally aligning at least one of the segments of the stent with the or each band of the mandrel, wherein the or each aligned segment is inward of an opposing end segment of the stent; and effecting relative radial movement between the segment and the mandrel to form the segment around the mandrel such that the or each segment longitudinally aligned with the or each band is radially expanded relative to other segments not longitudinally aligned with the or each band.

[0035] At least one circumferential edge of the or each band may be aligned with each gap between successive segments in a series, in which case connectors extending between successive segments may be received in respective angularly spaced grooves in the band that intersect the or each circumferential edge.

[0036] Each series of segments may include struts arranged in a circumferentially extending undulating array, in which case interconnections between a segment aligned with a band and an adjacent segment not aligned with the band may be made by connectors extending between opposing valleys of the undulating arrays. Conversely, interconnections between segments in a group all aligned with a band may be made by connectors extending between opposing peaks of the undulating arrays.

[0037] A stepped shape may be formed between a portion of the stent aligned with a band or one of the bands and an adjacent portion not aligned with that band. A flared shape may be formed in the portion or portions aligned with a band or bands. A step may be formed between the portion having the flared shape and the adjacent portion of the stent.

[0038] A series of two or more consecutive groups of segments may be longitudinally aligned with a band that aligns all of the segments of the group, and the segments of the group may be pressed to conform to a concave formation in the band by locally applying radially inward pressure to a connector extending between the segments.

[0039] The stents of the present invention, for example, comprise a series of interconnected longitudinal tubular segments, enabling a method of securing the stent when the segments are deployed together within a patient, the method comprising concentrating a radially outward pressure of the stent on the surrounding anatomical structure into which the stent is deployed, the pressure being concentrated through at least one tubular segment or portion of the stent, the tubular segment or portion being preformed in a radially expanded configuration relative to at least one adjacent or interconnected adjacent segment or portion having a smaller radius, the radially expanded segment or portion being longitudinally inward of an end segment or portion of the stent.

[0040] The stent may be placed, for example, to treat a non-thrombosed iliac vein lesion. Thus, the surrounding anatomical structure may be an iliac vein, in which case the or each radially expanding segment or portion of the stent may be aligned with the iliac vein, more specifically the common iliac vein. A proximal end segment or portion of the stent may protrude from the iliac vein into the inferior vena cava.

[0041] More generally, the surrounding anatomical structure may be a blood vessel, and at least one radially expanding segment or portion of the stent may extend in a downstream direction relative to blood flow within the vessel.

[0042] The surrounding anatomical structure may be engaged with the radially enlarged segments or portions or their respective edges, e.g., with serrations on the edges, which may be defined by struts of the radially enlarged segments or portions arranged as circumferentially extending waves.

[0043] In summary, the objective of the present invention is to reduce the risk of stent device migration, which is achieved by increasing the profile of the outer diameter of the stent.

[0044] The present invention contemplates various ways to achieve the expansion of the focal diameter, as described below: The radial expansion may be, for example, on the order of 1 mm compared to the adjacent portions on either side of the expanded portion.

[0045] The localized increase in focal diameter in the stent of the present invention provides one or more additional anchor points for the stent with minimal changes to the stent manufacturing process and the design, operation, and manufacture of a suitable stent delivery system. In use, the or each anchor point, aided by the serrations defined by the undulating struts, engages the surrounding vessel wall to resist stent migration. This not only strengthens the engagement between the stent and the surrounding vessel wall, but also makes the stent more resistant to incorrect sizing, particularly undersizing. The focal diameter may be increased or otherwise varied at one or more locations along the length of the stent. [Brief explanation of the drawings]

[0046] To put the present invention into context, reference has already been made to Figures 1 to 4 of the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram showing the convergence of the common iliac vein into the inferior vena cava, superimposed by the bifurcation of the abdominal aorta into the common iliac arteries, and superimposed in the lumbar region of the spine. [Figure 2a] FIG. 2a is a cross-sectional view taken along line II-II of FIG. 1, showing normal venous anatomy. [Figure 2b] FIG. 2b is a cross-sectional view taken along line II-II of FIG. 1, showing the left common iliac vein compressed against the spine by the overlying right common iliac artery. [Figure 3] 1 is a side view of a prior art stent that can be used to restore patency of the common iliac vein. [Figure 4] FIG. 1 is a schematic diagram showing a prior art stent placed in the left common iliac vein.

[0047] In order that the present invention may be more readily understood, reference will now be made, by way of example, to the remaining accompanying drawings in which: [Figure 5] 1A and 1B are schematic side views of first and second embodiments of the present invention, each showing a portion of a stainless steel. [Figure 6] 1A and 1B are schematic side views of first and second embodiments of the present invention, each showing a portion of a stent. [Figure 7] FIG. 1 is a schematic diagram showing a stent of the present invention being placed in the left common iliac vein. [Figure 8] 1 is a perspective view of a mandrel for forming a stent according to a first embodiment of the present invention. [Figure 9] FIG. 9 is an enlarged detailed side view of the mandrel of FIG. 8 as it forms the stent. [Figure 10] FIG. 10 is a schematic side view of a portion of a stent in a third embodiment of the present invention. [Figure 11] FIG. 11 is a schematic side view of a mandrel for forming the stent shown in FIG. [Figure 12] 10A and 10B are schematic side views of fourth and fifth embodiments of the present invention, each showing a portion of a stent. [Figure 13] 10A and 10B are schematic side views of fourth and fifth embodiments of the present invention, each showing a portion of a stent. [Figure 14] 13 is a schematic side view in longitudinal section showing how the stent shown in FIG. 12 engages with surrounding vessels within a patient's body. [Figure 15] FIG. 13 is an enlarged, detailed side view of a portion of a mandrel for forming the stent shown in FIG. 12. [Figure 16] 15, but showing a longitudinal cross-section of a mandrel used in forming the stent shown in FIG. [Figure 17] FIG. 10 is a schematic side view of a portion of a stent in a sixth embodiment of the present invention. [Figure 18a] 1A-1C are schematic side views showing the sequence of a balloon-expandable stent being formed in a blood vessel by expansion of an inner balloon having a stepped shape. [Figure 18b] 1A-1C are schematic side views showing the sequence of a balloon-expandable stent being formed in a blood vessel by expansion of an inner balloon having a stepped shape. DETAILED DESCRIPTION OF THE INVENTION

[0048] Figures 5, 6, 10, 12, and 13 are schematic diagrams illustrating portions of various embodiments of stents 38. Each stent 38 comprises an open skeletal frame that is formed when an elongated tube is radially expanded to the condition shown in these figures. The tube may be formed, for example, of nitinol that has been laser cut with a pattern of slits that define the members of the frame between the slits when the tube is expanded.

[0049] It is emphasized that Figures 5, 6, 10, 12, and 13 are schematic views intended to illustrate the principles of the invention rather than showing full details of an actual embodiment. For example, in practice, each slit will conveniently define the boundaries of adjacent frame members separated by the slit such that they have complementary or matching contours defined by the width, shape, and shape of the slit.

[0050] The expanded state of the stent 38, as shown in Figures 5, 6, 10, 12, and 13, may be an in-use state sufficient to support the surrounding vessel wall, or an insertion state that requires further radial expansion to the in-use state upon insertion, for example, using a balloon catheter.

[0051] Each stent 38 shown in Figures 5, 6, 10, 12, and 13 comprises a longitudinal array or series of rings, circumferential or tubular segments, or crowns 40 distributed along the length of the stent 38 and spaced apart by circumferential gaps 42 between them. The length of the stent 38, and therefore the number of crowns 40, is indefinite. Only a few of a potentially multiple number of such crowns 40 are shown in these figures.

[0052] Each crown 40 is circumferentially continuous and, in end view, rotationally symmetric about a central longitudinal axis 44 of the stent 38. Each crown 40 also extends parallel to the central longitudinal axis 44 and thus, together with the width of the gaps 42 between adjacent crowns 40 along that axis 44, defines a respective portion of the length of the stent 38.

[0053] Each crown 40 includes a circumferentially extending zigzag arrangement of struts 46, which are the main members of a skeletal frame. The zigzag arrangement can also be described as a triangular waveform that oscillates circumferentially around the crown 40. In these examples, the waveform has symmetrical rise and fall edges, although asymmetrical waveforms, such as a sawtooth waveform, are also possible.

[0054] Each strut 46 is inclined relative to a line that intersects the periphery of the associated crown 40 and extends parallel to the central longitudinal axis 44. The inclination of each strut 46 is opposite to the inclination of adjacent struts 46 of the same crown 40. In these examples, each strut 46 of a crown 40 is substantially straight and of substantially the same length as the other struts 46 of the same crown 40.

[0055] The circumferentially successive apices 48 where the struts 46 of each crown 40 join define peaks and valleys when viewed from the perspective of an adjacent crown 40. Apices are apices 48 that are relatively close to an adjacent crown 40, and valleys are apices 48 that are relatively far from an adjacent crown 40. The peaks and valleys of each crown 40 alternate circumferentially around the crown 40.

[0056] When the skeletal frame members are formed and defined between the slits in the tubular workpiece, the corrugated shape of each crown 40 will complement the shape of the adjacent crown 40 or each of their respective neighboring crowns 40. Thus, prior to longitudinal expansion of the slitted tube to form the stent 38, successive crowns 40 are in a nested relationship, with the peaks of each crown 40 aligned with and nested within the valleys of the adjacent crown 40. Thus, the peaks and valleys of the crowns 40 are angularly offset, or indexed, about the central longitudinal axis 44 relative to the peaks and valleys of the adjacent crowns 40. For symmetrical corrugations such as those shown in Figures 5, 6, 10, 12, and 13, the angular offset from one crown 40 to the next is one-half of a wavelength.

[0057] The crowns 40 are joined to the or each adjacent crown 40 by a set of connectors 50, 52 distributed circumferentially about the central longitudinal axis 44. The connectors 50, 52 extend longitudinally to fill the gaps 42 between successive crowns 40 and function as secondary members of the skeletal frame. More specifically, the stent arrangement shown in Figures 5, 6, 10, 12, and 13 includes two types of connectors 50, 52 between successive crowns 40: long connectors 50 extending from the valley of one crown 40 to the nearest valley of the adjacent crown 40, and short connectors 52 extending from the apex of one crown 40 to the nearest apex of the adjacent crown 40.

[0058] The sets of long connectors 50 and short connectors 52 are longitudinally alternated, with one gap 42 filled by a set of short connectors 52, the next gap 42 filled by a set of long connectors 50, and so on along the length of the stent 38. As a result, adjacent crowns 40 are joined together in pairs by short connectors 52, and the pairs of crowns 40 are joined to one or two adjacent crowns 40 by long connectors 50.

[0059] In these examples, the connectors 50, 52 are spaced apart by more than the wavelength of the crown 40. Thus, not all of the peaks and valleys are joined by connectors 50, 52. Specifically, in these examples, the angular spacing between the connectors 50, 52 alternates circumferentially between every third peak or valley and every fourth peak or valley. Thus, the connectors 50, 52 filling the gap 42 are not necessarily equiangularly spaced; in other words, the angular spacing between consecutive connectors 50, 52 within the gap 42 may vary circumferentially.

[0060] It will also be apparent that sets of longitudinally consecutive long connectors 50, as well as sets of consecutive short connectors 52, are angularly offset or indexed circumferentially about central longitudinal axis 44. The angular offset from one set of connectors 50, 52 to the next set of similar connectors 50, 52 is one wavelength of the waveform defining crown 40, and thus a rotation equal to the circumferential distance between successive peaks or valleys.

[0061] Before the stent 38 is expanded from the slit tube, when successive crowns 40 are in a nested relationship, the peaks of the crowns 40 are substantially aligned longitudinally with the valleys of adjacent crowns 40. As a result, there is an angular offset between the peaks and valleys of successive crowns 40 that face each other across the gaps 42 between the crowns 40. In these examples, that angular offset is approximately one-half of a wavelength. Therefore, the connectors 50, 52 must account for the resulting angular offset between their ends at the apexes 48 that define the peaks and valleys.

[0062] The connectors 50, 52 can be angled relative to the longitudinal direction or, as in these examples, curved or bent to allow for an angular offset between their ends. Specifically, the short connector 52 in these examples has an S-shape, continuously curving through opposing inflections. Conversely, the long connector 50 has straight longitudinal sections 54 joined by a central chicane 56 with opposing bends.

[0063] These configurations of connectors 50, 52 have the advantage of imparting flexibility to stent 38, including longitudinal extensibility that allows stent 38 to bend along its length and thus extend outward or outward from central longitudinal axis 44. Longer connectors 50, due to their greater length, tend to bend along their length, contributing additional flexibility in addition to that provided by shorter connectors 52.

[0064] The flexibility of the connectors 50, 52 from one crown 40 to the next is advantageous not only to allow the stent 38 to more easily conform to the internal contours of the vasculature during use, but also to allow the stent 38 to be shaped in accordance with the present invention without excessive local stresses when manufactured. In particular, the long connectors 50 effectively separate radially expanded anchor segments or crowns 40" from immediately adjacent body segments or crowns 40' of smaller radii, whether or not those crowns 40" are expanded. This allows those successive crowns 40 to move and flex to a useful degree independently of one another during manufacturing, deployment, and use.

[0065] 5 and 6 show an embodiment of a stepped stent 38 in which pairs of anchor crowns 40" joined apex-to-apex by short connectors 52 radially expand to a greater extent than the adjacent body crown 40' disposed outwardly of the pair on each side. These body crowns 40' are joined to each anchor crown 40" of the pair by respective long connectors 50 extending from valley to valley. The long connectors 50 are flexible enough to flex or deform in response to axial and bending loads, thereby accommodating the radial expansion of the inward pair of anchor crowns 40" without being overstressed.

[0066] In the embodiment of Figures 5 and 6, the radially expanding pair of anchor crowns 40" maintain a substantially uniform diameter along their lengths. Thus, when viewed in longitudinal cross section, these anchor crowns 40" have radially outermost circumferential surfaces 58 that are straight and parallel to the central longitudinal axis 44.

[0067] Nevertheless, due to their radial expansion, anchor crowns 40" project radially like flanges from the peripheral cylindrical contour of stent 38 defined by outer body crown 40'.

[0068] The flange-like radial protrusions of anchor crown 40" define circumferential formations 60 that are steps, edges, or shoulders between the smaller radius of main body crown 40' and the larger radius of expanded anchor crown 40" disposed therebetween. It will be apparent that these circumferential formations 60 improve the mechanical and frictional engagement of stent 38 with the surrounding vessel during use, and in particular, resist longitudinal movement, and therefore migration, of stent 38.

[0069] The protruding anchor crowns 40" also concentrate the radial expansion force of the stent 38 over a smaller portion of the outer surface area of ​​the stent 38, thereby increasing the outward pressure acting against the interior of the surrounding vessel wall and enhancing the mechanical and frictional engagement of the stent 38 with the vessel.

[0070] As an added advantage, the outer apexes 48 or peaks of the undulations of the anchor crowns 40" impart a sawtooth shape to the circumferential formations 60. As shown in FIG. 7, when the stent 38 is deployed within the common iliac vein 10 or other vessel, the sawtooth circumferential formations 60 of the anchor crowns 40" bite into and mechanically engage the surrounding wall of the vein 10. These formations 60 thus have a similar positioning function as the flared ends 30 of the prior art stent 22 shown in FIGS. 3 and 4, however, the inward location of the formations 60 provides an additional advantage.

[0071] In this regard, it is apparent that the inward location of the anchor crowns 40" and their circumferential formations 60, and therefore away from the ends of the stent 38, may better engage the surrounding vessel wall than corresponding enlarged portions at the ends of the stent. In this regard, it is recalled that the flared proximal end 30 of the prior art stent 22 shown in Figures 3 and 4 may not adequately engage the surrounding vessel wall in the region of the carina 36 located between the common iliac vein 10 at the lower end of the inferior vena cava 12. In contrast, the enlarged inner anchor crowns 40" of the embodiment shown in Figures 5 and 6 are located distal to the proximal end of the stent 38 and therefore reliably lie within the consistently circular or elliptical cross-section of the common iliac vein 10, as shown in Figure 7.

[0072] 5 and 6 show different lengths of the anchor crowns 40" in a direction parallel to the central longitudinal axis 44. Specifically, the lengths of all crowns 40 along the length of the stent 38 are uniform in FIG. 5. Conversely, FIG. 6 shows that at least one of the anchor crowns 40", in this example both, is a different length than the other main body crowns 40' of the stent 38, and in this example is longer.

[0073] The length of a crown 40, and therefore the length of the struts 46 that make up the crown 40, can be varied within a size range to match the radial force exerted by the struts 46 of adjacent crowns 40. For example, the radial force, expressed as radial outward force per unit area, can be reduced by lengthening the struts 46 or increased by shortening the struts 46.

[0074] FIGS. 8 and 9 illustrate an apparatus and method for forming a stent 38 having twin radially expanding anchor crowns 40" as shown in FIGS. 5 and 6. The stent 38 is formed on an elongated cylindrical mandrel 62 as shown in FIG. 8, which fits into the lumen of the stent 38 as shown in FIG. 9. The forming step may conveniently be performed in conjunction with a final heat treatment step.

[0075] The mandrel 62 has an integral collar defining a shallow circumferential flange or band 64 that defines a focal region of increased outer radius. As seen in FIG. 8 , the length of the band 64 corresponds to the combined length of the pair of anchor crowns 40″ of the stent 38, which are joined by short connectors 52 that fill the gap 42 between them. The bands 64 terminate at their ends in rounded or chamfered steps or shoulders 66 that longitudinally align with the gaps 42 between the pair of anchor crowns 40″ and the adjacent body crown 40′ of the stent 38 immediately outboard of the pair. Specifically, the shoulders 66 align with the chicanes 56 of the long connectors 50 that fill these gaps 42.

[0076] Thus, when the stent 38 is forced radially inward against the mandrel 62, thereby plastically deforming it to conform to the outer shape of the mandrel 62, the radial projections of the bands 64 create a radial expansion of the inward pair of anchor crowns 40" relative to the outer side body crowns 40', as seen in FIGS. 5 and 6. The stent 38 retains this set shape when it is removed from the mandrel 62.

[0077] The longitudinal grooves 68 in the band 64 extend from the closed inner end to the open outer end where they meet and intersect with shoulders 66 of the band 64. The radius of the mandrel 62 at the base of each groove 68 corresponds to the radius of the mandrel 62 on the outer side of the band 64.

[0078] The grooves 68 in the band 64 are grouped in oppositely facing pairs and are angularly spaced around the circumference of the band 64 to join the body crowns 40' to the respective anchor crowns 40" of the enlarged pairs to match the angular positions of the long connectors 50 extending from valley to valley.

[0079] The grooves 68 of each pair approach each other at their inner ends but do not meet, and in this example are angularly offset from each other to match the aforementioned angular offset between successive long connectors 50 along the length of the stent 38. The grooves 68 thereby accommodate the long connectors 50 and allow the long connectors 50 to bend smoothly inwardly and outwardly without undue stress as they fill the gaps 42 between the body crown 40' and the radially enlarged anchor crowns 40". The stepped chicanes 56 of the long connectors 50 also help the long connectors 50 provide a low-stress transition between the body crown 40' and the radially enlarged anchor crowns 40".

[0080] As mentioned above, shoulder 66 defines locating formation 60 that provides a sharp, gradual transition between body crown 40′ and radially enlarged anchor crown 40″. Formation 60 strongly resists movement of stent 38 during use. Advantageously, however, that sharp transition is provided without a corresponding sharp transition in long connector 50, thus mitigating stress and fatigue challenges.

[0081] Turning now to FIG. 10 , this embodiment of the stent 38 illustrates that two or more pairs of radially expanding crowns 40 can function as anchor crowns 40″, and that these crowns 40″ can be radially expanded to different degrees. In this example, the pairs of anchor crowns 40″ decrease in diameter in stepwise opposite outward directions from a central pair of anchor crowns 40″ of maximum diameter. Thus, the stent 38 is convex when viewed in longitudinal cross section or side view. This configuration is also advantageous because it concentrates the greatest constraining pressure at locations inward of the ends of the stent 38 when the stent 38 is in use. However, the longitudinal progression of diameter from one pair of crowns 40 to the next can differ from that shown in FIG. 10 , for example, having a concave shape that increases to two or more maximum diameters spaced longitudinally along the stent 38.

[0082] 10 thus illustrates that the diameter of stent 38 can vary along the length of stent 38. This focuses an outward radial force against the surrounding vessel wall, as in the previous embodiment, but also allows stent 38 to be tailored to fit not only the size, but also, to some extent, the shape or geometry of the target vessel surrounding the lesion being treated. This tailored fit and resulting mechanical engagement securely anchors stent 38 even if stent 38 is imprecisely sized for the vessel.

[0083] This change in diameter can be in a stepped manner, as shown in Figure 10, or can be more continuous, for example, if at least some of the crowns 40 have a frustoconical shape, as shown in Figures 12 and 13. Also, as in Figure 6, the length of the struts 46, and therefore the length of the crowns 40, can be modified from one crown 40 to the next to adjust the radial force or pressure along the length of the stent 38.

[0084] The stepped shape of the stent 38 shown in Figure 10 can be formed by a modification of the mandrel 62 shown in Figures 8 and 9, with a corresponding series of bands 64 whose diameters increase stepwise in opposite inward directions. Such a mandrel 62 is shown in Figure 11. The stepped outer edges of the bands 64 intersect with longitudinal grooves 68 that are angularly aligned with the long connectors 50 of the stent 38.

[0085] 12 and 13 show stent variations 38 in which inward pairs of anchor crowns 40" connected to one another by short connectors 52 flare in opposite outward directions. In these variations, the orientation of some struts 46 is changed so that the associated anchor crowns 40" flare away from the longitudinal centerline of the stent 38. In other words, each anchor crown 40" of the inner pair is plastically deformed such that its radially outermost circumferential surface 58 is transformed from a straight-walled cylindrical shape of uniform diameter to a frusto-conical shape whose diameter increases outward. Thus, the outer ends of the struts 46 of these anchor crowns 40" are raised to project radially outward from the straight-walled cylindrical shape of their outer, narrower main crowns 40'.

[0086] The outer apexes 48 or peaks of the undulations of the flared anchor crown 40" thereby create teeth or barbs of oppositely facing bifurcated serrated edges 70. These edges 70 have a similar positioning function as the flared ends 30 of the prior art stent 22 shown in FIG. 3, however, the inward location of the edges 70 is beneficial for the same reasons as described with respect to the enlarged inner anchor crown 40" of FIG. 7.

[0087] 12, the splayed anchor crowns 40" are radially expanded in the manner of the configuration shown in FIGS. 5 and 6, whereas in FIG. 13, the anchor crowns 40" are expanded without any radial expansion other than that due to the expansion itself. Thus, in FIG. 12, the inner longitudinal edges of the splayed anchor crowns 40" are on a radius that is outer than the radius of the outer main body crowns 40', whereas in FIG. 13, the inner longitudinal edges of the splayed anchor crowns 40" are on the same radius as the outer main body crowns 40'. In other words, the diameter of the stent 38 from one crown 40 to the next does not change; only the orientation of at least some of the struts 46 relative to a line parallel to the central longitudinal axis 44 of the stent 38 changes.

[0088] When the stent 38 of FIG. 12 or FIG. 13 is placed in a common iliac vein 10 or other vessel, as shown in FIG. 14, the serrated edges 70 of the flared crowns 40 bite into and mechanically engage the surrounding wall of the vein 10. As their edges 70 engage the wall of the vein 10, the leading or downstream flared anchor crowns 40″, relative to the direction of blood flow, tend to flare or stretch to resist downstream movement of the stent 38. Further mechanical engagement between the stent 38 and the vein 10 is provided by the stepped, radially enlarged shape of the flared anchor crowns 40″ shown in FIG. 12. These anchor crowns 40″ project radially from the surrounding body of the stent 38 and emboss recesses 72 in the interior wall of the vein 10 that complement and accommodate the protruding portions of the anchor crowns 40″.

[0089] Two or more pairs of anchor crowns 40" can be splayed as shown in FIG. 12 or FIG. 13, the diameter or length of these splayed anchor crowns 40" can vary along the length of the stent 38 as shown in FIG. 5, FIG. 6, or FIG. 10, or splayed anchor crowns 40" can be combined with other radially expanding, non-splayed anchor crowns 40" within the same stent 38. Two or more anchor crowns 40" can also have matching frustoconical tapers so that the resulting stent 38 has unidirectional location characteristics, e.g., preferentially resist downstream displacement when the splayed anchor crowns 40" are oriented in a vessel to flare outward in the downstream direction.

[0090] Also, the expanded shape of anchor crown 40" shown in Figures 12 and 13 can be imparted to stent 38 by a mandrel 62 similar to that shown in Figures 8 and 9, but with bands 64 of mandrel 62 shaped to produce and thus complement the desired shape of anchor crown 40". In this example, as shown in Figure 15, circumferential bands 64 of mandrel 62 have a waisted shape defined by shallow circumferential grooves 74 that define recessed formations between frustoconical surfaces 76 that taper inwardly toward their interface. FIG. 16 shows how, in this case, tension applied to a circumferential loop 78 of wire surrounding the stent 38 and mandrel 62 around the neck of the band 64 can force the anchor crowns 40″ aligned with the band 64 into the grooves 74. This reduces the diameter of the loop 78 around the stent 38, particularly aligning the opposing flared anchor crowns 40″ with where the short connectors 52 join.

[0091] It will be apparent that a flared, but not radially expanded, version of the stent 38 shown in Figure 13 may also be made with a mandrel 62 similar to that shown in Figures 15 and 16. However, in that case, the base of the grooves 74 is on the same radius as the portion of the mandrel 62 outside the bands 64.

[0092] There may be two or more bands 64 longitudinally spaced along the mandrel 62. It is also possible for one or more bands 64 to have only one frustoconical surface 76. In this manner, one anchor crown 40" may be flared, while the other crowns 40 of the stent 38 have a constant diameter along their length. For example, one anchor crown 40" of an inner pair of crowns 40 may be flared, while the other crown 40 of the inner pair may be of a constant diameter, whether the same diameter as the outer main crown 40' of the pair or stepped to result in an anchor crown 40" of a larger diameter than the main crown 40'. It is also possible for one frustoconical surface 76 of the mandrel 62 to underlie two or more anchor crowns 40" of the stent 38, causing both of these anchor crowns 40" to correspondingly flare in succession, with their flared surfaces aligned at an angle to one another.

[0093] 17 shows a sixth embodiment of the present invention, illustrating that one or more portions may be radially and / or longitudinally expanded along the length of the stent 38. In this example, expanded portions 40" are spaced longitudinally along the stent 38 and are separated by similarly unexpanded main body portions 40'.

[0094] Finally, referring to Figures 18a and 18b, these figures illustrate how a balloon-expandable stent 38 can be radially expanded into the stepped configuration shown in Figure 18b. This is accomplished by inflating a corresponding stepped balloon 80 disposed within the lumen of the stent 38, as shown in Figure 18a.

[0095] As shown in Figure 18a, when stent 38 is delivered to a target location within blood vessel 10, inflation and radial expansion of balloon 80 also expands radially enlarged circumferential bands 82 of balloon 80. For example, the wall thickness of balloon 80 may be locally increased to define bands 82. Balloon 80 and bands 82 are then forced outward against the interior of stent 38, imparting a corresponding stepped shape to stent 38 that engages the wall of blood vessel 10, similar to the approach shown in Figure 14, as shown in Figure 18b.

[0096] Figures 17, 18a, and 18b illustrate that the stent need not have a segmented configuration, but may comprise a continuous tubular wall, for example, woven or formed from a mesh.

[0097] Many other variations are possible within the concept of the present invention. For example, the crown struts may follow different vibration waveforms, such as undulating waveforms typified by sine waves. More generally, as shown in Figures 5, 6, 10, 12, and 13, the transitions or apexes where the struts join successively in the circumferential direction may be rounded or arcuate rather than at sharp or abrupt angles. Also, the struts need not be straight, as shown in Figures 5, 6, 10, 12, and 13, but may be curved, either continuously along their length or with one or more smooth or sharp inflections or bends along their length, and thus may be wavy, twisted, dogleg, or chicane-like.

[0098] The number of connectors may vary depending on the length of the stent. For example, additional connectors may be used between crowns at or near the ends of the stent to provide additional rigidity to the skeletal framework. Indeed, additional connectors may be used anywhere else where additional rigidity may be beneficial, such as between radially expanded and / or flared pairs or other groups of anchor crowns.

[0099] Although radially expanded and / or flared anchor crowns are preferably grouped in pairs joined by short connectors, there may be more than one such anchor crown in a group joined by a short connector, provided that the outermost anchor crown in the group is joined to the body crown immediately outside the group by a long connector. Conversely, a single radially expanded and / or flared anchor crown may be joined to one adjacent body crown by a long connector and to another adjacent crown by a long or short connector. In this regard, short connectors may be suitable at the radially inward ends of flared anchor crowns, particularly when the anchor crowns are not radially expanded, as shown in FIG. 12 .

[0100] In a broader sense, the present invention is not limited to segmented stents, but can encompass stents having enlarged portions that do not correspond to one or more segment units. For example, the present invention can be applied to woven stents, mesh pattern stents, or spiral crown stents, as described above.

Claims

1. 1. A stent comprising a tubular body extending longitudinally between a proximal open end and a distal open end, The tubular body has an enlarged portion extending longitudinally between the proximal open end and the distal open end, and in an expanded state has a radially enlarged configuration relative to at least both longitudinally adjacent portions of the tubular body.

2. The stent of claim 1 , wherein the enlarged portion is preformed in a radially enlarged configuration relative to the proximal and distal open ends.

3. a series of circumferential tubular segments longitudinally separated by and alternating with gaps between a series of opposing end segments along the length of the stent; each of said series of segments comprising struts arranged in a circumferentially extending wave-like array; the series of consecutive segments are interconnected by connectors that bridge the respective gaps; 3. The stent of claim 1 or 2, wherein the series of segments disposed between the end segments comprises at least one anchor segment having, in an expanded state, a radially expanded configuration relative to at least one interconnected adjacent main body segment.

4. 4. The stent of claim 3, wherein at least one anchor segment is of substantially constant diameter along its longitudinal length.

5. 5. The stent of claim 3 or 4, wherein at least one anchor segment extends longitudinally along its length.

6. The stent of claim 5 , wherein the or each flared anchor segment extends longitudinally toward one of the end segments.

7. 7. The stent of claim 5 or 6, comprising at least two opposing longitudinally extending anchor segments.

8. The stent according to any one of claims 3 to 7, wherein the connector extends between the apexes of each of the undulating sequences of successive segments.

9. The stent of claim 8 , wherein valley connectors extend between opposing valleys of the undulating array of consecutive segments.

10. The stent of claim 9 , wherein the valley connector connects at least one anchor segment to the series of at least one body segment.

11. The stent of any one of claims 8 to 10, wherein apex-to-apex connectors extend between opposing apexes of the undulating array of successive segments.

12. The stent of claim 11 , wherein the apex-to-apex connectors connect the series of consecutive anchor segments and / or consecutive body segments.

13. The stent of any one of claims 3 to 12, wherein the connector has successive opposing bends or inflections along its length.

14. The stent according to any one of claims 3 to 13, wherein at least two of the anchor segments are grouped consecutively in the longitudinal direction.

15. A stent according to any one of claims 3 to 14, wherein at least one anchor segment extends longitudinally to a substantially different extent than at least one other segment in the series.

16. A stent according to any one of claims 3 to 15, comprising groups of anchor segments, the radius of the anchor segments increasing and / or decreasing along the group.

17. The stent of any one of claims 3 to 16, comprising at least two anchor segments spaced longitudinally along the series and separated by at least one body segment.

18. A stent according to any one of claims 3 to 17, wherein the or each body segment is of substantially the same diameter as the end segment.

19. The stent of any preceding claim, wherein a stepped outer profile is defined between the enlarged portion and the longitudinally adjacent portion.

20. 20. The stent of claim 19, wherein the stepped outer shape includes radially extending circumferential shoulders.

21. 21. The stent of claim 19 or 20, wherein the stepped outer shape is circumferentially sawtooth.

22. 22. The stent of claim 21, wherein the serrations of the stepped exterior profile are defined by a wave-like arrangement of struts.

23. 1. A method of manufacturing a stent, comprising: inserting a mandrel having at least one radially projecting circumferential band into the lumen of the stent; longitudinally aligning at least a portion of the stent with the or each band of the mandrel, the or each aligned portion of the stent being inward of opposing ends of the stent; forming the stent about the mandrel by effecting relative radial movement between the stent and the mandrel such that the or each portion longitudinally aligned with the or each band is radially expanded relative to other portions not longitudinally aligned with the or each band.

24. The portion of the stent comprises a series of longitudinally interconnected circumferential tubular segments, and the method comprises: longitudinally aligning at least one of the segments of the stent with the or each band of the mandrel, the or each aligned segment being inward of an opposing end segment of the stent; and forming the segments around the mandrel by effecting relative radial movement between the segments and the mandrel such that the or each segment longitudinally aligned with the or each band is radially expanded relative to other segments not longitudinally aligned with the or each band.

25. 25. The method of claim 24, including aligning at least one circumferential edge of the or each band with a respective gap between said series of consecutive segments.

26. 26. The method of claim 25, including receiving connectors extending between successive segments in angularly spaced grooves in each of the bands intersecting the or each circumferential edge.

27. 27. The method of any one of claims 24 to 26, wherein each of the series of segments includes struts arranged in a circumferentially extending undulating array, and the interconnection between a segment aligned with the band and an adjacent segment not aligned with the band is made by a connector extending between opposing valleys of the undulating arrays.

28. 28. The method of claim 27, wherein the interconnections between the segments of a group of segments all aligned with one band are made by connectors extending between opposite vertices of their corrugated arrangement.

29. 29. A method according to any one of claims 22 to 28, comprising longitudinally aligning the series of two or more consecutive groups of segments with one band that is aligned with all the segments of the group.

30. 30. The method of claim 29, comprising forcing the segments of the group to conform to concave formations in the band by locally applying radially inward pressure to connectors extending between the segments.

31. 31. The method of any one of claims 21 to 30, comprising forming a stepped shape between a portion of the stent aligned with the band or one of the bands and an interconnecting or adjacent portion of the stent not aligned with the band.

32. A method according to any one of claims 21 to 31, comprising forming an expanded shape into the or each portion of the stent which is aligned with the or each band.

33. 33. The method of claim 32, comprising forming a step between a portion of the stent having an expanded configuration and an interconnected or adjacent portion of the stent.

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