Laser-cut stent

Abstract

A stent comprises a tubular body defined by a longitudinal succession of annular crowns each comprising struts disposed in a circumferentially-extending waveform. Sets of connectors interconnect successive crowns, namely long connectors and short connectors that effect, respectively, trough-to-trough and peak-to-peak connections between the waveforms of successive crowns. The stent has a first end portion, a central portion and a second end portion. Each of the end portions comprises, respectively, an outermost ultimate crown, a penultimate crown and an antepenultimate crown in longitudinally inward succession. In each of the end portions, more connectors are disposed between the ultimate and penultimate crowns than are disposed between the penultimate and antepenultimate crowns. A set of the long connectors is disposed between the penultimate and antepenultimate crowns of one of the end portions and a set of the short connectors is disposed between the penultimate and antepenultimate crowns of the other end portion.

Description

[0001] Laser-cut stent

[0002] This invention relates to stents, especially stents for the treatment of occlusions in blood vessels.

[0003] Stents are typically inserted into a vessel in a narrowed initial state and are then expanded radially to support the surrounding wall of the vessel, hence restoring or maintaining its patency. Some stents self-expand elastically when released from within a sleeve or catheter. Others expand plastically either when activated, for example by heat acting on a shape-memory alloy, or by being pressed radially outwardly from within using an instrument such as a balloon catheter.

[0004] Figure 1 shows, in solid lines, the convergence of the common iliac veins 10 into the lower end of the inferior vena cava 12 in a human individual. The iliac veins 10 drain blood from the lower abdomen and the lower limbs into the inferior vena cava 12 and from there to the heart. The inferior vena cava 12 extends up to the heart beside the abdominal aorta 14, shown here in dotted lines, which reciprocally carries blood from the heart to the lower abdomen and the lower limbs. The abdominal aorta 14 bifurcates at its lower end into the common iliac arteries 16.

[0005] The inferior vena cava 12 and the abdominal aorta 14 lie beside each other in front of the vertebral column 18, whose outline is represented schematically in Figure 1 by parallel dashed lines. The bifurcation of the abdominal aorta 14 is typically aligned with the fourth vertebra of the lumbar spine, known as L4. As Figure 1 is a front view, the abdominal aorta 14, shown here to the right, lies 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 to the right and so on.

[0006] It will be apparent from Figure 1 that the right common iliac artery 16 crosses and overlies the left common iliac vein 10. The positional relationship between the common iliac veins 10 and the common iliac arteries 16 can also be appreciated in the cross- sectional views of Figures 2a and 2b.

[0007] Figures 2a and 2b show that the common iliac veins 10 and the common iliac arteries 16 also lie in front of the vertebral column 18, typically in front of the lowermost lumbar vertebra, known as L5. It follows that the left common iliac vein 10 is disposed between the vertebral column 18 and the overlying right common iliac artery 16, where the right common iliac artery 16 crosses over the left common iliac vein 10. The left common iliac vein 10 is therefore susceptible to compression by the right common iliac artery 16 and hence to a substantial reduction of patency in this region, as shown in Figure 2b in contrast to its uncompressed state in Figure 2a.

[0008] Luminal compression of the left common iliac vein is common in the population, occurring in nearly a quarter of healthy individuals. The condition is largely asymptomatic but, in some cases, the loss of patency becomes clinically significant and gives rise to May-Thurner syndrome, also known as iliac vein compression syndrome. May-Thurner syndrome is characterised by swelling, pain, deep venous thrombosis, skin discolouration, ulcers and / or the formation of collateral blood vessels, all caused by changes in venous flow or venous pressure arising from limited blood flow out of the affected leg. Its symptoms can severely impact an individual’s quality of life.

[0009] When properly diagnosed, luminal compression of the common iliac vein is referred to as a non-thrombotic iliac vein lesion or NIVL 20, which 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.

[0010] Venous stenting has become the standard technique for treating occlusive blockages in the iliac and femoral veins. In particular, patency of the common iliac vein can be restored successfully by placing a stent device across the blockage of a NIVL. The stent pushes the wall of the vein back against the overlying artery to restore normal blood flow, thereby enabling venous drainage.

[0011] More generally, it is well known to employ venous stents to treat obstruction of venous outflow that is a characteristic of iliofemoral occlusive disease. Indeed, venous stenting has become the standard technique for treating occlusive blockages in the iliac and femoral veins. For example, venous stents are used to reduce pain and swelling and to promote healing of ulcers in patients suffering from post-thrombotic syndrome (PTS) following an episode of DVT. Venous stents can also be used to treat patients presenting with an acute DVT to prevent subsequent development of PTS.

[0012] In principle, braided or woven stents can be used in venous applications if they have sufficient radial strength or crush resistance. Currently, however, most self-expanding stents used to treat venous disease are laser-cut from tubes of nitinol. Laser-cut stents are cut in various patterns to create skeletal frame structures when expanded or opened out. Such structures typically comprise a longitudinal array or series of crowns, being circumferential, annular, or tubular segments or rings distributed along the length of the stent and extending parallel to its central longitudinal axis. Each segment comprises a continuous, circumferentially-extending zig-zag waveform arrangement of struts that are the principal members of the skeletal frame. The crowns are spaced apart by circumferential gaps that are bridged by connectors extending longitudinally from one crown to the next in the series.

[0013] US 7645297 discloses an example of a laser-cut nitinol intravascular stent.

[0014] As mentioned above, stents are typically inserted into a vessel in a radially narrowed initial state and are then expanded radially to support the surrounding wall of the vessel. The stent is held in the narrowed initial state by a catheter or sheath so that the stent can be navigated through the vasculature to the intended deployment site.

[0015] During deployment, it is known that typical self-expanding laser-cut stents have a tendency to ‘jump’ out of the surrounding catheter once a major distal portion of the stent has been deployed from the catheter. In other words, radial expansion of the partially- deployed stent acting on the distal end of the catheter generates a distal axial thrust force that pulls on the minor proximal portion of the stent remaining within the catheter. Eventually, when friction between the proximal portion of the stent and the surrounding catheter is insufficient to resist that thrust force, a runaway uncontrolled deployment of the proximal portion of the stent occurs.

[0016] Uncontrolled deployment may lead to distortion of the stent pattern and / or misalignment of the stent in the vein of the patient. In either case, there is an increased risk that the struts of the segments may protrude into the wall of the vessel, which could promote thrombosis at the stent deployment site. Uncontrolled deployment can also result in the stent being deployed at an incorrect longitudinal position in the vein.

[0017] It is against this background that the present invention has been devised. In one aspect, a stent comprises a longitudinally-extending tubular body defined by a longitudinal succession of annular crowns each comprising struts disposed in a circumferentially- extending waveform. Sets of connectors interconnect successive crowns by bridging respective gaps between the successive crowns, those sets comprising sets of long connectors and sets of short connectors that effect, respectively, trough-to-trough and peak-to-peak connections between the waveforms of the successive crowns.

[0018] The stent comprises a first end portion, a central portion and a second end portion in longitudinal succession. Each of the end portions comprises, respectively, an outermost ultimate crown, a penultimate crown and an antepenultimate crown in longitudinally inward succession. In each of the end portions, the set of connectors disposed between the ultimate and penultimate crowns contains more connectors than the set of connectors disposed between the penultimate and antepenultimate crowns.

[0019] In each of the end portions, the set of connectors disposed between the ultimate and penultimate crowns may contain more connectors than in sets of connectors disposed between crowns of the central portion. The number of connectors joining the ultimate and penultimate crowns of both the first and second end portions may be equal.

[0020] The penultimate and antepenultimate crowns of the first end portion may be joined by a set of the long connectors. The penultimate and antepenultimate crowns of the second end portion may be joined by a set of the short connectors. More generally, a set of the long connectors may be disposed between the penultimate and antepenultimate crowns of one end portion whereas a set of the short connectors may be disposed between the penultimate and antepenultimate crowns of the other end portion.

[0021] In each of the end portions, the set of connectors disposed between the ultimate and penultimate crowns can contain twice as many connectors as the set of connectors disposed between the penultimate and antepenultimate crowns.

[0022] A set of the short connectors may be disposed between an outermost crown of the central portion and the antepenultimate crown of at least one of the end portions. In that case, the antepenultimate crowns of the end portions may be joined to respective outermost crowns of the central portion by equal numbers of the short connectors.

[0023] The central portion can comprise sets of the long connectors and sets of the short connectors that alternate in longitudinal succession. A set of the short connectors can join the ultimate and penultimate crowns of each end portion. All of the crowns inboard of the penultimate crowns of the end portions may be joined by equal numbers of the connectors. A set of the short connectors may join the penultimate and antepenultimate crowns of at least one of the end portions.

[0024] The central portion may comprise a repeating pattern of crown pairs, each crown pair comprising two crowns joined by a set of the short connectors. Successive crown pairs of the repeating pattern may be joined by respective sets of the long connectors. The central portion may be terminated at its opposed ends by respective terminal crowns disposed outboard of respective crown pairs and joined to those crown pairs by respective sets of the long connectors. The terminal crowns may be joined to respective antepenultimate crowns of the end portions by respective sets of the short connectors.

[0025] At least one of the crowns of the central portion may be radially enlarged relative to at least one adjoining crown of the central portion when the stent is in an expanded state. Similarly, at least one of the crown pairs of the central portion may be radially enlarged relative to at least one of the adjoining crown pairs of the central portion when the stent is in an expanded state. At least one of the crowns of the central portion may be preformed with a radially enlarged configuration relative to at least one adjoining crown.

[0026] The or each radially enlarged crown may be at a position offset longitudinally closer to one of the end portions than to the other of the end portions. The or each radially enlarged crown may be of substantially constant diameter along its length in a longitudinal direction or may be flared along its length in a longitudinal direction. At least two crowns can be flared in opposed longitudinal directions. The or each radially enlarged crown can be joined to an adjoining crown by a set of the long connectors.

[0027] The ultimate crown of each end portion may comprise a set of identification features, which features can differ between one end portion and the other end portion.

[0028] When the stent is deployed in vivo, the first end portion may be disposed cranially and the second end portion may be disposed caudally within a patient’s vasculature. Where the penultimate and antepenultimate crowns of the first end portion are joined by a set of the long connectors and the penultimate and antepenultimate crowns of the second end portion are joined by a set of the short connectors, the first end portion may be disposed cranially and the second end portion may be disposed caudally within a patient’s vasculature when the stent is deployed in vivo. The inventive concept embraces a stent of the invention and a deployment device in combination, where the first end portion of the stent is disposed distally and the second end portion of the stent is disposed proximally with respect to the deployment device.

[0029] The inventive concept also extends to a method of progressively deploying a stent of the invention from a deployment device, the method comprising deploying the first end portion of the stent and subsequently deploying the second end portion of the stent from a distal end of a surrounding catheter or sheath of the deployment device. Another method of deploying a stent of the invention into a patient’s vasculature comprises: inserting a deployment device into the patient’s vasculature: navigating the deployment device to a target location in the patient’s vasculature; and deploying the stent from the deployment device into the patient’s vasculature such that the first end portion is disposed cranially and the second end is disposed caudally.

[0030] In summary, a stent of the invention comprises a tubular body defined by a longitudinal succession of annular crowns each comprising struts disposed in a circumferentially- extending waveform. Sets of connectors interconnect successive crowns, namely long connectors and short connectors that effect, respectively, trough-to-trough and peak-to- peak connections between the waveforms of successive crowns.

[0031] The stent has a first end portion, a central portion and a second end portion. Each of the end portions comprises, respectively, an outermost ultimate crown, a penultimate crown and an antepenultimate crown in longitudinally inward succession. In each of the end portions, more connectors are disposed between the ultimate and penultimate crowns than are disposed between the penultimate and antepenultimate crowns. A set of the long connectors is disposed between the penultimate and antepenultimate crowns of one of the end portions and a set of the short connectors is disposed between the penultimate and antepenultimate crowns of the other end portion.

[0032] To put the invention into context, reference has already been made to Figures 1 , 2a and 2b of the accompanying drawings, in which:

[0033] Figure 1 is a schematic diagram showing the convergence of the common iliac veins into the inferior vena cava, superimposed by the bifurcation of the abdominal aorta into the common iliac arteries and superimposed on the lumbar region of the vertebral column; and Figures 2a and 2b are cross-sectional views on line ll-ll of Figure 1, Figure 2a showing normal vein anatomy and Figure 2b showing the left common iliac vein compressed against the vertebral column by the overriding right common iliac artery.

[0034] In order that the invention may be more readily understood, reference will now be made, by way of example, to the remainder of the accompanying drawings in which:

[0035] Figure 3 is a complete and flattened schematic view of an embodiment of a stent of the invention;

[0036] Figure 4 is an enlarged schematic detail view of a repeating pair of crowns of a central portion of the stent of Figure 3;

[0037] Figure 5 corresponds to Figure 4 but shows a pair of crowns that is longitudinally and radially enlarged relative to adjoining pairs of crowns of the central portion;

[0038] Figure 6 is an enlarged schematic detail view of a first end portion of the stent of Figure 3;

[0039] Figure 7 is a partial cross-sectioned schematic side view of the first end portion of the stent of Figure 6, further including a radially-enlarged pair of crowns inboard of the first end portion;

[0040] Figure 8 is an enlarged schematic detail view of a second end portion of the stent of Figure 3;

[0041] Figure 9 is a partial cross-sectioned schematic side view of the second end portion of the stent of Figure 8, further including other crowns inboard of the second end portion; and

[0042] Figures 10A to 10F are a sequence of views showing a stent of the invention being deployed from within a catheter in a test environment in which a liquid-filled transparent tube emulates a blood vessel. Figure 3 shows an embodiment of a complete stent 100 of the invention in a flattened form, where in effect the tubular stent is slit longitudinally and flattened out. The stent 100 comprises an open skeletal frame that may, for example, be formed from a nitinol tube that is laser-cut with a pattern of slits to define members of the frame between the slits when the tube is expanded radially.

[0043] In practice, each slit will conveniently define the boundaries of adjacent frame members divided by the slit so that those members have width, shape and complementary or matching outlines defined by the shape of the slit. However, it is emphasised that the figures illustrate principles of the invention rather than showing full detail of practical embodiments.

[0044] The stent 100 comprises a longitudinal array or series of rings, annuluses, circumferential or tubular segments, hereinafter described as crowns 102, distributed along the length of the stent 100 and spaced apart by interstitial circumferential gaps 104 that alternate with the crowns 102 longitudinally. The length of the stent 100 and hence the number of crowns 102 is indeterminate. The number of crowns 102 shown in Figure 3 is provided by way of example only.

[0045] Each crown 102 is circumferentially continuous and, in end view, is rotationally symmetrical about a central longitudinal axis 106 of the stent as shown in Figures 7 and 9. Each crown 102 also extends parallel to the central longitudinal axis 106 and therefore defines a respective portion of the length of the stent 100, in conjunction with the width of the gaps 104 between neighbouring crowns 102 along that axis 106.

[0046] Each crown 102 comprises a circumferentially extending zig-zag arrangement of struts 108 being the principal members of the skeletal frame. The zig-zag arrangement may also be described as a triangular waveform oscillating circumferentially around the crown 102. In these examples, the rise and fall of the waveform is symmetrical but an asymmetric waveform such as a sawtooth is also possible. Furthermore, a more sinusoidal, rounded or wavy pattern is possible, for example where apices 110 of the waveform have a rounded form.

[0047] Each strut 108 is inclined relative to a projection of the central axis 106 on the circumference of the associated crown 102 and extending parallel to the central axis 106. The inclination of each strut 108 opposes the inclination of the adjoining struts 108 of the same crown 102. In these examples, each strut 108 of a crown 102 has opposed bends or inflections in succession along their length, for example being ogee-curved, and is of substantially the same length as other struts 108 of the same crown 102. It is possible that each of the struts 108 may be substantially straight along their length.

[0048] The apices 110 where the struts 108 of each crown 102 join in circumferential succession define peaks 110’ and troughs 110” when viewed from the perspective of neighbouring crowns 102. The peaks 110’ are apices 110 that are relatively close to a neighbouring crown 102 whereas troughs 110” are apices 110 that are relatively far from the same neighbouring crown 102. The peaks 110’ and troughs 110” of each crown 102 alternate circumferentially around the crown 102.

[0049] The waveform shape of each crown 102 complements the shape of the, or each, neighbouring crown 102. Specifically, the peaks 110’ and troughs 110” of a crown 102 are offset angularly or indexed about the central axis 106 relative to the peaks 110’ and troughs 110” of the, or each, neighbouring crown 102. In the case of a symmetrical waveform such as that shown in Figure 3, the angular offset from one crown 102 to the next is half a wavelength.

[0050] The length of the stent 100 is divided into three sections or portions; a first end portion 112, a second end portion 114 and a body or central portion 116 that connects the first and second end portions 112, 114 in longitudinal succession. The first end portion 112 is intended to be a distal end portion when the stent 100 is loaded into a catheter or other deployment device (not shown), hence to be the first end portion to be deployed.

[0051] Correspondingly, the second end portion 114 is intended to be a proximal end portion when the stent 100 is loaded into a catheter or other deployment device, hence to be the second end portion to be deployed. . The first and second end portions 112, 114 will be discussed in detail below.

[0052] Successive crowns 102 are interconnected with or joined to each other by sets of connectors 118 that are distributed circumferentially around the central longitudinal axis 106. The connectors 118 extend longitudinally to bridge the gaps 104 between successive crowns 102 and so serve as secondary members of the skeletal frame. More specifically, the stent arrangements shown in Figures 3 to 9 comprise two types of connectors 118 between successive crowns 102, namely: long connectors 118’ that extend from a trough 110” of one crown 102 to a closest trough 110” of an adjacent crown 102; and short connectors 118” that extend from a peak 110’ of one crown 102 to a closest peak 110’ of an adjacent crown 102.

[0053] In the central portion 116, the sets of the long and short connectors 118’, 118” alternate longitudinally. For example, one gap 104 is bridged by a set of long connectors 118’, the next gap 104 is bridged by a set of short connectors 108” and so on in sequence along the length of the central portion 116. In other words, the central portion 116 comprises a series of a repeating pattern of crown pairs 120 as shown in Figure 3. Figure 4 shows an isolated view of one of the crown pairs 120 that repeat along in the central portion. The result is that adjacent crown pairs 120 are joined to each other by long connectors 118’ and that the adjacent crowns 102 forming each crown pair 120 are joined to each other by short connectors 118”.

[0054] The central portion 116 includes, and is terminated at its opposed ends by, respective terminal crowns 140 as shown in Figure 3. The terminal crowns 140 are disposed outboard of respective crown pairs 120 of the central portion 116 and are joined to those crown pairs 120 by respective sets of the long connectors 118’. Conversely, the terminal crowns 140 are connected to, and so connect the central portion 116 to, the respective end portions 112, 114 via respective sets of the short connectors 118”. In this example, the terminal crowns 140 do not form part of the crown pairs 120 of the central portion 116.

[0055] The connectors 118 are circumferentially spaced apart by more than the wavelength of the crown 102. Consequently, not all of the peaks 110’ and troughs 110” are joined by connectors 118. In one example, the angular spacing between the connectors 118 alternates circumferentially between every fourth peak 110’ or trough 110”. Thus, the connectors 118 that bridge a gap 104 are spaced equiangularly. However, this is not intended to be limiting as the angular spacing between successive connectors 118 in a gap 104 can be designed to vary circumferentially in an alternative arrangement.

[0056] It will also be apparent that longitudinally successive sets of the connectors 118 are offset angularly or indexed circumferentially about the central longitudinal axis 106. The angular offset from one set of connectors 118 to the next set of like connectors 118 is one wavelength of the waveforms defining the crowns 102, hence being a rotation equal to the circumferential distance between successive peaks 110’ or troughs 110”. As the successive crowns 102 are in nested relation before the stent 100 is expanded from a slit tube, the peaks of a crown 102 are substantially aligned in a longitudinal direction with the troughs 110” of a neighbouring crown 102. Consequently, there is an angular offset between the peaks 110’ and the troughs 110” of successive crowns 102 that face each other across the gaps 104 between the crowns 102. In these examples, that angular offset is about half a wavelength. It follows that the connectors 118 must allow for the resulting angular offset between their ends at the apices 110 defining the peaks 110’ and the troughs 110”.

[0057] The connectors 118 allow for the angular offset between their ends either by being inclined relative to the longitudinal direction or, as in these examples, being curved or kinked. Specifically, the short connectors 118” in these examples have an S-shape, being curved continuously through mutually-opposed inflections. Conversely, the long connectors 118’ have straight longitudinal portions joined by a central chicane comprising bends in mutually-opposed directions.

[0058] These configurations of the connectors 118 have the benefit of conferring flexibility on the stent 100, including longitudinal extensibility to allow the stent 100 to bend along its length and therefore to extend on the extrados or outboard side of the central longitudinal axis 106. By virtue of their greater length making them easier to bend along their length, the long connectors 118’ contribute flexibility additional to that provided by the short connectors.

[0059] Flexibility in the connectors 118 from one crown 102 to the next is advantageous not only in use, so that the stent 100 can more readily conform to internal contours of the vasculature, but also in manufacture so that the stent 100, as manufactured, can be shaped in accordance with the invention without experiencing excessive local stress.

[0060] Figure 5 shows an embodiment of a radially enlarged crown pair 122 or stepped portion, comprising radially enlarged crowns 124 joined peak-to-peak by short connectors 118”. The crowns 124 of the radially enlarged crown pair 122 are expanded radially to a greater extent than neighbouring or adjoining crowns 102, like those shown in Figure 4, disposed outboard of that pair 122 to each side. The adjoining radially smaller crowns 102 are joined to respective radially enlarged crowns 124 by respective long connectors 118’ extending trough-to-trough. The flexibility of the long connectors 118’ to deflect or deform in response to axial and bending loads accommodates the radial expansion of the radially enlarged crowns 124 without experiencing excessive stress.

[0061] The long connectors 118’ connecting the radially enlarged crowns 124 to the radially smaller crowns 102 effectively decouple the radially enlarged crowns 124 from the immediately adjacent crowns 102 of lesser radius. This allows the radially enlarged crowns 124 and the radially smaller crowns 102 to move and flex independently of each other to a helpful extent during manufacture, placement and in use.

[0062] The long connectors 118’ allow the pair of radially enlarged crowns 124 shown in Figure 5, and later in Figure 7, to remain of substantially uniform diameter along their length. In other words, the radially enlarged crowns 124 have radially outermost circumferential faces that are straight-sided and parallel to the central longitudinal axis 106 when viewed in longitudinal section as in Figure 7. Nevertheless, by virtue of their radial enlargement, the radially enlarged crowns 124 protrude radially, like a flange, from the surrounding cylindrical outline of the stent 100 defined by the radially smaller crowns 102 that adjoin them. It is also possible for either or both of the crowns 124 of a radially-enlarged crown pair 122 to be flared in a frusto-conical shape that tapers in either longitudinal direction.

[0063] The flange-like radial protrusion of the radially enlarged crowns 124 defines external formations being steps, edges or shoulders between the greater radius of the expanded radially enlarged crowns 124 and the lesser radius of the smaller crowns 102 that adjoin them. It will be apparent that these circumferential external formations will improve mechanical and frictional engagement of the stent with a surrounding vessel in use and, in particular, will resist longitudinal movement and hence migration of the stent 100.

[0064] Advantageously, the presence of long connectors 118’ between an enlarged crown 124 and an adjoining smaller crown 102 decouples the corresponding apices 110 of the enlarged crown 124 from the smaller crown 102. These unconstrained apices 110 on the outboard edges of the radially enlarged crown pair 122 allow for a beneficially sharp or sudden diametric step change along the length of the stent 100, enhancing engagement of the stent 100 with the surrounding wall of the vasculature to resist migration of the stent 100.

[0065] The protruding radially enlarged crowns 124 also focus the radial expansion force of the stent 100 on a smaller portion of the overall outer surface area of the stent 100. This increases the outward pressure acting against the interior of the surrounding vessel wall to enhance mechanical and frictional engagement of the stent 100 with the vessel.

[0066] To further benefit, the outboard apices 110 or peaks 110’ of the waveforms of the crowns 124 in the radially enlarged crown pair 122 lend a serrated profile to the external formations. When the stent 100 is in situ within a common iliac vein or other vessel, the serrated external formations of the radially enlarged crowns 124 dig into and engage mechanically with the surrounding wall of the vein.

[0067] As also shown in Figure 5 in comparison to Figure 4, the radially enlarged crowns 124 may be longer than the adjoining radially smaller crowns 102 in a direction parallel to the central longitudinal axis 106. Specifically, the lengths of all of the radially smaller crowns 102 shown in Figures 3 and 4 along the length of the stent 100 are uniform. Conversely, as shown in Figure 3, and more clearly in Figure 5, at least one, in this example both, of the radially enlarged crowns 124 is of different length to, in this example longer than, the radially smaller crowns 102 of the stent 100.

[0068] The length of a crown 102, and hence the length of struts 108 making up a crown 102, can be varied to match the radial force applied by struts 108 of adjacent crowns 102 within a sizing range. For example, struts 108 can be lengthened to reduce radial force or can be shortened to increase radial force locally, expressed as radially outward pressure per unit area.

[0069] Moving on, Figures 6 and 7 show an embodiment of a first end portion 112 of the stent 100 of the invention. In Figure 6, the first end portion 112 is depicted in a flattened state to show features extending around the full circumference of the stent 100. Conversely, Figure 7 shows a radial or side view of the same stent 100 in cross section through and along the central axis 106 in a tubular configuration and in an expanded, deployed condition. Consequently, about half of the circumference of the stent 100 is visible in Figure 7.

[0070] As mentioned above, the first end portion 112 represents the distal or longitudinally outermost end of the stent 100 when it is loaded into a catheter or similar deployment device. The longitudinally outermost or outboard crown, shown in Figures 6 and 7 as the left-most crown, can be regarded as the ultimate crown 126 of the first end portion 112 of the stent 100. Correspondingly, the crown adjacent to and immediately inboard of the ultimate crown 126 can be regarded as the penultimate crown 128 of the first end portion 112. Likewise, the crown adjacent to and immediately inboard of the penultimate crown 128 can be regarded as the antepenultimate crown 130 of the first end portion 112.

[0071] As shown in the example in Figures 6 and 7, each of the crowns 126, 128, 130 have twenty-four struts 108, which define twelve apices 110 of the waveform, whether peaks 110’ or troughs 110”, per side of each crown 126, 128, 130.

[0072] Six short connectors 118” interconnect the ultimate and penultimate crowns 126, 128. These short connectors 118” join to every second apex 110 around the circumference of the crowns 126, 128 ensuring that they are evenly distributed, and therefore equiangularly spaced, around the circumference of the tubular body of the stent 100. In contrast, there are three long connectors 118’ between the penultimate and antepenultimate crowns 128, 130. , Thus, one long connector 118’ joins to every fourth trough 110” around the circumference of the crowns 128, 130.

[0073] Similarly, there are three short connectors 118” between the antepenultimate crown 130 and the adjacent terminal crown 140 of the central portion 116. This is the boundary where the first end portion 112 of the stent 100 ends and the central portion 116 of the stent 100 begins. The set of long connectors 118’ that connect the penultimate and antepenultimate crowns 128, 130 is two wavelengths out of phase with the set of short connectors 118” that join the antepenultimate crown 130 to the terminal crown 140 of the central portion 116. In other words, those long connectors 118’ join to inboard apices 110 of the antepenultimate crown 130 that are equiangularly spaced from, and between, circumferentially-adjacent short connectors 118”.

[0074] For an equiangular or evenly spaced distribution about the circumference of the crowns 126, 128, 130, the number of connectors 118 between both the ultimate and penultimate crowns 126, 128 and the penultimate and antepenultimate crowns 128, 130 is a divisor of the number of struts 108 in the crowns, or, correspondingly, the number of apices 110 on the corresponding side of the crown. In other words, the number of struts 108 of the crown or of apices 110 of the crown is a multiple of the number of connectors 118 between the ultimate and penultimate crowns 126, 128 and the penultimate and antepenultimate crowns 128, 130. Beneficially, the arrangement of crowns 126, 128, 130 and connectors 118 on the first end portion 112 of the stent 100 provides a stable foundation or base for the stent 100 to initiate deployment but without unduly affecting flexibility of the stent 100. The relatively numerous short connectors 118” between the ultimate and penultimate crowns 126, 128 of the first end portion 112 tie the apices 110 of those crowns 126, 128 together relatively rigidly. Conversely, the fewer long connectors 118’ between the penultimate and antepenultimate crowns 128, 130 decouple the opposed troughs 110” of those crowns 128, 130, allowing them to deploy independently of each other. This allows the ultimate and penultimate crowns 126, 128 to deploy distally from a catheter quickly as a pair, while the antepenultimate crown 136 is still held within the catheter. Beneficially, this quick deployment and engagement of the ultimate and penultimate crowns 126, 128 with the surrounding wall of the vessel provides a stable anchor for deployment of the remainder of the stent 100, reducing the risk of unintended stent migration.

[0075] Corresponding to Figures 6 and 7, Figures 8 and 9 show an embodiment of a second end portion 114 of the stent 100 of the invention. Again, Figure 8 depicts, the second end portion 114 in a flattened state to show features extending around the full circumference of the stent 100. Conversely, Figure 9 shows a radial or side view of the same stent 100 in cross section through and along the central axis 106 in a tubular configuration and in an expanded, deployed condition. So, again, about half of the circumference of the stent 100 is visible in Figure 9.

[0076] The second end portion 114 represents the proximal end or longitudinally innermost end of the stent 100 when it is loaded into a catheter or similar deployment device. The outermost crown, shown in Figures 8 and 9 as the right-most crown, may be regarded as the ultimate crown 132 of the second portion 114 of the stent 100. Correspondingly, the crown adjacent to and immediately inboard of the ultimate crown 132 may be regarded as the penultimate crown 134 of the second portion 114and likewise, the crown adjacent to and immediately inboard of penultimate crown 134 may be regarded as the antepenultimate crown 136 of the second portion 114.

[0077] As before, each of the crowns 132, 134, 136 have twenty-four struts 108, which defines twelve apices 110 of the waveform per side of the crown. Six short connectors 118” interconnect the ultimate and penultimate crowns 132, 134. These short connectors 118” join to every second apex 110 around the circumference of the crowns 132, 134 and so are evenly distributed, and therefore equiangularly spaced, around the circumference of the tubular body of the stent 100.

[0078] The second end portion 114 also has three short connectors 118” between the penultimate and antepenultimate crowns 134, 136. Thus, there is one short connector 118” for every fourth peak 110’ around the circumference of the crowns 134, 136. The connection between the antepenultimate crown 136 and the adjoining terminal crown 140 of the central portion 116 also consists of three short connectors 118” distributed around the circumference at every fourth apex 110. This is the boundary where the second end portion 114 ends, and the central portion 116 begins. The set of short connectors 118” that connect the penultimate and antepenultimate crowns 134, 136 is one-and-a-half wavelengths out of phase with the set of short connectors 118” that join the antepenultimate crown 136 to the terminal crown 140 of the central portion 116.

[0079] This arrangement of crowns 132, 134, 136 and respective connectors 118 in the second end portion 114 serves to stabilise and control deployment of the stent 100 from a catheter or other deployment device. Beneficially control of the stent deployment is enhanced by resisting the tendency for the second end portion 114 of the stent 100 to jump out from the catheter as deployment reaches the final stages. This effect is achieved by the implementation of short connectors 118” between the ultimate, penultimate and antepenultimate crowns 132, 134, 136 of the second end portion 114. The facing apices of each of those crowns 132, 134, 136 are thereby tied together so that the second end portion 114 forms a more rigid unit. Control is enhanced further by providing more short connectors 118” between the ultimate and penultimate crowns 132, 134 than between the penultimate and the antepenultimate crowns 134, 136.

[0080] Increasing the number of short connectors 118” in the second end portion 114 between the terminal crown 140 of the central portion 116 and the ultimate crown 132 reduces the distal axial thrust force generated by impingement of the radially-expanding stent 100 on the distal end of the catheter and increases the frictional and mechanical resistance of the second end portion 114 to premature or disorganised deployment in response to that thrust force. Thus, the stent 100 is fully deployed from the catheter when the distal end of the catheter is closer to the proximal end of the stent 100.

[0081] Moreover, the crowns 132, 134, 136 are more tightly connected to each other to form a unit with greater structural integrity and bending stiffness than more distal portions of the stent 100. Those crowns 132, 134, 136 are therefore less susceptible to move relative to each other and thereby to become misaligned relative to the central longitudinal axis of the vessel into which the stent 100 is being deployed. In other words, crowns 132, 134, 136 tend to behave as a unit to reduce distal axial thrust and to resist or to mitigate premature or misaligned deployment. The resultant control over deployment helps to prevent pattern distortion of the stent 100, misalignment of the stent 100 in the vasculature and / or incorrect longitudinal positioning of the stent 100.

[0082] Identification features, exemplified in Figures 3 and 6 to 9 by identification tags 138, allow for quick identification of each end portion 112, 114 of the stent 100 during assembly with a deployment device and also after deployment of the stent 100 in a patient’s vasculature. As the tags 138 are manufactured from the same laser-cut nitinol material as the rest of the stent 100, the tags 138 will be visible in X-ray, MRI or other commonly-used scanning methods.

[0083] The first end portion 112 of the stent 100 supports two examples of a first tag 138’, shown here as a flat paddle-like feature with rounded longitudinal edges, and one example of a second tag 138”, shown as a similar flat paddle-like feature but with straight longitudinal edges. Conversely, the second end portion 114 of the stent 100 comprises identification features in the form of three tags 138 similar to the first tags 138’ of the first end portion 112, hence all with rounded edges, to distinguish the second end portion 114 from the first end portion 112.

[0084] The shape, position or quantity of the identification tags 138 is not intended to be limiting, as long as there is some visible differentiation between the two end portions 112, 114 of the stent 110. Additionally, a combination or pattern of identification tags 138 could be used to identify the type or model of the stent 100.

[0085] The advantageous deployment characteristic of the stent 100 is illustrated in the sequence shown in Figures 10A to 10F, which shows the stent 100 deploying distally from the distal end of a catheter 142 in a test environment. The stent 100 is being deployed within a liquid-filled transparent tube 144 that emulates a blood vessel. In this example, the distal end of the catheter 142 retracts proximally along the tube 144 during deployment of the stent 100. In Figure 10A, the terminal crown 140 between the central portion 116 and the second end portion 114 is beginning to deploy from the distal end of the catheter 142. The second end portion remains within the catheter 142 at this stage. In Figure 10B, the terminal crown 140 is partially deployed and the antepenultimate crown 136 of the second end portion 114 is beginning to deploy. In Figure 10C, the terminal crown 140 is almost completely deployed, the antepenultimate crown 136 is partially deployed and the penultimate crown 134 of the second end portion 114 is beginning to deploy.

[0086] It will be noted that the stent 100 adopts a substantially regular or rotationally symmetrical conical shape as it deploys from the catheter 142 and flares distally into contact with the wall of the surrounding tube 144. The symmetry of that flared shape helps to hold the catheter 142 centrally within the lumen of the tube 144 and to maintain acceptable alignment of the stent 100 with the central longitudinal axis of the tube 144 throughout deployment.

[0087] In Figure 10D, the terminal crown 140 is completely deployed against the wall of the surrounding tube 144. The antepenultimate crown 136 is almost completely deployed, the penultimate crown 134 is partially deployed and the ultimate crown 132 is beginning to deploy.

[0088] In Figure 10E, the antepenultimate crown 136 is completely deployed against the wall of the surrounding tube 144. The penultimate crown 134 is almost completely deployed and the ultimate crown 132 is partially deployed. Only the identification tags 138 remain within the distal end of the catheter 142 at this stage. Finally, Figure 10F shows the second end portion 114, including the identification tags 138, now fully out of the catheter 142 as the stent 100 is fully deployed.

[0089] The number and arrangement of struts 108 and connectors 118 discussed above is provided by way of example and is not necessarily limiting. The inventive concept contemplates other configurations and combinations of struts 108 and connectors 118 wherein the connectors 118 are substantially equally distributed about the circumference of the stent 100. Such a distribution may be achieved if the number of struts 108 is a multiple of both the number of connectors 118 disposed between the ultimate and penultimate crowns 126, 128, 132, 134 and the penultimate and antepenultimate crowns 128, 130, 134, 136 of either or both end portions 112, 114 of the stent 100. The inventive concept also contemplates configurations and combinations of struts 108 and connectors 118 in which the connectors 118 are not equally distributed about the circumference of the stent 100.

[0090] The inventive concept also contemplates a combination of the stent 100, as described above, contained within a stent deployment device. Stent deployment devices are well known in the art and comprises a catheter or sheath in which the stent 100 is held in a radially compressed state. When the stent 100 is loaded into the deployment device, the first end portion 112 of the stent 100 is disposed distally and the second end portion 114 is disposed proximally. The catheter can be withdrawn proximally relative to the stent 100 contained within or the stent 100 can be propelled distally from and relative to the catheter. As the stent 100 is freed from the catheter, the stent 100 begins to expand radially against the wall of the vessel into which the stent 100 is being deployed.

Claims

Claims1. A stent comprising a longitudinally-extending tubular body defined by a longitudinal succession of annular crowns each comprising struts disposed in a circumferentially-extending waveform, wherein: sets of connectors interconnect successive crowns by bridging respective gaps between the successive crowns, those sets comprising sets of long connectors and sets of short connectors that effect, respectively, trough-to-trough and peak- to-peak connections between the waveforms of the successive crowns; the stent comprises a first end portion, a central portion and a second end portion in longitudinal succession, each of the end portions comprising, respectively, an outermost ultimate crown, a penultimate crown and an antepenultimate crown in longitudinally inward succession; and in each of the end portions, the set of connectors disposed between the ultimate and penultimate crowns contains more connectors than the set of connectors disposed between the penultimate and antepenultimate crowns.

2. The stent of Claim 1 , wherein a set of the short connectors joins the penultimate and antepenultimate crowns of at least one of the end portions.

3. The stent of Claim 2, wherein the penultimate and antepenultimate crowns of the first end portion are joined by a set of the long connectors.

4. The stent of Claim 2 or Claim 3, wherein the penultimate and antepenultimate crowns of the second end portion are joined by a set of the short connectors.

5. The stent of any preceding claim, wherein a set of the long connectors is disposed between the penultimate and antepenultimate crowns of one of the end portions and a set of the short connectors is disposed between the penultimate and antepenultimate crowns of the other end portion.

6. The stent of any preceding claim, wherein in each of the end portions, the set of connectors disposed between the ultimate and penultimate crowns contains more connectors than in sets of connectors disposed between crowns of the central portion.

7. The stent of any preceding claim, wherein the number of connectors joining the ultimate and penultimate crowns of both the first and second end portions is equal.

8. The stent of any preceding claim, wherein a set of the short connectors is disposed between an outermost crown of the central portion and the antepenultimate crown of at least one of the end portions.

9. The stent of Claim 8, wherein the antepenultimate crowns of the end portions are joined to respective outermost crowns of the central portion by equal numbers of the short connectors.

10. The stent of any preceding claim, wherein the central portion comprises sets of the long connectors and sets of the short connectors that alternate in longitudinal succession.

11. The stent of any preceding claim, wherein a set of the short connectors joins the ultimate and penultimate crowns of each end portion.

12. The stent of any preceding claim, wherein all of the crowns inboard of the penultimate crowns of the end portions are joined by equal numbers of the connectors.

13. The stent of any preceding claim, wherein in each of the end portions, the set of connectors disposed between the ultimate and penultimate crowns contains twice as many connectors as the set of connectors disposed between the penultimate and antepenultimate crowns.

14. The stent of any preceding claim, wherein the central portion comprises a repeating pattern of crown pairs, each crown pair comprising two crowns joined by a set of the short connectors.

15. The stent of Claim 14, wherein successive crown pairs of the repeating pattern are joined by respective sets of the long connectors.

16. The stent of Claim 14 or Claim 15, wherein the central portion is terminated at its opposed ends by respective terminal crowns disposed outboard of respective crown pairs and joined to those crown pairs by respective sets of the long connectors.

17. The stent of Claim 16, wherein the terminal crowns are joined to respective antepenultimate crowns of the end portions by respective sets of the short connectors.

18. The stent of any of Claims 14 to 17, wherein at least one of the crowns of the central portion is radially enlarged relative to at least one adjoining crown of the central portion when the stent is in an expanded state.

19. The stent of Claim 18, wherein at least one of the crown pairs of the central portion is radially enlarged relative to at least one of the adjoining crown pairs of the central portion when the stent is in an expanded state.

20. The stent of Claim 18 or Claim 19, wherein at least one of the crowns of the central portion is pre-formed with a radially enlarged configuration relative to at least one adjoining crown.

21. The stent of any of Claims 18 to 20, wherein the or each radially enlarged crown is at a position offset longitudinally closer to one of the end portions than to the other of the end portions.

22. The stent of any of Claims 18 to 21, wherein the or each radially enlarged crown is of substantially constant diameter along its length in a longitudinal direction.

23. The stent of any of Claims 18 to 21 wherein the or each radially enlarged crown is flared along its length in a longitudinal direction.

24. The stent of Claim 23, comprising at least two crowns that are flared in opposed longitudinal directions.

25. The stent of Claim 24, wherein the or each radially enlarged crown is joined to an adjoining crown by a set of the long connectors.

26. The stent of any preceding claim, wherein the ultimate crown of each end portion comprises a set of identification features.

27. The stent of Claim 26, wherein the identification features differ between one end portion and the other end portion.

28. In combination, the stent of any preceding claim and a deployment device, wherein the first end portion of the stent is disposed distally and the second end portion of the stent is disposed proximally with respect to the deployment device.

29. The stent of any of Claims 1 to 27, wherein when the stent is deployed in vivo, the first end portion is disposed cranially and the second end portion is disposed caudally within a patient’s vasculature.

30. The stent of any of Claims 1 to 27, wherein: the penultimate and antepenultimate crowns of the first end portion are joined by a set of the long connectors; the penultimate and antepenultimate crowns of the second end portion are joined by a set of the short connectors; and when the stent is deployed in vivo, the first end portion is disposed cranially and the second end portion is disposed caudally within a patient’s vasculature.

31. A method of progressively deploying the stent of any of Claims 1 to 27 from a deployment device, the method comprising deploying the first end portion of the stent and subsequently deploying the second end portion of the stent from a distal end of a surrounding catheter or sheath of the deployment device.

32. A method of deploying the stent of any of Claims 1 to 27 into a patient’s vasculature, the method comprising: inserting a deployment device into the patient’s vasculature:navigating the deployment device to a target location in the patient’s vasculature; and deploying the stent from the deployment device into the patient’s vasculature such that the first end portion is disposed cranially and the second end is disposed caudally.

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