WO2022128757A1

WO2022128757A1 - Laser cut stent

Info

Publication number: WO2022128757A1
Application number: PCT/EP2021/085116
Authority: WO
Inventors: Scott Robert WILSON; Jake MERTENS
Original assignee: Koninklijke Philips N.V.
Priority date: 2020-12-16
Filing date: 2021-12-10
Publication date: 2022-06-23

Abstract

A stent (10) includes a hollow tube (12) with a laser cut pattern defining: a plurality of circumferential rings (20) of cells (22) having a shape; and at least three connectors (24) connecting neighboring pairs of the circumferential rings. In some examples, a ratio of a number of the cells (22) in each circumferential ring (20) to a number of connectors (24) connecting the neighboring pairs of circumferential rings is 3:1 or higher.

Description

LASER CUT STENT

FIELD

[0001] The following relates generally to the stent arts, stent manufacturing arts, stent configuration arts, and related arts.

BACKGROUND

[0002] Stents constructed as self-expandable, metal support structures, delivered via intravascular devices, are commonly used in the treatment in intravascular disease, as well as in larger regions of the anatomy such as the esophagus. Self-expanding stents are typically made from a braided wire mesh or from laser cut tubes.

[0003] Current stents used to treat intravascular diseases are either open cell or closed cell. The open cell designs are made such that when placed in a curved vessel, the stent wires or struts can protrude into the inner lumen, creating a potential for thrombus formation. The closed cell designs reduce this potential for protrusion, but lack flexibility to conform to the vessel in curved vessels.

[0004] The following discloses certain improvements to overcome these problems and others.

SUMMARY

[0005] In some embodiments disclosed herein, a stent includes a hollow tube with a laser cut pattern defining: a plurality of circumferential rings of cells having a shape; and at least three connectors connecting neighboring pairs of the circumferential rings.

[0006] In some embodiments disclosed herein, a stent includes a hollow tube with a laser cut pattern defining: a plurality of circumferential rings of cells wherein each circumferential rings of cells includes a one-dimensional array of cells; and at least three longitudinal connectors connecting each neighboring pair of the circumferential rings. A ratio of a number of the cells in each circumferential ring of cells to a number of longitudinal connectors connecting each neighboring pair of circumferential rings is 3 : 1 or higher.

[0007] In some embodiments, a method of forming a stent includes laser cutting a hollow tube using a laser to form a laser cut pattern defining: a plurality of circumferential rings of cells having a shape; and at least three connectors connecting each neighboring pair of the circumferential rings.

[0008] One advantage resides in providing a laser cut stent with an improved combination of crush resistance, flexibility, and resistance against protrusion into the inner blood vessel lumen. [0009] Another advantage resides in providing a stent with a laser cut pattern with improved radial force at the ends of the stent.

[0010] Another advantage resides in providing a stent with a laser cut pattern with improved conformability.

[0011] Another advantage resides in providing a stent made from Nitinol for improved durability.

[0012] Another advantage resides in providing a stent with a high number of cells and short connector lengths for improved crush resistance.

[0013] A given embodiment may provide none, one, two, more, or all of the foregoing advantages, and/or may provide other advantages as will become apparent to one of ordinary skill in the art upon reading and understanding the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The disclosure may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the disclosure.

[0015] FIGURE 1 diagrammatically illustrates a stent in accordance with the present disclosure.

[0016] FIGURES 2-4 diagrammatically illustrates different embodiments of the stent of FIGURE 1.

[0017] FIGURE 5 diagrammatically illustrates a method of forming the stent of FIGURE 1.

DETAILED DESCRIPTION

[0018] The following relates to improvements in a self-expanding laser cut stent. Such stents are typically manufactured from a Nitinol tube (Nitinol is a metal alloy of nickel and titanium where the Ni and Ti are present in roughly equal atomic percentages) with a diameter of about 4 mm (more generally, the outer diameter the expanded laser cut stent is typically designed to be slightly larger than the inner lumen diameter of the blood vessel into which the stent is to be placed, so that the expanded stent is held in place inside the vessel by compression). A pattern is cut in the tube which removes most of the material, after which the tube is expanded to a larger diameter, e.g., 16 mm, and then heat set at typically 400-500 °C. The resulting stent is selfexpanding, so that it can be radially compressed to fit into a catheter tip or other delivery instrument and then expands into position in the vein (or artery) when placed.

[0019] The improvement disclosed herein relates to the pattern cut into the Nitinol tube. Existing patterns that are mostly open can lead to the stent having poor crush resistance and low radial strength. Large openings in the stent can also trap tissue providing locations for thrombus formation. On the other hand, patterns that are mostly closed can fail to conform well to the blood vessel lumen and can adversely impact blood flow through the stent. The improved design provides circumferential rings of higher density, for example a circumferential ring of a dozen or more cells; with the circumferential rings connected by a lower density of connectors, e.g., as few as three or four connectors between a pair of neighboring circumferential rings in some embodiments. The high density of material in the circumferential rings provide crush resistance and reduce likelihood of trapping tissue, while the sparsity of connectors between neighboring circumferential rings provides the laser cut stent with a high degree of flexibility.

[0020] In some embodiments disclosed herein, the improved pattern includes circumferential rings of cells, in which the cells may have shapes such as “V”, “Z”, or diamond shapes. The circumferential rings are connected by longitudinal connectors (which may be straight or have some curvature, e.g., S-shaped). The number of cells in each circumferential ring is large, e.g., 16 cells in the illustrative example; whereas the number of connectors between neighboring circumferential rings is low, but preferably at least three. The illustrative examples include four connectors between neighboring circumferential rings. More generally, the ratio of cells in the ring to connectors between neighboring rings may be, for example, at least 4: 1 in some embodiments. [0021] In a variant embodiment disclosed herein, the number of connectors securing an end ring of the stent may be higher, e.g., while interior ring pairs may be connected by four connectors, the end ring may be connected by 16 connectors. In a further variant, the outermost two (or three, et cetera) circumferential rings may be connected by the larger number of connectors. In yet another variant, the outermost two (or three, et cetera) rings may be directly connected with no intervening connectors. In effect, this forms a closed cell pattern at the ends of the stent. [0022] The use of higher numbers of connectors at the end ring(s), and/or a closed cell pattern at the ends, advantageously improves crush resistance and radial strength at the ends of the stent which can be especially susceptible to deformation. These approaches can be employed at both ends of the stent, or at only one end if that one end is identified as being under greater compressional force in the implanted position.

[0023] While described in the context of laser cut venous stents, the disclosed approaches are suitable for use in arterial stents and other types of self-expanding laser cut stents such as esophageal stents. While Nitinol is the preferred material for the stent, other metals with very high elasticity could be used instead.

[0024] With reference to FIGURE 1, an illustrative stent 10 (e.g., an arterial, venous, or esophageal stent) is shown in a “rolled out” or “flat pattern” view in the main drawing of FIGURE 1, and is shown in a perspective view in FIGURE 1, Inset A. As shown in FIGURE 1, Inset A, the stent 10 comprises a hollow tube or tubular structure 12. Inset A also indicates a cylindrical coordinate system used in describing the tubular stent 10, which includes a longitudinal coordinate or axis denoted as the z-axis, and an angular coordinate or axis denoted as the (p-axis. FIGURE 1, main drawing shows the tubular stent 10 with its longitudinal axis z oriented horizontally and its radial axis (p unrolled vertically. Note that the laser cut pattern is depicted in the main drawing of FIGURE 1 but is not depicted in Inset A, which is only intended to illustrate a perspective view of the overall cylindrical shape of the stent 10 and clarify the cylindrical coordinates (<p,z). The tube 12 can be made from Nitinol, or any other suitable material with high elasticity. The hollow tube 12 includes a first (i.e., left) end portion 16, a second, opposing (i.e., right) end portion 18, and a middle portion 14 interposed between the end portions 16, 18.

[0025] As shown in FIGURE 1, the hollow tube 12 has a laser cut pattern to form the stent 10. The laser cut pattern in FIGURE 1 includes a plurality of struts or circumferential rings 20 that each have a number of cells 22. Each circumferential ring 20 lies in a plane that is transverse to the longitudinal or z-axis and parallel with the angular or cp-axis. The cells 22 can have a predefined shape. As shown in FIGURE 1, the cells 22 have a V-shape; although the cells 22 can have any other suitable shape, such as a Z-shape, S-shape, or a diamond shape. FIGURE 1 also shows that a number of connectors 24 connect adjacent or neighboring pairs of rings 20 to each other. The illustrative connectors 24 are straight connectors that are aligned with the longitudinal or z-axis. More generally, each connector 24 lies at least approximately parallel with the longitudinal or z-axis, and hence may also be referred to herein as a longitudinal connector 24. However, it will be appreciated that the longitudinal connectors 24 may deviate from perfect alignment with the z-axis. For example, the longitudinal connectors may have an “S” shape, or may be straight connectors that are oriented at an angle of, e.g., 45° or less, and more preferably 30° or less, to the z-axis.

[0026] Each circumferential ring 20 is relatively dense to provide adequate radial force for the stent 10, so that it is robust against radially inward compressive forces such as may be applied by the inner lumen of a blood vessel within which the stent 10 is placed. To provide adequate radial crush resistance, each circumferential ring 20 has a high number of cells 22 around a circumference (i.e., over the full circumferential angular range (p=0°-360°) of the tube 12, and each ring 20 extends longitudinally over a short length L in the longitudinal or z-direction, with a longitudinal distance D between neighboring circumferential rings 20. On the other hand, the connectors 24 are relatively sparse, providing the stent 10 with flexibility to conform with curvature of a blood vessel within which the stent 10 is placed.

[0027] As shown in FIGURE 1, the connectors 24 are straight connectors oriented perpendicularly to the circumferential rings 20. The connectors 24 can have any other suitable shape or orientation. For example, the connectors 24 can be straight connectors oriented non- perpendicularly to the circumferential rings 20. In another example, the connectors 24 can be S- shaped connectors. The stent 10 includes at least three connectors 24 to connect the neighboring pairs of rings 20. Six total connectors 24 are shown in FIGURE 1, which connect five rings 20. This is merely an illustrative example and should not be construed as limiting.

[0028] FIGURE 2 shows another embodiment of the stent 10. In this embodiment, the laser cut pattern again provides the stent 10 with adequate radial force with the flexibility to conform without strut protrusion into a vessel wall. As shown in FIGURE 2, the tube 12 includes five rings 20, in which each ring 20 has sixteen cells 22 around a circumference N of the tube 12. Four connectors 24 are disposed between each neighboring ring 20. Each ring 20 has a length of 2.5-3.0 mm, and a distance of .30-.50 mm between neighboring rings 20. These dimensions can allow the stent 10 to have a flexibility to conform to a 1.0 cm radius without protrusion of one or more of the rings 20 into a vessel wall. This is merely an illustrative example and should not be construed as limiting. [0029] In some embodiments, a ratio of the number of the cells 22 in each circumferential ring 20 to the number of connectors 24 connecting the neighboring pairs of circumferential rings 20 is 3 : 1 or higher, and in some embodiments 4: 1 or higher. As shown in FIGURE 2, for example, with each ring 20 having sixteen cells 22, and four connectors 24 disposed between neighboring rings 20, this ratio is 4: 1. This is merely an illustrative example and should not be construed as limiting. The ratio can be any suitable ratio that is 3: 1 or higher, and more preferably 4: 1 or higher. As a result, a number of the circumferential rings 20 of cells 22 in the laser cut pattern is greater than a number of the connectors 24 in the laser cut pattern. In some embodiments, each circumferential ring 20 includes a one-dimensional array of at least eight cells 22 having the shape (e.g., the V-, Z-, or diamond shape). In some such embodiments in which each circumferential ring 20 includes a one-dimensional array of at least eight cells 22, the ratio of the number of cells per ring to the number of connectors between neighboring rings is 3: 1 or higher, and in some preferred embodiments is 4: 1 or higher. Such patterns advantageously have relatively dense circumferential rings 20 due to the high number of cells 22 per ring thus providing good resistance against crushing due to inwardly applied radial compression (e.g., from a surrounding blood vessel); while the pattern also has relatively sparse regions between the rings due to the low number of connectors 24 thus providing flexibility for the stent 10 to conform to curvature of the blood vessel within which the stent 10 is placed.

[0030] With continuing reference to FIGURE 2, the circumferential rings located at the ends of the stent 10 are referred to herein as end circumferential rings 20E, or just end rings 20E, one of which is disposed at the first end portion 16 of the tube 12, and the other is disposed at the second end portion 18 of the tube 12. The stent 10 also includes at least two (and typically more than two) middle circumferential rings disposed between the two end rings 20E on the middle portion 14 of the tube 12. As shown in FIGURE 2, the stent 20 includes two end circumferential rings 20E, and three middle circumferential rings 20M disposed between the two end rings 20E. In the embodiment of FIGURE 2, the number of connectors 24 connecting the end rings 20E to one of the middle rings 20M is the same as than a number of connectors 24 connecting neighboring middle circumferential rings 20M. For example, as shown in FIGURE 2, the end rings 20E at both of the first end portion 16 and the second end portion 18 of the tube 12 are connected to their respective neighboring middle ring 20M with four connectors 24, and each middle ring 20M is also connected to each other with four connectors 24. [0031] With reference to FIGURE 3, however, the number of connectors 24 connecting each end ring 20E to its corresponding neighboring middle ring 20M can be higher than the number of connectors 24 connecting between two neighboring middle ring 20M. This advantageously provides greater crush resistance at the ends of the stent, as one or both ends 16, 18 of the stent 10 often experience higher inward radial compression force than the middle of the stent 10 when the stent 10 is placed in a blood vessel. In a variant embodiment, the number of connectors 24 connecting one of the end rings 20E to its corresponding neighboring middle ring 20M can be different than the other of the end rings 20E to its corresponding neighboring middle ring 20M. In addition, the number of connectors 24 connecting the neighboring middle rings 20M can be different from each other (e.g., the first and second middle rings 20M can be connected to each other with six connectors 24, while the second and third middle rings 20M can be connected to each other with seven connectors 24). These are merely illustrative examples and should not be construed as limiting.

[0032] FIGURE 3 shows another embodiment of the stent 10, which illustrates having more connectors 24 secured to the end rings 20E. The stent 10 shown in FIGURE 3 is substantially identical to the stent 10 shown in FIGURE 2, except that each end ring 20E is connecting to its corresponding neighboring middle ring 20M with sixteen connectors 24, and each middle ring 20M is connected to a neighboring middle ring 20M with four connectors. This is merely an illustrative example and should not be construed as limiting. As similarly described for FIGURE 2, the number of connectors 24 can vary between both end rings 20E and their corresponding neighboring middle ring 20M, in addition to a number of connectors 24 between neighboring middle rings 20M can vary.

[0033] FIGURE 4 shows another embodiment of the stent 10. Compared with the embodiment of FIGURE 3, in the embodiment of FIGURE 4 the three outermost rings on the left side 16 of the stent (labeled as region LI in FIGURE 4) are directly joined together without intervening connectors. This provides even greater radial strength than the approach of FIGURE 3 in which the number of connectors is increased for the end rings 20E. In this embodiment, the stent 10 could have multiple zones of flexibility to fit the treatment needs for the specific anatomy (e.g., vessel). In a particular example, the stent 10 can have a high radial force section near the confluence of the iliac veins to treat May-Thurner Syndrome (also referred to non-thrombotic iliac vein lesion or NIVL). As the stent 10 extends distally into a vessel, there is a need for more flexibility to traverse the venous anatomy. The stent 10 can include a hybrid combination of a high radial force section and a more flexible section. As shown in FIGURE 4, the “high radial force” section (denoted as LI) has a fully closed cell design (similar to the cell design in FIGURE 3). The flexible section (denoted as L3) has four connectors 24, and a transition section (denoted as L2) provides an intermediate flexibility to transition between the closed cell and the flexible sections. Note that the rightmost portion of the stent 10 is not shown in FIGURE 4. (The ellipsis at the right end diagrammatically indicates the stent continues to the right).

[0034] In addition, the connectors 24 can have varying orientations and shapes depending on which section the connectors are located. In the L3 flexible section, the connectors 24 are straight connectors oriented perpendicularly to the circumferential rings 20. In the LI rigid section and the L2 transition section, the connectors 24 can be S-shaped connectors oriented non- perpendicularly to the circumferential rings 20.

[0035] FIGURE 5 shows an example of a flowchart showing a method 100 of forming the stent 10. At an operation 102, a hollow tube 12 is laser cut with a laser to form a laser cut pattern. The pattern can include, for example, a plurality of circumferential rings 20 of cells 22 having a shape; and at least three connectors 24 connecting each neighboring pair of the circumferential rings 20. At an operation 104, the hollow tube 12 is expanded from its initial diameter (e.g., 4 mm in one non-limiting embodiment) to the intended diameter of the stent (e.g., 16 mm in one nonlimiting embodiment). This expansion typically occurs in a series of steps to ensure the Nitinol material of the hollow tube 12 does not crack or fracture due to high strains. In an operation 106, the hollow tube 12 is heat set with the laser cut pattern, e.g., at 400-500 °C which is suitable for heat setting nitinol, to form the stent 10. Note that the operations 104 and 106 are repeated until a final diameter of the hollow tube 12 is achieved.

[0036] The disclosure has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

9 CLAIMS:

1. A stent (10), comprising: a hollow tube (12) with a laser cut pattern defining: a plurality of circumferential rings (20) of cells (22) having a shape; and at least three connectors (24) connecting neighboring pairs of the circumferential rings.

2. The stent (10) of claim 1, wherein a ratio of a number of the cells (22) in each circumferential ring (20) to a number of connectors (24) connecting the neighboring pairs of circumferential rings is 3 : 1 or higher.

3. The stent (10) of claim 2, wherein the ratio of the number of the cells (22) in each circumferential ring (20) to the number of connectors (24) connecting the neighboring pairs of circumferential rings is 4: 1 or higher.

4. The stent (10) of either one of claims 2 and 3, wherein each circumferential ring (20) includes a one-dimensional array of at least eight cells (22) having the shape.

5. The stent (10) of any one of claims 1-4, wherein a number of the circumferential rings (20) of cells (22) in the laser cut pattern is greater than a number of the connectors (24) in the laser cut pattern.

6. The stent (10) of any one of claims 1-5, wherein the connectors (24) are straight connectors oriented perpendicularly to the circumferential rings (20).

7. The stent (10) of any one of claims 1-5, wherein the connectors (24) are straight connectors oriented non-perpendicularly to the circumferential rings (20).

8. The stent (10) of any one of claims 1-7, wherein the connectors (24) are S-shaped connectors.

9. The stent (10) of any one of claim 1-8, wherein: the plurality of circumferential rings (20) includes two end circumferential rings (20E) and at least two middle circumferential rings (20M); and a number of connectors (24) connecting the end rings to one of the at least two middle circumferential rings is higher than a number of connectors connecting neighboring middle circumferential rings.

10. The stent (10) of any one of claim 1-8, wherein the laser cut pattern further defines: closed circumferential end-rings (20E) wherein each closed circumferential endring includes a two-dimensional array of cells (22); and wherein each circumferential end-ring is connected to an adjacent circumferential ring (20M) by at least three connectors (24).

11. The stent (10) of claim 10, wherein: a number of connectors (24) connecting one of the closed circumferential end-rings (20E) to its adjacent middle circumferential ring (20M) is higher than a number of connectors connecting the other closed circumferential end-ring (20E) to its adjacent middle circumferential ring (20M).

12. The stent (10) of any one of claims 1-11, wherein the cells (22) of the circumferential rings (20) have a V-shape.

13. The stent (10) of any one of claims 1-11, wherein the cells (22) of the circumferential rings (20) have a Z-shape.

14. The stent (10) of any one of claims 1-11, wherein the cells (22) of the circumferential rings (20) have a diamond-shape. 11

15. The stent (20) of any one of claims 1-14, wherein the hollow tube (12) is comprised of nitinol.

16. A stent (10), comprising: a hollow tube (12) with a laser cut pattern defining: a plurality of circumferential rings (20) of cells (22) wherein each circumferential rings of cells includes a one-dimensional array of cells; and at least three longitudinal connectors (24) connecting each neighboring pair of the circumferential rings; wherein a ratio of a number of the cells in each circumferential ring of cells to a number of longitudinal connectors connecting each neighboring pair of circumferential rings is 3:1 or higher.

17. The stent (10) of claim 16, wherein the longitudinal connectors (24) are: straight connectors oriented perpendicularly to the circumferential rings of cells; straight connectors oriented non-perpendicularly to the circumferential rings of cells; or S-shaped connectors.

18. The stent (10) of either one of claims 16 and 17, wherein the laser cut pattern further defines: closed circumferential end-rings (20E) at the ends of the hollow tube (12), wherein each closed circumferential end-ring includes a two-dimensional array of cells (22).

19. A method (100) of forming a stent (10), comprising: laser cutting a hollow tube (12) using a laser to form a laser cut pattern defining: a plurality of circumferential rings (20) of cells (22) having a shape; and at least three connectors (24) connecting each neighboring pair of the circumferential rings.

20. The method (100) of claim 19, further comprising: after the laser cutting, heat setting the hollow tube (12) with the laser cut pattern.