Self-expanding stents

Abstract

The present invention relates to a self-expanding stent (1) for implantation in the abdominal aorta of a human body for the treatment of abdominal aortic aneurysm, the stent (1) comprising an expandable framework (2) formed from a shape memory alloy and having a distal end (4), a proximal end (6), and an interior volume extending along a central axis from the distal end (4) to the proximal end (6), the framework (2) having at least a distal end ring (8) and a proximal end ring (10) with peaks (12) and valleys (13), and optionally at least one ring (14, 15) disposed between the distal end ring (8) and the proximal end ring (10), the framework (2) having a length LF from the distal end (4) to the proximal end (6) of at least 10 mm, the stent having a compressed state having a minimum diameter (Dmin), an expanded state having a nominal diameter (DN), and a relaxed state having a maximum diameter (Dmax). According to the present invention, at least one of the distal ring (8), the proximal ring (10), and the optional rings (14, 15) of the stent (1) exhibits a nominal radial resistance pressure (RRP-N) of 100 mmHg or greater at a nominal diameter (DN). The present invention also relates to a method.

Description

[Technical Field]

[0001] The present invention relates to a self-expanding stent that is implanted in a blood vessel of the human body. [Background technology]

[0002] The present invention relates to a self-expanding stent for implantation in a blood vessel of the human body, comprising an expandable framework formed from a shape memory alloy and having a distal end, a proximal end, and an interior volume extending along a central axis from the distal end to the proximal end, the framework having at least distal and proximal end rings with peaks and valleys, and optionally at least one ring disposed between the distal and proximal end rings, the length of the framework from the distal end to the proximal end being at least 10 mm, the stent having a compressed state having a minimum diameter, an expanded state having a nominal diameter, and a relaxed state having a maximum diameter. The present invention further relates to a method for selecting a stent of the type described above.

[0003] Stents of the aforementioned type are widely used in the human body, for example, to treat vascular stenosis, repair ruptured blood vessels or blood vessels with aneurysms, or to fixate prosthetic devices such as artificial valves within body lumens in the circulatory system. It is known that a stent graft itself can function as a prosthesis, and can exclude aneurysms from the circulatory system. It is also known that uncovered or covered stents can be used to repair stenosis.

[0004] Furthermore, U.S. Patent No. 10,779,964 and the scientific article "Segmental Aortic Stiffness Contributes to the Development of Experimental Abdominal Aortic Aneurysms" published in Circulation 2015;131:1783-1795 by the inventors described herein demonstrate that segmental aortic stiffness generates aortic wall stress and induces aneurysm growth as an early pathological mechanism, regardless of AAA shape. This is because the aneurysmal portion of a blood vessel, such as the aorta, has a stiffer wall than adjacent portions of the vessel (e.g., the AAA neck), and wall stresses occur at the transition between the stiff aneurysm and the healthy, more flexible portion of the vessel, resulting in aneurysm growth.

[0005] U.S. Patent No. 10,779,964 proposes a method for treating abdominal aortic aneurysms, including targeting and treating a segment of the aorta axially adjacent to the abdominal aortic aneurysm in a subject, thereby increasing the mechanical stiffness of the aortic segment. The concept of the invention disclosed in U.S. Patent No. 10,779,964 is to increase the mechanical stiffness of the aortic segment adjacent to the abdominal aortic aneurysm in a subject. In one embodiment, increasing the mechanical stiffness of the aortic segment includes placing an intravascular stent that reinforces the aortic segment. The stiffening of the segment adjacent to the aortic aneurysm reduces the stiffness gradient between the aneurysm itself (AAA sac) and healthy portions of the vessel, thereby reducing the growth of the aneurysm itself. According to this disclosure, the stent is an expandable stent configured to expand into contact with the inner wall of the aorta, thereby providing support and mechanical stiffness to the length of the aorta in contact with the stent. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 10,779,964 [Patent Document 2] International Publication No. 2022 / 253522 [Non-patent literature]

[0007] [Non-Patent Document 1] The scientific paper, "Segmental aortic stiffness contributes to the development of experimental abdominal aortic aneurysms," was published in Circulation 2015;131:1783-1795. Summary of the Invention

[0008] Self-expanding stents made of shape-memory alloy materials, such as nitinol, are known to exhibit hysteresis in their force-diameter profiles. This means that the force profile during expansion is typically lower than the force profile required to compress the stent. The force profile during expansion is typically referred to as "chronic outward force," commonly abbreviated as COF. The force overcome when compressing the stent is referred to as "radial resistance pressure," commonly abbreviated as RRF. Stents with high RRF are typically used after balloon angioplasty for vascular stenosis to prevent recoil of the vessel wall and keep the lumen open. Meanwhile, COF can be used to select stents, as it is an indicator of the force required to secure devices, such as valves and vascular prostheses, to the vessel. Furthermore, COF is important in considering mechanical damage to the vessel and vascular remodeling. Remodeling occurs when permanent forces act on the vessel's inner wall, causing the vessel to expand. The vessel then grows larger in diameter through growth or remodeling, allowing the stent to expand further. This is usually undesirable due to the risk of stent loosening, so care must be taken to select a COF that is not so high as to cause vascular remodeling.

[0009] It is an object of the present invention to provide a stent that is more compatible with the physiology of the human body, more user-friendly, and can be used in the above-mentioned procedures for treating aneurysms, particularly as disclosed in U.S. Pat. No. 10,779,964 and the publication "Segmental Aortic Sclerosis Contributes to the Development of Experimental Abdominal Aortic Aneurysms."

[0010] This object is achieved by a stent according to claim 1, a first aspect of the present invention, as described herein. The stent according to the first aspect of the present invention is formed by the method described above, and in particular exhibits a nominal radial resistance pressure of 100 mmHg or greater, preferably greater than 100 mmHg, at its nominal diameter. The nominal diameter refers to the diameter of the vessel after stent deployment, or the diameter it should have. That is, diameters smaller than the nominal diameter, such as the delivery diameter, typically have a higher RRP, while diameters larger than the nominal diameter, such as after vascular remodeling, typically have a lower RRP. The minimum diameter of the stent refers to the diameter of the stent in its crimped state, particularly the diameter of the stent when delivered and / or contained within a delivery system. The maximum diameter of the stent in its relaxed state refers to the diameter of the stent without external constraints, i.e., the diameter of the stent in its relaxed, undeployed state.

[0011] Because the vessel wall generally has a certain degree of flexibility (stiffness, compliance), the inventors characterized the mechanical interaction between the stent and the vessel and discovered that the equivalent intraluminal pressure of the stent is far more important than force to achieve optimal interaction. The vessel wall responds to intraluminal pressure and provides resistance to prevent vessel collapse, even in healthy vessels.

[0012] In particular, in the above-mentioned methods of stiffening blood vessels to treat abdominal aortic aneurysms, radial resistive pressure is the decisive measure, while the chronic outward force traditionally used is less important in designing an appropriate stent. The inventors have found that radial resistive pressures equivalent to intraluminal pressures of 100, 110, 120, 130, and more preferably 150 mmHg or greater are particularly beneficial for strengthening the vessel wall sufficiently to treat aneurysm growth. The ratio behind this specific value is that the typical aorta has a tapered diameter-pressure diagram. That is, in the low-pressure range, the vessel wall is much more elastic due to elastin recruitment, while in the high-pressure range, the vessel wall becomes stiffer due to predominantly collagen recruitment. Between these ranges, a transition from slightly elastic to slightly stiff is defined, typically between 90 and 135 mmHg, although this varies from individual to individual. For most patients with normal vessels, a radial resistive pressure of 100 mmHg or greater, preferably 150 mmHg, has been shown to be appropriate. A nominal radial resistance pressure of 100 mmHg or greater, preferably 150 mmHg, is effective in preventing the vessel from collapsing and ensuring that the vessel is sufficiently strengthened to allow treatment of the abdominal aortic aneurysm.

[0013] Generally, the radial resistance pressure (RRP) can be determined by determining the outward pressure (extravascular pressure) required to compress the stented portion. Similarly, the chronic outward pressure (COP) can be determined by determining the internal pressure (intravascular pressure) required to dilate the vessel.

[0014] The nominal radial resistance pressure (RRP-N) can be calculated based on the nominal diameter (DN) of the stent, the length (L) of the stent or stent segment, and the radial resistance pressure (RRF-N) at this nominal diameter by the formula: RRP-N = (RRF-N) x k / (DN x L x π), where k is in N / mm 2 is a correction factor for converting from π to mmHg. In this disclosure, the common conversion 1 mmHg = 133,322 Pa is used in the calculations.

[0015] Each ring segment may exhibit the above-mentioned nominal radial resistance pressure, or only one ring segment, two or more ring segments, or the entire stent may exhibit the above-mentioned nominal radial resistance pressure, i.e., the stent may have different nominal radial resistance pressures along its length.

[0016] The exact structure of the stent, i.e., the distal and proximal ring segments, as well as the optional one or more ring segments disposed between the distal and proximal ring segments, can be selected depending on the particular design of the cells, struts, peaks, valleys, etc. For example, for the treatment of abdominal aortic aneurysms, a total of three segments with a total stent length of 30 mm to 50 mm has been shown to be sufficient, although other sizes and lengths are contemplated. Specific examples of suitable stents are disclosed in the same applicant's International Publication No. WO 2022 / 253522.

[0017] The disclosure of this application is incorporated herein by reference. Another specific example is given below. Preferably, the stent is made of a shape memory alloy, such as Nitinol, is preferably manufactured from a tube, preferably a single tube, has a constant wall thickness, i.e., radial thickness, and / or is uncoated. In a further aspect of the present invention disclosed herein, the stent may have only a single ring. Thus, such a stent has neither a distal nor a proximal ring, and in this case, has only a single ring, which is not referred to as a distal or proximal ring. Hereinafter, the term "ring" refers to a structure, composed of interconnected struts, preferably cut from a raw material tube, forming a portion of a stent or a complete stent, such that the structure is self-supporting and integral. Hereinafter, the single ring will be referred to as a "proximal end ring," a "distal end ring," or a "middle ring" when its location is specified, but may also be referred to as a "first ring," a "second ring," etc. when its location is not specified. Thus, a "first ring" may refer to either a single ring, a proximal ring, a distal ring, or an intermediate ring that makes up the stent.

[0018] According to claim 1, the stent is adapted to be implanted in the abdominal aorta of a human body to treat an abdominal aortic aneurysm, although in other embodiments, the stent may be adapted to be implanted more generally in a blood vessel of a human body. Thus, generally speaking, the stents disclosed herein are implanted in the abdominal aorta of a human body to treat an abdominal aortic aneurysm. The stents disclosed herein have an expandable framework and may have at least a distal ring and at least a proximal stent ring. The distal ring and / or the proximal ring may have peaks and valleys. In one aspect described herein, the distal ring, the proximal ring, or any of the optional rings of the stent may exhibit a nominal radial resistance pressure (RRP-N) at the nominal diameter (DN) of 100 mmHg or greater. In other embodiments, this value may be higher or lower. The preferred embodiment described below refers to a more general aspect and is not limited to the embodiment described in claim 1.

[0019] Preferably, the stent is made solely of the shape memory alloy, without any therapeutic agents, including coatings or other additional elements, and is non-biodegradable, non-braided, and uncoated.

[0020] The terms "proximal" and "distal" are defined relative to the stent according to its intended orientation relative to the heart of the subject in which it is implanted.

[0021] In stents with two or more rings, the rings are typically connected to one another by connectors, but may also be directly connected. The connectors are preferably made of multiple connector wires cut from a raw tube and integrally formed with each ring. The connectors or connector wires typically connect only adjacent rings, not to each other. Therefore, the connector element disposed between two adjacent ring segments is typically not freestanding or integrally formed as a single "connector ring."

[0022] In preferred embodiments, the stent or at least one ring segment has a nominal radial resistance pressure (RRP-N) of 250 mmHg or greater at the nominal diameter. Values ​​between 150 mmHg and 250 mmHg or greater are also contemplated and preferred. For example, values ​​such as 160 mmHg, 170 mmHg, 180 mmHg, 190 mmHg, 200 mmHg, 210 mmHg, 220 mmHg, 230 mmHg, 240 mmHg, 260 mmHg, and 270 mmHg are preferred. The nominal radial resistance pressure is preferably less than 2000 mmHg, 1500 mmHg, 1000 mmHg, 750 mmHg, 500 mmHg, 350 mmHg, or 300 mmHg.

[0023] More preferably, the stent or at least one ring segment has a chronic outward pressure (COP-N) at its nominal diameter of 50 mmHg or greater. Preferably, the stent has a chronic outward pressure (COP-N) at its nominal diameter of 100 mmHg or greater, and more preferably 150 mmHg or greater. Depending on the intended use of the stent, particularly the intended treatment, a combination of relatively low chronic outward pressure and high radial resistance can be beneficial. This is particularly true in the aforementioned abdominal aortic aneurysm (AAA) application.

[0024] To calculate the nominal chronic outward pressure, the same formula as above applies, except that chronic outward force (COF) is used instead of radial resistive force (RRF).

[0025] When a stent is used as a scaffold for a valve or other prosthetic implant, it is beneficial to continuously increase the outward pressure to ensure a strong structural bond between the stent and the vessel wall and adequately anchor the device. In particular, a chronic outward pressure (COP-N) of 150 mmHg or greater is desirable. In all cases, it is beneficial to limit the nominal chronic outward pressure (COP-N) to 250 mmHg, and more preferably to 240 mmHg, 230 mmHg, 220 mmHg, or 200 mmHg.

[0026] For particularly preferred stents, the d0 (unexpanded stent diameter / maximum crimped diameter) and d max The AUC (area under the curve) value of the RRP-diameter curve from (maximum expanded diameter / relaxed stent diameter) is at least 4000 mmHg*mm, preferably at least 5000 mmHg*mm, and preferably at least 7000 mmHg*mm. Preferably, the AUC value is less than 20,000 mmHg*mm, preferably less than 15,000 mmHg*mm, and more preferably 13,500 mmHg*mm or less. If one or more additional stent rings are present, their AUC values ​​may be the same, similar, or lower. The stents of the present invention have a relatively large diameter, particularly for use in the abdominal aorta, and are relatively strong, particularly for dilating and stiffening the abdominal aorta. Therefore, the AUC parameter effectively represents the interaction of these two related aspects.

[0027] This embodiment, and optionally the following embodiments, are also covered by one or more aspects of the present invention and may be defined independently of the other preferred features described above. Thus, the problem set forth in the introduction is also solved by a self-expanding stent for implantation in a blood vessel of a human body, the stent comprising an expandable framework formed from a shape memory alloy and having a distal end, a proximal end, and an internal volume extending along a central axis from the distal end to the proximal end, the framework having at least distal and proximal end rings with peaks and valleys, and optionally at least one ring disposed between the distal and proximal end rings, the length LF from the distal end to the proximal end of the framework being at least 10 mm, the stent having a compressed state with a minimum diameter (Dmin), an expanded state with a nominal diameter (DN), and a relaxed state with a maximum diameter (Dmax), the AUC (area under the curve) under the RRP diameter curve between the minimum diameter (Dmin) and the maximum diameter (Dmax) of the stent is at least 4000 mmHg*mm, preferably 5000 mmHg*mm, preferably at least 7000 mmHg*mm, preferably at least in the distal end ring (8).

[0028] For particularly preferred stents, the pressure diameter (PDP) product of the distal ring (PDP is calculated as nominal radial resistance pressure (RRP-N) * (nominal diameter)) is at least 1800 mmHg*mm, preferably at least 3000 mmHg*mm. If one or more additional stent rings are present, their values ​​may be the same, similar, or lower. The stents of the present invention are relatively large in diameter, since they are specifically intended for the abdominal aorta, and relatively strong, since they are specifically intended to dilate and stiffen the abdominal aorta. The parameter PDP therefore effectively represents the interaction of these two related aspects.

[0029] Furthermore, when the stent has two or more stent rings, one of which forms the distal end ring and one of which forms the proximal end ring, preferably the formula: AUC dist / AUC prox >1 is satisfied. AUCdist is the AUC parameter calculated for the distal ring as described above, and AUC prox is the above-mentioned AUC parameter calculated for the proximal end ring. Preferably, the parameter AUC dist / AUC prox is in the range of 1.5 to 4, more preferably 2 to 4, and further preferably 3 to 4.

[0030] A further preferred parameter describing the stent of the present invention is the COP- when the stent has two or more stent rings, one of which forms the distal end ring and one of which forms the proximal end ring. dist / COP- prox It is the ratio of COP- dist is the (nominal) COP value of the distal ring of the stent, COP- prox is the (nominal) COP value of the proximal ring of the stent. This parameter may be different for stents with generally high RRP or RRP-N values ​​than for stents with generally low RRP or RRP-N values. However, preferably, the ratio COP- dist / COP- prox ranges from 2 to 4, and may range from 2 to 3 for stents with an overall low RRP.

[0031] In a preferred embodiment, the overall axial length of the stent is L( tot ), and if a distal ring is present, its axial length is L( dist ), and the axial length of the proximal end ring is L( prox ) Optionally, the axial length of one or more intermediate stent rings is L( int-n ) (n=1, 2, etc.) dist ) and L( tot ) is preferably in the range of 0.3 to 1.0, more preferably 0.3 to 0.9, 0.4 to 0.8, 0.4 to 0.7, or 0.4 to 0.6. prox ) and L( tot) is preferably in the range of 0.1 to 0.4, preferably 0.1 to 0.3, and more preferably 0.1 to 0.2. It should be understood that two or more stent rings (if present) are axially connected to one another by connectors. Such connectors increase the overall axial length but are not taken into account when measuring the axial length of the stent rings. Additionally, the stent may have holders for radiopaque markers that may extend beyond the axial ends of the end rings. Such holders and other additional components are not taken into account when measuring the axial length of the entire stent or a single stent ring. Also, because stents typically shorten slightly upon expansion, measurements are taken in the maximally crimped state (crimped to the cutting tube diameter).

[0032] A further preferred parameter describing the innovative stents disclosed herein is the difference between the radial resistance pressure (RRP) and the chronic outward pressure (COP) at a given diameter. Preferably, at the nominal diameter, the difference between the nominal radial resistance pressure (RRP-N) and the nominal chronic outward pressure (COP-N) is at least 50 mmHg, preferably 75 mmHg. Preferably, this applies not only to the nominal diameter, but also to the range of 22 mm to 25 mm, preferably 20 mm to 28 mm.

[0033] In a preferred embodiment, the framework has a radially measured thickness of 0.2 mm to 1.0 mm, particularly 0.2 mm to 0.7 mm, more preferably 0.2 mm to 0.6 mm, even more preferably 0.3 mm to 0.6 mm, even more preferably 0.4 mm to 0.6 mm, and even more preferably 0.3 mm to 0.5 mm. Furthermore, the first stent ring of the stent preferably comprises two or more struts such that the strut length (L) / strut width (B) satisfies the following relationship: 20, 19, 18, 17, 16, 15, 14, 13, and especially preferably 12. Preferably, the struts, together with their respective crests or peaks, define cells that may be diamond-shaped, open-celled or closed-celled, and may have regular or irregular shapes, and may be defined by the same or different struts.

[0034] In a further preferred embodiment, the first ring (preferably the distal ring) comprises two or more struts, and the first ring has a force (N) per mm of radial deformation (mm) per mm of length at the nominal diameter of 0.08 N / mm. 2 ~0.12N / mm 2 Preferably, the second ring segment (preferably the proximal end ring) comprises two or more struts, and the second ring has a radial stiffness in the range of 0.01 N / mm 2 ~0.03N / mm 2 , preferably 0.02N / mm 2 ~0.03N / mm 2 Preferably, the second ring segment (preferably the proximal end ring) comprises two or more struts, and the second ring has a radial stiffness in the range of 0.01 N / mm 2 ~0.03N / mm 2 , preferably 0.02N / mm 2 ~0.03N / mm 2 The radial stiffness ranges from .

[0035] Preferably, the chronic outward pressure at the nominal diameter (COP-N) is non-uniform along the length of the framework. Preferably, the chronic outward pressure decreases from the distal end to the proximal end, i.e., the chronic outward pressure is higher at the distal end of the stent than at the proximal end. Desirably, proximal and distal are defined relative to the human heart. Elements farther from the heart in the deployed state are defined as distal, and elements closer to the heart are defined as proximal. In certain embodiments, the definitions of proximal and distal may, but need not, coincide with the conventional definitions of proximal and distal in a stent delivery system. Alternatively, the chronic outward pressure decreases from the proximal end to the distal end.

[0036] The radial resistance pressure at the nominal diameter (RRP-N) may be constant or non-uniform along the length of the framework. Preferably, the radial resistance pressure at the nominal diameter also decreases from distal to proximal, i.e., is higher at the distal end of the framework than at the proximal end of the framework. Alternatively, the radial resistance pressure decreases from the proximal end to the distal end.

[0037] Both the chronic outward pressure and the radial resistance pressure at the nominal diameter may decrease gradually, i.e., from ring segment to ring segment, although it is contemplated that two or more adjacent ring segments may exert the same chronic outward pressure and / or radial resistance pressure. Also, one or more intermediate ring segments between the proximal and distal ring segments at the nominal diameter may exert a higher or lower chronic outward pressure or radial resistance pressure than the distal ring segment. Notably, even if the overall radial resistance pressure or chronic outward pressure decreases from distal to proximal (or vice versa), a single ring segment in between may cause the pressure to increase again. Furthermore, the gradient of the chronic outward pressure from the distal end to the proximal end of the stent may differ from the gradient of the radial resistance pressure from the distal end to the proximal end of the stent. For example, the gradient of the radial resistance pressure may be greater than the gradient of the chronic outward pressure, e.g., 10%, 20%, 30%, or more.

[0038] In a preferred embodiment, the ratio of the chronic outward pressure at the nominal diameter of the distal ring to the chronic outward pressure at the nominal diameter of the proximal ring is in the range of 10:1 to 1.5:1, preferably 8:1 to 1.5:1, and preferably 6:1 to 2:1. This parameter may be different for stents with an overall high RRP or RRP-N value than for stents with an overall low RRP or RRP-N value. However, preferably, the ratio COP-N is the same regardless of the particular RRP value of the stent according to the present disclosure. dist / COP- prox ranges from 4:1 to 2:1, and for stents with an overall lower RRP it can range from 3:1 to 2:1.

[0039] The same applies to the radial resistance pressure, where again the ratio of the radial resistance pressure at the nominal diameter of the distal end ring to the radial resistance pressure at the nominal diameter of the proximal end ring is in the range of 10:1 to 1.5:1, preferably 9:1 to 2:1, preferably 8:1 to 3:1, preferably 8:1 to 4:1, preferably 7:1 to 5:1, preferably 4:1 to 2:1, more preferably 3:1 to 2:1.

[0040] Preferably, the peaks and valleys of each ring segment are formed by peaks connected by struts, and the struts are substantially straight. In other embodiments, the struts may be curved, bell-shaped, S-shaped, or serpentine, or the struts of a ring segment may be serpentine without peaks. Preferably, at least two adjacent ring segments are arranged in an out-of-phase relationship, such that the peaks forming the valleys of one ring are connected to the peaks forming the peaks of the other ring. Preferably, at least two adjacent rings are arranged in phase and connected to each other by at least two nonlinear links. The number of links between the rings of the stent may be the same for all ring segments or may vary between ring segments. Preferably, the stent has open and closed cells, or only closed cells. Closed cells have the advantage that the stent can be easily retracted into a delivery system when needed.

[0041] In a preferred embodiment or aspect of the present invention, the stent includes an intermediate stent ring disposed between the distal end ring and the proximal end ring. The stent may include multiple intermediate stent rings, e.g., two, three, four, or more, which may be referred to as a "first intermediate stent ring," a "second intermediate stent ring," or the like. When only one intermediate stent ring is provided, the intermediate stent ring is connected to the distal end ring via a first connector and to the proximal end ring via a second connector. The connectors typically do not independently exert radial force or pressure; rather, their function is to maintain the integrity of the stent and the desired spacing of the single stent rings. However, it should be understood that, depending on the specific configuration of the connector, the connector may exert force or pressure on the inner wall of the vessel because the stent ring holds the connector in proximity to the vessel wall and exerts a radial force.

[0042] Preferably, the intermediate stent ring comprises at least one third circumferential ring segment and at least one fourth circumferential ring segment, each having a different structure. All of the features disclosed above with respect to the first and second circumferential ring segments are also applicable to the third and fourth circumferential ring segments. This allows one, some, or all of the features described above to be applied. In such a configuration, the intermediate stent ring may also exhibit different expansion characteristics depending on the diameter, as previously described.

[0043] Preferably, the chronic outward force at nominal diameter (COF-N) or chronic outward pressure at nominal diameter (COP-N) of the intermediate stent ring is lower than the chronic outward force at nominal diameter (COF-N) and chronic outward pressure at nominal diameter (COP-N) of the distal-end ring, respectively. Preferably, the chronic outward force at nominal diameter (COF-N) or chronic outward pressure at nominal diameter (COP-N) of the intermediate stent ring is higher than or equal to the chronic outward force at nominal diameter (COF-N) and chronic outward pressure at nominal diameter (COP-N) of the proximal-end ring. In particular, the above-described configuration in which third and fourth circumferential ring segments are used is beneficial when the COF-N and COP-N of the intermediate stent ring are higher than the COF-N and COP-N of the proximal-end ring, thereby beneficially providing the "expansion margin" as described above.

[0044] In a preferred embodiment, the third circumferential ring segment includes struts having a third circumferential width W3, and the fourth circumferential ring segment includes struts having a fourth circumferential width W4, the third circumferential width W3 being greater than the fourth circumferential width W4. Preferably, the first circumferential width W1 is greater than the third circumferential width W3, and the second circumferential width W2 is greater than the third circumferential width W3.

[0045] If an intermediate stent ring is present, the ratio of the chronic outward pressure (COP-N) at the nominal diameter (DN) of the intermediate stent ring to the chronic outward pressure at the nominal diameter (DN) of the proximal ring is preferably in the range of 1.0 to 8.0. The ratio of the chronic outward pressure (COP-N) at the nominal diameter (DN) of the distal ring to the chronic outward pressure at the nominal diameter (DN) of the proximal ring is preferably in the range of 10.0 to 1.5 as described above, but the ratio between the intermediate stent ring and the proximal stent ring is in a lower range and may be the same as that of the proximal ring. Preferably, the ratio (COP-N- mid ) / (COP-N- prox ) ratio is (COP-N- dist ) / (COP-N- prox) is approximately 35% or less. dist " is the chronic outward pressure (COP-N) at the nominal diameter (DN) of the distal ring, and "COP-N- mid " is the chronic outward pressure (COP-N) at the nominal diameter (DN) of the intermediate stent ring, and "COP-N- prox " is the chronic outward pressure (COP-N) at the nominal diameter (DN) of the proximal ring. Preferably, (COP-N- mid ) / (COP-N- prox ) ratio is (COP-N- dist ) / (COP-N- prox ) ratio is approximately 30%, 25%, 20%, and 15% or less.

[0046] The same ratio may be applied to the radial resistance pressures at the nominal diameters of the distal ring, the intermediate ring, and the proximal ring.

[0047] Preferably, the third circumferential ring segment comprises struts having a third length LS3 and the fourth circumferential ring segment comprises struts having a fourth length LS4, the third length LS3 being greater than the fourth length LS4.

[0048] In a preferred embodiment or further aspect of the present invention, the first connector includes a straight connector, which is beneficial for ensuring tubular shape stability and preventing excessive radial twisting of the distal ring segment upon stent release. In one embodiment, the first connector includes only a straight connector.

[0049] Preferably, a straight connector connects the first circumferential ring segment of the distal ring to the third circumferential ring segment of the intermediate stent ring, thereby connecting the circumferential segments of the distal ring and the intermediate stent ring to generate a substantially radial force, thereby ensuring stent integrity and providing increased support to the vessel wall via the straight connector.

[0050] Preferably, the first connector comprises a bow-shaped connector. In one embodiment, the first connector comprises only a bow-shaped connector. Specifically, the bow-shaped connector resembles a W-shape with two protruding ends and an elongated central portion of the W. Preferably, the bow-shaped connector connects the second circumferential ring segment of the distal end ring to the fourth circumferential ring segment of the intermediate stent ring. When the first and third circumferential ring segments are connected via a straight connector, the bow-shaped connector connecting the second and fourth circumferential ring segments can accommodate different shortenings during expansion of the different circumferential segments.

[0051] In a preferred embodiment or other aspect of the present invention, each proximal-facing crest of the distal ring is connected to one connector of the first connector. Preferably, each proximal-facing crest of the intermediate stent ring is connected to one connector of the second connector. The smaller the proximal projections of a ring connected to one connector, the easier it is to pull the stent back into the delivery system for implantation. The configuration of the stents of the present invention described herein is important, as there may be situations in which a surgeon will pull the stent back into the delivery system and at least slightly compress it to reposition it. Because the stents of the present invention described herein are relatively stiff, i.e., have a relatively high COP, it can be difficult to pull the stent back after delivery to a certain extent. The crest design described herein allows the stent to be pulled back into the delivery system as needed.

[0052] Preferably, the first connector is connected to the crests and valleys of the middle stent rings, particularly the crests of the third circumferential ring segment and the valleys of the fourth circumferential ring segment, which is beneficial in accounting for differences in axial shortening rates of the different circumferential ring segments.

[0053] In a further preferred embodiment, the second connector comprises an arcuate connector. Preferably, the second connector comprises only an arcuate connector to provide axial flexibility and allow for shortening of the connected ring segments.

[0054] In a further aspect of the present invention, the problem described in the introduction is solved by a method for determining pressure for treating abdominal aortic aneurysms (AAA). The method includes the following steps: receiving intraluminal pressure data; receiving aortic diameter data with reference to the received pressure data; determining a transition pressure between the elastin phase and the collagen phase of the vessel based on the pressure data and the aortic diameter data; determining a stent framework length LF, preferably a length L1 of at least a first ring segment; and determining a nominal radial resistance pressure based on the transition pressure. Preferably, the nominal radial resistance pressure is determined based on the aortic diameter data, the framework length LF, and / or the length L1 of the first ring segment. The first ring segment may be the proximal ring segment, the distal ring segment, or an optional ring segment therebetween.

[0055] Preferably, the nominal radial resistance pressure is selected to be 10%, 15%, 20%, 25%, 30% higher than the transition pressure. The pressure data of the intraluminal pressure and / or the luminal diameter data of the aortic diameter may be provided by a computer device such as a pressure transducer or an ultrasound device, or may be provided by a storage means, a physical storage means, a cloud service, or the like. Preferably, the pressure data and aortic diameter data include pressure and aortic diameter data of the target vessel, preferably the patient's abdominal aorta, and preferably include pressure and aortic diameter data obtained under patient stress, i.e., physical stress or pharmacological stress.

[0056] The method may further include determining a stent placement location based on the received image data, particularly including a representation of the abdominal aorta having an abdominal aortic aneurysm. The stent placement location may be defined proximal to the aneurysm sac, and in particular, the distal end of the framework should be positioned as close as possible to the aneurysm sac. For a definition of the stent placement location, see commonly assigned European Patent Application No. 22188215.1, which is incorporated herein by reference. Furthermore, the stent placement location may also be defined in accordance with U.S. Pat. No. 10,779,964, which is also incorporated herein by reference.

[0057] The method preferably further includes determining the total number of ring segments of the stent, the chronic outward pressure of the stent, the chronic outward pressure and radial resistance pressure of a single ring segment of the stent, and / or the number of ring segments.

[0058] In a further aspect, the present invention solves the above mentioned problem by a computer program comprising executable code which, when run on a computer, causes the computer to carry out the method according to the second aspect of the invention.

[0059] In a further aspect, the present invention solves the above-mentioned problem by a method of treating an abdominal aortic aneurysm, comprising the steps of providing a stent according to any of the above-mentioned preferred embodiments of a stent according to the first aspect of the invention, and deploying the stent in a blood vessel adjacent an aneurysmal sac of the abdominal aortic aneurysm to increase the mechanical stiffness of the aortic segment.

[0060] For a better understanding of the present invention, the present invention will now be described in detail with reference to the accompanying drawings. The detailed description illustrates and explains preferred embodiments of the present invention. Of course, it should be understood that various modifications and changes in form or detail can be readily made without departing from the spirit of the present invention. Therefore, the present invention is not intended to be limited to the exact forms and details shown and described herein, nor to less than the entire invention disclosed and claimed herein. Moreover, features described in the specification, drawings, and claims disclosing the invention may be essential to the invention considered alone or in any combination. In particular, reference signs in the claims should not be construed as limiting the scope of the invention. The word "comprises" does not exclude other elements or steps. The words "a" or "an" do not exclude a plurality. The word "a number of" includes not only one, i.e., a single element, but also two, three, four, etc. [Brief explanation of the drawings]

[0061] [Figure 1] 1 shows a typical pressure-diameter diagram illustrating the elasticity of the aorta. [Figure 2] 1 shows a pressure-diameter diagram of a stent (segment) according to the invention and an elasticity diagram of the aorta. [Figure 3] 1 shows another pressure diameter diagram for a stent (segment) according to the present invention. [Figure 4] 1 shows a schematic diagram of a stent according to the present invention. [Figure 5a] 1 shows ring segments of a stent according to the present invention in three different expanded states. [Figure 5b] 1 shows ring segments of a stent according to the present invention in three different expanded states. [Figure 5c] 1 shows ring segments of a stent according to the present invention in three different expanded states. [Figure 6] 10 shows another ring segment of a stent according to the present invention in a crimped state. [Figure 7] 10 shows another ring segment of a stent according to the present invention in a crimped state. [Figure 8] 1 shows a portion of a human aorta with an AAA and a stent inserted. [Figure 9] 1 shows a first embodiment of a stent suitable for the present invention. [Figure 10] 2 shows a second embodiment of a stent suitable for the present invention. [Figure 11] Schematic pressure diameter diagrams for the stents shown in Figures 9 and 10 are shown, one graph per stent ring. [Figure 12] FIG. 1 is a full cutaway side view of a rendering of a fully expanded stent. [Figure 13] FIG. 1 is a perspective view of a fully expanded stent. DETAILED DESCRIPTION OF THE INVENTION

[0062] Figure 1 shows a typical graph of the relationship between aortic diameter and aortic pressure. As can be seen, the curve is relatively steep in the first section, indicating a rapid increase in aortic diameter as pressure increases. In the second section, despite the high pressure, the aortic diameter does not change as dramatically as at lower pressures, and the blood vessel itself responds by becoming more stiff. This is because elastin is primarily activated in the first section, while collagen is activated under high pressure in the second section, limiting the vessel diameter. There is a transition between these sections, and the average aorta in a healthy individual is approximately 120 mmHg. The present inventors have discovered that this mechanical behavior of the aorta can be exploited to stiffen the blood vessel, thereby modulating the growth of abdominal aortic aneurysms. This finding is disclosed in the scientific paper "Segmental Aortic Stiffness Contributes to the Development of Experimental Abdominal Aortic Aneurysms," published in Circulation 2015;131:1783-1795.

[0063] The present invention is based on the idea that a stent providing a radial resistance pressure (RRP-N) of at least 100 mmHg at its nominal diameter, and preferably 150 mmHg or greater, is beneficial for the treatment of abdominal aortic aneurysms (AAAs). A schematic diagram illustrating this innovative idea is shown in Figure 2. In this figure, the vertical and horizontal axes are swapped compared to Figure 1, with the horizontal axis representing diameter and the vertical axis representing pressure. The thick dashed line represents the vessel, which is identical to the graph in Figure 1. The upper thin dashed line represents the radial resistance pressure of the stent, and the lower dashed-dotted line represents the chronic outward pressure of the stent, both relative to the stent diameter. As is commonly known with respect to the force exerted by a stent, the so-called chronic outward force, or radial outward force (COF), dramatically decreases as the stent expands and reaches a nearly constant value defined by the stent's nominal diameter, DN. The same is true for the chronic outward pressure. This plateau is typically used as the nominal diameter, ensuring a relatively constant outward force or pressure is continuously applied for small diameter deviations. The radial resistance force or pressure is the force or pressure that the stent must overcome to recompress the stent into the crimped state. Therefore, in FIG. 2, the graph of chronic outward force (COF) or chronic outward pressure (COP) should be plotted from left to right, and the graph of radial resistance force (RRF) or radial resistance pressure (RRP) should be plotted from right to left. As shown in FIG. 2, there is a significant hysteresis between the radial resistance pressure RRP and the chronic outward pressure COP, which can be significant. In the specific embodiment shown in FIG. 2, the radial resistance pressure at the nominal diameter RRF-N is slightly above 150 mmHg, consistent with the present invention. The chronic outward pressure COP-N at the nominal diameter DN is 100 mmHg or less. Comparing these values ​​to the graph showing the vessel response (FIG. 1), it can be seen that the chronic outward pressure at the nominal diameter is in the first portion of the vessel graph, i.e., the portion where elastin is recruited, and the radial resistance pressure at the nominal diameter RRF-N is in the portion of the vessel graph showing collagen recruitment. Thus, this radial resistive pressure acts to reinforce the vessel (vascular recoil) as the vessel diameter decreases.This has been shown to be highly beneficial in the treatment of abdominal aortic aneurysms, as described in the scientific paper cited above.

[0064] Figure 3 shows a specific measurement diagram of a stent or distal stent ring according to the present invention. Here, too, a graph of the chronic outward pressure (COP) versus the radial resistance pressure (RRP) is shown. In the first use case, the nominal diameter (DN) is approximately 13-16 mm, while in the second use case, it would be preferable to set DN-2 to 18-29 mm. It can be seen that in the first use case, the chronic outward pressure at the nominal diameter (COP-N) is 150 mmHg, while the radial resistance pressure at the nominal diameter (RRF-N) in this first use case is approximately 280 mmHg. Such a stent is suitable not only for resisting vascular contraction / recoil during the vascular elastin replenishment phase, but also for firmly anchoring a valve or artificial graft to a hardened vascular wall. In particular, a COP-N of 150 mmHg actively expands the vascular wall to the "hard" stage of the pressure-diameter curve, forming a solid abutment optimal for stent anchorage. For the second use case, nominal diameter DN-2 (= 10-29 mm), the chronic outward pressure at nominal diameter COP-N is less than 100 mmHg in this example, while the radial resistance pressure at nominal diameter RRF-N in this second use case is approximately 150 mmHg. Such a stent or stent ring is suitable for resisting vascular contraction / recoil during the vascular elastin replenishment phase, thereby effectively strengthening the vascular wall.

[0065] 4-7 show and will be described three different embodiments of a stent or ring segment of a stent, respectively.

[0066] FIG. 4 shows a schematic diagram of a stent 1. The stent 1 includes a framework 2 having a distal end 4, a proximal end 6, and an interior space extending along a central axis from the distal end 4 to the proximal end 6. While the interior space is not visible in FIG. 4, FIG. 4 is a two-dimensional representation of the stent 1 in an unfolded state, and one skilled in the art would recognize that the framework 2 shown in FIG. 4 has a tubular shape. The framework 2 includes at least a distal end ring 8 and a proximal end ring 10 (also referred to as ring segments 8 and 10). Each ring segment 8 and 10 has a peak 12 and a valley 13. In the embodiment shown in FIG. 4, two additional intermediate rings 14 and 15 are positioned between the distal end ring 8 and the proximal end ring 10. It should be understood that frameworks having only two ring segments, one ring segment, three ring segments, five ring segments, or more ring segments are also contemplated and disclosed herein. While the ring segments 8, 10, 14, and 15 are shown as identical in FIG. 4, they may be different. The ring segments 8, 10, 14, 15 are connected to one another by non-linear links 16 (only one shown with a reference number). In the embodiment shown in Figure 4, the non-linear links 16 attach the single ring segments 8, 10, 14, 15 in an out-of-phase relationship with one another, i.e., the links 16 connect the peaks 12 of adjacent ring segments 8, 10, 14, 15 to one another. It should be understood that the framework 2 may be configured out-of-phase, in which case the links 16 would connect the peaks of one ring segment to the valleys of an adjacent ring segment.

[0067] Each ring segment 8, 10, 14, 15 is made up of struts 20 connected by crests 22. In the embodiment shown in Figure 4, the struts 20 and crests 22 of one ring segment 8, 10, 14, 15 are arranged to form diamond-shaped cells. All of the cells in the framework 2 shown in Figure 4 are closed cells, although open cells and ring segments with different cell structures are also contemplated. The crests 22 form peaks 12 or valleys 13 depending on their location and the method of attachment of the struts 20.

[0068] The stent 1 shown in FIG. 4 has an overall length LF, and from left to right in FIG. 4, the individual rings have first, second, third, and fourth lengths L1, L2, L3, and L4, respectively. Stent 1 has a nominal radial resistance pressure (RRP-N) of 150 mmHg or greater and a nominal chronic outward pressure of 100 mmHg. While all of the rings 8, 10, 14, and 15 may exert the same pressure as one another so that the stent 1 as a whole exerts the specified pressure across the length FL, it is also preferred in this example that only one or some of the rings 8, 10, 14, and 15 exert the aforementioned pressure across their respective lengths L1 through L4. The overall length of the framework LF is preferably at least 10 mm, but may be shorter, e.g., 8 mm, while the lengths L1 through L4 of the first ring segments are at least 4 mm, but may be at least 5 mm, 5.5 mm, or 6 mm.

[0069] 5a, 5b, 5c, 6 and 7 each show only the distal end ring 8 of the framework 2, it should be understood that additional ring segments can be added via links 16 as described with respect to FIG. 4.

[0070] Figures 5a-5c illustrate one embodiment of a stent usable in the present invention. All three figures show the circumference of the ring segments 8 in a deployed state. However, it should be understood that the stent 1 is actually annular, and therefore the end shown at the top of each of Figures 5a-5c is connected to the end shown at the bottom of each figure. These figures may also be understood as cut patterns for a laser cutting process. Figure 5a shows the crimped state of the ring segments 8 with a minimum diameter Dmin, Figure 5b shows the nominal diameter DN of the ring segments 8, and Figure 5c shows the relaxed, fully expanded state with a maximum diameter Dmax.

[0071] Unlike the embodiment shown in Figure 4, the ring segment 8 according to Figures 5a-5c has three first circumferential segments 120 and three second circumferential segments 122 with differently shaped struts. As best shown in Figures 5a and 5c, the first circumferential segment 120 is comprised of three cells containing a total of 12 struts, specifically, first struts 104, while the second circumferential segment 122 is comprised of one second cell 242 defined by four second struts 106. The first struts 104 are configured to provide the expansion force, i.e., radial outward force and radial resistance, for expansion to the nominal diameter DN, while the second circumferential segment 122 with the second struts 106 is not as strong as the first circumferential segment 120, allowing the stent 1 to further expand beyond the nominal diameter DN to a maximum diameter Dmax. This particular feature is used to provide expansion reserve for stent 1 to account for further remodeling of the vessel after stent 1 is implanted. For details of the construction of the two different circumferential segments of this particular stent, see commonly assigned PCT application PCT / EP2022 / 062278 and EP application EP22188715.1, both of which are incorporated herein by reference. With this particular design with first circumferential segment 120 and second circumferential segment 122, the chronic outward force COF and radial resistance force RRF graphs shown in FIG. 2 are comprised of flattened end portions above the nominal diameter DN.

[0072] The stent 1 and ring segments 8 shown in Figures 5a-5c can be formed from a tubular Nitinol material or other shape memory alloy, particularly using laser cutting. The radial thickness of the framework 2 can range from 0.2 to 1.0 mm, particularly 0.3 to 0.5 mm. In this embodiment, the first struts 104 have a first length LS1, and the second struts 106 have a second length LS2. The first struts 104 have a first width W1, and the second struts 106 have a second width W2. In particular, because the first circumferential segment 120 plays a crucial role in the chronic outward pressure (COP) and radial resistance pressure (RRP), or chronic outward force (COF) and radial resistance force (RRF), discussed herein, only the first struts 104 will be discussed below.

[0073] FIG. 6 again shows the distal ring segment 8 only in a crimped state. The length LS1 of the first strut 104 is in the range of approximately 5-7 mm, and in the illustrated embodiment, is in the range of 6-7 mm. It also has a width of approximately 0.35-0.4 mm. The width in the region of the crest 22 may be slightly wider, in the range of 0.4-0.5 mm, and in particular 0.45 mm, to achieve a relatively high radial resistance pressure. In this embodiment shown in FIG. 6, the radial resistance pressure of the ring segment is 150 mmHg. Therefore, the distal ring segment shown in FIG. 6 belongs to a stent and may exhibit the graph shown in FIG. 2.

[0074] FIG. 7 shows a further embodiment of a crimped distal ring segment 8, again comprising three first circumferential segments 120 and three second circumferential segments 122, as described with respect to FIGS. 5a-5c. Here, four cells are formed per first circumferential segment 120 instead of three, as can be seen by counting the crests 22 per first circumferential segment 120. Compared to FIG. 6, the length LS1 is slightly shorter and the width W1 of the first struts 104 is slightly increased. This also improves the chronic outward pressure COP and radial resistance pressure RRP. In particular, in the embodiment shown in FIG. 7, the chronic outward pressure COP is 150 mmHg, while the radial resistance pressure is approximately 300 mmHg. Therefore, the distal ring segment 8 shown in FIG. 7 belongs to a stent that may represent the graph shown in FIG. 3.

[0075] Specifically, the length LS1 of the embodiment shown in FIG. 7 is in the range of 6 mm, and the width W1 is in the range of 0.4-0.5 mm, specifically 0.48 mm. FIG. 8 illustrates a vascular structure 303 including an abdominal aorta 324 having an abdominal aortic aneurysm (AAA) 310. The abdominal aortic aneurysm 310 includes an aneurysmal sac 327 and an aneurysmal neck 328. Above the aneurysmal neck 328, the lower renal artery (LRA) 330 and the upper renal artery (HRA) 334 are shown. Also shown in FIG. 8 is the superior mesenteric artery 338. In accordance with the previously cited U.S. Pat. No. 10,779,964, a stent 1 according to the present invention is positioned within the aneurysmal neck 328 such that its distal end 4 is positioned near the distal end 329 of the aneurysmal neck 328, i.e., at the proximal end of the aneurysmal sac 327, and thus directly adjacent to the aneurysmal sac 327. Superiorly, i.e., proximally, stent 1 protrudes above the lower and upper renal arteries (LRA, HRA), but not above the superior mesenteric artery 338. Stent 1 functions to stiffen the aneurysm neck 328 into collagenous sections by providing a nominal radial resistive pressure of at least 150 mmHg (see Figures 1 and 2).

[0076] FIG. 9 shows a first embodiment of a stent 1 according to the present invention, and FIG. 10 shows a second embodiment of a stent 1 according to the present invention. The stent 1 comprises an expandable framework 2 having a distal end 4, a proximal end 6, and an interior volume extending along a central axis from the distal end 4 to the proximal end 6. While the interior volume is not visible in FIGS. 9 and 10, FIGS. 9 and 10 show two-dimensional representations of the deployed stent 1, and one skilled in the art will understand that the framework 2 shown in FIGS. 9 and 10 will have a tubular shape. The main difference between the embodiments of FIGS. 9 and 10 is the axial length LF of the stent 1, which is in the range of 25-35 mm, particularly about 30 mm, in FIG. 9, whereas it is in the range of 35-45 mm, particularly about 40 mm, in FIG. 10. The axial length LF (or total axial length L( tot )) is measured only for the expandable framework 2; therefore, holders 130, such as optional radiopaque markers, as described in more detail below, are not taken into account when measuring the length of the expandable framework 2. The stent 1 shown in FIGS. 9 and 10 is made of a shape memory alloy and is self-expanding. It is cut from a tubular material using a laser cutting method, although other cutting methods, such as a water jet, may also be used. Furthermore, a tubular material is not required; the stent 1 may also be formed, for example, using a monofilament or additive manufacturing method. The stent 1 is shown in a crimped state in both FIGS. 9 and 10 and has a minimum diameter Dmin.

[0077] The stent 1 in the illustrated embodiment (FIGS. 9 and 10) has three stent rings: a distal ring 8, a proximal ring 10, and a middle ring 14. The stent rings 6, 10, and 14 are also referred to simply as the first, second, and third stent rings. The stent 1 may be configured with one, two, four, or more rings. The terms "distal ring" and "proximal ring" refer to the desired location of the stent and may be referred to as a "directive stent." However, depending on the actual design and applied radial force / pressure, the stent may be non-directional, in which case the "distal ring" may simply be referred to as the "first stent ring" and may be positioned distally or proximally, depending on the surgeon's preference.

[0078] The distal ring 8, the intermediate stent ring 14, and the proximal ring 10 are connected to one another using a first connector or link 16 and a second connector or link 17. The first connector 16 connects the distal ring 8 to the intermediate stent ring 14, and the second connector 17 connects the intermediate stent ring 14 to the proximal ring 10. The first connector 16 has a first connector axial length LC1, and the second connector 17 has a second connector axial length LC2. The structure of the first connector 16 and the second connector 17 will be described in more detail below.

[0079] First, we will discuss the distal ring 8. The distal ring 8 shown in Figures 9 and 10 has three first circumferential ring segments 120 and three second circumferential ring segments 122, each with a different strut configuration. The first circumferential ring segment 120 is composed of three closed cells 240 formed by a total of 12 struts, specifically the first struts 104, while the second circumferential ring segment 122 is composed of one closed cell 242 defined by four second struts 106. Because the stent 1 is shown in a crimped state, the cells 240 and 242 are contracted. The arrangement of the first struts 104 and second struts 106 forms the peaks 12 and valleys 13.

[0080] The first circumferential ring segment 120, having the first struts 104 forming the first cells 240, is configured to provide the expansion force, i.e., radial outward force and radial resistance, for expansion to the nominal diameter DN, while the second circumferential ring segment 122, having the second struts 106, is not as strong as the first circumferential ring segment 120, allowing the stent 1 to further expand beyond the nominal diameter DN to a maximum diameter Dmax. This feature is used to provide the stent 1 with an "expansion reserve" that accounts for further remodeling of the blood vessel after deployment of the stent 1. For more information regarding expansion reserve, see commonly assigned WO 2022 / 253522, which is incorporated herein by reference. With this particular design of the first circumferential ring segment 120 and the second circumferential ring segment 122, the graph of chronic outward force COF and radial resistance force RRF as shown in FIG. 2 is comprised of flattened end portions beyond the nominal diameter DN.

[0081] The radial thickness of the expandable framework 2 can range from 0.2 to 1.0 mm, particularly 0.3 to 0.5 mm. In this embodiment, the first strut 104 has a first length LS1, and the second strut 106 has a second length LS2. The first strut 104 has a first width W1, and the second strut 106 has a second width W2. In particular, the first circumferential segment 120 has a critical impact on the chronic outward pressure (COP) and radial resistance pressure (RRP), or chronic outward force (COF) and radial resistance force (RRF), discussed herein, and therefore the following discussion will primarily focus on the first strut 104.

[0082] The length LS1 of the first struts 104 is approximately 5-8 mm, preferably 6-7 mm in the illustrated embodiment, and the width is approximately 0.35-0.6 mm, preferably 0.4-0.5 mm. The width in the region of the crests 22 can be slightly wider, preferably 0.4-0.7 mm, preferably 0.45 mm. This allows for a relatively high radial resistance. In this embodiment, the radial resistance of the distal ring 8 shown is 150 mmHg, which results in the stent 1 having the shape shown in FIG. 2.

[0083] The distal end ring 8 is provided with a total of three holders 130 (only one is shown by a reference number in FIGS. 3 and 4). These holders are generally closed in a ring shape and can receive radiopaque markers. These holders can also be used to engage with release devices of the respective delivery systems for controlled release of the stent 1. In the illustrated embodiment, one holder 130 is provided on each of the three first circumferential ring segments 122, but a different number of holders can also be provided. The holders 130 can also have other shapes, such as a T-shape, an oval shape, or a hexagonal shape.

[0084] The intermediate stent ring 14 of the embodiment shown in Figures 9 and 10 includes only open cells formed by struts interconnected in a zigzag or serpentine pattern. Such open cell structures typically exert lower forces than the closed cell structures desired herein.

[0085] 9 and 10 includes three third circumferential ring segments 124 and three fourth circumferential ring segments 126. Similar to the second circumferential ring segment 122 of the distal end ring 8, the fourth circumferential ring segment 126 of the intermediate stent ring 14 provides expansion margin and is substantially "weaker" than the third circumferential ring segment 124. To achieve this optional feature, the intermediate stent ring 14 of this embodiment is formed from third struts 107 and fourth struts 108, with the third struts 107 forming the third circumferential ring segment 124 and the fourth struts 108 forming the fourth circumferential ring segment 126. However, it should be understood that embodiments are also contemplated in which the intermediate stent ring 14 (or multiple intermediate stent rings) does not include distinct circumferential ring segments and is simply a unitary ring without expansion margin.

[0086] All struts 107, 108 of the intermediate stent ring 14 in this embodiment have the same third strut length LS3, where the axial length in the crimped state is L( mid) In the embodiment shown in Figures 8 and 9, the third strut length is in the range of 3.0 mm to 6.0 mm, particularly 3.5 mm to 5.5 mm, and more preferably 3.8 mm to 4.5 mm. The difference in force generated by the third circumferential ring segment 124 and the fourth circumferential ring segment 126 is created by changing the widths of the third strut 107 and the fourth strut 108. In this embodiment, the third width W3 of the third strut 107 is in the range of 0.15 to 0.3 mm, more preferably 0.18 to 0.3 mm, and even more preferably 0.18 to 0.22 mm. In this embodiment, the fourth width W4 of the fourth strut 108 is in the range of 0.10 to 0.22 mm, preferably 0.13 to 0.20 mm, and even more preferably 0.15 to 0.20 mm. The ratio W3 / W4 of the third width W3 to the fourth width W4 is preferably in the range of 1.01 to 3.0, and more preferably 1.05 to 1.15.

[0087] Instead of, or in addition to, providing third circumferential ring segment 124 and fourth circumferential ring segment 126 with different widths, third strut 107 and fourth strut 108 may be provided with different lengths.

[0088] In the proximal end ring 10, the struts are connected in a zigzag or serpentine pattern to form an open cell structure, similar to the intermediate stent ring 14 of this embodiment (FIGS. 8 and 9). The proximal end ring 10 of this embodiment (FIGS. 8 and 9) is one piece and does not have structurally distinct first and second circumferential ring segments, as described for the distal end ring 8 and the intermediate stent ring 14. The distal end ring 10 is formed by a fifth strut 110, and the fifth strut length LS5 is equal to the axial length L( prox 3 and 4, the fifth strut length is in the range of 5.0 mm to 10.0 mm, preferably 5.0 mm to 8.0 mm, and more preferably 6.0 mm to 8.0 mm or 7.0 mm.

[0089] In this embodiment, the holder 131 is provided with a peak or crest 12 that faces proximally of the proximal end ring 10. The holder 131 is similar or identical to the holder 130 attached to the distal end ring 8. In this regard, please refer to the description of the holder 130.

[0090] Next, the connector will be described in more detail. The main difference between the first embodiment in Figure 9 and the second embodiment in Figure 10 is that the shape of the connector is different and the three ring segments are identical.

[0091] In this embodiment, the first connector 16 includes a linear first connector 140 and a first arcuate connector 142. The first linear connector 140 is used to connect the first circumferential ring segment 120 of the distal end ring 8 to the intermediate stent ring 14, particularly to the third circumferential ring segment 124 of the intermediate stent ring 14. In this embodiment, a linear first connector 140 is provided at each of the proximally facing peaks or crests 144 of the first circumferential ring segment 120. The linear first connectors 140 preferably have a relatively wide width, preferably in the range of 0.2 mm to 0.5 mm, particularly 0.3 mm to 0.4 mm. This is particularly beneficial when the distal end ring 8 has a relatively high strength. The first linear connector 140 is connected to a distally facing peak or crest 145 of the intermediate stent ring 14, preferably the crest of the third circumferential ring segment 124.

[0092] The first arcuate connector 142 in this embodiment connects the second circumferential ring segment 122 to the intermediate stent ring 14, specifically the fourth circumferential ring segment 126. The first arcuate connector is attached to a proximal peak or crest of the distal ring 8, preferably a valley 145 of the intermediate stent ring 14, preferably the fourth circumferential ring segment 126. When viewed axially, the first arcuate connector 142 generally resembles a W-shape, including a short section bent downward, a narrow section bent upward, and another short section bent downward. In particular, the connections and shape of the arcuate connector are designed to account for the varying degrees of axial shortening of distal rings 8 having different strut lengths. The width of the first arcuate connector 142 may be narrower than the width of the first straight connector 140, specifically by about 20% to 70%, and more specifically by about 40% to 60%.

[0093] The second connectors in this embodiment include only substantially C-shaped second arcuate connectors 146. Each of the proximal peaks or crests of the intermediate stent rings 14 is connected to one of the second arcuate connectors 146. In this case, each of the distal peaks or crests of the proximal end rings 8 is also connected to one second connector.

[0094] FIG. 11 shows a schematic representation of three COP / diameter curves for three different stent rings of the stent 1 shown in FIGS. 9 and 10. The top curve, shown by the thick dashed line, represents the distal ring 8, and the chronic outward pressure COP ( dist ) which is similar to the curves in FIG. 2. The middle dashed curve represents the middle stent ring 14, and the small dashed bottom curve represents the proximal ring 10. It can be seen that the COP of the middle stent ring 14 is closer to that of the proximal ring 10 than that of the distal ring 8. The curve for the middle stent ring 14 also shows a bow or drop in COP after the nominal diameter DN, which is due to the structural differences between the third ring segment 124 and the fourth circumferential ring segment 126, as discussed above.

[0095] 12 and 13 show a fully deployed view of stent 1, with cells 240 of first circumferential ring segment 120 and cells 252 of second circumferential ring segment 122 both fully open and the stent in a relaxed state. At a nominal diameter, cells 242 of second circumferential ring segment 122 would typically be closed or nearly closed. Cell 242 is seen to be smaller than cell 240 because the individual struts comprising cell 242 are shorter. However, as can be readily seen from FIGS. 12 and 13, distal end ring 8 includes only closed cells 240, 242.

[0096] In contrast, the proximal end ring 10 and the intermediate stent ring 14 have only open cells, as can be easily inferred from the renderings, and it can also be easily seen that each of the proximally facing crests is connected to a single connector.

[0097] In the fully expanded position (FIGS. 12 and 13), the arcuate connector 142 is slightly elongated to balance the shortening of the distal end ring 8 due to expansion. [Explanation of symbols]

[0098] 1 stent 2. Framework 4 distal end 6 Proximal end 8 Distal Ring, Ring Segment 10 Proximal end ring, ring segment 12 Peak 13 Valley 14, 15 Intermediate ring, ring segment 16 Nonlinear link, first connector or link 17 Second Connector or Link 20 Strut 22 Crest (top) 104 First Strut 106 Second Strut 120 First Circumferential Segment 122 Second Circumferential Segment 130, 131 Holder 140 First Connector 142 First Bow Connector 144 Crest 240 Closed Cell 242 Second Cell, Closed Cell 303 Vascular structure 310 Abdominal aortic aneurysm 324 Abdominal aorta 327 Aneurysm sac 328 Aneurysm Neck 329 Distal end 330 Lower renal artery (LRA) 334 Upper renal artery (HRA) 338 Superior mesenteric artery

Claims

1. A self-expanding stent (1) for implantation in the abdominal aorta of a human body for the treatment of abdominal aortic aneurysms, comprising: an expandable framework (2) formed from a shape memory alloy and having a distal end (4), a proximal end (6), and an interior volume extending along a central axis from the distal end (4) to the proximal end (6); the framework (2) has at least a distal end ring (8) and a proximal end ring (10) having peaks (12) and valleys (13), and optionally at least one ring (14, 15) disposed between the distal end ring (8) and the proximal end ring (10); The framework (2) has a length LF from the distal end (4) to the proximal end (6) of at least 10 mm. The stent has a compressed state having a minimum diameter (Dmin), an expanded state having a nominal diameter (DN), and a relaxed state having a maximum diameter (Dmax); A self-expanding stent (1) in which at least one of the distal end ring (8), the proximal end ring (10), or the optional rings (14, 15) of the stent (1) exhibits a nominal radial resistance pressure (RRP-N) of 100 mmHg or more at a nominal diameter (DN).

2. 2. The stent of claim 1, wherein at least one of the distal ring (8), the proximal ring (10), or the optional rings (14, 15) of the stent (1) exhibits a nominal radial resistance pressure (RRP-N) at a nominal diameter (DN) of 250 mmHg or greater.

3. 3. The stent of claim 1, wherein at least one of the distal ring (8), the proximal ring (10), or the optional rings (14, 15) of the stent (1) exhibits a chronic outward pressure (COP-N) at nominal diameter (DN) of 50 mmHg or greater.

4. 4. The stent of claim 3, wherein at least one of the distal ring (8), the proximal ring (10), or the optional rings (14, 15) of the stent (1) exhibits a chronic outward pressure (COP-N) at nominal diameter (DN) of 100 mmHg or greater.

5. 5. The stent of claim 4, wherein at least one of the distal ring (8), the proximal ring (10), or the optional rings (14, 15) of the stent (1) exhibits a chronic outward pressure (COP-N) at nominal diameter (DN) of 150 mmHg or greater.

6. 6. The stent according to any one of claims 1 to 5, wherein at least one of the distal ring (8), the proximal ring (10), or the optional rings (14, 15) of the stent (1) exhibits a chronic outward pressure (COP-N) at nominal diameter (DN) of 250 mmHg or less.

7. 7. The stent according to any one of claims 1 to 6, wherein the AUC (area under the curve) under the RRP diameter curve between the minimum diameter (Dmin) and the maximum diameter (Dmax) of the stent is at least 4000 mmHg*mm, preferably 5000 mmHg*mm, preferably at least 7000 mmHg*mm, preferably at least in the distal end ring (8).

8. 8. The stent according to any one of claims 1 to 7, wherein the pressure diameter product (PDP) of the stent is calculated by the formula: PDP = (nominal radial resistance pressure (RRP-N)) * (nominal diameter), and preferably the distal end ring (8) is at least 1800 mmHg*mm, preferably at least 3000 mmHg*mm.

9. The stent according to any one of claims 1 to 8, wherein the framework (2) is made of Nitinol material.

10. The stent of any one of claims 1 to 9, wherein the framework is uncovered and uncoated.

11. A stent according to any one of the preceding claims, wherein the framework (2) has a thickness measured in the radial direction in the range of 0.2 mm to 1.0 mm.

12. The stent according to any one of claims 1 to 11, wherein the distal end ring (8) comprises two or more struts (20) satisfying the relationship (strut length) / (strut width) of 20 or less.

13. The distal end ring (8) has two or more struts (20) and has a radial deformation of 0.08 N / mm, as measured by force per length. ２ to 0.12 N / mm ２ The stent of any one of claims 1 to 12, having a radial stiffness in the range of

14. The stent of any one of claims 1 to 13, wherein the chronic outward pressure at nominal diameter (DN) (COP-N) is non-uniform along the length of the framework (2).

15. 15. The stent of claim 14, wherein the ratio of the chronic outward pressure at the nominal diameter (DN) of the distal end ring (8) to the chronic outward pressure at the nominal diameter (DN) of the proximal end ring (10) is in the range of 10:1 to 1.5:

1.

16. 16. A stent according to any one of claims 1 to 15, wherein the peaks (12) and valleys (13) of each ring segment (8, 10, 14, 15) are formed by crests (22) connected by struts (20), said struts (20) being substantially straight.

17. 17. The stent of claim 16, wherein at least two adjacent ring segments (8, 10, 14, 15) are arranged in an out-of-phase relationship such that a crest (22) forming a valley (13) of one ring (8, 10, 14, 15) is connected to a crest (22) forming a peak (12) of an adjacent ring (8, 10, 14, 15).

18. 18. The stent according to claim 16 or 17, wherein at least two adjacent rings (8, 10, 14, 15) are arranged in phase relationship and connected to each other by at least two non-linear links (16).

19. A self-expanding stent (1) for implantation in a blood vessel of the human body, comprising: an expandable framework (2) formed from a shape memory alloy and having a distal end (4), a proximal end (6), and an interior volume extending along a central axis from the distal end (4) to the proximal end (6); the framework (2) has at least a distal end ring (8) and a proximal end ring (10) having peaks (12) and valleys (13), and optionally at least one ring (14, 15) disposed between the distal end ring (8) and the proximal end ring (10); The framework (2) has a length LF from the distal end (4) to the proximal end (6) of at least 10 mm. The stent has a compressed state having a minimum diameter (Dmin), an expanded state having a nominal diameter (DN), and a relaxed state having a maximum diameter (Dmax); A self-expanding stent (1), wherein the AUC (area under the curve) under the RRP diameter curve between the minimum diameter (Dmin) and the maximum diameter (Dmax) of the stent is at least 4000 mmHg*mm, preferably 5000 mmHg*mm, preferably at least 7000 mmHg*mm, preferably at least in the distal end ring (8).

20. 1. A method for determining pressure equivalents in the treatment of abdominal aortic aneurysms (AAA), comprising: receiving intraluminal pressure data; receiving aortic diameter data by referring to the received pressure data; determining a transition pressure between the elastin phase and the collagen phase of a blood vessel based on the pressure data and the aortic diameter data; determining the length (L) of the stent framework; determining a nominal radial resistance pressure (RRP-N) based on the transition pressure; A method for determining pressure equivalent, comprising:

21. 21. A computer program comprising executable code which, when executed on a computer, causes the computer to carry out the method of claim 20.

22. 1. A method for treating abdominal aortic aneurysms (AAA), comprising: Providing a stent according to any one of claims 1 to 19; deploying a stent within the vessel adjacent to the aneurysm sac of the abdominal aortic aneurysm to increase the mechanical stiffness of the aortic segment; A method of treatment comprising:

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