Self-expandable stent

Abstract

The invention relates to a self-expandable stent (1) for implantation into 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 (6) end, 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) placed 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, and 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). According ro the invention, at least one of the distal end ring (8), the proximal end ring (10) or any of the optionally rings (14, 15) of the stent (1) exhibit at the nominal diameter (DN) a nominal radial resistive pressure (RRP-N) of ≥ 100 mmHg. The invention further relates to a method.

Description

[0001] Self-expandable stent

[0002] Description

[0003] The invention relates to a self-expandable stent for implantation into a blood vessel of a 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 a distal end ring and a proximal end ring with peaks and valleys, and optionally at least one ring placed between the distal end ring and the proximal end ring, the framework having a length from the distal end to the proximal end of at least 10 mm, and the stent having a compressed state with a minimum diameter, an expanded state with a nominal diameter, and a relaxed state with a maximum diameter. The invention further relates to a method for selecting a stent of the aforementioned type.

[0004] Stents of the aforementioned type are widely used to, for example, treat a stenosis of a blood vessel in the human body, repair a ruptured vessel or a vessel having an aneurysm, or to fix prosthetic devices, such as prosthetic valves within a body lumen of the circulation system. It is known to use stent-grafts which themselves can act as a prosthesis and / or exclude aneurysms from the circulation; it is also known to use uncovered or covered stents in order to repair a stenosis. Additionally, from US 10,779,964 B2 and the scientific publication “Segmental Aortic Stiffening Contributes to Experimental Abdominal Aortic Aneurysm Development” published in “Circulation” 2015; 131 :1783-1795 of the same inventors as named herein, it is known that segmental aortic stiffening as an early pathomechanism generates aortic wall stress and triggers aneurysmal growth - independently of the AAA geometry. The reason is that an aneurysmal portion of a vessel, as e.g. the aorta, has a higher wall stiffness than the other adjacent parts on the vessel (e.g. the AAA neck), which introduces wall stress in the transition between the stiff aneurysm and the healthy and more compliant portion of the vessel, which in turn leads to the growth of the aneurysm.

[0005] For treating an abdominal aortic aneurysm in US 10,779,964 B2, a method has been proposed, which comprises treating, in a targeted manner, an aortic segment axially adjacent the abdominal aortic aneurysm in the subject, whereby a mechanical stiffness of the aortic segment is increased. The idea of the invention disclosed in US 10,779,964 B2 is to increase the mechanical stiffness of an aortic segment adjacent to the abdominal aortic aneurysm in the subject. Increasing mechanical stiffness of the aortic segment in one embodiment may comprise deploying an intravascular stent that stiffens the aortic segment. In that the segment adjacent to the aortic aneurysm is stiffened, a stiffness gradient between the aneurysm itself (AAA sac) and the healthy portion of the vessel is reduced which in turn reduces growth of the aneurysm itself. According to this disclosure, the stent may be an expandable stent that is configured to expand into contact with the inner wall of the aorta, thereby providing support and mechanical stiffness to the length of the aorta with which the stent is in contact.

[0006] For self-expanding stents made of a shape memory alloy material, such as Nitinol, it is known that the force diameter profile describes a hysteresis. That is, the graph for the force exerted when expanding describes usually a lower curve than a graph drawn for force required to compress the stent again into a crimped state. The force exerted while expanding is usually called the “chronical outward force”, typically abbreviated as COF, and the force to overcome when compressing the stent is called “radial resistive force”, typically abbreviated with RRF. Usually, following balloon angioplasty of vascular stenosis, stents exhibiting a high RRF are used to prevent a recoil of the vessel wall and keep the vascular lumen open. On the other hand, stents may also be selected based on the COF exerted, as this force is indicative e.g. for the force necessary to anchor a device, such as a valve or prosthetic graft, to a vessel. Moreover, the COF is important when considering mechanical vessel injury and remodeling of a vessel. Remodeling is an effect, which occurs when permanently a force acts on the inner vessel wall to expand the vessel. The vessel then will grow or remodel to a larger diameter, allowing the stent to expand further. As this is usually unwanted due to the risk of loosening of the stent, attention is paid to the fact that a COF is selected, which is not so high as to cause remodeling of the vessel.

[0007] The object of the present invention is to provide a stent, which is better adapted to the physiology of the human body, which is improved in terms of usability, and which in particular is usable for the above-described procedure of treating an aneurysm, as disclosed in US 10,779,964 B2 and the publication “Segmental Aortic Stiffening Contributes to Experimental Abdominal Aortic Aneurysm Development”.

[0008] This object is solved in a first aspect of the invention described herein by a stent according to claim 1 . The stent according to the first aspect of the invention is formed of the aforementioned manner and in particular exhibits at the nominal diameter a nominal radial resistive pressure of > 100 mmHg, preferably > 100 mmHg. The nominal diameter is the diameter the vessel has or should have after the stent has been deployed. This means, typically the RRP is higher for diameters smaller than the nominal diameter as e.g. a delivery diameter, and is smaller for diameters above the nominal diameter, e.g. after the vessel has undergone a remodeling. The minimum diameter of the stent is the diameter in a crimped state of the stent, in particular the diameter in which the stent is delivered and / or received in a delivery system. The maximum diameter of the stent in the relaxed state is the diameter of the stent without any exterior restriction, i.e. the diameter the stent has when not implanted and relaxed.

[0009] Because the vessel wall in general has a certain flexibility (stiffness, compliance), the inventors have found that in particular the intraluminal pressure equivalent for a stent is much more important than a force to characterize and achieve optimal mechanical stent-vessel interaction. Vessel walls react to intraluminal pressure which also in healthy vessels provides a resistive force to ensure that the vessel does not collapse.

[0010] In particular, in the above-mentioned method of stiffening a vessel in order to treat an abdominal aortic aneurysm, the radial resistive pressure is the decisive measure and the traditionally used chronical outward force is of minor importance in designing a suitable stent. The inventors have found that in particular a radial resistive pressure equivalent to an intraluminal pressure of > 100, 110, 120, 130, more preferred 150 mmHg is particularly beneficial in order to stiffen the vessel wall sufficiently to treat aneurysmal growth. The ratio behind this particular value is that a typical aorta has a diameter-pressure-diagram with a degressive shape: in a lower pressure range, the vessel is much more elastic due to elastin recruitment in the vessel wall than in a higher pressure range, where collagen is mainly recruited and therefore the vessel wall is stiffer. Between those ranges, a transition from rather elastic to rather stiff can be defined which may typically be at about 90- 135 mmHg, depending on the specific individual. It has shown that a radial resistive pressure of > 100, preferably 150 mmHg is suitable for the most patients with a normal vessel. A nominal radial resistive pressure of > 100, preferably 150 mmHg is effective to ensure that the vessel does not collapse and is effective to ensure that the vessel is sufficiently stiffened to allow treatment of an abdominal aortic aneurysm.

[0011] In general, the radial resistive pressure (RRP) can be determined by determining the external (extravascular) pressure that needs to be exceeded in order to compress the stented segment. Accordingly, the chronic outward pressure (COP) can be determined by determining the internal (intravascular) pressure that needs to be exceeded in order to expand the vessel.

[0012] The nominal radial resistive 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 resistive force (RRF-N) at this nominal diameter by means of the formula

[0013] RRP-N = (RRF-N) x k / (DN x L x rt ), wherein k is a correcting factor to transform units from N / mm2into mmHg. For calculations, the general transformation 1 mmHg = 133,322 Pa is used in this disclosure.

[0014] Each of the ring segments may exhibit the above nominal radial resistive pressure, only one ring segment, two or more of the ring segments, or the complete stents may exhibit the above nominal radial resistive pressure. That means, the stent may have different nominal radial resistive pressures along its length.

[0015] The exact structure of the stent, i.e. how the distal and proximal ring segment and the optional one or more ring segments placed between the distal end and the proximal end ring segments can be chosen according to the specific design of cells, struts, peaks and valleys and the like. It has shown that for example for the treatment of an abdominal aortic aneurysm, three segments in total are sufficient with an overall length of the stent of 30 mm to 50 mm, however other sizes and lengths are also envisaged. A specific example of a suitable stent is disclosed in WO 2022 / 253522 A1 of the same applicant. The disclosure of this application is incorporated herein by means of reference. Another specific example will be discussed below. Preferably, the stent is made of a shape memory alloy, e.g. Nitinol material, and preferably it is produced from a tube material, preferably from a single tube material, has a constant wall thickness, i.e. radial thickness, and / or is uncovered. In a further aspect of the invention disclosed herein, the inventive stent may only have one single ring. Such stent consequently does also not have a distal or proximal ring, but only said one single ring which in this case is not referred to as distal or proximal. In the following the term “ring” described a structure, forming portion of a stent or the complete stent, which is comprised of struts connected to each other and preferably cut from a tube as a raw material, so that the structure is self supporting and integral. The single rings may be referred to in the following as “proximal end ring”, “distal end ring” or “intermediate ring”, when their position is specified, but may also be referred to as “first ring”, “second ring”, and so forth, when their position is not specified. A “first ring” may thus be as single ring of the stent, a proximal or distal end ring or any intermediate ring.

[0016] Even though according to claim 1 the stent is adapted for implantation into the abdominal aorta of the human body for treating an abdominal aortic aneurysm, in other embodiments the stent may more generally be adapted for implantation into a blood vessel of the human body. Thus, in general terms, a stent disclosed herein may be for implantation into an abdominal aorta of the human body for treating an abdominal aortic aneurysm. A stent disclosed herein may have an expandable framework and may have at least a distal end ring and may have at least a proximal stent ring. The distal and I or proximal end rings may have peaks and may have valleys. In one aspect discussed herein, the distal end ring, the proximal end ring or any of the optionally rings of the stent may exhibit at the nominal diameter (DN) a nominal radial resistive pressure (RRP-N) of > 100 mmHg. In other embodiments this value might be higher and lower. In the preferred embodiments described in the following, reference is made to the more general aspects; they are not limited to the embodiment according to claim 1 , only.

[0017] Preferably, the stent is made from shape-memory alloy, only, without any therapeutics containing covering or other additional elements. The stent is non-biodegradable. The stent has a non-braided structure. The stent is uncovered.

[0018] The terms “proximal” and “distal” are defined for the stent according to its intended placement direction and relative to the heart of the subject having the stent implanted. In a stent with two or more rings, such rings are typically connected to each other by connectors, though they may also be attached to each other directly. Connectors may comprise a number of connector wires also preferably cut from the raw material tube so that they are integrally formed with the respective rings. The connectors or connector wires are typically only connected to the adjacent rings but not interconnected with each other. A connector element placed between two adjacent rings segments thus typically is not self-supporting and not integrally formed as one single “connector ring”.

[0019] In a preferred embodiment, the stent or at least one of the ring segments exhibits at the nominal diameter a nominal radial resistive pressure (RRP-N) of > 250 mmHg. Other values between 150 mmHg and 250 mmHg and beyond are also envisaged 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, 270 mmHg are also preferred. Preferably, the nominal radial resistive pressure is lower than 2000 mmHg, 1500 mmHg, 1000 mmHg, 750 mmHg, 500 mmHg, 350 mmHg, or 300 mmHg.

[0020] It is further preferred that the stent or at least one of the ring segments exhibits at the nominal diameter a chronic outward pressure (COP-N) of > 50 mmHg. Preferably, the stent exhibits at the nominal diameter a nominal chronic outward pressure (COP-N) of > 100 mmHg, further preferred > 150 mmHg. Depending on the envisaged usage of the stent, in particular on the envisaged treatment, a rather low chronic outward pressure combined with a high radial resistive pressure is beneficial. This is in particular true for the application of the abdominal aortic aneurysm (AAA) discussed above.

[0021] For calculation of the nominal chronic outward pressure the same formula as above applies with the difference that the chronic outward force (COF) is used instead of the radial resistive force (RRF).

[0022] When the stent is used as a scaffold for a valve or other prosthetic implant, an increased chronic outward pressure is beneficial to allow a sufficient device anchoring with a tight structural bond between the stent and the vessel wall. In particular, a chronic outward pressure (COP-N) of 150 mmHg or above is desirable. In any case, it is beneficial if the nominal chronic outward pressure (COP-N) is restricted by a pressure of 250 mmHg, further preferred 240 mmHg, 230 mmHg, 220 mmHg, 200 mmHg.

[0023] For a particularly preferred stent, an AUC (area under the curve) value for a RRP- diameter curve from do (unexpanded stent diameter / max crimped diameter) and dmax (maximally expanded / relaxed stent diameter) of the stent or a distal end ring is at least 4000 mmHg*mm, preferably at least 5000 mmHg*mm, preferably at least 7000 mmHg*mm. Preferably, the AUC value is below 20.000 mmHg*mm, preferably 15.000 mmHg*mm, even more preferred 13.500 mmHg*mm and below. If present one or more further stent rings may have the same, similar or lower values. The stent according to the invention is comparatively large in diameter because it is in particular intended for the abdominal aorta, and comparatively strong because it is in particular intended to widen the abdominal aorta and stiffen it. The parameter AUC thus is a parameter beneficially describing the interplay of both relevant aspects.

[0024] This and optionally the following embodiments are also subject to one or multiple aspects of the invention and may be claimed independently of other preferred features described above. As such, the problem stated in the introductory portion also is solved by selfexpandable stent for implantation into 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 a distal end ring and a proximal end ring with peaks and valleys, and optionally at least one ring placed between the distal end ring and the proximal end ring, the framework having a length LF from the distal end to the proximal end of at least 10 mm, and 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), wherein an AUC (area under the curve) under the RRP-diameter curve between the mini-mum diameter (Dmin) and the maximum diameter (Dmax) of the stent, preferably at least the distal end ring (8) is at least 4000 mmHg*mm, preferably 5000 mmHg*mm, preferably at least 7000 mmHg*mm.

[0025] For a particularly preferred stent a pressure-diameter product (PDP), calculated by PDP = (nominal radial resistive pressure (RRP-N))*(nominal diameter) of the distal end ring is at least 1800 mmHg*mm, preferably at least 3000 mmHg*mm. If present, the one or more further stent rings may have the same, similar or lower values. The stent according to the invention is comparatively large in diameter because it is in particular intended for the abdominal aorta, and comparatively strong because it is in particular intended to widen the abdominal aorta and stiffen it. The parameter PDP thus is a parameter beneficially describing the interplay of both relevant aspects.

[0026] Further, in case the stent has two or more stent rings, out of which one forms the distal end ring and one forms the proximal end ring, preferably the following equation is met: AUCdist / AUCprox > 1 , wherein AUCdist is the above AUC parameter calculated for the distal end ring, and AUCprox is the above AUC parameter calculated for the proximal end ring. Preferably, the parameter AUCdist / AUCprox is within a range from 1 .5 to 4, more preferably 2 - 4, even more preferred 3 - 4.

[0027] A further preferred parameter for describing the inventive stent is the ratio of COP-dist I COP-prox, in case the stent has two or more stent rings, out of which one forms the distal end ring and one forms the proximal end ring. COP-dist is the (nominal) COP value for the distal end ring, and COP-prox is the (nominal) COP value for the proximal end ring of the stent. This parameter may be different for a stent with an overall higher RRP or RRP- N value and a stent with an overall rather lower RRP or RRP-N value. But preferably irrespective of the specific RRP value for a stent according to the present disclosure a ratio COP-dist I COP-prox preferable is in a range of 2 to 4, and can be for stents with overall lower RRP in a range from 2 to 3.

[0028] In a preferred embodiment, the stent has an overall axial length L(tot) and if present a distal end ring has an axial length of L(dist) and a proximal end ring has an axial length of L(prox). Optionally one or more intermediate stent rings may have an axial length of L(int- n), wherein n=1 , 2, etc. A ratio of L(dist) to L(tot) is preferably in the range of 0.3 to 1.0, more preferred 0.3 to 0.9, 0.4 to 0.8, 0.4 to 0.7, 0.4 to 0.6. A ratio of L(prox) to L(tot) preferably is in the range of 0.1 to 0.4, preferably 0.1 to 0.3, even more preferred 0.1 to 0.2. It is to be understood that two or more stent rings (if present) are axially connected to each other by means of connectors. Such connectors add to the overall axial length but are not taken into account when measuring the axial length of a stent ring. Moreover, the stent may have holders for radiopaque markers which may extend beyond axial ends of the end rings. Also such holders or other add-on elements are not taken into account when measuring the axial length of either the stent in total or a single stent ring. Moreover, measurement is made in the maximally crimped state (crimped to cutting tube diameter), because usually the stent will slightly shorten when expanding.

[0029] A further preferred parameter for describing the innovative stent disclosed herein is the difference between the radial resistive pressure (RRP) und chronic outward pressure (COP) at a given diameter. Preferably, at the nominal diameter a difference between the nominal radial resistive pressure (RRP-N) und nominal chronic outward pressure (COP- N) is as least 50 mmHg, preferably 75 mmHg. Preferably, this is true not only at the nominal diameter but also over a range of 22 mm to 25 mm, preferably 20 mm to 28 mm.

[0030] In a preferred embodiment, the framework has a thickness measured in radial direction in a range of 0.2 mm to 1 .0 mm, in particular 0.2 mm to 0.7 mm, further preferred 0.2 mm to 0.6 mm, further preferred 0.3 mm to 0.6 mm, further preferred 0.4 mm to 0.6 mm, further preferred 0.3 mm to 0.5 mm. Furthermore, it is preferred that a first stent ring of the stent comprises two or more struts which satisfy the relationship length of the strut (L) / width of the strut (B) < 20, 19, 18, 17, 16, 15, 14, 13, particularly preferred 12. Preferably, the struts define together with respective crests or peaks cells which may have a diamond shape, may be open or closed cells, may have a regular or irregular shape, and may be defined by identical or different struts.

[0031] In a further preferred embodiment, a first ring (preferably the distal end ring) comprises two or more struts, wherein the first ring has a radial stiffness in a range from 0.08 N / mm2to 0.12 N / m2at the nominal diameter, measures in force (in N) per length (in mm) per radial deformation (in mm). Preferably, a second ring segment (preferably the proximal end ring) comprises two or more struts, wherein the second ring has a radial stiffness in a range from 0.01 N / mm2to 0.03 N / mm2, preferably 0.02 N / mm2to 0.03 N / mm2. Furthermore, preferably a third ring segment provided between the first and the second ring segment comprises two or more struts, wherein the third ring segment has a radial stiffness in a range from 0.04 N / mm2to 0.06 N / mm2.

[0032] Preferably, a chronic outward pressure at the nominal diameter (COP-N) is non-uniform along the length of the framework. Preferably, the chronic outward pressure decreases in a direction 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. Proximal and distal in this regard is preferably defined relative to the heart of the human body. Elements, which are in a deployed state further away from the heart are defined to be distal, while elements closer to the heart are defined to be proximal. There may be particular embodiments in which the definition of proximal and distal is concurrent with a usual definition of proximal and distal with respect to a delivery system for the stent, but this is not necessarily the case. Alternatively, the chronic outward pressure decreases in a direction from the proximal end to the distal end.

[0033] The radial resistive pressure at the nominal diameter (RRP-N) may be constant along the length of the framework, or also be non-uniform. Preferably, also the radial resistive pressure at the nominal diameter decreases from a distal to a proximal direction, i.e. is higher at the distal end of the framework than at the proximal end of the framework. Alternatively, the radial resistive pressure decreases in a direction from the proximal end to the distal end.

[0034] Both, the chronic outward pressure and the radial resistive pressure at the nominal diameter may decrease in a stepped manner, i.e. from ring segment to ring segment, while it is also contemplated that two or more of neighboring ring segments may exert the same chronic outward pressure and / or radial resistive pressure. It may also be the case that one or more of intermediate ring segments between the proximal and the distal ring segments at the nominal diameter exert a higher or lower chronic outward pressure or radial resistive pressure than the distal ring segment. In particular, it may be provided that even though the overall radial resistive pressure or chronic outward pressure decreases from distal to proximal or vice versa that single ring segments in between may again increase the pressure. Also, a gradient of the chronic outward pressure from the distal to the proximal end of the stent may be different from the gradient of the radial resistive pressure from the distal to the proximal end of the stent. For example, the gradient of the redial resistive pressure is higher than the gradient of the chronic outward pressure, for example by 10%, 20%, 30% or more.

[0035] In a preferred embodiment, the ratio between a chronic outward pressure at the nominal diameter of the distal end ring and a chronic outward pressure at the nominal diameter of the proximal end ring is in a range of 10:1 to 1 .5:1 , preferably 8:1 to 1 .5:1 , preferably 6:1 to 2:1 . This parameter may be different for a stent with an overall higher RRP or RRP-N value and a stent with an overall rather lower RRP or RRP-N value. But preferably irrespective of the specific RRP value for a stent according to the present disclosure a ratio COP-dist I COP-prox preferable is in a range of 4:1 to 2:1 , and can be for stents with overall lower RRP in a range from 3:1 to 2:1 .

[0036] The same may be applied to the radial resistive pressure, where also a ratio between a radial resistive pressure at the nominal diameter of the distal end ring and a radial resistive pressure at the nominal diameter of the proximal end ring is in a 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 in a range of 4:1 to 2:1 , even more preferred 3:1 to 2:1.

[0037] Preferably, the peaks and valleys of each ring segment are formed by crests connected by struts, wherein the struts are substantially linear. In other embodiments, the struts may also be curved, bell-shaped, S-shaped or meander-shaped, or the struts of a ring segment are meander-shaped without crests. Preferably, at least two adjacent ring segments are positioned in an out-of-phase relationship so that crests forming valleys of one ring are connected to crests forming peaks of the adjacent ring. Preferably, at least two adjacent rings are positioned in an in-phase relationship and connected to each other by at least two non-linear links. The number of links between rings of the stent may be the same between all the ring segments, or may vary between ring segments. Preferably, the stent has open and closed cells, or only closed cells. Closed cells provide the benefit that the stent may be retracted into a delivery system easier in case this is necessary.

[0038] In a preferred embodiment or aspect of the invention, the stent comprises a middle stent ring placed between the distal end ring and the proximal end ring. The stent may comprise more than one middle stent ring, for example two, three, four or more middle stents rings, which may be referred to as “first middle stent ring”, “second middle stent ring” etc. In a case where only one middle stent ring is provided, the middle stent ring is connected via first connectors to the distal end ring and via second connectors to the proximal end ring. The connectors typically do not develop a radial force or pressure, independently, but rather the function of the connectors is to maintain integrity of the stent and the desired spacing of the single stent rings. It should however be understood that dependent on the specific construction of the connectors, they may exert a force or pressure to the inner vessel wall, as they are carried and maintained on close relationship to the vessel wall by means of the stent rings, which generate the radial force.

[0039] Preferably, the middle stent ring comprises at least one third circumferential ring segment and at least one fourth circumferential ring segment, which are structurally different from each other. All the above features disclosed with respect to the first and second circumferential ring segments may also apply to the third and fourth circumferential ring segments. Hereby, only a single, some or all of the above features may apply. In such a configuration, also the middle stent ring may show different expansion characteristics dependent on the diameter as described above.

[0040] Preferably, a chronic outward force at the nominal diameter (COF-N) or chronic outward pressure at the nominal diameter (COP-N) of the middle stent ring is lower than the chronic outward force at the nominal diameter (COF-N) and chronic outward pressure at the nominal diameter (COP-N), respectively of the distal end ring. Preferably, a chronic outward force at the nominal diameter (COF-N) or chronic outward pressure at the nominal diameter (COP-N) of the middle stent ring is higher than or identical to the chronic outward force at the nominal diameter (COF-N) and chronic outward pressure at the nominal diameter (COP-N), respectively of the proximal end ring. The above configuration using the third and fourth circumferential ring segments in particular is beneficial, when the COF-N and COP-N of the middle stent ring is higher than that of the proximal end ring, so that it is beneficial that also the middle stent ring provides the “expansion reserve” as described above.

[0041] In a preferred embodiment, the third circumferential ring segment comprises struts with a third circumferential width W3 and the fourth circumferential ring segment comprises struts with a fourth circumferential width W4, wherein the third circumferential width W3 is 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.

[0042] If a middle stent ring is present, a ratio in a chronic outward pressure (COP-N) at the nominal diameter (DN) of the middle stent ring to a chronic outward pressure at the nominal diameter (DN) of the proximal end ring is preferably in a range of 1.0 to 8.0. While the ratio in a chronic outward pressure (COP-N) at the nominal diameter (DN) of the distal end ring to a chronic outward pressure at the nominal diameter (DN) of the proximal end ring is preferably in a range of 10.0 to 1.5, as stated above, the ratio of the middle stent ring to the proximal stent ring is in a lower range, and might even be identical to the proximal end ring. Preferably, the ratio of (COP-N-mid) I (COP-N-prox) is approximately 35% or less of the ratio (COP-N-dist) I (COP-N-prox); wherein “COP-N-dist” is the chronic outward pressure (COP-N) at the nominal diameter (DN) of the distal end ring; “COP-N-mid” is the chronic outward pressure (COP-N) at the nominal diameter (DN) of the middle stent ring; “COP-N-prox” is the chronic outward pressure (COP-N) at the nominal diameter (DN) of the proximal end ring. Preferably, the ratio of (COP-N-mid) I (COP-N-prox) is approximately 30%, 25%, 20%, 15% or less of the ratio (COP-N-dist) I (COP-N-prox).

[0043] The same ratios may also apply to the respective radial resistive pressures at the nominal diameter of the distal end ring, the middle ring and the proximal end ring.

[0044] Preferably, the third circumferential ring segment comprises struts with a third length LS3 and the fourth circumferential ring segment comprises struts with a fourth length LS4, wherein the third length LS3 is greater than the fourth length LS4. In a preferred embodiment or a further aspect of the invention, the above described first connectors include straight connectors. Straight connectors are beneficial to provide tubular shape stability and prevent extreme radial kinking of the distal ring segment during stent release. In an embodiment, the first connectors exclusively include straight connectors.

[0045] Preferably, the straight connectors connect the first circumferential ring segment of the distal end ring to the third circumferential ring segment of the middle stent ring. Thus, the straight connectors connect the circumferential segments of the distal end ring and the middle stent ring which substantially develop the radial force. This ensures integrity of the stent and also may provide additional support to the vessel wall via the straight connectors.

[0046] Preferably, the first connectors include bow-shaped connectors. In an embodiment, the first connectors exclusively include bow-shaped connectors. In particular, the bow-shaped connectors resemble a W-shape with two show end portions and an elongated middle portion of the W. Preferably, the bow-shaped connectors connect the second circumferential ring segment of the distal end ring to the fourth circumferential ring segment of the middle stent ring. In case the first and third circumferential ring segments are connected via straight connectors, the bow-shaped connectors connecting the second and fourth circumferential ring segments may account for a different shortening when expanding of the different circumferential segments.

[0047] In a preferred embodiment or another aspect of the invention, each proximally facing crest of the distal end ring is attached to one connector of the first connectors. Preferably, each proximally facing crest of the middle stent ring is attached to one connector of the second connectors. The lesser of the proximally facing crests of the rings are attached to one connector, the easier it is to pull the stent back into a delivery system while implanting. The placement of the inventive stent described herein is important and there might be situations where the surgeon aims at pulling the stent back into the delivery system for compressing it at least slightly to reposition it. Because the inventive stent described herein is relatively string, i.e. exerts a relatively high COP, it might by difficult to pull the stent back once it has been delivered to a certain extend. The design of the crests described herein supports pulling the stent back into the delivery system, if needed.

[0048] Preferably, the first connectors are connected to crests and valleys of the middle stent ring, in particular crests of the third circumferential ring segment and valleys of the fourth circumferential ring segment. This arrangement may be beneficial in order to account for the different axial shortening of the different circumferential ring segments.

[0049] In a further preferred embodiment, herein the second connectors include bow-shaped connectors. Preferably, the second connectors exclusively include bow-shaped connectors to provide axial flexibility and allow foreshortening of the connected ring segments.

[0050] In a further aspect of the invention, the problem stated in the introductory portion is solved by a method for determining a pressure for treatment of an abdominal aortic aneurysm (AAA). The method comprises the steps: receiving pressure data of an intraluminal pressure; receiving aortic diameter data in reference to the above received pressure date; determining based on said pressure data and said aortic diameter data a transition pressure of the vessel between elastin and collagen phase; determining a length LF of a framework of a stent and preferably determining at least a length L1 of a first ring segment; and determining a nominal radial resistive pressure based on said transition pressure. Preferably, the determination of said nominal radial resistive pressure is also based on said aortic diameter data, said length LF of the framework, and / or said length L1 of the first ring segment. The first ring segment may be the proximal or distal ring segment or any ring segment between them.

[0051] Preferably, a nominal radial resistive pressure is chosen to be 10%, 15%, 20%, 25%, 30% higher than said transitional pressure. The pressure data of an intraluminal pressure and / or aortic diameter data of a luminal diameter may be provided by a computer device, such as a pressure transducer or an ultrasound device, may be provided by a storage means, a physical storage means or a cloud service or the like. Preferably, the pressure data and aortic diameter data includes pressure and aortic diameter data of the target vessel, preferably the abdominal aorta of a patient, and preferably includes pressure and aortic diameter data obtained under stress of a patient, either stress by means of physical stress or stress by means of a medication.

[0052] The method may further include determining a stent placement position for the stent, in particular based on the image data received which includes a representation of the abdominal aorta with the abdominal aortic aneurysm. A stent placement position may be defined to be proximal adjacent to the aneurysmal sac, in particular the distal end of the framework should be placed as close as possible to the aneurysmal sac. Further, for defining a stent placement position, reference is made to application EP 22188215.1 of the same applicant which is incorporated herein by means of reference. Moreover, a stent placement position may also be defined in accordance with US 10,779,964 B2, which is also incorporated herein by means of reference.

[0053] The method further preferably includes steps of determining a total number of ring segments of the stent, a chronic outward pressure of the stent, chronic outward pressure and radial resistive pressure of single ring segments of the stent, and / or number of ring segments.

[0054] In a further aspect, the 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.

[0055] In a further aspect, the invention solves the above problem by a method for treating an abdominal aortic aneurysm comprising the steps: providing a stent according to any of the above-mentioned described preferred embodiments of a stent according to the first aspect of the invention, and deploying the stent in the vessel adjacent to an aneurysmal sac of the abdominal aortic aneurysm in order to increase a mechanical stiffness of the aortic segment.

[0056] For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawings. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and as claimed herein after. Further, the features described in the description, the drawings and the claims disclosing the invention may be essential for the invention considered alone or in combination. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording “comprising” does not exclude other elements or steps. The word “a” or “an” does not exclude the plurality. The wording “a number of’ items comprising also the number 1 , i.e. a single item, and further numbers like 2, 3, 4 and so forth. In the accompanying drawings:

[0057] Fig. 1 shows a general pressure-diameter diagram showing elasticity of the aorta; Fig. 2 shows a diagram showing the elasticity of the aorta as well as a pressure diameter diagram of a stent (segment) according to the invention;

[0058] Fig. 3 shows another pressure diameter diagram of a stent (segment) according to the invention;

[0059] Fig. 4 shows a schematic view of a stent according to the invention;

[0060] Fig. 5a-c show a ring segment of a stent according to the invention in three different expansion states;

[0061] Fig. 6 shows another ring segment of a stent according to the invention in the crimped state;

[0062] Fig. 7 shows another ring segment of a stent according to the invention in the crimped state;

[0063] Fig. 8 shows a portion of the human aorta with an AAA and a stent;

[0064] Fig. 9 shows a first embodiment of a stent suitable in the invention;

[0065] Fig. 10 shows a second embodiment of a stent suitable in the invention;

[0066] Fig. 11 shows a schematic pressure diameter diagram of the stent according to

[0067] Figs. 9 and 10 with one graph per stent ring;

[0068] Fig. 12 a full cut side view of a rendering of a fully expanded stent; and

[0069] Fig. 13 a perspective elevated view of the fully expanded stent rendering.

[0070] Fig. 1 shows a general diagram of the aortic diameter over the aortic pressure. As one can see, in a first portion, the curve is relatively steep showing that the diameter of the aorta increases rapidly when the pressure increases. In a second portion for higher pressures, the diameter does not change as dramatically as it does for lower pressures and thus the vessel itself reacts more stiffly. This is due to the fact that in the first portion mainly elastin is active, while in the second portion for higher pressures collagen is active and restricts the diameter of the vessel. Between those portions a transition is indicated, which for healthy average aorta of individuals is about 120 mmHg. The inventors of this application have found that using this mechanical behavior of the aorta to stiffen the vessel may be used to modulate the growth of an abdominal aortic aneurysm as disclosed in the scientific publication “Segmental Aortic Stiffening Contributes to Experimental Abdominal Aortic Aneurysm Development” published in “Circulation” 2015; 131 :1783-1795.

[0071] The present invention is based on the idea that for treating abdominal aortic aneurysms (AAA), a stent is beneficial, which provides a radial resistive pressure RRP-N at the nominal diameter of at least 100 mmHg, preferably 150 mmHg or more. A general schematic view illustrating this innovative idea is shown in Fig. 2. In this diagram, the ordinate and the abscissa are interchanged with respect to Fig. 1 so that the abscissa shows a diameter while the ordinate shows a pressure. The bold dashed line shows the vessel which is thus identical to the graph shown in Fig. 1 . The upper narrow dashed line shows the radial resistive pressure of the stent and the lower dot-and-dash line shows the chronic outward pressure of the stent, both with respect to the stent diameter. As generally known with respect to forces exerted by the stent, the so called chronic outward force or radial outward force (COF) dramatically decreases when the stent expands and reaches a plateau approximately where the nominal diameter DN of the stent is defined. The same is true for the chronic outward pressure. This plateau usually is used as the nominal diameter so that a rather constant chronic outward force or pressure is provided for small diameter deviations. The radial resistive force or pressure is the force or pressure of the stent which has to be overcome to compress the stent again to the crimped state. Thus, the chronic outward force (COF) or chronic outward pressure (COP) graph has to be drawn from the left to the right with respect to Fig. 2 and the radial resistive force (RRF) or radial resistive pressure (RRP) from the right to the left. As shown in Fig. 2, there is a hysteresis between the radial resistive pressure RRP and chronic outward pressure COP which can be quite large. In the particular embodiment shown in Fig. 2, the radial resistive pressure at the nominal diameter RRF-N is slightly higher than 150 mmHg and thus in line with the invention. The chronic outward pressure COP-N at the nominal diameter DN is in the range of 100 mmHg or even lower. When comparing those values to the graph showing the reaction of the vessel (Fig. 1), one can see that the chronic outward pressure at the nominal diameter is in the first portion of the graph showing the vessel, thus the portion where elastin is recruited, and the radial resistive pressure at the nominal diameter RRF-N is in the portion of the vessel graph showing the collagen recruitment. Thus, the radial resistive pressure provides a stiffening function for the vessel when the vessel diameter decreases (recoiling of the vessel). This has been shown to be very beneficial for treating an abdominal aortic aneurysm as described in the above scientific article.

[0072] Fig. 3 now shows a specific measured diagram of a stent or distal stent ring according to the invention. Again, the graphs for the chronic outward pressure COP and the radial resistive pressure RRP are shown. The nominal diameter DN in a first use case is approximately DN-1 = 13 to 16, but could in a second use case preferably also be DN-2 = 18 to 29mm. One can see that for the first use case the chronic outward pressure at the nominal diameter COP-N is 150 mmHg, while the radial resistive pressure in this first use case at the nominal diameter RRF-N is approximately 280 mmHg. Such stent is suitable not only to resist any contraction I recoiling of the vessel in the elastin recruitment phase of the vessel, but also to firmly anchor a valve or prosthetic graft in the stiffened vessel wall. In particular, the COP-N of 150 mmHg ensures that the vessel wall is actively expanded into the “stiff’ phase of its pressure-diameter curve to form a solid abutment optimal for stent fixation. In the second use case at nominal diameter DN-2 (= 10 to 29 mm), the chronic outward pressure at the nominal diameter COP-N is in this example <100 mmHg, while the radial resistive pressure in this second use case at the nominal diameter RRF-N is approximately 150 mmHg. Such stent or stent ring is suitable to resist any contraction I recoiling of the vessel in the elastin recruitment phase of the vessel, thereby effectively stiffening the vessel wall.

[0073] Figs. 4 to 7 show three different embodiments of a stent or ring segment of the stent, respectively, which will now be described.

[0074] In Fig. 4, a schematic view of a stent 1 is shown. The stent 1 comprises a framework 2 with 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 interior volume cannot be seen in Fig. 4, however, it should be understood that Fig. 4 shows a 2D representation of the stent 1 , unfolded, and the ones skilled in the art will understand that the framework 2 shown in Fig. 4 should have a tubular shape. The framework 2 has at least a distal end ring 8 and a proximal end ring 10, also called ring segments 8, 10. Each ring segment 8, 10 has peaks 12 and valleys 13. In the embodiment shown in Fig. 4, two additional intermediate rings 14, 15 are arranged between the distal and the proximal end rings 8, 10. It should be understood that also frameworks with only two ring segments, or even only one ring segment, three ring segments, five ring segments or more are envisaged and disclosed herein, too. Even though the ring segments 8, 10, 14, 15 in Fig. 4 are shown to be identical, they can be different. The single ring segments 8, 10, 14, 15 are connected to each other by non-linear links 16 (only one shown with reference sign). In the embodiment shown in Fig. 4, the non-linear links 16 attach the single ring segments 8, 10, 14, 15 in an out-of-phase relationship with each other, that is, the links 16 connect peaks 12 of adjacent ring segments 8, 10, 14, 15 to each other. It should be understood that the framework 2 can also be in an out-of-phase configuration, in which links 16 would connect peaks of one ring segment with valleys of an adjacent ring segment.

[0075] Each ring segment 8, 10, 14, 15 is comprised of struts 20 connected by crests 22. In the embodiment shown in Fig. 4, the struts 20 and crests 22 of one ring segment 8, 10, 14, 15 are arranged to form diamond-shaped cells. All cells of the framework 2 shown in Fig. 4 are closed cells, even though also ring segments with open cells or a different cell design are envisaged. Crests 22 may form peaks 12 or valleys 13, dependent on their position and attachment of the struts 20.

[0076] The stent 1 shown in Fig. 4 has an overall length LF, and the single rings from the left to the right in Fig. 4 have a first length L1 , a second length L2, a third length L3, and a fourth length L4. The stent 1 may have a nominal radial resistive pressure RRP-N of 150 mmHg or more and a nominal chronic outward pressure of 100 mmHg. While all of the rings 8, 10, 14, 15 may provide such pressures and pressures which are identical to each other so that the stent 1 in total may exert the stated pressure over the length FL, it is also preferred that only one or some of the rings 8, 10, 14, 15 exert the above pressure over their respective lengths L1 to L4 in this instance. While the overall length of the framework LF preferably is at least 10 mm, but also could be shorter as e.g. 8 mm, the length L1 to L4 of a first ring segment is at least 4 mm, but could be at least 5 mm, 5.5 mm or 6 mm.

[0077] Figs. 5a, 5b, 5c, 6 and 7 each show only the distal end ring 8 of the framework 2, however, it should be understood that via the links 16 additional ring segments as described with respect to Fig. 4 may be added.

[0078] Figs. 5a to 5c illustrate an embodiment of the stent usable in the invention. All three figures show the circumference of the ring segment 8 in an unwound view. However, it should be understood that the stent 1 actually is annular and thus the end shown at the top of each of Figs. 5a to 5c is connected to the end shown in the bottom of each of the drawings. The illustrations can also be understood as a cutting pattern for a laser cutting process. Fig. 5a shows the ring segment 8 in the crimped state with minimum diameter Dmin, Fig. 5b shows the ring segment 8 at a nominal diameter DN and Fig. 5c at a maximum diameter Dmax, in a relaxed and fully expanded state.

[0079] Different to the embodiment shown in Fig. 4, the ring segment 8 according to Figs. 5a to 5c has three first circumferential segments 120 and three second circumferential segments 122 which have differently shaped struts. As best can be seen in Fig. 5a and 5c, the first circumferential segments 120 are comprised of three cells, including in total 12 struts, in particular first struts 104, while the second circumferential segments 122 comprise one second cell 242 defined by four second struts 106. The first struts 104 are formed to provide the expansion force, i.e. radial outward force and radial resistive force for an expansion to the nominal diameter DN and the second circumferential segments 122 with the second struts 106 are not as strong as the first circumferential segments 120 and allow a further expansion of the stent 1 beyond the nominal diameter DN to a maximal diameter Dmax. This particular feature is used to provide an expansion reserve for the stent 1 which may take into account further remodeling of the vessel once the stent 1 has been implanted. For details regarding the structure of this particular stent to / two different circumferential segments, reference is made to the application No. PCT / EP 2022 / 062278 and EP 22188715.1 of the same applicant as the present application. Both applications are incorporated herein by means of reference. Due to this specific design with the first and second circumferential segments 120, 122, the graphs for the chronic outward force COF and the radial resistive force RRF as shown in Fig. 2 comprise the flattened end portion beyond the nominal diameter DN.

[0080] Stent 1 and ring segment 8 as shown in Figs. 5a to 5c may be formed from a tubeshaped Nitinol material or other shape memory alloy, in particular using laser cutting. A radial thickness of the framework 2 may be in the range of 0.2 to 1 .0 mm, in particular, 0.3 to 0.5 mm. The first struts 104 in this embodiment 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. Since in particular the first circumferential segments 120 are decisive for the herein discussed chronic outward pressure COP and redial resistive pressure RRP or chronic outward force COF and the radial resistive force RRF, only the first struts 104 are discussed in the following.

[0081] Fig. 6 shows again the distal ring segment 8, only in a crimped state. The length LS1 of the first struts 104 is approximately in a range of 5 to 7 mm, in the shown embodiment in particular in the range of 6 to 7 mm, and has a width of approximately 0.35 to 0.4 mm. A width in the range of the crest 22 may be slightly increased and may be in the range of 0.4 to 0.5 mm, in particular 0.45 mm. This can help to provide a relatively high radial resistive pressure, in this embodiment shown in Fig. 6, the radial resistive pressure of the ring segment shown is 150 mmHg and thus the distal ring segment shown in Fig. 6 belongs to a stent, which may exhibit the diagram shown in Fig. 2.

[0082] In a further embodiment shown in Fig. 7, again a distal ring segment 8 in the crimped state is shown, again with three first circumferential segments 120 and three second circumferential segments 122 as described with respect to Figs. 5a to 5c. Here, instead of three cells per first circumferential segment 120, four cells are formed, which can be seen by counting the crests 22 per first circumferential segment 120. Compared to Fig. 6, the length LS1 is slightly shortened while the width W1 of the first struts 104 is slightly increased. By this, also the chronic outward pressure COP and radial resistive pressure RRP can be increased. The embodiment shown in Fig. 7 in particular exhibits a chronic outward pressure COP of 150 mmHg, while the radial resistive pressure is almost 300 mmHg. Thus, the distal ring segment 8 shown in Fig. 7 belongs to a stent which can exhibit the graph shown in Fig. 3.

[0083] In particular, the length LS1 of the embodiment shown in Fig. 7 is in the range of 6 mm, while the width W1 is in the range of 0.4 to 0.5 mm, in particular 0.48 mm. Fig. 8 now illustrates a vascular structure 303, including an abdominal aorta 324 with an abdominal aortic aneurysm (AAA) 310. The abdominal aortic aneurysm 310 includes an aneurysm sac 327 and an aneurysm neck 328. Above the aneurysm neck 328, a lower renal artery (LRA) 330 and a higher renal artery (HRA) 334 are shown. Moreover, also a superior mesenteric artery 338 is shown in Fig. 8. In accordance with the above cited US 10,779,964 B2, a stent 1 according to the present invention is placed in the aneurysm neck 328 with its distal end 4 placed close to the distal end 329 of the aneurysm neck 328, thus at the proximal end of the aneurysm sac 327 and thus directly adjacent the aneurysm sac 327. In an upward and thus proximal direction, the stent 1 protrudes over the lower and higher renal arteries (LRA, HRA), but not above the superior mesenteric artery 338. The stent 1 acts to stiffen the aneurysm neck 328 into the collagen portion (see Figs. 1 and 2) by providing a nominal radial resistive pressure of at least 150 mmHg.

[0084] Fig. 9 shows a first embodiment of a stent 1 according to the invention and Fig. 10 shows a second embodiment of a stent 1 according to the invention. The stent 1 comprises an expandable framework 2 with 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 interior volume cannot be seen in Fig. 9, 10, however, it should be understood that Fig. 9, 10 show a 2D representation of the stent 1 , unfolded, and the ones skilled in the art will understand that the framework 2 shown in Fig. 9, 10 should have a tubular shape. The main difference between the embodiments in Fig. 9 and Fig. 10 is the axial length LF of the stent 1 , which in Fig. 9 may be in the range of 25 to 35 mm, in particular about 30 mm, and in Fig. 10 may be in the range of 35 to 45 mm, in particular about 40 mm. The axial length LF (or total axial length L(tot)) is measured for the expandable framework 2, only, so that optionally provided holders 130 for radiopaque markers or the like, 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 Fig. 9 and Fig. 10 is made from a shapememory alloy and self expanding. It is cut from a tube material as raw material, in particular using laser cutting, even though other cutting methods such as waterjet may also be used. Moreover, a tube as raw material is not essential and the stent 1 may also be formed e.g. using single wires or an additive manufacturing method. Stent 1 is shown in the crimped state in both Fig. 9 and Fig. 10 and thus has the minimum diameter Dmin.

[0085] Stent 1 in the shown embodiments (Fig. 9, 10) has a three stent rings, namely a distal end ring 8, a proximal end ring 10 and a middle stent ring 14. The stent rings 6, 10, 14 may also just be referred to as first, second and third stent ring. Stent 1 may also comprise just one ring, two rings, four rings or more. The terms “distal end ring” and “proximal end ring” indicate the desired position of the stent, which can be referred to as a “directive stent”. However, dependent on the actual design and radial forces I pressure exerted, the stent may also be non-directive and insofar the “distal end ring” may just be called a “first stent ring” and may be placed distal or proximal dependent on the selection of the surgeon.

[0086] The distal end ring 8, middle stent ring 14 and proximal end ring 10 are connected to each other using first connectors or links 16 and second connectors or links 17. The first connectors 16 connect the distal end ring 8 to the middle stent ring 14, and the second connectors 17 connect the middle stent ring 14 to the proximal end ring 10. The first connectors 16 have a first connector axial length LC1 and the second connectors 17 have a second connector axial length LC2. The structure of the first and second connectors 16, 17 will be described in more detail below.

[0087] First, the distal end ring 8 will be described. Distal end ring 8 according to Figs. 9, 10 has three first circumferential ring segments 120 and three second circumferential ring segments 122 which have differently shaped struts. First circumferential ring segments 120 are comprised of three closed cells 240, formed by in total 12 struts, in particular first struts 104, while the second circumferential segments 122 comprise one closed second cell 242 defined by four second struts 106. Because the stent 1 is shown in crimped state, the cells 240, 242 are collapsed. The arrangement of the first and second struts 104, 106 form peaks or crests 12 and valleys 13.

[0088] The first circumferential ring segments 120 with the first struts 104, which form the first cells 240 are formed to provide the expansion force, i.e. radial outward force and radial resistive force for an expansion to the nominal diameter DN and the second circumferential segments 122 with the second struts 106 are not as strong as the first circumferential ring segments 120 and allow a further expansion of the stent 1 beyond the nominal diameter DN to a maximal diameter Dmax. This particular feature is used to provide an “expansion reserve” for the stent 1 which may take into account further remodeling of the vessel once the stent 1 has been implanted. For details regarding the expansion reserve, reference is made to WO 2022 / 253522 A1 of the same applicant as the present application, which incorporated herein by means of reference. Due to this specific design with the first and second circumferential ring segments 120, 122, the graphs for the chronic outward force COF and the radial resistive force RRF as shown in Fig. 2 comprise the flattened end portion beyond the nominal diameter DN.

[0089] A radial thickness of the expandable framework 2 may be in the range of 0.2 to 1.0 mm, in particular, 0.3 to 0.5 mm. The first struts 104 in this embodiment 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. Since in particular the first circumferential segments 120 are decisive for the herein discussed chronic outward pressure COP and redial resistive pressure RRP or chronic outward force COF and the radial resistive force RRF, mainly the first struts 104 are discussed in the following.

[0090] The length LS1 of the first struts 104 is approximately in a range of 5 to 8 mm, in the shown embodiment in particular in the range of 6 to 7 mm, and has a width of approximately 0.35 to 0.6 mm, in particular 0.4 to 0.5 mm. A width in the range of the crest 22 may be slightly increased and may be in the range of 0.4 to 0.7 mm, in particular 0.45 mm. This can help to provide a relatively high radial resistive pressure, in this embodiment the radial resistive pressure of the distal end ring 8 shown is 150 mmHg and thus the stent 1 may exhibit the diagram shown in Fig. 2.

[0091] The distal end ring 8 is provided with in total three holders 130 (only one indicated with reference sign in Fig. 3, 4). Those holders are generally ring shaped and closed and may receive a radiopaque marker. They may also be used to engage a releasing device of a respective delivery system in order for a controlled release of the stent 1 . In the shown embodiment, each of the three first circumferential ring segments 122 is provided with one holder 130, but different numbers of holders may also be provided. Also, other shapes of the holders 130 are envisaged, as e.g. T-shaped, oval, hexagonal, etc.

[0092] The middle stent ring 14 in the embodiments shown in Fig. 9, 10 only comprises open cells, which are formed by struts attached to each other in a zig-zag or meandering pattern. Such an open cell structure usually develops a lower force than a closed cell structure, which is desired in the present case.

[0093] The middle stent ring 14 in the embodiments shown in Fig. 9, 10 comprises three third circumferential ring segments 124 and three fourth circumferential ring segments 126. Similar to the second circumferential ring segments 122 of the distal end ring 8, in the middle stent ring 14, the fourth circumferential ring segments 126 provide an expansion reserve and are substantially “weaker” than the third circumferential ring segments 124. To achieve this optional function, the middle stent ring 14 in this embodiments is formed from third and fourth struts 107, 108, wherein the third struts 107 form the third circumferential ring segments 124 and the fourth struts 108 form the fourth circumferential ring segments 126. However, it shall be understood that also embodiments are envisaged in which the middle stent ring 14 (or middle stent rings) do not comprise different circumferential ring segments but are just a unitary ring without expansion reserve.

[0094] All struts 107, 108 of the middle stent ring 14 in this embodiment have the same third strut length LS3, which here is identical to the axial length L(mid) in the crimped state. In the embodiment shown in Fig. 8, 9, the third strut length is in the range of 3.0 mm to 6.0mm, in particular 3.5 mm to 5.5 mm and more preferred 3.8 mm to 4.5 mm. The different forces developed by the third and fourth circumferential ring segments 124, 126 is provided by a varying width of the third and fourth struts 107, 108. A third width W3 of the third struts 107 in this embodiment is in a range of 0.15 to 0.3 mm, more preferred 0.18 to 0.3 mm, more preferred 0.18 to 0.22 mm. A fourth width W4 of the fourth struts 108 in this embodiment is in in a range of 0.10 to 0.22 mm, preferably 0.13 to 0.20 mm, more preferred 0.15 to 0.20 mm. A ratio W3 / W4 between the third width W3 and fourth width W4 preferably is in a range of to 1 .01 to 3.0, preferably 1 .05 to 1.15. Alternatively or additionally to providing different widths for the third and fourth circumferential ring segments 124, 126, different length of the third and fourth struts 107, 108 may be provided.

[0095] In the proximal end ring 10, similar to the middle stent ring 14 in this embodiment (Fig. 8, 9), the struts are connected in a zig-zag or meandering pattern to form an open cell structure. The proximal end ring 10 in this embodiment (Fig. 8, 9) is unitary and does not have structurally different first and second circumferential ring segments as described for the distal end ring 8 and the middle stent ring 14. The distal end ring 10 is formed by fifth struts 110, which have a fifth strut length LS5, which is identical to the axial length of the proximal end ring L(prox) in the crimped state. In the embodiments of Fig. 3, 4 the fifth strut length in the range of 5.0 mm to 10.0 mm, preferably 5.0 mm to 8.0 mm, even more preferred 6.0 mm to 8.0 or 7.0 mm.

[0096] Proximally directing peaks or crests 12 of the proximal end ring 10 are provided with holders 131 in this embodiment. The holder 131 are similar or identical to holders 130 attached to the distal end ring 8. Insofar reference is made to the description of the holders 130.

[0097] Now, the connectors will be described in more detail. The first embodiment of Fig. 9 mainly differs from the second embodiment of Fig. 10 in that the connectors are differently shaped, while the three ring segments are identical.

[0098] The first connectors 16 comprise straight first connectors 140 and bow-shaped first connectors 142 in this embodiment. The first straight connectors 140 are used to connect the first circumferential ring segments 120 of the distal end ring 8 to the middle stent ring 14, in particular the third circumferential ring segments 124 of the middle stent ring 14. In this embodiment, each proximally directing peak or crest 144 of the first circumferential ring segment 120 is provided with a straight first connector 140. The straight first connectors 140 preferably have a relative great width in a range of 0.2 mm to 0.5 mm in particular 0.3 to 0.4 mm. This is in particular beneficial when the distal end ring 8 is relatively strong. The first straight connectors 140 are connected to distally facing peaks or crests 145 of the middle stent ring 14, preferably crests of the third circumferential ring segments 124.

[0099] The first bow-shaped connectors 142 in this embodiment connect the second circumferential ring segment 122 to the middle stent ring 14, in particular to the fourth circumferen- tial ring segment 126. The first bow-shaped connectors are attached to proximally directing peaks or crests of the distal end ring 8 and preferably to valleys 145 of the middle stent ring 14, preferably the fourth circumferential ring segments 126. The first bowshaped connectors 142 generally resemble a W shape in that looking in axial direction they first comprise a short section downwardly bent, then an elongated section upwardly bent and then again a short section downwardly bent. In particular the connection and shape of the bow-shaped connectors takes into account the varying axial shortening of the distal end ring 8 with the different strut length. The first bow-shaped connectors 142 may have a smaller width than the first straight connectors 140, in particular by about 20% to 70%, in particular about 40 % to 60 %.

[0100] The second connectors in this embodiment only include second bow-shaped connectors 146, which are substantially C shaped. Each of the proximally facing peaks or crests of the middle stent ring 14 are connected to one of the second bow-shaped connectors 146. In this case, also each of the distally facing peaks or crests of the proximal end ring 8 are connected to one second connector.

[0101] Fig. 11 illustrates schematically three COP I diameter curves for the three different stent rings of the stent 1 shown in Fig. 9, 10. The uppermost curve in bold dashed lines depicts the distal end ring 8 and shows the chronic outward pressure COP(dist) of the distal end ring 8. It is similar to the curve of Fig. 2. The middle curve dashed-dotted depicts the middle stent ring 14 and the lowermost curve in small dashed lines depicts the proximal end ring 10. What can be seen is that the COP of the middle stent ring 14 is closer to that of the proximal end ring 10 than to the distal end ring 8. Also, the curve of the middle stent ring 14 has a kink or drop in COP after the nominal diameter DN, which is due to the structural difference of the third and fourth circumferential ring segments 124, 126 described above.

[0102] Fig. 12 and 13 show a rendering the stent 1 in a fully expanded view, in which both the cells 240 of the first circumferential ring segments 120 and the cells 252 of the second circumferential ring segments 122 are fully open and the stent is in a relaxed state. At a nominal diameter, typically the cells 242 of the second circumferential ring segments 122 should be closed, or almost closed. It can be seen that cells 242 are smaller than cells 240, because the respective struts defining cells 242 are shorter. However, distal end ring 8 only includes closed cells 240, 242 as can be easily seen in Fig. 12 and 13. The proximal end ring 10 and the middle stent ring 14 in contrast comprise only open cells as easily can be inferred from the renderings. What also can be seen easily is that each of the proximally directing crests are attached to one connector.

[0103] The bow-shaped connectors 142 in the maximally expanded position (Fig. 12, 13) are slightly stretched in order to balance the foreshortening of the distal end ring 8 due to expansion.

Claims

Claims1. Self-expandable stent (1) for implantation into an abdominal aorta of the human body for treating an abdominal aortic aneurysm, 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 (6) end, 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) placed 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, and 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), wherein at least one of the distal end ring (8), the proximal end ring (10) or any of the optional rings (14, 15) of the stent (1) exhibit at the nominal diameter (DN) a nominal radial resistive pressure (RRP-N) of > 100 mmHg.

2. Stent according to claim 1 , wherein at least one of the distal end ring (8), the proximal end ring (10) or any of the optionally rings (14, 15) of the stent (1) exhibit at the nominal diameter (DN) a nominal radial resistive pressure (RRP-N) of > 250 mmHg.

3. Stent according to claim 1 or 2, wherein at least one of the distal end ring (8), the proximal end ring (10) or any of the optionally rings (14, 15) of the stent (1) exhibit at the nominal diameter (DN) a chronic outward pressure (COP-N) of > 50 mmHg.

4. Stent according to claim 3, wherein at least one of the distal end ring (8), the proximal end ring (10) or any of the optionally rings (14, 15) of the stent (1) exhibit at the nominal diameter (DN) a chronic outward pressure (COP-N) of > 100 mmHg.

5. Stent according to claim 4, wherein at least one of the distal end ring (8), the proximal end ring (10) or any of the optionally rings (14, 15) of the stent (1) exhibit at the nominal diameter (DN) a chronic outward pressure (COP-N) of > 150 mmHg.

6. Stent according to any of the preceding claims, wherein at least one of the distal end ring (8), the proximal end ring (10) or any of the optionally rings (14, 15) of the stent (1) exhibit at the nominal diameter (DN) a chronic outward pressure (COP-N) of < 250 mmHg.

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

8. Stent according to any of the preceding claims, wherein a pressure-diameter product (PDP), calculated by PDP = (nominal radial resistive pressure (RRP-N))*(nominal diameter) of the stent, preferably the distal end ring (8) is at least 1800 mmHg*mm, preferably at least 3000 mmHg*mm.

9. Stent according to any of the above claims, wherein the framework (2) is formed from a Nitinol material.

10. Stent according to any of the above claims, wherein the framework is uncovered and uncoated.11 . Stent according to any of the above claims, wherein the framework (2) has a thickness measured in radial direction in a range of 0.2 mm to 1.0 mm.

12. Stent according to any of the above claims, wherein the distal end ring (8) comprises two or more struts (20) which satisfy the relationship (length of the strut) I (width of the strut) < 20.

13. Stent according to any of the above claims, wherein the distal end ring (8) comprises two or more struts (20) and has a radial stiffness in a range from 0,08 N / mm2to 0,12 N / mm2, measure in force per length per radial deformation.

14. Stent according to any of the above claims, wherein a chronic outward pressure (COP-N) at the nominal diameter (DN) is non-uniform along the length of the framework (2).

15. Stent according to claim 14, wherein a ratio between a chronic outward pressure at the nominal diameter (DN) of the distal end ring (8) and a 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. Stent according to any of the above claims, wherein the peaks (12) and valleys (13) of each ring segment (8, 10, 14, 15) are formed by crests (22) connected by struts (20), wherein the struts (20) are substantial linear.

17. Stent according to claim 16, wherein at least two adjacent ring segments (8, 10, 14, 15) are positioned in an out-of-phase relationship so that crests (22) forming valleys (13) of one ring (8, 10, 14, 15) are connected to crests (22) forming peaks (12) of the adjacent ring (8, 10, 14, 15).

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

19. Self-expandable stent (1) for implantation into 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 (6) end, 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) placed 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, and 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),wherein an AUC (area under the curve) under the RRP-diameter curve between the minimum diameter (Dmin) and the maximum diameter (Dmax) of the stent, preferably at least the distal end ring (8) is at least 4000 mmHg*mm, preferably 5000 mmHg*mm, preferably at least 7000 mmHg*mm.

20. Method for determining a pressure equivalent for treatment of an abdominal aortic aneurysm (AAA), comprising the steps:- receiving pressure data of an intraluminal pressure;- receiving aortic diameter data in reference to the above received pressure date- determining based on said pressure data and said aortic diameter data a transition pressure of the vessel between elastin and collagen phase;- determining a length (L) of a framework of a stent; and- determining a nominal radial resistive pressure (RRP-N) based on said transition pressure.21 . Computer program comprising executable code which when executed on a computer causes the computer to carry out a method of claim 20.

22. Method for treating of an abdominal aortic aneurysm (AAA), comprising the steps:- providing a stent according to any of the preceding claims 1 to 19; and- deploying the stent in the vessel adjacent to an aneurysmal sac of the abdominal aortic aneurysm in order to increase a mechanical stiffness of the aortic segment.

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