Stent for treating an abdominal aortic aneurysm

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). The framework (2) having a distal end ring (8) and a proximal end ring (10). 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 distal end ring (8) has a first expansion characteristic in a first diameter range (D1) smaller than the nominal diameter (DN) and a second expansion characteristic in a second diameter range (D2) above the nominal diameter (DN), the second expansion characteristic is different from the first expansion characteristic. A ratio in a chronic outward pressure (COP-N-dist) of the distal end ring (8) to a chronic outward pressure (COP-N-prox) of the proximal end ring (10) is 1.8 or more.

Description

[0001] Angiolutions GmbH

[0002] Vahrenwalder StraBe 269A, 30179 Hannover, DE

[0003] Stent for treating an abdominal aortic aneurysm

[0004] 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.

[0005] Stents of the aforementioned type are in the prior art 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.

[0006] 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.

[0007] 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.

[0008] 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. From WO 2022 / 253522 A1 of the inventors of the present invention, a self-expanding flexible intravascular stent for insertion into a vessel is known. The stent comprises two or more axially interconnected ring segments, each of which is formed from a plurality of struts which are interconnected in meander shape by means of bows. The stent has a crimped state with a reduced diameter and an expanded state with a nominal diameter. The ring segments have, in a first diameter range of less than the nominal diameter, a first expansion characteristic and, in a second diameter range of greater than the nominal diameter, a second expansion characteristic, which is different from the first expansion characteristic. This means, the stent disclosed in WO 2022 / 253522 A1 in particular has an expansion reserve which in particular is useful in case of remodeling of the vessel into which the stent is implanted.

[0009] 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”.

[0010] This object is solved inter alia in a first aspect of the invention described herein by a stent according to claim 1 .

[0011] A self-expandable stent for implantation into a blood vessel of the human body disclosed herein may comprise an expandable framework. The framework may be formed from a shape memory alloy but in embodiments may also be formed to be balloon-expandable or may be formed from wires. The framework usually has 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 may have two or more stent rings from which one is a distal end ring and one is a proximal end ring. Embodiments of the invention described herein however may also comprise just one single stent ring. Each ring may be formed from interconnected struts with define peaks or crests and valleys. If the stent has three or more stent rings, there will be at least one stent ring placed between the distal end ring and the proximal end ring. This stent ring may be referred to as middle stent ring or middle stent rings in general or first, second, and so forth middle stent rings.

[0012] Stents according to the invention disclosed herein may have 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). For stents formed from a shape memory alloy the maximum diameter may be greater than the nominal diameter. This is because usually it is desired that the stent is able to exert a radial force (chronic outward force) or radial pressure (chronic outward pressure) in the implanted state to the inner vessel wall. For a balloon-expandable stent, the maximum diameter and the nominal diameter may be identical.

[0013] 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.

[0014] According to a first aspect of the invention, but not limiting other aspects of the invention, the distal end ring has a first expansion characteristic in a first diameter range smaller than the nominal diameter (DN) and a second expansion characteristic in a second diameter range (D2) above the nominal diameter (DN), wherein the second expansion characteristic is different from the first expansion characteristic. In other aspects of the invention described herein, the distal end ring may only have one single expansion characteristic which does not differ in diameter ranges below and above the nominal diameter.

[0015] According to the first aspect of the invention, but not limiting other aspects of the invention, the proximal end ring has a third expansion characteristic over the complete expansion range from the minimum diameter (Dmin) to the maximum diameter (Dmax). In other aspects of the invention described herein, the proximal end ring may have two different expansion characteristics for diameter ranges below and above the nominal diameter as described above.

[0016] According to the first aspect of the invention, but not limiting other aspects of the invention, a 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 1.8 or more. Further preferred ratios are: 10:1 to 1.5:1 , preferably 8:1 to 1.5:1 , preferably 6:1 to 2:1 , even more preferred 4:1 to 2:1. Thus, according to the preliminarily claimed first aspect of the invention the stent shows a gradient in chronic outward pressure and thus also in the chronic outward force acting on a single portion of the vessel from the distal to the proximal end. In other word, the distal end ring is stronger than the proximal end ring. This is particularly beneficial when treating an aortic aneurysm as described in the above cited scientific publication “Segmental Aortic Stiffening Contributes to Experimental Abdominal Aortic Aneurysm Development” published in “Circulation” 2015; 131 :1783-1795. As described above, the distal end ring may have two different expansion characteristics below and above the nominal diameter. Preferentially it is provided that the distal end ring has a first diameter radial stiffness in the first diameter range, and a second diameter radial stiffness in the second diameter range, wherein the first diameter radial stiffness is higher than the second diameter radial stiffness. The distal end ring initially expands at a high predefinable first radial force (F1) or to the level of the predefinable first radial force (F1) until a specific nominal diameter is reached. Beyond the nominal diameter, the distal end ring allows further expansion until a specific maximum diameter is reached. The difference between the nominal and maximum diameters corresponds to an “expansion reserve” of the distal end ring. If the stent, in particular distal end ring, enters from its nominal diameter into the expansion reserve, its radial force decreases abruptly (in steps) to a considerably lower radial force level of a predefinable second radial force (F2), which acts until the maximum diameter is reached.

[0017] Here, it is preferably provided that the first expansion characteristic causes an expansion with a first chronic outward force (COF1) or first chronic outward pressure (COP1) and the second expansion characteristic causes an expansion with a second chronic outward force (COF2) or chronic outward pressure (COP2) that is lower than the first permanent outward force (COF1) or chronic outward pressure (COP2), respectively.

[0018] In this way, a stepped radial force or radial pressure profile can be achieved, which allows the stent, in particular distal end ring, to expand up to the nominal diameter and the corresponding vessel to expand to the nominal diameter, but beyond the nominal diameter only allows the stent, in particular distal end ring, to widen along with it, applying only a very small radial force or chronic outward force I pressure in this region. The radial force or chronic outward force (COF2) I chronic outward pressure (COP2) in the second diameter range, i.e., in the range beyond the nominal diameter to the maximum diameter, is preferably chosen to be as small as possible and to follow the vessel wall during adaptive remodeling. The radial force or the second chronic outward force (COF2) I chronic outward pressure (COP2) in the second diameter range should preferably be selected so that active further expansion of the vessel does not occur, but the radial force I pressure is merely selected so that the stent continues to be in close contact with and follow the inner surface of the vessel. Thus, in the area larger than the nominal diameter, the stent should only apply such a force that ensures contact between the stent and the vessel wall. The force should be selected so that the vessel does not have to “pull” on the stent during remodeling, but ideally as little physical action as possible is exerted on the vessel by the stent. In other words, instead of or in addition to the first and second expansion characteristics, the stent according to an aspect of the invention can also be described in terms of the first and second radial forces F1 , F2, and COF I COP, respectively, or radial force I pressure levels to which the radial force I pressure falls in the first and second diameter regions. Furthermore, instead of or in addition to the first and second expansion characteristics, the stent, preferably distal end ring, according to the invention can be described by the radial force I pressure characteristic during expansion of the stent, which has at least one kink, at least one, preferably two, inflection points or at least one step. According to an aspect of the invention, the radial force I pressure caused by the stent, or distal end ring in particular, decreases sharply beyond the nominal diameter and drops to a very low level, preferably such that vessel remodeling does not occur or occurs only to a very small extent. Preferably, the second diameter range is at least 10% of a maximum diameter Dmax, so the second diameter range accounts for 10% or more of the total expansion. Preferably, the second diameter range is at least 15%, 20%, 25%, 30%, 40%, 50%, 60%, or 70% of the maximum diameter. Thereby it is preferably provided that the first diameter range comprises at most 90% of the maximum diameter Dmax, preferably 80%, further preferably 75%, 70%, 65%, 60%, 55%, or 50%.

[0019] It is further preferred that the radial force and / or pressure in the first diameter range drops to a first radial force and / or pressure level during expansion and drops to a second radial force and / or pressure level in the second diameter range, which is lower than the first radial force and / or pressure level. Preferably, the first radial force and / or pressure level is greater than the second radial force and / or pressure level by a factor, the factor being in a range from 2 to 20, preferably in a range from 2 to 10, more preferably from 3 to 10, more preferably from 4 to 10, more preferably from 5 to 9.

[0020] In a preferred further embodiment, a radial force and / or pressure diameter profile of the stent, or at least the distal end ring, has a kink or step. A radial force-diameter and / or pressure-diameter profile represents the progression of the radial force I pressure starting from a crimped state to the maximum diameter plotted over the diameter. In conventional stents, a radial force-diameter profile has no kink or step; instead, the radial force decreases essentially continuously, in particular degressively, from the crimped state to the maximum diameter and then ends abruptly. The stent described herein has a radial forcediameter and / or pressure-diameter profile having at least one kink, preferably at least two or more kinks. The radial force-diameter profile has at least one, preferably two inflection points plotted as a graph. Further preferably, the radial force-diameter profile in the first diameter range, starting from the crimped state during expansion, initially has a section with a first slope, then a section with a second slope, and in the second diameter region, starting from the nominal diameter, a third section with a third pitch and a fourth section with a fourth pitch, wherein the first pitch and is greater than the second pitch and the fourth pitch, and the third pitch is greater than the second pitch and the fourth pitch. The third slope may be greater than the first slope. The second slope may be greater than the fourth slope. The first slope is preferably greater than the second slope by at least a first slope factor, wherein the first slope factor is at least 2.0; 2.5; 3.0; 3.5; 4.0; 4.5; 5.0; 5.5; 6.0; 7.0; 8.0; 9.0; 10.0; 12.0; 15.0. Preferably, the third pitch is greater than the second and / or fourth pitch by at least a second pitch factor, the first pitch factor being at least 2.0; 2.5; 3.0; 3.5; 4.0; 4.5; 5.0; 5.5; 6.0; 7.0; 8.0; 9.0; 10.0; 12.0; 15.0. Preferably, the radial force-diameter profile of the stent, starting from the crimped state to the expanded state, has the following course: in the first diameter range, first a pitch decrease followed by a pitch increase, then, upon transition, when passing into the second diameter range, a further decrease in pitch and, preferably, finally, a further increase in pitch. The progression can also be described as degressive-progressive-degressive. Further preferably, the first diameter region defines a first radial stiffness profile section and the first radial stiffness profile section is degressive, regressive or linear. A degressive or regressive stiffness as the diameter of the stent increases provides a more rapid decrease in force as it expands. Preferably, the radial force in the first diameter region is substantially constant or only slightly decreasing over at least one section, and in the second diameter region is also substantially constant. This can be achieved by the radial stiffness being degressive or regressive.

[0021] In a preferred embodiment or aspect of the invention, the distal end ring only includes closed cells. In a preferred embodiment or aspect of the invention, the proximal end ring only includes open cells. Typically, using closed cells a higher radial force can be generated than using open cells. Therefore, such structure allows for stent with a radial force I pressure gradient which is beneficial for treating an aneurysmal.

[0022] In a preferred embodiment or aspect of the invention, the distal end ring comprises at least one first circumferential ring segment and at least one second circumferential ring segment, which are structurally different from each other. By this structural difference, the distal end ring may provide the first and second expansion characteristics as described above. In this way, the different first and second circumferential ring segments can provide the different radial forces for the first and second diameter regions. Preferably, in the first diameter range, the first and second circumferential ring segments are dominantly acting, while when the nominal diameter is reached, the first circumferential ring segments are fully expanded and only the second circumferential ring segments continue to act, but only with a smaller force, namely the second permanent outward force. Thus, preferably, the second circumferential ring segments start to expand only when the first circumferential ring segments have fully expanded to a substantially relaxed state.

[0023] Preferably, the first circumferential ring segments are configured to have or define a first radial stiffness and the second circumferential ring segments are configured to have or define a second radial stiffness. Preferably, the second radial stiffness of the second circumferential ring segments is negligible relative to the first radial stiffness of the first circumferential ring segments.

[0024] In a preferred embodiment, the first circumferential ring segment comprises struts with a first circumferential width W1 and the second circumferential ring segment comprises struts with a second circumferential width W2, wherein the first circumferential width W1 is greater than the second circumferential width W2. The first circumferential ring segments may also be referred to as "hard stent segments" and the second circumferential ring segments as "soft stent segments". "Hard stent segments," "hard circumferential segments," or "hard annular segments" may be understood to mean those that define the first radial force. "Soft stent segments", "soft circumferential segments", or "soft annular segments" may be understood to mean those defining the second radial force. "Hard stent segments" are thus those that substantially define the first radial stiffness, and "soft stent segments" are those that substantially define the second radial stiffness.

[0025] A circumferential ring segment is understood to be a sequence, running transversely to the longitudinal direction of the stent, of struts or webs arranged in a zigzag or meandering manner in the expanded state, which are connected to one another by peaks or crests, preferably a plurality of circumferential ring segments being arranged next to one another and forming the stent ring.

[0026] Preferably, the distal end ring has at least two first circumferential stent segments and at least two second circumferential stent segments. Preferably, they are arranged around the circumference in an alternating manner. Also other numbers like 3, 4, 5 etc. are preferred.

[0027] In a preferred embodiment, the first circumferential ring segment comprises struts with a first length LS1 and the second circumferential ring segment comprises struts with a second length LS2, wherein the first length LS1 is greater than the second length LS2. This may restrict the expansion diameter of the second circumferential ring segment. 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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).

[0032] 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.

[0033] Preferred embodiments as described herein may also form basis for a stent of a further aspect which solves the problem stated in the introductory portion. As such, for example a stent is disclosed 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 at least one middle stent 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, and the stent having a compressed state with a minimum diameter (Dmin), an expand-ed state with a nominal diameter (DN), and a relaxed state with a maximum diameter (Dmax). Preferably, a ratio in a chronic outward pressure (COP-N- dist) at the nominal diameter (DN) of the distal end ring to a chronic outward pressure (COP-N-prox) at the nominal diameter (DN) of the proximal end ring is 1 .8 or more. Preferably, a ratio in a chronic outward pressure (COP-N-mid) at the nominal diameter (DN) of the middle stent ring to the chronic outward pressure (COP-N-prox) at the nominal diameter (DN) of the proximal end ring is 1 .0 or more. Preferably, the ratio of (COP-N- mid) / (COP-N-prox) is 35% or less of the ratio of (COP-N-dist) / (COP-N-prox).

[0034] 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.

[0035] In a preferred embodiment or a further aspect of the invention, the above described first connectors include straight connectors. Straight connectors are beneficial because 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Preferably, the first connector 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. Alternatively, the first connectors are each only connected valleys of the middle stent ring. Preferably, in every valley of the middle stent ring a first connector is received and attached.

[0040] It is further preferred, that the proximal stent ring comprises at least one fifth circumferential ring segment and at least one sixth circumferential ring segment which are structurally different from each other. Thus, also the proximal stent ring may provide the previously discussed expansion reserve and may exhibit the two different expansion characteristics.

[0041] In an example, the fifth circumferential ring segment comprises struts with a fifth circumferential width and the sixth circumferential ring segment comprises struts with a sixth circumferential width, wherein the fifth circumferential width is greater than the sixth circumferential width. The values discussed above for the middle stent ring may also apply here in an identical manner. Preferably the fifth circumferential ring segment comprises struts with a fifth length and the sixth circumferential ring segment comprises struts with a sixth length, wherein the fifth length is greater than the sixth length. Again, the values discussed above for the middle stent ring may also apply here in an identical manner.

[0042] 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. In an alternative, the second connector include straight connectors, and preferably exclusively include straight connectors.

[0043] In a preferred embodiment, the second connectors are connected to crests and valleys of the proximal stent ring. Preferably, the second connectors are each only connected valleys of the proximal stent ring. Preferably, in every valley of the proximal stent ring a second connector is received and attached.

[0044] Preferably, the stent described herein has a nominal diameter in the range of 18 to 30 mm. This is a diameter which has shown to be suitable in order to in particular treat abdominal aortic aneurysms. However, this range also is suitable for treating other aortic aneurysms. When not defined otherwise, the nominal diameter refers to the “working diameter” which the stent should approximately have after delivering into the vessel. It shall be assumed that the stent then has a cylindrical shape. If in doubt, the distal end ring shall be decisive for defining the nominal diameter.

[0045] An overall axial length L(tot) of the inventive stent preferably is in a range of 25 mm to 55 mm. There may be different lengths, but the above range has shown to be suitable in most applications, in particular a range of 28 mm to 42 mm.

[0046] 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 middle stent rings may have an axial length of L(mid-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 as described above. 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.

[0047] In general, the stent or at least the distal end ring exhibits at the nominal diameter a nominal radial resistive pressure (RRP-N) of > 100 mmHg, preferably > 100 mmHg.

[0048] In particular, in the above-mentioned method of stiffening a vessel in order to treat an abdominal aortic aneurysm, the radial resistive pressure is important. In particular a radial resistive pressure equivalent to an intraluminal pressure of > 100, 110, 120, 130, more preferred 150 mmHg is 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.

[0049] 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.

[0050] 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 ring / segment and the radial resistive force (RRF-N) at this nominal diameter by means of the formula

[0051] 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.

[0052] Each of the stent rings may exhibit the above nominal radial resistive pressure, only one stent ring (in this case preferably the distal end ring), two or more of the stent rings, or the complete stent may exhibit the above nominal radial resistive pressure. That means, the stent may have different nominal radial resistive pressures along its length.

[0053] In a preferred embodiment, the stent or at least one of the stent rings (in this case preferably the distal end ring) 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.

[0054] It is further preferred that the stent or at least one of the stent rings (in this case preferably the distal end ring) exhibits at the nominal diameter a chronic outward pressure (COP- N) of > 50 mmHg. Preferably, the stent or at least one of the stent rings (in this case preferably the distal end ring) 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 can be beneficial. This is in particular true for the application of the abdominal aortic aneurysm (AAA) discussed above.

[0055] 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).

[0056] 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.

[0057] In a further preferred embodiment, a first stent 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, measured in force (in N) per length (in mm) per radial deformation (in mm). Preferably, a second stent ring (preferably the proximal end ring) comprises two or more struts, wherein the second stent 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 stent ring provided between the first and the second stent rings comprises two or more struts, wherein the third stent ring has a radial stiffness in a range from 0.04 N / mm2to 0.06 N / mm2.

[0058] Further preferred, the framework is formed from a shape memory alloy, preferably a Titanium-Nickel-Alloy, preferably Nitinol, and is cut from a cylindrical tube as the raw material. The stent preferably has a cylindrical shape, in particular a cylindrical shape in the relaxed state.

[0059] Also disclosed herein is a method for treating of an abdominal aortic aneurysm (AAA), comprising the steps: providing a stent according to any of the previously described preferred embodiments of a stent; 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. Preferably, the stent is placed directly adjacent the aneurysmal sac. Preferably, the stent is not extending into the aneurysmal sac and not covering the aneurysm.

[0060] 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:

[0061] Fig. 1 shows a general pressure-diameter diagram showing elasticity of the aorta;

[0062] Fig. 2 shows a diagram showing a pressure diameter diagram of a distal end ring of a stent according to the invention;

[0063] Fig. 3 shows a first embodiment of a stent according to the present invention; Fig. 4 shows a second embodiment of a stent according to the present invention;

[0064] Fig. 5 shows a schematic pressure diameter diagram of the stent according to

[0065] Figs. 3 and 4 with one graph per stent ring;

[0066] Fig. 6 a full cut side view of a rendering of a fully expanded stent;

[0067] Fig. 7 a perspective elevated view of the fully expanded stent rendering;

[0068] Fig. 8 shows a third embodiment of a stent according to the present invention;

[0069] Fig. 9 shows a fourth embodiment of a stent according to the present invention;

[0070] Fig. 10 shows a full cut side view of a rendering of a fully expanded stent of Fig. 9;

[0071] Fig. 11 shows a fifth embodiment of a stent according to the present invention; and

[0072] Fig. 12 shows a sixth embodiment of a stent according to the present invention.

[0073] 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.

[0074] The inventive stent disclosed herein, is suited for treating abdominal aortic aneurysms (AAA). It may also be suited to treat other vascular defects. In embodiments disclosed herein, the stent or at least the distal end ring, 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 in Fig. 2 illustrates a pressure-diameter diagram. 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. 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 beneficial for treating an abdominal aortic aneurysm as described in the above scientific article. When other vascular defects are to be treated, other pressure values still can be used within the scope of the present disclosure.

[0075] The RRP or COP is usually measured using an iris type measurement device. When only a specific ring of the stent shall be measured, only this ring is placed in the iris and the other portion of the stent sticks out of the iris.

[0076] Fig. 3 shows a first embodiment of a stent 1 according to the invention and Fig. 4 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. 3, 4, however, it should be understood that Fig. 3, 4 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. 3, 4 should have a tubular, i.e. cylindrical shape. The main difference between the embodiments in Fig. 3 and Fig. 4 is the axial length LF of the stent 1 , which in Fig. 3 may be in the range of 25 to 35 mm, in particular about 30 mm, and in Fig. 4 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. 3 and Fig. 4 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 be used as well. 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. 3 and Fig. 4 and thus has the minimum diameter Dmin. Fig. 6, 7 in contrast show the stent (a rendering of the stent) in the fully expanded view with maximum diameter Dmax.

[0077] Stent 1 in the shown embodiments (Fig. 3, 4) has 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.

[0078] 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. It shall be noted that not all connectors of the first connector 16 and / or all connectors of the second connectors 17 have the identical length. Thus, the first and second connectors 16, 17 may include connectors of different length. The structure of the first and second connectors 16, 17 will be described in more detail below.

[0079] First, the distal end ring 8 will be described. Distal end ring 8 according to Figs. 3, 4 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 preferably three or four closed cells 240 (in the shown embodiment four), formed by preferably in total 12 or 16 struts (in the shown embodiment 16), 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.

[0080] 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 is 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.

[0081] 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.

[0082] 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 approxi- mately 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.

[0083] 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.

[0084] The middle stent ring 14 in the embodiments shown in Fig. 3, 4 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.

[0085] The middle stent ring 14 in the embodiments shown in Fig. 3, 4 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.

[0086] 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. 3, 4, the third strut length is in the range of 3.0 mm to 6.0mm, in particular 3.5mm 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.

[0087] 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.

[0088] In the proximal end ring 10, similar to the middle stent ring 14 in this embodiment (Fig. 3, 4), 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. 3, 4) 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 proximal 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.

[0089] 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.

[0090] Now, the connectors will be described in more detail. The first embodiment of Fig. 3 mainly differs from the second embodiment of Fig. 4 in that the connectors are differently shaped, while the three rings 8, 10, 14 are identical.

[0091] 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 rela- tively 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.

[0092] 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 circumferential ring segment 126. The first bow-shaped connectors 142 are attached to proximally directing peaks or crests 144 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 bow-shaped 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 %.

[0093] The second connectors 17 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 17.

[0094] Fig. 5 illustrates schematically three COP I diameter curves for the three different stent rings of the stent 1 shown in Fig. 3, 4. 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.

[0095] Fig. 6 and 7 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. 6 and 7.

[0096] 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.

[0097] The bow-shaped connectors 142 in the maximally expanded position (Fig. 6, 7) are slightly stretched in order to balance the foreshortening of the distal end ring 8 due to expansion.

[0098] Fig. 8 shows a third embodiment of a stent 1 according to the invention and Fig. 9 shows a fourth 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. In general, the embodiments of Figs. 8 and 9 are based on the embodiments of Fig. 3 and 4 and similar and identical elements are shown in Figs. 8 and 9 with the same reference numbers as in Figs. 3 and 4 and insofar reference is made to the above description. In the following mainly the differences to the first and second embodiments (Figs. 3, 4) are highlighted. All features not discussed in the following may just be the same as in either embodiment of Figs. 3 and 4.

[0099] One difference of the third and fourth embodiments (Fig. 8, 9) compared to the first and second embodiments (Fig. 3, 4) is that the first connectors 16 in the proximal direction are always connected to valleys 145 only of the middle stent ring 14 and not to distally facing crests, as the second straight connectors 140 do in Fig. 3. Moreover, also the second connectors 17 each are connecting a proximally facing crest of the middle stent ring 14 to a valley of the proximal stent ring 10. When on the one side of a ring the valleys are used for connectors and on the opposite side of the same ring the crests are used, there is a direct material bridge from the one connectors to the other connectors, as can be easily seen in Fig. 8 and 9. In conjunction with straight connectors such an arrangement has shown to be beneficial for maintaining axial stability and preventing kinking of the stent 1 during delivery, in particular of the middle ring 14 and proximal end ring 10, which exert only a low radial force. The first straight connectors 140 and the second straight connectors 147 have a relatively great width in the third and fourth embodiments, even though this is only optional. In particular, the width of the first and second straight connectors 140, 147 is about 1.5 to 2.5 times the width of the struts 107, 108 of the middle stent ring 14 and / or the struts 110, 111 of the proximal end ring 10. Also this may be beneficial to prevent kinking.

[0100] In the third and fourth embodiments (Fig. 8, 9) the first straight connectors 140 are tapering from the distal end ring 8 towards the proximal end 6. In the third embodiment (Fig. 8) the first straight connectors 140 are substantially tapering constantly until their final width is reached, which gives them a trapezoidal shape with two essentially straight opposite edges.

[0101] Similar, also the first straight connectors 140 according to the fourth embodiment (Fig. 9) are tapered, but taper slightly degressively, giving them a concave shape. The concave shape allows for a slightly increased flexibility.

[0102] While the struts 107, 108 of the middle stent ring 14 have the same length, and the struts 110, 111 of the proximal end ring 10 have the same length, as it is also shown in the first and second embodiments (Fig. 3, 4), they have different lengths in the fourth embodiment.

[0103] The fourth embodiment (Fig. 9) uses in all three stent rings 8, 10, 14 respective first and second circumferential ring segments which differ in their structure so that the above discussed expansion reserve is provided by each of the stent rings. In particular, the middle stent ring 14 comprises a third circumferential ring segment 124 and a fourth circumferential ring segment 126, which is structurally different from the third circumferential ring segment 124. The middle stent ring 14 comprises three third circumferential ring segments 124 and three fourth circumferential ring segments 126 in an alternating arrangement. The proximal end ring 10 preferably comprises a fifth circumferential ring segment 148 and a sixth circumferential ring segment 150, which is structurally different from the fifth circumferential ring segment 148. The proximal end ring 10 comprises three fifth circumferential ring segments 148 and three sixth circumferential ring segments 150 in an alternating arrangement. In the embodiment shown in Fig. 9, the fourth circumferential ring segment 126 differs from the third circumferential ring segment 124 in that fourth struts 108 forming the fourth circumferential ring segment 126 are shorter in length than third struts 107 forming the third circumferential ring segments 124. In the particular example by approximate 20%, but could also be any value between 5% and 50%. They are in this embodiment shortened from the distal side toward the proximal side, but this is not necessary and also they could be shortened from the proximal side towards the distal side, or from both sides with equal or different values. In the shown embodiment, the third and fourth struts 107, 108 have the same width, but in other embodiments they have different width as discussed above. This may be in addition or alternatively to the different length.

[0104] In the embodiment shown in Fig. 9, the sixth circumferential ring segment 150 differs from the fifth circumferential ring segment 148 in that sixth struts 111 forming the sixth circumferential ring segment 150 are shorter in length than fifth struts 110 forming the fifth circumferential ring segments 148. In the particular example by approximate 20%, but could also be any value between 5% and 50%. They are in this embodiment shortened from the distal side toward the proximal side, but this is not necessary and also they could be shortened from the proximal side towards the distal side, or from both sides with equal or different values. In the shown embodiment, the fifth and sixth struts 110, 111 have the same width, but in other embodiments they have different width as discussed above. This may be in addition or alternatively to the different length.

[0105] In the embodiments shown in Fig. 8 and 9, the connectors 149, which are connected to valleys of the sixth circumferential ring segments 150 are also straight connectors, but have a smaller width than the connectors 147, which are connected to valleys of the fifth circumferential ring segments 148. In other embodiments, connectors 147 are bow shaped, similar as connectors 142 are. Alternatively, also connectors 142 are straight connectors.

[0106] Fig. 10, very similar to Fig. 6 and 7 shows the stent of the fourth embodiment (Fig. 9) in a fully expanded state with the maximum diameter. As can well be seen from Fig. 10, the first straight connectors 140 and second straight connectors 147 form a single straight line and maintain a straight bar through the three segments, other than e.g. shown in Fig. 6, 7.

[0107] Fig. 11 shows a fifths embodiment of the stent 1 , which is based on the fourth embodiment (Fig. 9) with some modifications. In the following, mainly the differences are described, while for the other features complete reference is made to Fig. 9. One difference is in the overall axial length of the stent 1 . While the stent in Fig. 9 may for example have a length of about 30 mm to 40 mm, or e.g. 35 mm, the stent in Fig. 11 has an overall length of about 50 mm or could even have more.

[0108] The stent 1 in Fig. 11 shows different elements, which may be used to achieve a greater length. One option is to use lengthened connectors, in particular lengthened first connectors, in this embodiment first straight connectors 140 and / or first bow-shaped connectors 142. Also the other connectors, e.g. second connectors and / or third connectors may be lengthened. Lengthened means, that they occupy a larger total amount of the axial length compared to another embodiment. In ths shown embodiment, only the first connectors are lengthened.

[0109] Another option is to use more than one middle stent ring 14. In the shown embodiment there are two middle stent rings, 14, 214, which in this embodiment are also shaped identical. Thus, the (first) middle stent ring 14 is connected via the second connectors 147, 149 to the (second) middle stent ring 214, and the second middle stent ring 214 then in turn is connected via third connectors 240, 242 to the proximal end ring 10. While in the shown embodiment, the first and second middle stent rings 14, 214 are generally shaped identical, i.e. have the same struts and crests, with the same width, etc., in other embodiments, they can be different, in particular can have a lower COP than the first middle stent ring 14 and a higher COP than the proximal stent ring 10.

[0110] Fig. 12 shows a sixth embodiment which is similar to the embodiment shown in Fig. 9. The main difference to Fig. 9 is that the stent 1 shown in Fig. 12 only has straight connectors 140, 142 in the first connectors 16. All connectors of the stent 1 in Fig. 12 are straight connectors. In addition to the above described benefits, this may also have benefits in manufacturing and material efficiency.

Claims

Claims1. 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 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) 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), and the stent (1) 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 the distal end ring (8) has a first expansion characteristic in a first diameter range (D1) smaller than the nominal diameter (DN) and a second expansion characteristic in a second diameter range (D2) above the nominal diameter (DN), wherein the second expansion characteristic is different from the first expansion characteristic, wherein the proximal end ring (10) does have a third expansion characteristic over the complete expansion range from the minimum diameter (Dmin) to the maximum diameter (Dmax), and wherein a ratio in a chronic outward pressure (COP-N-dist) at the nominal diameter (DN) of the distal end ring (8) to a chronic outward pressure (COP-N-prox) at the nominal diameter (DN) of the proximal end ring (10) is 1 .8 or more.

2. Self-expandable stent (1) according to claim 1 , wherein the distal end ring (8) only includes closed cells (240, 242).

3. Self-expandable stent (1) according to any of the preceding claims, wherein the proximal end ring (10) only includes open cells.

4. Self-expandable stent (1) according to any of the preceding claims, wherein the distal end ring (8) comprises at least one first circumferential ring segment (120) and at least one second circumferential ring segment (122), which are structurally different from each other.

5. Self-expandable stent (1) according to claim 4, wherein the first circumferential ring segment (120) comprises struts (104) with a first circumferential width (W1) and the second circumferential ring segment (122) comprises struts (106) with a second circumferential width (W2), wherein the first circumferential width (W1) is greater than the second circumferential width (W2).

6. Self-expandable stent (1) according to claim 4 or 5, wherein the first circumferential ring segment (120) comprises struts (104) with a first length (LS1) and the second circumferential ring segment (122) comprises struts (106) with a second length (LS2), wherein the first length (LS1) is greater than the second length (LS2).

7. Self-expandable stent (1) according to any of the preceding claims, comprising a middle stent ring (14) placed between the distal end ring (8) and the proximal end ring (10).

8. Self-expandable stent (1) according to claim 7, wherein the middle stent ring (14) is connected via first connectors (16) to the distal end ring (8) and via second connectors (17) to the proximal end ring (10).

9. Self-expandable stent (1) according to claim 7 or 8, wherein the middle stent ring (14) comprises at least one third circumferential ring segment (124) and at least one fourth circumferential ring segment (126), which are structurally different from each other.

10. Self-expandable stent (1) according to claim 9, wherein the third circumferential ring segment (124) comprises struts (107) with a third circumferential width (W3) and the fourth circumferential ring segment (126) comprises struts (108) with a fourth circumferential width (W4), wherein the third circumferential width (W3) is greater than the fourth circumferential width (W4).11 . Self-expandable stent (1) according to claim 9 or 10, wherein the third circumferential ring segment (124) comprises struts (107) with a third length (LS3) and the fourth circumferential ring segment (126) comprises struts with a fourth length (LS4), wherein the third length (LS3) is greater than the fourth length (LS4).

12. Self-expandable stent (1) according to claim 5 and 10, wherein the first circumferential width (W1) is greater than the third circumferential width (W3), and wherein preferably the second circumferential width (W2) is greater than the third circumferential width (W3).

13. Self-expandable stent (1) according to claim 8, wherein the first connectors (16) include straight connectors (140).

14. Self-expandable stent (1) according to claim 13, wherein the straight connectors (140) connect the first circumferential ring segment (120) of the distal end ring (8) to the third circumferential ring segment (124) of the middle stent ring (14).

15. Self-expandable stent (1) according to claim 8, 13 or 14, wherein the first connectors (17) include bow-shaped connectors (142).

16. Self-expandable stent (1) according to claim 15, wherein the bow-shaped connectors (142) connect the second circumferential ring segment (122) of the distal end ring (8) to the fourth circumferential ring segment (126) of the middle stent ring (14).

17. Self-expandable stent (1) according to claim 8, wherein the distal end ring (8) comprises a plurality of proximally facing crests (144) and each proximally facing crest (144) of the distal end ring (8) is attached to one connector of the first connectors (16).

18. Self-expandable stent (1) according to claim 8 or 17, wherein the middle stent ring (14) comprises a plurality of proximally facing crests and each proximally facing crest of the middle stent ring (14) is attached to one connector of the second connectors (17).

19. Self-expandable stent (1) according to claim 8, 17 or 18, wherein the first connectors (16) are connected to crests (144) and valleys (145) of the middle stent ring (14), in particular crests (144) of the third circumferential ring segment (124) and valleys (145) of the fourth circumferential ring segment (126).

20. Self-expandable stent (1) according to claim 8, 17 or 18, wherein the first connectors (16) are each only connected valleys (145) of the middle stent ring (14).

21. Self-expandable stent (1) according to claim 20, wherein in every valley (145) of the middle stent ring (14) a first connector (16) is received and attached.

22. Self-expandable stent (1) according to any of the preceding claims, wherein the proximal stent ring (10) comprises at least one fifth circumferential ring segment (148) and at least one sixth circumferential ring segment (150) which are structurally different from each other.

23. Self-expandable stent (1) according to claim 22, wherein the fifth circumferential ring segment (148) comprises struts (110) with a fifth circumferential width (W5) and the sixth circumferential ring segment (150) comprises struts (111) with a sixth circumferential width (W6), wherein the fifth circumferential width (W5) is greater than the sixth circumferential width (W6).

24. Self-expandable stent (1) according to claim 22 or 23, wherein the fifth circumferential ring segment (148) comprises struts (110) with a fifth length (LS5) and the sixth circumferential ring segment (150) comprises struts (111) with a sixth length (LS6), wherein the fifth length (LS5) is greater than the sixth length (LS6).

25. Self-expandable stent (1) according to claim 8, wherein the second connectors (17) include bow-shaped connectors (146) and / or straight connectors (147, 149).

26. Self-expandable stent (1) according to claim 8 or 25, wherein the second connectors (17) are connected to crests (144) and valleys (145) of the proximal stent ring (10).

27. Self-expandable stent (1) according to claim 8 or 25, wherein the second connectors (17) are each only connected valleys (145) of the proximal stent ring (10).

28. Self-expandable stent (1) according to claim 27, wherein in every valley (145) of the proximal stent ring (10) a second connector (16) is received and attached.

29. Self-expandable stent (1) according to any of the preceding claims, having a nominal diameter in the range of 18 to 30 mm.

30. Self-expandable stent (1) according to any of the preceding claims, having an axial length of 25 mm to 55 mm.

31. Self-expandable stent (1) according to any of the preceding claims, wherein the framework is formed from a shape memory alloy, preferably a Titanium-Nickel-Alloy, preferably Nitinol, and is cut from a cylindrical tube as the raw material.

32. Self-expandable stent (1) according to any of the preceding claims, wherein the stent (1) has a cylindrical shape, in particular a cylindrical shape in the relaxed state.

33. 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 at least one middle stent ring (14) 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), 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 a ratio in a chronic outward pressure (COP-N-dist) at the nominal diameter (DN) of the distal end ring (8) to a chronic outward pressure (COP-N-prox) at the nominal diameter (DN) of the proximal end ring (10) is 1.8 or more, and wherein a ratio in a chronic outward pressure (COP-N-mid) at the nominal diameter (DN) of the middle stent ring (14) to the chronic outward pressure (COP-N-prox) at the nominal diameter (DN) of the proximal end ring (10) is 1 .0 or more,and wherein the ratio of (COP-N-mid) / (COP-N-prox) is 35% or less of the ratio of (COP-N-dist) / (COP-N-prox).

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