DOPPEL TENT

Description

[0001] The invention relates to a double stent with two coaxially arranged stents, wherein a first membrane is arranged between a first inner stent and a second outer stent, and a second membrane is arranged on the second stent, wherein the membrane ends of the first and the second membrane are joined at the ends of the stent and folded over to the inside of the first stent and fixed there.

[0002] The double stent serves primarily as a stent graft to bridge vascular malformations, such as aneurysms and shunts, but also to reinforce labile, fragile, or thrombotic vessel walls. It is further used as a bridge at branches from stented vessels or prostheses.

[0003] Stent grafts for bridging vascular malformations are known in a variety of forms. They typically consist of a stent that is completely or partially covered with a membrane. The membrane seals off the vascular malformation from the vessel, while the stent keeps the vessel open and ensures that the membrane adheres tightly to the vessel wall.

[0004] One problem with stent grafts is anchoring the membrane to the stent. Double stents have been developed to address this, in which the membrane is held between an outer and an inner stent. When such a double stent expands, the membrane participates in the radial expansion but remains clamped between the two stents.

[0005] Such a double stent is known, for example, from DE 197 20 115 A1. The stent described there has proven itself in and of itself, but can be improved in two respects.

[0006] Firstly, problems with leakage often arise because the membrane does not lie directly against the vessel wall and / or is damaged during the expansion of the double stent. In both cases, the double stent fails to meet its intended requirements, namely the sealing off of, for example, a vascular malformation.

[0007] On the other hand, during the expansion of the double stent, the assembly of two stents and a membrane may lose cohesion, for example if the two stents have different expansion behaviors - perhaps due to local conditions.

[0008] Double stents, which consist of a combination of two balloon-expandable stents, typically exhibit high radial force, leading to reliable placement and fixation of the membranes. However, this high radial force comes at the cost of reduced flexibility. Furthermore, significant pressures are required for expansion. The wall thickness of such a membrane-equipped double stent should be kept within limits to avoid unnecessarily constricting the vessel volume without compromising functionality.

[0009] WO 2017 / 125312 A1 describes another double stent which, in addition to an inner and an outer stent, also has an inner and an outer membrane that complement each other.

[0010] The invention is therefore based on the objective of providing a double stent that meets the requirements for tightness and reliability, ensures the necessary cohesion, and exhibits a sufficiently high radial force. At the same time, the stent should possess sufficient flexibility.

[0011] This problem is solved with a double stent according to claim 1, in which the two stents are made of different materials and differ in length and radius. In the double stent according to the invention, the inner and outer stents differ in their properties and materials. One stent is a balloon-expandable stent that provides the required radial force, while the other stent consists of a different material with lower radial force, for example, a biodegradable material or a shape-memory alloy that is self-expanding. Such materials are known and have been described extensively. The stent with the lower radial force is more flexible, i.e., it can have a thinner wall. It serves in particular to fix the first and / or second membrane.

[0012] The balloon-expandable stent with high radial force is specifically a cobalt-chromium alloy stent, as conventionally used for vascular support. This balloon-expandable stent can be deployed both internally and externally, facing the vessel wall, thus serving as a first internal or second external stent. When deployed as the first internal stent, it also serves to fix the membrane ends. When deployed as the second external stent, it provides the necessary compression force, which serves both to fix the double stent to the vessel wall, potentially also to dilate the vessel, and to fix the outer membranes to the vessel wall.

[0013] The other stent with the lower radial force could, for example, be a biodegradable stent, such as those typically made from biodegradable plastics (polylactic acid and / or polygalactide) and widely described. Biodegradable metal stents, for example made of magnesium alloys, are also suitable. These stents are also widely described. Such a stent is only suitable as a second outer stent and serves to fix the outer membranes to the vessel wall and the inner membrane within the stent assembly.

[0014] Alternatively, the stent with the lower radial force can be made of a nickel-titanium alloy, such as nitinol. Such a stent can be used as either the first inner or the second outer stent. As the first inner stent, it secures the membrane ends and provides the necessary pressure for the inner membranes to adhere to the second outer stent. As the second outer stent, during the expansion phase, it ensures rapid fixation of the outer membranes to the vessel wall and a secure fit of the inner membrane between the two stents of the assembly.

[0015] A preferred combination is a stent made of a cobalt-chromium alloy with a self-expanding stent made of a nickel-titanium alloy, the latter particularly preferably forming the first inner stent of the double stent assembly.

[0016] In this case, the inner first stent is advantageously 5 to 10 mm, preferably 8 mm, longer than the outer second stent and, in its final state determined by shape memory, has a diameter 1 to 6 mm, preferably 3 mm, larger than that of the outer second stent. This excess diameter ensures that, in the final state, the inner membrane always remains sufficiently tightly clamped between the inner and outer stents.

[0017] To improve the anchoring of the double stent in a vessel or prosthesis, the inner first stent can additionally be provided with radially protruding barbs or a trumpet-like shape, which may be coated with ePTFE if necessary.

[0018] The double stent according to the invention comprises not only an inner and an outer stent, but also an inner and an outer membrane. The two membranes complement each other with regard to their sealing properties. The outer membrane serves to protect and complement the inner membrane; if the inner membrane is damaged during expansion, for example, if it tears, the outer membrane is able to compensate for this defect, and vice versa. Furthermore, the outer membrane holds the structure together, with the anchoring of the ends of the outer membrane – together with the ends of the inner membrane – to the inside of the inner stent contributing to this cohesion.

[0019] For the stents used according to the invention, conventional stent designs are suitable, such as those frequently developed for balloon-expandable and self-expanding stents. For balloon-expandable stents, conventional materials are suitable, for example, medical-grade steel alloys, cobalt-chromium alloys, and the like. For self-expanding stents, materials with shape memory, such as nickel-titanium alloys, are particularly suitable.

[0020] The stents are typically cut from a tube of suitable diameter using a laser beam. They have a mesh structure with ring segments and connecting bridges between the ring segments.

[0021] The stents can, for example, have a mesh structure, such as that formed by intersecting webs. Stents formed from a plurality of meandering ring segments are preferred, with the ring segments connected to adjacent ring segments by connecting webs. In this case, too, meshes are formed whose size is determined by the frequency of the connecting webs between two adjacent ring segments. Such a stent structure is suitable for at least partially compensating for the length reduction that occurs during expansion, depending on the arrangement and shape of the connecting webs.

[0022] Various methods can be used to fix the membranes to the inside of the inner stent. The membranes can be sutured or glued. Welding, for example with ultrasound, or fusing, even through the mesh of the inner stent if it undergoes initial dilation during fabrication, is preferred. The finished double stent is then crimped onto a balloon.

[0023] The membranes on the inner first stent can also be clamped, for example, by spring tabs located there. These spring tabs point outwards from the stent, i.e., towards the stent edge. Such spring tabs can, for example, be outward-pointing membrane arcs of the ring segments, with the film ends being clamped between the membrane arcs and connecting bridges extending from the same ring segment (WO 2012 / 084202 A2).

[0024] Clamping the membrane ends to the inside of the inner stent ensures reliable anchoring of the two membranes and strengthens the assembly of inner stent, inner membrane, outer stent and outer membrane.

[0025] Any suitable biological or synthetic material can be used for the membranes. Typically, the membranes consist of a plastic, preferably a plastic tube, which is stretched over the respective stent. A suitable material is, for example, polytetrafluoroethylene (PTFE), particularly ePTFE, which possesses the necessary elasticity for expansion. Other medically suitable plastics, such as polyesters, polyolefins, polyurethanes, polyurethane carbonate, and the like, can also be used.

[0026] It is understood that different designs can be used for the inner and outer stents, and that the inner and outer membranes can be made of different materials.

[0027] The use of two stents and two membranes naturally results in a relatively thick wall of the construct, which limits its maneuverability within a patient's vascular system. This can be countered by selecting a thin wall thickness for the tubes used to cut the stents, particularly for the stent with lower radial force, for example, in the range of 0.05 to 0.50 mm, preferably 0.10 to 0.20 mm, and especially approximately 0.15 mm. The web width can also be reduced to, for example, 0.05 to 0.50 mm, preferably 0.10 to 0.20 mm, and especially approximately 0.15 mm.

[0028] It is further preferred to provide the outer stent with smaller mesh sizes than the inner stent. This creates a compressive stress during expansion, which has a beneficial effect on the radial force and the cohesion of the structure. High strength and durability of the structure are achieved.

[0029] The double stent according to the invention is particularly suitable for being inserted into branches from stented vessels and for bridging the space formed between the stented vessel and the branch.

[0030] The invention is explained in more detail by the accompanying figures, which show preferred embodiments of the invention. It is understood that the features shown in the figures are each part of the invention in themselves and are not to be understood only in conjunction with other features shown in the figures. The figures show: Figure 1: schematic longitudinal section through the end region of the wall of a double stent according to the invention; Figure 2: a top view of the development of the wall of the inner stent in its end region; Figure 3: a variant of Figure 2 .

[0031] The in Figure 1 The double stent according to the invention, designated by reference numeral 1, comprises a first inner stent 2 and a second outer stent 3, which are arranged coaxially to each other. The outer stent 3 is slightly shorter than the inner stent 2. The entire double stent 1 is shown in its unexpanded state. A first inner membrane 4 is located between the inner stent 2 and the outer stent 3. The outer stent 3 is surrounded by a second outer membrane 5. Both membranes 4 and 5 are made of ePTFE.

[0032] The inner membrane 4 and the outer membrane 5 are joined at their ends and folded inwards around the upper edge of the double stent 1 into the cavity of the inner stent 2. One of several spring tongues 6, which are part of the inner stent 2, is shown as an example; these are bent inwards and serve to clamp the inwards-folded edges of the membranes 4 and 5.

[0033] The one from Figure 1The emerging inner stent 2 is expediently made of a suitable shape-memory alloy, e.g., nickel-titanium (Nitinol), and has a proximal excess length of 5 mm to 10 mm, preferably 8 mm. Furthermore, in its final state determined by shape memory, it has a diameter that is 1 to 6 mm, preferably 3 mm, larger than the diameter of the outer stent 3. This ensures that the inner membrane 4 remains sufficiently tightly clamped between the inner stent 2 and the outer stent 3 at all times. For improved anchorage in a vessel or prosthesis, the stent 2 can additionally be provided with radially projecting barbs or a trumpet-shaped protrusion, which may be coated with ePTFE if necessary.

[0034] Figure 2 The design of the wall of the inner stent 2 is shown in its also in Figure 1 depicted end area, specifically with a concrete design of the in Figure 1only schematically represented spring tongues 6.

[0035] As from Figure 2 As can be seen, the wall of the inner stent 2, along its length, consists of a plurality of ring segments 7, each of which has a circumferential, meandering band. These meandering bands are axially connected to one another by axially flexible connecting webs. In this respect, the wall structure of the inner stent 2 corresponds to the widely used, conventional structure of stents.

[0036] In contrast to conventional stents, the stent 2 features according to Figure 2 In the end area, two differently designed ring segments 7a and 7b appear to accommodate the ones above. Figure 1to provide the spring tongues of the first inner stent 2 designated by reference numeral 6. The ring segment 7a forms the final outer edge of the stent 2, while the ring segment 7b is arranged between the outer edge and the length of the stent 2, see DE 10 2015 106 052 A1.

[0037] The two ring segments 7a and 7b each also feature a circumferential, meandering band. The meander arcs of both ring segments 7a and 7b, pointing towards the length of the stent 2, are connected to each other by axially extending connecting webs 9. In contrast, the meander arcs of the two ring segments 7a and 7b, pointing towards the end of the stent 2, are not connected to each other. Instead, the meander arcs of ring segment 7b pointing towards the end of the stent 2 are provided with blind webs 10 that project into the meander arcs of ring segment 7a, which are oriented in the same direction, without being connected to them. These blind webs 10, together with the meander arcs of ring segment 7b that support them, form the Figure 1 only schematically depicted spring tongues, which are designated there with the reference symbol 6.

[0038] The Figure 3 This shows another possibility for the formation of the spring tongues discussed above, which in Figure 1are designated with reference numeral 6. For this purpose, a ring segment 7c is provided at the end of the inner stent 2, which also has a circumferential, meandering band. The meander arcs of this band, pointing towards the end of the stent 2, are provided with incisions 11 along their length, thus forming elastically deformable spring tongues that, like paper clips, hold the in Figure 1 The ends of membranes 4 and 5 shown can be clamped, see WO 2012 / 084202 A2.

Claims

1. Double stent comprising two coaxially arranged stents (2, 3), wherein a first membrane (4) is arranged between a first inner stent (2) and the second outer stent (3) and a second membrane (5) is arranged on the second stent (3), wherein the membrane ends of the first and the second membrane (4, 5) are brought together at the ends of the stents (2, 3) and are folded over onto the inner side of the first stent (2) and secured / fixed there, wherein the first inner stent (2) is made of a first material and the second outer stent (3) is made of a second material, characterized in that the second outer stent (3) consists of a cobalt-chromium alloy and the first inner stent (2) consists of a shape-memory alloy and in that the first inner stent (2) is 5 to 10 mm longer than the second outer stent (3) and, in its final form as determined by its shape memory characteristics, has a diameter 1 to 6 mm larger than the diameter of the second outer stent (3).

2. Double stent according to claim 1, characterized in that the first inner stent (2) consist of a nickel-titanium alloy.

3. Double stent according to claim 1 or 2, characterized in that the first inner stent (2) is 8 mm longer that the second outer stent (3).

4. Double stent according to any one of claims 1 to 3, characterized in that the first inner stent (2), in its final form as determined by its shape memory characteristics, has a diameter 3 mm larger than the diameter of the second outer stent (3)5. Double stent according to any one of claims 1 to 4, characterized in that the first inner stent (2) is provided at its proximal end with additional fixation elements.

6. Double stent according to claim 5, characterized in that the fixation elements are in the form of barbs and / or a trumpet-shaped widening.

7. Double stent according to any one of the preceding claims, characterized in that at least the first inner stent (2) is provided with a plurality of ring segments (7, 7a, 7b) arranged side by side and having a meandering structure, said ring segments being connected to one another by means of connecting webs (8, 9).

8. Double stent according to any one of the preceding claims, characterized in that the membranes (4, 5) are secured / fixed by gluing / bonding, sewing, welding or clamping.

9. Double stent according to any one of claims 1 to 8, characterized in that the membranes (4, 5) are clamped in place in or between the flexible tongues (6) formed by applying incisions in the meandering arches of the first stent (2).

10. Double stent according to claim 9, characterized in that the flexible tongues (6) point to the outside of the stent.

11. Double stent according to claim 9 or 10, characterized in that the flexible tongues (6) are arranged in the peripheral regions of the first stent (2).

12. Double stent according to claim 11, characterized in that the flexible tongues (6) are formed on ring segments (7b) which are arranged adjacent to the peripheral ring segments (7a).

13. Double stent according to any one of claims 7 to 12, characterized in that the connecting webs (8) of the first inner stent (2) and second outer stent (3) are spaced apart with gaps between.

14. Double stent according to any one of the preceding claims, characterized in that the first membrane (4) and / or second membrane (5) consists of plastic material.

15. Double stent according to claim 14, characterized in that the first membrane (4) and / or the second membrane (5) consists of PTFE.