Occluding stent with helical support structure

Abstract

The invention relates to a stent comprising a helically wound support structure having a predetermined winding pitch along a helix axis, wherein the support structure has a front and a rear side surface vertical to the helix axis, wherein the front and rear side surfaces are independently divided into segments and exactly one flat element projecting from the support structure is arranged on each segment selected from a predetermined subset of segments of the support structure, wherein the flat element is securely connected to the support structure along the selected segment and there is no connection of the flat element to the support structure outside the selected segment.

Description

[0001] Occluding stent with helical support structure

[0002] The invention relates to a medical implant which can be introduced in compressed form into a lumen of a living patient via a catheter and can then be expanded there.

[0003] Such an implant is generally referred to as a stent and comprises at least one support structure made of a wire or wire mesh which, when expanded, has a tubular - often cylindrical - shape. The wire material can be a metal, a metal alloy, or even a polymer plastic. Depending on the stent design and the material selection, the stent can be self-expanding, i.e. it reaches its expanded shape automatically after leaving the sleeve in the distal end of the catheter upon relaxation of the mechanical stress introduced during compression. Other stents must be actively expanded, for example, with the help of a balloon and compressed air.

[0004] Stents are now predominantly used in blood vessels and are commonly referred to as vascular stents. Their purpose is to influence blood flow through the vessel at the site of stent placement. Basically, the blood should be able to flow unhindered through the interior of the expanded stent tube. The support structure either rests on the vessel walls and, even when the stent is placed at a vessel bifurcation, usually represents a relatively minor obstacle to blood flow into a branching vessel. In pathologies such as aneurysms, however, a significant reduction in branching blood flow is desired, and this requires reduced stent permeability, at least on the side surface of the stent that is positioned before the branch during placement. Stents constructed with means to locally reduce permeability are also referred to as occluding stents.Occluding stents typically have surface elements with a predetermined fenestration, meaning the surface elements are open and the openings allow blood flow through the surface element. The shape, number, arrangement, and surface area of ​​the openings relative to the surface element are determined according to medical criteria. In particular, a wire mesh with a predetermined number, shape, and size of meshes is also a surface element with a predetermined fenestration.

[0005] Crimping a stent, especially an occluding stent, for insertion into a catheter sleeve can be a challenging task. The available volume within the sleeve limits the stent's material volume, and reducing the stent's expanded diameter to a fraction of its compressed size is essential. The stent must not sustain any damage, such as plastic deformation, and should preferably be self-expanding upon exiting the sleeve.

[0006] Helical stents are known, for example, from US Pat. Nos. 4,553,545 and 5,476,505 and essentially consist of a wire formed into a cylindrical spiral or helix, typically made of metal, particularly a superelastic shape-memory alloy such as Nitinol. They can be compressed particularly easily by being drawn into a sleeve, whereby the helix diameter decreases to approximately the diameter of the wire. Upon leaving the sleeve, the wire automatically returns to its helical shape, adhering to the vessel walls and exerting a force on them. Helical stents can be placed along a blood vessel with a non-uniform diameter or even along a vessel branch.The predetermined pitch of the helix turns in the expanded stent ex-situ can also be understood as a predetermined fenestration of its side wall, but during practical implantation, a different, significantly different fenestration may occur locally in-situ, which is difficult to control.

[0007] It has become a well-known approach for occluding stents to use the wire mesh of a stent as a support structure for a sheath structure, whereby the sheath structure has a predetermined, usually close-meshed fenestration. The sheath structure can be manufactured as a so-called "micromesh" using thin-film technology from metal and designed as a cylinder with regularly arranged, slit-shaped openings, as can be seen, for example, in the document US 2021 / 0251785 A1. The sheath structure can be slipped over the compressed support structure - e.g., a conventional endovascular stent - and expanded together with the support structure. In this process, the sheath structure is deformed into meshes, forming a net-like wire mesh structure with fenestration that can be adjusted by the extent of the expansion.The ratio of open to metal-covered area of ​​the shell structure is often referred to as the porosity of the surface or a surface element. In particular, the shell structure of US 2021 / 0251785 A1 can therefore also exhibit different porosities along its length or for different partial areas.

[0008] The prior art also discloses a helically wound support structure for a sheath structure in the manner of a "micromesh" from WO 2006 / 071244 A1. However, unlike in US 2021 / 0251785 A1, the support structure is not rigidly connected to the sheath structure, but rather threaded through slits in the wire mesh. This allows the sheath structure and support structure to move relative to each other, which is intended to prevent buckling of the sheath structure when the stent is placed in a vessel curvature. Here, too, the mesh-like shape of the otherwise flexible sheath structure means that the in-situ fenestration can deviate to a certain extent from a predetermined ex-situ fenestration due to vessel morphology.

[0009] Furthermore, from US 2020 / 0022800 A1 an implantable intraluminal stent graft device is known, wherein in some embodiments the stent graft devices provided herein are implantable in body conduits having side branches, and wherein the stent graft devices are operable to allow the flow of fluids between the conduit and the side branches.

[0010] From the document DE 10 2009 060 228 A1 a medical device is known with a tubular wall made of webs that delimit cells and a flexible membrane that forms at least one flap, wherein the latter has a first end that is connected to at least one first web of a cell and a free second end that is arranged opposite the first end in the longitudinal direction of the flap, wherein the flap can be transferred into a closed position in which the flap extends along the tubular wall and at least partially closes the cell, and into an open position in which the flap is deflected radially relative to the wall in order to release the cell in a valve-like manner.

[0011] The document DE 10 2010 026 830 A1 discloses a medical device with a wall made of a lattice structure with cells which each delimit a cell opening and are formed from webs, wherein the cell opening of at least one cell is partially closed or partially closeable by at least one cover which has - a web-shaped frame which forms the circumference of the cover and is connected to at least a first web of the cell, and - a membrane which spans the frame, wherein a free end of the frame is arranged at a distance from at least the first web of the cell and the circumference of the cover is smaller than the circumference of the cell opening (is such that the cover projects into the cell opening.

[0012] The invention now aims to combine the advantages of a helical stent with the ability to occlude with a precisely predetermined fenestration, even in situ.

[0013] This object is achieved by a stent comprising a helically wound support structure with a predetermined winding spacing along a helix axis, wherein the support structure has a front and a rear side surface vertical to the helix axis, characterized in that a. the front and the rear side surface are divided into segments independently of one another and b. exactly one surface element projecting from the support structure is arranged on each segment selected from a predetermined subset of segments of the support structure, wherein c. the surface element is firmly connected to the support structure along the selected segment and d. there is no connection between the surface element and the support structure outside the selected segment.

[0014] The subclaims specify advantageous embodiments of the stent.

[0015] The at least one surface element may extend over at least one non-selectable segment that is adjacent to the selected segment on which the surface element is arranged.

[0016] The at least one surface element can extend over exactly one adjacent, non-selectable segment, so that the surface element has a unidirectional extension along the support structure.

[0017] Furthermore, the at least one surface element can protrude from the support structure by more than the predetermined winding distance.

[0018] In one embodiment, a plurality of surface elements can extend over a plurality of non-selectable segments, wherein all surface elements have the same unidirectional extension along the support structure.

[0019] Each surface element can have its own predetermined fenestration.

[0020] Furthermore, in the helix shape, different surface elements can overlap and in the overlap area there can be a fenestration that deviates from the fenestrations of the surface elements.

[0021] The helically wound support structure can be coated with radiomarkers at least pointwise, preferably in a predetermined position relative to the selected segments of the support structure with the surface elements.

[0022] Furthermore, at least the surface elements can be formed from a superelastic shape memory material, preferably from a shape memory alloy.

[0023] The supporting structure and the surface elements can in particular be made of the same material and connected to one another in a material-to-material manner.

[0024] The stent according to the invention resembles a climbing plant in its shape, which has grown spirally around a rod-shaped support, forming individual leaves from the main stem that more or less adhere to the rod's surface. The main stem corresponds to the helically wound support structure of the stent, which is formed from an elastically deformable material such that the helix is ​​self-supporting and can be reversibly compressed by being drawn into a tube with a tube diameter smaller than the helix diameter. Suitable materials are typically metals and thermosetting polymers.

[0025] In its helical shape, the support structure has a helical axis that defines a front and a rear side surface of the support structure by virtue of these two side surfaces running vertically to the helical axis. In fact, vertical does not mean exactly perpendicular here, because these side surfaces are tilted more or less relative to the helical axis depending on the pitch of the helix. However, the helix mimics the surface of a cylinder around the helical axis, and the front and rear side surfaces are each characterized by the fact that their normal vectors are directed along this surface at every point on the helix. The front and rear side surfaces are clearly distinguished in particular by the fact that their normal vectors are directed in opposite directions.

[0026] According to the invention, surface elements are arranged on the front and / or rear side surface of the helical support structure and are firmly connected to the support structure, with the surface elements projecting from the support structure. The surface elements thus extend along the helix axis over at least part of the winding pitch or beyond.

[0027] Each of the segments of one of the side surfaces of the support structure can be provided for the arrangement of a surface element; alternatively, only a predetermined subset of the segments, which does not include all segments, can be intended to be equipped with surface elements, ie there then exist non-selectable segments which are not intended to carry any surface elements.

[0028] Each surface element is arranged on exactly one selected segment of the front or rear side surface and is firmly connected to the support structure at that same location. To ensure that the surface element maintains its orientation relative to the segment of the side surface on which it is arranged, the fixed connection extends along the support structure, which is limited to the selected segment. If necessary, the surface elements can be curved along the curvature of the support structure itself, so that they lie primarily within the cylindrical surface spanned by the helix.

[0029] A solid connection within the meaning of the invention can be the results of conventional joining techniques (e.g., bonding, soldering, fusing), as well as residual structures resulting from material-removing shaping (e.g., etching, laser cutting), and built-up connecting structures (e.g., 3D printing, sputtering). The connection is referred to as solid here because it cannot be removed without destruction. For use as a vascular stent, very precise connections on the micrometer scale are usually required.

[0030] A key feature of the invention is that a surface element outside the selected segment has no connection to the support structure. This applies to all surface elements of the stent according to the invention, regardless of the number and distribution of the surface elements along the support structure. In particular, there are no movement-impeding restrictions between the turns of the helical support structure. The stent according to the invention can thus be drawn into a catheter sleeve by folding the surface elements in like a conventional helical stent.

[0031] The invention is explained in more detail below with reference to figures.

[0032] It shows:

[0033] Fig. 1 a helical stent according to the invention with occluding

[0034] Surface elements (left) and a section of the same stent in unrolled - planar - form (right);

[0035] Fig. 2 a) to d) show some examples of planar stent designs according to the present invention;

[0036] Fig. 3a) a stent according to the invention with a helical support structure, which, like the

[0037] Surface elements are provided with fenestration;

[0038] Fig. 3b) the retraction of the stent from Fig. 3 a) with automatic folding of the

[0039] Surface elements.

[0040] Figure 1 shows a photograph of a stent according to the present invention on the left. The noticeably thicker helical support structure carries leaf-shaped surface elements on its front and rear side surfaces, each of which is in turn provided with a fenestration. The fixed connections of the surface elements to the support structure are located at the same height along the support structure on both side surfaces.

[0041] From Fig. 1 on the right, which shows a section of the stent in its unrolled, planar form, it can be seen that the surface elements are connected to the support structure along opposing paths. It is also within the scope of the invention that the connecting paths along the selected segment may be incomplete, i.e., provided with interruptions.

[0042] Typically, the stent according to the invention is first manufactured in its planar form and subsequently converted into the helical shape. Several techniques are known for manufacturing the planar stent design; laser cutting and magnetron sputtering are preferred if the stent is to be formed from metals. A well-known and also very preferred embodiment of the invention is to use superelastic shape memory materials, particularly preferably a shape memory alloy, e.g., based on nickel and titanium, as materials for the stent. It is considered advantageous to form at least the surface elements from a superelastic shape memory material. It is particularly advantageous to form the support structure and the surface elements from the same material and to bond them together in a material-to-material manner.

[0043] The stent in Fig. 1 was initially produced from a nickel-titanium alloy using sputtering technology as a planar design. It obtains its helical shape by wrapping a shaped cylinder and subsequent heat treatment to crystallize the shape memory alloy in the austenite phase. Alloys suitable for biological implants are well known in the art. In the example shown in Fig. 1, the support structure is 42 micrometers thick and 300 micrometers wide, while the protruding surface elements have a thickness of 7 micrometers. In sputtering, the cross-section of the support structure is usually trapezoidal or even rectangular, but other processes allow for other cross-sectional shapes, so the terms "front and rear side surfaces" have been introduced here regardless of the cross-sectional shape.

[0044] It is possible and can be advantageous for at least one surface element to protrude from the support structure by more than the embossed coil spacing. However, this is not determined in the planar stent design alone, but only finally during the embossing of the helical coils.

[0045] Figure 2 shows examples of some other planar stent designs consistent with the invention described here, intended to illustrate the possible variations. In Figure 2, the support structure is always shown hatched, and the surface elements are always checkered. It should be emphasized that this is intended to indicate a functional difference, not necessarily a material difference. Furthermore, no fenestrations are shown in Figure 2, which is not intended to rule out the possibility of such fenestrations being created.

[0046] Fig. 2 a) shows an arrangement of approximately semicircular surface elements on the front (top in the image) and rear (bottom in the image) side surfaces of the support structure. On the rear side surface, all segments have been selected for arranging surface elements, whereas on the front side surface only a subset of the possible segments is predetermined, meaning that there are non-selectable segments that remain free. It should be noted that there is no direct connection between the immediately adjacent surface elements on the rear side surface, but rather only a connection to the support structure. Fig. 2 b) shows a stent design with several surface elements arranged opposite one another, the shape of which is selected such that the surface elements extend laterally along the support structure beyond the selected segments on which they are arranged.This means that the surface elements extend not only into the space extending vertically from the supporting structure over the selected segments, but also into the neighboring spaces that exist above the adjacent non-selectable segments without surface elements.

[0047] It is merely an exemplary special case that all surface elements have the same shape and size. In extreme cases, the stent may have only a single surface element, which is connected to the support structure at a predetermined segment.

[0048] In principle, it is an advantageous embodiment of the invention that the at least one surface element extends over at least one non-selectable segment that borders the selected segment on which the surface element is arranged. In fact, it may even be particularly advantageous for the at least one surface element to extend over precisely one adjacent, non-selectable segment. In this case, the surface element extending only on one side over a non-selectable segment has a unidirectional extension along the support structure.

[0049] For the sake of completeness, it should be mentioned that the shape of the surface elements makes it entirely possible for a surface element to extend both over an adjacent, non-selectable segment and over an adjacent, second, selected segment where a second surface element is located. Overlaps of the surface elements in the planar form are avoidable and not intended.

[0050] A preferred embodiment of the aforementioned stent with a unidirectional extension consists in that a plurality of surface elements extend over a plurality of non-selectable segments, with all surface elements having the same unidirectional extension along the support structure. Such an example is shown in Fig. 2 c), in which the surface elements are now arranged alternately on both side surfaces of the support structure.

[0051] The practical advantage of this design is that when the helical support structure is drawn into a sleeve in such a way that the pulling direction is selected opposite to the unidirectional extension of the surface elements, the surface elements can fold automatically. This is even easier if the surface element edges are also beveled along the extension direction. In the example of Fig. 2 c), beveling the respective right-hand edges of the surface elements along their common extension direction (to the left) could significantly simplify the folding of the surface elements when the support structure is drawn into a sleeve arranged on the right side.

[0052] As a consequence, the occluding stent design according to the invention makes it possible to completely return the stent back into the sleeve even in-situ during a medical procedure, for example, to change its placement.

[0053] Finally, Fig. 2 d) shows a stent design according to the invention, whose selected segments are predefined for the arrangement of surface elements over a very extended area along the support structure. This design can also be retracted into a sleeve by automatically folding the surface elements, although the width of their fixed connection to the support structure means that the surface elements have less freedom of movement than in previous examples. Especially for the central region of a selected segment, the sleeve must be able to provide sufficient volume to accommodate the support structure and the folded surface element.

[0054] This can be achieved by making the support structure of Fig. 2 d) itself compressible in the region between the opposing surface elements, for example and preferably by providing a fenestration of the support structure there. Fig. 3 a) shows a photograph of a stent according to Fig. 2 d) with a helix diameter of approximately 4 mm, which has a largely uniform fenestration of the surface elements and the intermediate support structure. By selecting the arrangement and size of the openings (or fluid passages) in the stent structure, enough material is removed to allow it to fold automatically into a sleeve with a diameter of 0.5 mm, as shown in Fig. 3 b).

[0055] Further advantageous embodiments of the stent according to the invention include the fact that each surface element has its own predetermined fenestration. In particular, different surface elements can have different fenestrations; for example, the stent can have surface elements with a mesh structure and others without any openings. This allows a stent to be custom-made to a patient's medical requirements. Depending on the patient's pre-diagnosed vascular structure, surface elements with precisely predetermined porosity can be precisely arranged on the helical support structure to enable optimal treatment.

[0056] Furthermore, it is considered advantageous that various surface elements can overlap in the helical shape, with a fenestration in the overlapping area that differs from the fenestrations of the surface elements. This can be used by the physician to vary the occlusion even during a procedure, without requiring structural modifications to the stent.

[0057] Finally, it is an advantageous embodiment for the helically wound support structure to be coated with radiomarkers at least pointwise, preferably in a predetermined position relative to the selected segments of the support structure with the surface elements. Common radiomarkers are materials containing elements with a high atomic number, e.g., tantalum, gold, or platinum. The provision of such markers allows intraoperative monitoring of the position of the stent and can be used—for example, with the aid of computer-assisted data analysis—to assess the shape of the blood vessel, the position of branches, and the actual occlusion achieved by the stent, and to immediately communicate this information to the physician.

Claims

CLAIMS 1. Stent comprising a helically wound support structure with a predetermined winding spacing along a helix axis, wherein the support structure has a front and a rear side surface vertical to the helix axis, characterized in that a. the front and the rear side surface are divided into segments independently of one another and b. exactly one surface element projecting from the support structure is arranged on each segment selected from a predetermined subset of segments of the support structure, wherein c. the surface element is firmly connected to the support structure along the selected segment and d. there is no connection between the surface element and the support structure outside the selected segment.

2. Stent according to claim 1, characterized in that the at least one surface element extends over at least one non-selectable segment which is adjacent to the selected segment on which the surface element is arranged.

3. Stent according to claim 2, characterized in that the at least one surface element extends over exactly one adjacent, non-selectable segment, so that the surface element has a unidirectional extension along the support structure.

4. Stent according to one of the preceding claims, characterized in that the at least one surface element protrudes from the support structure by more than the predetermined winding distance.

5. Stent according to claim 3, characterized in that a plurality of surface elements extend over a plurality of non-selectable segments, wherein all surface elements have the same unidirectional extension along the support structure.

6. Stent according to one of the preceding claims, characterized in that each surface element has a specially predetermined fenestration.

7. Stent according to one of claims 5 or 6, characterized in that in the helical shape, different surface elements overlap and in the overlapping region there is a fenestration which deviates from the fenestrations of the surface elements.

8. Stent according to one of the preceding claims, characterized in that the helically wound support structure is coated with radiomarkers at least pointwise or in a predetermined position relative to the selected segments of the support structure with the surface elements.

9. Stent according to one of the preceding claims, characterized in that at least the surface elements are formed from a superelastic shape memory material or from a shape memory alloy.

10. Stent according to claim 9, characterized in that the support structure and the surface elements are formed from the same material and are integrally connected to one another.

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