Balloon catheter-stent structure combination

Abstract

The invention relates to a combination of a balloon catheter (1) through which a lumen extends in the longitudinal direction, wherein, in the distal portion of the balloon catheter (1), a balloon (2) is arranged which can be expanded by pressurisation with a fluid passing through the lumen, and a stent structure (5) composed of interwoven wires or interconnected webs (7), wherein the stent structure (5) can be applied to the balloon (2) of the balloon catheter (1) and can be brought into an expanded form by expansion of the balloon (2), wherein the stent structure (5) is elastic and designed so that without external forces acting on it the stent structure (5) assumes a reduced-diameter form in which it is firmly seated on the balloon (2). With the aid of the combination according to the invention, stubborn stenoses in particular can be effectively dilated.

Description

[0001] Balloon catheter-stent structure combination

[0002] The invention relates to a combination of a balloon catheter through which a lumen extends in the longitudinal direction, wherein a balloon is arranged in the distal section of the balloon catheter, which balloon can be expanded by pressurizing it with a fluid passed through the lumen, and a stent structure which is constructed from interwoven wires or interconnected webs, wherein the stent structure can be applied to the balloon of the balloon catheter and can be brought into an expanded form by expansion of the balloon.

[0003] The use of balloon catheters is now standard in everyday clinical practice. Their use in intravascular interventions usually involves the dilation of narrowed vascular sites, either with the balloon catheter itself or in combination with other medical devices such as balloon-expandable stents. In percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA) for the coronary arteries, a balloon catheter is guided to the site of the stenosis via a guidewire and a guiding catheter and expanded by the introduction of a fluid under pressure (approximately 4 to 12 bar). Deposits present in the area of ​​the stenosis are pushed into the vessel wall. In addition, a stent (vascular endoprosthesis) can be inserted to keep the blood vessel permanently open.To prevent the recurrence of stenosis due to vascular overgrowth at the enlarged site, drug-coated balloon catheters can also be used. These release an active ingredient such as paclitaxel at the site of the stenosis upon expansion. After treatment and subsequent collapse of the balloon, the balloon catheter is withdrawn from the vascular system and removed. In many cases, balloon angioplasty has replaced conventional bypass surgery.

[0004] The femoral artery in the groin is often chosen as the access site for balloon catheters. The femoral artery, at least partially, runs relatively superficially and is therefore easily accessible to the treating physician, both for treatments in the coronary region and for other areas of the vascular system, such as the brain or extremities. Furthermore, relatively large-lumen catheters with large outer diameters can be inserted through the femoral artery (femoral artery).

[0005] Atherosclerosis is a common disease of modern society and responsible for a large number of deaths worldwide. Atherosclerotic plaques, composed of calcium salts and often relatively hard, and fibrotic tissue form on the inner walls of arteries. This can narrow the vessels to such an extent that blood flow is severely impaired. Cutting balloons or scoring balloons are currently used to dilate such stenoses. These are balloons attached to balloon catheters with metal wires attached to the outside. As the balloon expands, these metal wires move into the formed atherosclerotic plaques and break them up. This type of treatment is particularly important in the coronary arteries or in peripheral areas such as the leg arteries.

[0006] Such a balloon catheter, known as the Barath cutting balloon, is described in US Pat. No. 5,196,024. When the balloon expands, the cutting edges attached to the balloon are capable of making longitudinal incisions in the vessel walls, thereby increasing the vessel diameter and preventing cell proliferation or restenosis, which often occurs with conventional angioplasty. The longitudinal incisions are made in fibrotic or calcified tissue. Since the cutting edges are fixed both distally and proximally to the balloon catheter, they follow the expansion and deflation of the balloon. US Pat. No. 2005 / 0245864 A1 describes a cutting balloon with which the incisions in fibrotic or calcified tissue are not made radially evenly, but in a specific radial region of the inner vessel wall. For this purpose, the balloon is mounted eccentrically to the guide wire axis.In this way, it is avoided that unaffected areas of the inner vessel wall are affected.

[0007] Scoring and cutting balloons have established themselves in artery dilation, but conventional balloon catheters are still used in the majority of cases. A disadvantage of using scoring or cutting balloons is that they represent a significant modification of a conventional balloon catheter and, in case of doubt, must be kept in the clinic alongside conventional balloon catheters.

[0008] The task was therefore to provide the treating physician with a flexible option to modify a balloon catheter so that it has an improved effect in dilating problematic stenoses.

[0009] This object is achieved according to the invention by a combination of

[0010] - a balloon catheter through which a lumen extends in the longitudinal direction, wherein a balloon is arranged in the distal section of the balloon catheter, which balloon can be expanded by pressurising it with a fluid passed through the lumen, and

[0011] - a stent structure constructed from interwoven wires or interconnected webs, wherein the stent structure can be applied to the balloon of the balloon catheter and brought into an expanded form by expansion of the balloon, wherein the stent structure is elastic and adjusted in such a way that it assumes a diameter-reduced shape in which it sits firmly on the balloon without external forces acting on the stent structure.

[0012] Unlike the scoring or cutting balloons described above, the present invention uses a typical balloon catheter. A stent structure, usually a separate object composed of interwoven wires or interconnected struts, is placed on the balloon section. As the balloon expands, the stent structure also expands, forcing the struts / wires into the inner vessel wall. Especially in the presence of severely fibrotic or calcified tissue, this breaks up the vascular constriction and thus supports balloon dilation.

[0013] In contrast to the usual placement of a stent using a balloon catheter, the stent structure used according to the invention is not intended to be permanently placed in the blood vessel, but rather is intended to merely support the dilation of the blood vessel and then be removed again. For this reason, the stent structure is pre-adjusted in such a way that it "wants" to assume a contracted or compressed shape in which it sits firmly on the balloon in such a way that retraction of the balloon with stent structure in a proximal direction is possible. The stent structure can thus be brought into an expanded shape by the action of external forces, namely by expansion of the balloon, in which it exerts the described effect on the inner wall of the vessel. However, as soon as the balloon contracts again, the stent structure also returns to a contracted shape with a significantly smaller outer diameter, in which it sits on the deflated balloon.The balloon can then be retracted proximally together with the stent structure sitting on the deflated balloon and removed from the blood vessel system.

[0014] A large number of stents are known from the prior art which have an imprinted secondary structure which the stent assumes when no external forces act on the stent. These are self-expanding stents, which are usually made of a metal with shape memory properties. However, the presetting of the stent in these cases is exactly the opposite of that of the invention. Self-expanding stents expand of their own accord as soon as they are released from a catheter which has previously prevented their expansion and held them in a compressed state. They then remain in the blood vessel to keep it permanently open. In contrast, the stent structure according to the invention is intended to contract of its own accord or reduce its diameter and is only expanded by external forces, namely the expansion of the balloon. As soon as these forces are no longer acting, the stent structure contracts back into its reduced-diameter shape.In contrast to self-expanding stents, it is not intended to remain permanently in the blood vessel, but is to be removed together with the balloon catheter.

[0015] In order for the stent structure to spontaneously assume the intended contracted, reduced-diameter shape, it must possess sufficient elasticity to allow it to retract after expansion. It is particularly advantageous if the stent structure possesses superelasticity, also known as pseudoelasticity. Pseudoelastic alloys, also known as shape memory alloys, are characterized by the ability to return to their original shape upon release, even after considerable deformation. Compared to conventional spring steels, pseudoelastic alloys can be stretched up to ten times more without being permanently deformed. Accordingly, materials with shape memory properties can be used for the stent structure. A stent structure that is at least partially constructed from a shape memory material, in particular a shape memory alloy, is therefore particularly advantageous.

[0016] Nickel-titanium alloys, such as Nitinol, as well as ternary nickel-titanium-chromium alloys or nickel-titanium-copper alloys, have proven particularly effective as shape memory alloys. However, other shape memory materials, such as other alloys or even shape memory polymers, are also conceivable.

[0017] The use of cobalt-chromium or cobalt-chromium-nickel alloys is also possible. Such alloys are also frequently used in the field of medical technology. In particular, the use of an alloy known as Elgiloy is possible; this consists of 39 to 41 wt.% cobalt, 19 to 21 wt.% chromium, 14 to 16 wt.% nickel, 11.3 to 20.5 wt.% iron, 6 to 8 wt.% molybdenum, 1.5 to 2.5 wt.% manganese, and a maximum of 0.15 wt.% carbon. The use of stainless steel is also possible.

[0018] However, the stent structure does not have to be composed of a single material; combinations of different materials, particularly different metals and alloys, are also possible. It is possible to manufacture individual wires or bars of the stent structure from one material and use a different material for other wires or bars. For example, radiopaque materials can be used for individual wires / bars to allow the treating physician to visualize the treatment. Examples of radiopaque materials include platinum and platinum alloys such as platinum-iridium or tantalum.

[0019] It is also possible to use wires / bridges composed of multiple materials. So-called DFT® (Drawn Filled Tubing) wires, for example, are known from the prior art. These wires have a core made of a different material than the sheath surrounding the core. For example, a wire / bridge can have a core made of an X-ray-visible material and a sheath made of a material with shape memory properties. The X-ray-visible materials can, in particular, be those mentioned above. DFT® wires are marketed, for example, by Fort Wayne.

[0020] The stent structure as part of the inventive combination is referred to here as a stent structure, but this term refers to the structure of the object, not its function. Conventional stents are implants designed to remain permanently in the blood vessel and keep it open. In contrast, the stent structure according to the invention is intended to be removed from the vascular system after treatment and dilation of the blood vessel. However, following balloon dilation, a conventional stent can be placed in the area of ​​the dilated stenosis to prevent restenosis.

[0021] Stents and similarly constructed medical devices are generally classified as braided and cut structures. Braided structures are composed of individual wires that form a wire mesh. Accordingly, the mesh is easily adaptable to both expanded and reduced diameter configurations. Expansion typically involves a significant shortening of the stent structure, while contraction involves a significant lengthening.

[0022] Another class of stents consists of structures composed of interconnected struts. These stents are usually laser-cut, meaning the desired structure is cut out of a tube using a laser. The interconnected struts form a lattice structure composed of a multitude of cells defined by the struts. The cells can be closed, meaning they are completely enclosed by struts, and / or open. In particular, individual cells can be closed, while others can be open.

[0023] Both variants are possible for the stent structure according to the invention: braided structures made of individual wires and (laser-)cut structures made of individual webs. Other options for manufacturing a stent structure, such as 3D printing, are also conceivable.

[0024] The wires or struts of the stent structure preferably have a shape that allows them to penetrate well into the deposits and growths on the inner walls of the vessels. The wires / struts can have a round or oval cross-section for this purpose, but it is also possible to provide the wires / struts with a cross-section that decreases radially outwards. For example, the wires / struts can have a triangular cross-section, with one edge of the wires / struts pointing radially outwards in order to be able to penetrate the deposits / growths like a blade. A triangular cross-section is also understood to mean one in which the side surfaces of the wire / strut are more or less rounded. Wires or struts with a rectangular, square, or trapezoidal cross-section are also conceivable, although here too the side surfaces can be rounded. In the context of the invention, proximal is understood to mean in the direction of the outside of the body, i.e.The term "radial" refers to the direction toward the treating physician, while "distal" refers to the opposite direction, i.e., toward the target position. The longitudinal direction is the direction from proximal to distal, or vice versa. Radial refers to the plane perpendicular to the longitudinal axis of the balloon catheter.

[0025] According to one embodiment of the invention, the stent structure and the balloon catheter are designed as separate components. This allows the treating physician to decide individually, depending on the nature of the stenosis, whether dilating the vessel with the balloon catheter alone is sufficient or whether the stent structure according to the invention should also be applied to the balloon of the balloon catheter. In the case of a stenosis that is relatively easy to dilate, the physician will generally forgo the additional stent structure; however, in the case of a stubborn stenosis, for example, one with severe fibrotic or calcified stenosis, he or she will, in case of doubt, opt for placing or crimping the stent structure onto the balloon of the balloon catheter. Because the stent structure has a small cross-section in its resting state, which it assumes when no external forces act on the stent structure, it fits tightly against the deflated balloon catheter.Accordingly, it is possible both to advance the stent structure on the balloon in the distal direction when inserting the balloon catheter and to retract the stent structure in the proximal direction when withdrawing the balloon catheter.

[0026] According to an alternative embodiment, however, one end of the stent structure could also be fixed to the balloon catheter, while the rest of the stent structure extends over the balloon. Typically, the fixation occurs immediately adjacent to the balloon, i.e., immediately proximal or distal to the balloon. In this case, fixation of the proximal end of the stent structure to the balloon catheter is preferred, namely proximally adjacent to the balloon of the balloon catheter. In this embodiment, the unfixed end of the stent structure is free and can be freely expanded and contracted. In this context, the end of the stent structure is understood not only to mean the outermost end of the stent structure in the longitudinal direction; it is sufficient if the stent structure is fixed to the balloon catheter in the region of one end, which does not preclude small parts of the stent structure from extending further proximally or distally beyond the fixation point.

[0027] In this embodiment, due to the fixation of the stent structure to the balloon catheter, unwanted detachment or slippage of the stent structure relative to the balloon catheter is eliminated when the balloon catheter is either advanced distally or withdrawn proximally. On the other hand, with this embodiment, the physician has less flexibility in deciding whether the treatment should be performed with or without the stent structure in place.

[0028] It makes sense for the outer diameter of the stent structure in its expanded form to be approximately two to four times larger than in its reduced-diameter form. This ensures, on the one hand, that the stent structure has a small cross-section in its reduced-diameter state, so that the balloon catheter with the stent structure attached can be easily maneuvered even through narrow-lumen blood vessels. On the other hand, the stent structure in its expanded state has a cross-section that ensures effective elimination of the stenosis. A typical diameter of the stent structure in its reduced-diameter form is 0.8 to 0.9 mm for the coronary region and 0.8 to 1.5 mm for the peripheral region; a typical diameter of the stent structure in its expanded form is 2 to 3 mm for the coronary region and 2 to 6 mm for the peripheral region.In general, the exact dimensions depend heavily on the type of blood vessel the balloon catheter is intended for. For example, peripheral lower leg arteries have a larger lumen than arteries in the cardiovascular or neurovascular region.

[0029] The balloon catheter typically has a shaft through which the lumen for fluid delivery extends. Typically, a second lumen extends at least partially longitudinally through the shaft, serving to accommodate a guidewire. This lumen can extend to the distal end of the balloon catheter, meaning the guidewire can exit from the distal end of the balloon catheter. Accordingly, a guidewire can first be brought to the desired target position before the balloon catheter itself is advanced over the guidewire to the target position.

[0030] In this context, essentially two different systems are known from the prior art, namely over-the-wire (OTW) and rapid exchange (Rx) balloon catheters. The balloon catheter according to the invention can be available as either an OTW or an Rx balloon catheter. While in an OTW catheter the lumen for the guidewire extends over the entire length of the catheter from proximal to distal, the Rx catheter has a separate feed port for the guidewire (Rx port), at which the guidewire exits the catheter well distal to the proximal end of the catheter. Accordingly, in the case of an OTW balloon catheter, the lumens for fluid supply and the guidewire run concentrically or parallel to each other from the proximal end of the catheter to the balloon, whereas in an Rx catheter this is only the case between the Rx port and the balloon. The section between the Rx port and the proximal end, however, has only one lumen for fluid supply.The lumens may be concentric in areas where the catheter has two lumens, i.e. the narrower inner lumen for the guidewire passes through the wider outer lumen for fluid delivery.

[0031] A balloon, as used herein, is understood to be the element of a balloon catheter that can be expanded by the supply of a fluid, regardless of the shape of the expandable element or the material it is made of. Balloon catheters are generally well known in the art and have an elongated shaft running from proximal to distal and a balloon arranged in the distal section. It is a catheter whose dimensions are tailored to its insertion into the respective blood vessel system. The exact dimensions can vary depending on whether the blood vessel is, for example, a coronary artery, an intracranial blood vessel, or a lower leg artery. Furthermore, the balloon catheter has means for supplying a fluid to the balloon in the form of a supply lumen that extends the length of the balloon catheter.The lumens running through the shaft are usually each formed by a tubular or tubular tube. The term tube is used in this context to mean a tube or hose that extends at least partially through the balloon catheter in the longitudinal direction and has a lumen running through the interior of the tube. The tube can be in the shape of a hollow cylinder with a circular or elliptical cross-section, but this is not absolutely necessary. Viewed in cross-section, almost any other shape is conceivable. A circular or elliptical cross-section, however, has the advantage that one tube can be easily guided through the other, with the second tube usually being placed through the first.

[0032] In the case of a compliant or semi-compliant balloon, the balloon can be made at least partially of an elastic material. The elastic material can be, for example, a polyurethane, a polyolefin copolymer, a polyethylene, or a silicone. Other suitable materials are thermoplastic elastomers, in particular polyether block amides (PEBA). This is a thermoplastic elastomer obtained by polycondensation of a carboxylic acid polyamide with a polyether with terminal OH groups. In particular, PEBA is marketed under the name PEBAX® by Arkema. Polyamides such as nylon (polyhexamethylene adipamide) or polyamides such as those marketed under the name Grilamid® by EMS-GRIVORY can also be used.

[0033] The pressure applied to the balloon to expand in the blood vessel is typically between 4 and 12 bar, preferably 6 to 8 bar. The fluid used can be, for example, water mixed with contrast agent or a saline solution mixed with contrast agent. The dimensions of the balloon can vary greatly depending on the area of ​​application. The diameter when expanded can, for example, be between approximately 1 and approximately 50 mm, and the length between approximately 5 and approximately 300 mm. However, the dimensions may deviate from these values, for example when the balloon / balloon catheter is used in urology or veterinary medicine. The shaft of the balloon catheter can be made from standard materials, although different materials can also be used, for example to make the distal section softer than the proximal section.Common materials include polymers such as polyethylene, polyurethane, polyvinyl chloride, polyamides, polyimides, silicones, polyetheramides, polytetrafluoroethylene, EPDM (ethylene propylene diene rubber), polyether block amides (PEBA), or polyamides, such as those sold under the name Grilamid® by EMS-GRIVORY. In some cases, the proximal areas of the shaft, in particular, can also be made of metal, e.g., stainless steel.

[0034] The length of the shaft, including the balloon-carrying area but excluding hubs or similar connectors located proximally to the shaft, is typically at least 90 cm. Accordingly, it is possible to introduce the balloon catheter via the femoral artery in the groin and advance it to various locations in the vascular system.

[0035] If necessary, the balloon catheter can have a drug-coated balloon, also called a drug-eluting balloon. The drug is preferably selected from the group: tretinoin, orphan receptor agonists, elafin derivatives, corticosteroids, steroid hormones, paclitaxel, rapamycin (sirolimus), tacrolimus, hydrophobic proteins, heparin, and / or hormone-like or cell proliferation-altering substances. Paclitaxel, tacrolimus, and sirolimus are particularly preferred. Mixtures of these drugs can also be used. Derivatives of the aforementioned drugs can also be used, with derivatives being understood to mean, in particular, salts, esters, and amides. Examples of steroid hormones that can be used include methylprednisolone, dexamethasone, or estradiol.

[0036] At the proximal end of the balloon catheter, adjacent to the shaft, there is usually a so-called catheter hub, i.e. a connector for the device for fluid supply and pressurization. The connection can be a conventional Luer or Luer-Lock connection, for example. It is particularly useful to provide two Luer-Lock connectors, typically female connectors, one of which connects the first lumen to a balloon dilator and another for inserting the guidewire into the balloon catheter. The connectors can be made of polycarbonate, for example. The guidewire running through the balloon catheter can be held at its proximal end by a torque wrench, which facilitates handling of the usually very thin guidewire.

[0037] Radiopaque markers may be placed at various positions along the balloon catheter and / or stent structure to aid visualization of the catheter in X-ray images. These markers may be made of platinum or a platinum alloy.

[0038] The balloon catheters according to the invention are preferably used in blood vessels, as described, particularly in the field of angioplasty. In this case, the target location of the balloon is a blood vessel, with blood vessels in various areas being considered, in particular cardiovascular, neurovascular, and peripheral, whereby the combination according to the invention is particularly suitable for cardiovascular and peripheral applications. However, it is also possible to use the combination of balloon catheter and stent structure according to the invention in other medical fields. One possible application is in urology, where balloon catheters are inserted into the urinary bladder as bladder catheters. The catheter is secured via the balloon. Here, the balloon can be provided with a coating, for example, with heparin, that prevents bacterial colonization and encrustation.

[0039] In pulmonology, balloon catheters can be used to dilate or close a bronchus. Balloon catheters can also be used in gynecology. In the field of orthopedics, balloon catheters can be used to treat vertebral fractures by realigning the vertebrae using balloon expansion (balloon kyphoplasty). The balloon catheter-stent structure combination according to the invention can be used in all areas of medicine in which balloon catheters are used, with the balloon catheter being particularly important for insertion into blood vessels and the treatment of atherosclerosis. The invention is explained in more detail using the accompanying figures. They show:

[0040] Fig. 1 : A stent structure on the balloon catheter in the folded state;

[0041] Fig. 2 a stent structure on the balloon catheter in the expanded state; and

[0042] Fig. 3 a stent structure on the balloon catheter after deflation of the balloon.

[0043] Fig. 1 shows a side view of the combination of balloon catheter 1 and stent structure 5 according to the invention, with left meaning proximal and right meaning distal in the representation chosen here. A balloon 2 is arranged in the distal section of the balloon catheter 1 shown here, but the largest part of the proximal shaft of the balloon catheter 1 is not shown. The balloon catheter 1 has a longitudinally extending lumen 4 for receiving a guide wire 3 extending distally beyond the balloon catheter 1. Arranged concentrically around this lumen 4 is a further lumen (not shown here), through which a fluid can be introduced into the balloon 2. In addition, the balloon catheter 1 has radiopaque markings 6 that allow the attending physician to visualize the correct placement of the balloon catheter 1 in the region of a stenosis using imaging techniques.

[0044] A stent structure 5, shown in its reduced-diameter form in Fig. 1, is placed or crimped onto the balloon 2. Accordingly, it can be brought to the target position together with the balloon catheter 1. This is a laser-cut stent structure 5 composed of interconnected webs 7 that form a lattice structure, with the lattice structure comprising a plurality of cells.

[0045] Fig. 2 shows the same combination of balloon catheter 1 and stent structure 5, but with an expanded balloon 2. Accordingly, the stent structure 5 also expands and is able to exert forces on the inner vessel wall. The webs 7 of the stent structure 5 cut into calcifications and fibrotic tissue in the area of ​​the stenosis, disrupting them.

[0046] Finally, Fig. 3 shows the combination of balloon catheter 1 and stent structure 5 after deflation of balloon 2, i.e., the fluid expanding balloon 2 has been withdrawn. The elastic design of stent structure 5 causes the stent structure 5 to contract again and once again assume a reduced diameter. Accordingly, stent structure 5 is firmly seated on balloon 2 and can be retracted proximally together with balloon catheter 1.

Claims

Patent claims 1. Combination of - a balloon catheter (1) through which a lumen extends in the longitudinal direction, wherein a balloon (2) is arranged in the distal section of the balloon catheter (1) which can be expanded by pressurizing it with a fluid passed through the lumen, and - a stent structure (5) which is constructed from interwoven wires or interconnected webs (7), wherein the stent structure (5) can be applied to the balloon (2) of the balloon catheter (1) and can be brought into an expanded shape by expanding the balloon (2), characterized in that the stent structure (5) is elastic and is adjusted so that, without external forces acting on the stent structure (5), it assumes a diameter-reduced shape in which it sits firmly on the balloon (2).

2. Combination according to claim 1, characterized in that the stent structure (5) is at least partially composed of a shape memory material.

3. Combination according to claim 2, characterized in that the stent structure (5) is at least partially composed of a nickel-titanium or nickel-titanium-copper alloy.

4. Combination according to claim 1, characterized in that the stent structure (5) is at least partially composed of a cobalt-chromium or cobalt-chromium-nickel alloy.

5. Combination according to one of claims 1 to 4, characterized in that the wires or webs (7) of the stent structure (5) have a round or oval cross-section.

6. Combination according to one of claims 1 to 5, characterized in that the wires or webs (7) of the stent structure (5) have a radially outward pointing edge.

7. Combination according to one of claims 1 to 6, characterized in that the wires or webs (7) of the stent structure (5) have a triangular cross-section.

8. Combination according to one of claims 1 to 7, characterized in that one end of the stent structure (5) is fixed to the balloon catheter (1).

9. Combination according to claim 8, characterized in that the proximal end of the stent structure (5) is fixed to the balloon catheter (1).

10. Combination according to one of claims 1 to 9, characterized in that the outer diameter of the stent structure (5) in the expanded form is two to four times larger than in the diameter-reduced form.

11. Combination according to one of claims 1 to 10, characterized in that the stent structure (5) in the diameter-reduced form has an outer diameter of 0.8 to 1.5 mm.

12. Combination according to claim 11, characterized in that the stent structure (5) in the diameter-reduced form has an outer diameter of 0.8 to 0.9 mm.

13. Combination according to one of claims 1 to 12, characterized in that the stent structure (5) in the expanded form has a It has an outer diameter of 2 to 6 mm.

14. Combination according to claim 13, characterized in that the stent structure (5) in the expanded form has an outer diameter of 2 to 3 mm.

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