X-ray-proof coating for endovascular devices

Description

[0001] The invention relates to an X-ray-proof coating for endovascular devices, wherein the coating is selectively applied to the device in order to influence the mechanical properties of the device as little as possible through the coating.

[0002] Endovascular devices such as stents and other implants, filters, thrombectomy devices, or flow diverters are typically very delicate objects. For successful placement and use within the vascular system, it is crucial to visualize their precise position on X-ray imaging during the intervention. However, due to their low mass and the materials used, many endovascular devices exhibit only minimal contrast on X-ray images.

[0003] Accordingly, endovascular devices often include markers made of radiopaque materials such as gold or platinum, which allow the treating physician better visualization of the device during the intervention under fluoroscopy. However, these markers usually only mark specific areas of the device, such as the beginning or end of a stent.

[0004] EP 1 265 651 A2 concerns the selective coating of endovascular stents with a radiopaque material, whereby the selective coating applies in particular to stents for bifurcations and is intended to enable identification of the fenestration during the intervention. Accordingly, the document primarily proposes coating the ends and the fenestration of the stent.

[0005] Ideally, however, it would be desirable for not only specific areas of the device to be better visualized in the X-ray image, but for the entire device to be visible. Visualizing only the end regions of a device provides little or no information about whether, for example, it has expanded as required in the area in between.

[0006] To improve the X-ray visibility of the device, the entire device can be coated with a suitable radiopaque material. However, depending on the material and radiopaque coating used, this also alters the mechanical properties of the devices.

[0007] Conventional materials such as steel or gold exhibit linear elastic behavior, meaning that stresses and strains within the material increase proportionally under load until the elastic limit is reached. Within this range, the stressed material returns to its original shape after the load is removed. If the load is increased and the stress or strain is pushed beyond the elastic limit, irreversible plastic deformation occurs.

[0008] Pseudoelastic alloys, also known as shape memory alloys, are characterized by non-linear elastic behavior. They possess the property of returning to their original shape even after considerable deformation when the load is removed.

[0009] Such pseudoelastic alloys, such as Nitinol, NiTiCu, CuZn, CuZnAl or CuAINi, can be stretched up to ten times more than conventional spring steels without being permanently deformed.

[0010] The material undergoes a stress-strain hysteresis cycle with a loading and a unloading plateau.

[0011] For endovascular devices whose basic structure consists of pseudoelastic alloys, a complete coating, which may also include a radiopaque material, has at least one crucial disadvantage. The applied layer increasingly restricts the pseudoelasticity of the material with increasing layer thickness. Important factors such as radial forces, device setup forces, and microcatheter insertion forces are affected by this.

[0012] Accordingly, especially when coating endovascular devices with shape memory alloys, a compromise must always be found between good visibility - through a higher layer thickness - and mechanical performance - through a lower layer thickness.

[0013] It is therefore an object of the invention to provide a coating and a coating method for endovascular devices made of shape memory alloys that do not have the disadvantages of known coatings and that enable improved X-ray visibility of the endovascular devices without unduly impairing the mechanical properties of the endovascular devices.

[0014] This problem is solved by the invention with the features of claims 1 and 16, and by a method with the features of claims 6 and 9. Advantageous embodiments are the subject of the dependent claims. It should be noted that the features listed individually in the claims can also be combined with one another in any technologically meaningful way, thus revealing further embodiments of the invention.

[0015] The main objective of the invention is to find a compromise between a coating that is as complete as possible in terms of radiopaque properties, enabling the device to be as visible as possible in the X-ray image, and having as little impact as possible on the mechanical properties of the device.

[0016] The essential inventive concept is therefore based on coating only those areas of the device that are largely negligible with regard to its mechanical properties. Tests have shown that these are those areas of the device that experience only minimal elongation during use.

[0017] Among the important mechanical properties of an endovascular device in this context are, on the one hand, its ability to counteract external influences. radial resistive force (RRF), i.e., the force that the device exerts against the externally acting forces, and the force emanating from the device itself chronic outward force (COF), which the device exerts on the surrounding tissue, for example the vessel wall, during and after release.

[0018] For a device made of a shape memory alloy, the two quantities RRF and COF give rise to various considerations, because the diameter of the target vessel in which the device is used is usually smaller than the diameter of the device in its freely unfolded state.

[0019] When the initially compressed device is released from its transport system, such as the delivery catheter, it expands until it comes into contact with the vessel wall, which prevents further expansion. Since the device tends to return to its original shape, a small, continuous force (COF) acts on the vessel wall at this point. The smaller the diameter of the device, i.e., the smaller its radial expansion after release, the greater the COF acting on the vessel.

[0020] Another important parameter to mention is the RRF. RRF describes the force required to compress the device back to a smaller diameter, for example, by applying external pressure.

[0021] During storage or use of the device, individual areas are stretched beyond the elastic limit of a conventional coating material, such as gold, which may be applied to the device as an X-ray-proof marker. In contrast to the shape-memory alloy of the device, this X-ray-proof layer of conventional coating material is thus permanently plastically deformed. This deformation, with increasing layer thickness, impairs the pseudoelasticity of the device's basic structure and consequently important performance characteristics of the device, such as RRF and COF.

[0022] For example, the desired COF may no longer be achieved, or a high RRF may have to be overcome to (re)insert the device into the transport system or microcatheter.

[0023] In the selective coating according to the invention, only those areas or sections of the device that do not contribute, or contribute only negligibly, to mechanical performance, such as COF and RRF, are coated. These are areas that exhibit little mechanical stress and deformation during storage, insertion into the patient, and use. In this way, radiopaque visibility can be improved by applying high layer thicknesses to those areas of the device that do not, or only negligibly, affect mechanical performance. Therefore, the advantages of the shape memory alloy do not have to be forgone.

[0024] The invention relates accordingly to an endovascular device made of pseudoelastic alloys, comprising a selective coating of x-ray-dense materials, wherein the coating only includes areas or sections of the endovascular device which, in the radially maximally loaded state of the device, exhibit a strain in the corresponding area of ​​less than 5%, preferably less than 3%, more preferably less than 1.5% and in particular less than 1% compared to the device in the radially unloaded state.

[0025] In other words, the selective coating does not include areas and sections of the endovascular device that, in the radially maximally loaded state of the device, exhibit an elongation of at least 5%, preferably at least 3%, more preferably at least 1.5%, and in particular at least 1%, compared to the device in the radially unloaded state.

[0026] It has been shown that by limiting the coating to the areas or sections which, in the radially maximally loaded state of the device, exhibit an elongation of less than 5%, preferably less than 3%, even more preferably less than 1.5% and in particular less than 1% as defined, a sufficient improvement in the X-ray visibility of the device can be achieved while maintaining the important mechanical properties.

[0027] Preferably, the coating further comprises only areas or sections of the endovascular device which exhibit an elongation in the corresponding area of ​​less than 5%, preferably less than 3%, more preferably less than 1.5% and in particular less than 1% compared to the device in the radially unloaded state, both in the radially maximally loaded state of the device and in the radially nominally loaded state.

[0028] By definition, the elongation of the device is understood to be the relative change in the length of a region of the device in a radially loaded state, for example, the radially maximally or radially nominally loaded state, relative to the radially unloaded state. Essential to the inventive concept is the relative elongation of the device or regions of the device in the maximally loaded state or in the maximally and nominally loaded states.

[0029] As described, the selective coating excludes areas or sections exhibiting elongation that reaches at least the defined limit. Ideally, this means the coating covers all areas below this limit.

[0030] In practice, it has been shown that for the desired improvement in the mechanical properties of the device, it is sufficient if the section of the device encompassing the area with the strain that reaches at least the defined limit is not coated. For example, in the case of a stent, the corresponding section of the respective strut is not coated.

[0031] When defining a section, it is important to ensure that it cannot be arbitrarily large, thus potentially encompassing an unreasonably large number of areas below the defined strain limits. Accordingly, a section should be defined as a part of the device that includes precisely those areas reaching at least the defined strain limit. An area that reaches at least the defined limit should also be called a strain zone.

[0032] Using the example of a stent-like device such as a stent, a thrombectomy device or a flow diverter, this means that at most the section of a strut should be defined as a section and therefore not coated, which exactly encloses the strain area, i.e., begins at the beginning of the strain area and ends at the end of the strain area, where the terms beginning and end refer to the course of the strain area along the device, i.e., along a strut.

[0033] If several expansion zones are to be assigned to one section, because these expansion zones are, for example, on different sides of a strut but directly within this section, then at most the part of the strut that exactly encloses all these expansion zones should be defined as a section and not coated, i.e., starting at the beginning of the first expansion zone and ending at the end of the last expansion zone, whereby the beginning and end can also be part of the same expansion zone if it extends over all other expansion zones of the section.

[0034] An analogous definition is suitable for other endovascular devices.

[0035] The method used to manufacture the endovascular device from shape memory alloys is irrelevant to the invention. The device can be manufactured, for example, by cutting, particularly laser cutting, or by braiding, for instance, wires, although greater elongation is more likely in cut devices, such as those laser-cut from a tube. However, other manufacturing methods are also conceivable, such as additive manufacturing processes in which a structure is built up gradually by adding material. One such additive manufacturing process is 3D printing.

[0036] The radially maximally stressed state is, by definition, the state of the device in which it experiences its maximum radial compression. The device experiences this radially maximally stressed state, for example, in the delivery catheter before and during an intervention. If the device is intended for use with a delivery catheter with an inner diameter of 0.53 mm, then the device experiences its radially maximally stressed state when compressed to a diameter of 0.53 mm. For this device, radial compression to a diameter of 0.53 mm is the radially maximally stressed state.

[0037] If the device is intended for use with delivery catheters of different inner diameters, the radially maximally loaded state for this device shall be the state that the device assumes in the delivery catheter with the smallest inner diameter intended for this device.

[0038] If it is appropriate not to determine the radially maximally loaded state of the device as a function of a delivery catheter, the radially maximally loaded state can alternatively be defined as the state in which the device reaches the limit of its pseudoelasticity and, under radial loading, just barely does not exhibit any areas that are permanently, i.e., irreversibly, deformed. Such a limit is generally reached in a device made of shape memory alloys when, under radial compression, it exhibits areas that show a strain of 10% compared to the radially unloaded state.

[0039] Such an alternative definition of the radially maximally loaded state may be suitable in certain cases to create a further objective reference value.

[0040] The radially nominally loaded state is, by definition, the state of the device in which it experiences its nominal radial compression. The device experiences this state, for example, during its intended use, such as during implantation or other use in a vessel, for example, as a vascular support, filter, or for thrombectomy. If the device is designed for use in vessels with a diameter of 2 mm, it experiences its radially nominally loaded state when subjected to radial compression to a diameter of 2 mm. For this device, radial compression to a diameter of 2 mm constitutes the radially nominally loaded state.

[0041] A radially loaded state of a device, whether the nominally loaded state or the maximally loaded state, should always be understood as a state with a uniformly distributed radial load on the device due to external force, as is achieved, for example, in a blood vessel or a feeding catheter, or, modeled, in the uniform compression of the device within a uniform straight tube.

[0042] The radially unloaded state is, by definition, the state of the device in which it experiences no radial compression. The device experiences this state, for example, in its freely expanded state outside a vessel or catheter without external restrictions. Selective coating, as defined by the invention, is achieved through any coating process suitable for providing a ready-to-use end product with only partial coating. The method used to achieve this selective coating of the end product is irrelevant.

[0043] For example, in the coating process, the entire device can first be coated, and the coating can then be partially removed mechanically, chemically, or electrochemically. Areas that are not to be coated can also be masked or covered beforehand with various materials such as plastics, adhesives, or masking lacquers. These masks can then be removed after coating or left on the device. Furthermore, auxiliary elements can be attached inside and / or outside the device to serve as stencils during the coating process.

[0044] Last but not least, only the parts to be coated can be selectively coated. Experts are familiar with various methods that lead to the desired selective coating.

[0045] The pseudoelastic alloys, or shape memory alloys, can be, in particular, nitinol (NiTi) or nickel-titanium-copper (NiTiCu). Other pseudoelastic alloys are known to those skilled in the art.

[0046] The material for the radiopaque coating can be selected from the group comprising platinum, palladium, platinum-iridium, tantalum, gold, and tungsten. The radiopaque coating can also comprise a combination of two or more of these materials or alloys thereof. Accordingly, the radiopaque coating comprises at least one of the aforementioned materials. Further radiopaque materials are selected by a person skilled in the art according to specific requirements and, if necessary, combined with the aforementioned materials.

[0047] The invention accordingly comprises a method for the selective coating of an endovascular device made of pseudoelastic alloys comprising the following steps: (A) Providing an endovascular device made of pseudoelastic alloys in the radially unloaded state; (D) Compressing the endovascular device to the radially maximally loaded state by radially loading the device; (E) Determining the areas of the endovascular device that exhibit an elongation of at least 5% compared to the radially unloaded expanded state in the radially maximally loaded state; (F) Coating the endovascular device except for the areas determined in step (E).

[0048] In a preferred embodiment, the method for selectively coating an endovascular device with pseudoelastic alloys further comprises the following steps: (B) Compressing the endovascular device to the radially loaded state by radially loading the device; (C) Determining the areas of the endovascular device that, in the radially loaded state, exhibit an elongation of at least 5% compared to the device in the radially unloaded expanded state;

[0049] Steps (B) and (C) are, as their names suggest, usually performed after step (A) and before step (D).

[0050] In this variant of the process, the coating according to step (F) is carried out accordingly, excluding the areas identified in steps (C) and (E).

[0051] Steps (B) and (C) can also be performed instead of steps (D) and (E). The coating according to step (F) is then carried out accordingly, excluding the areas identified in step (C).

[0052] An alternative method for the selective coating of an endovascular device with pseudoelastic alloys comprises the following steps: (A') Providing an endovascular device made of pseudoelastic alloys in the radially unloaded state; (D') Compressing the endovascular device to the radially maximally loaded state by radially loading the device; (E') Determining the areas of the endovascular device that exhibit a strain of at least 5% compared to the radially unloaded expanded state in the radially maximally loaded state, and subsequently determining the sections of the endovascular device that comprise the corresponding areas of defined strain; (F') Coating the endovascular device except for the sections determined in step (E').

[0053] In a preferred embodiment, the method for selectively coating an endovascular device with pseudoelastic alloys further comprises the following steps: (B') Compressing the endovascular device to the radially loaded state by radially loading the device; (C') Determining the areas of the endovascular device which, in the radially loaded state, exhibit an elongation of at least 5% compared to the device in the radially unloaded expanded state, and subsequently determining the sections of the endovascular device which comprise the corresponding areas of defined elongation;

[0054] Steps (B') and (C') are usually performed after step (A') and before step (D'), as their names suggest.

[0055] In this variant of the process, the coating according to step (F') is carried out excluding the sections identified in steps (C') and (E').

[0056] Steps (B') and (C') can also be performed instead of steps (D') and (E'). The coating according to step (F') is then carried out, excluding the sections identified in step (C').

[0057] It is clear to a person skilled in the art that steps (B) and (C) and steps (D) and (E) can also be interchanged in order, i.e., after step (A), steps (D) and (E) are performed first, followed by steps (B) and (C). The same applies to steps (B') and (C') and steps (D') and (E'). These, too, can be interchanged in order, so that after step (A'), steps (D') and (E') are performed first, followed by steps (B') and (C').

[0058] The strain according to steps (C) and (E) or according to steps (C') and (E') can preferably be at least 3%, more preferably at least 1.5% and in particular at least 1% compared to the radially unloaded state.

[0059] The device can be compressed to the radially nominally loaded state according to process step (B) or (B') preferably into a straight tube with a corresponding inner diameter. The inner diameter of the tube should correspond to the outer diameter of the device in the radially nominally loaded state. The tube is advantageously rigid and does not yield during the expansion of the device. This allows comparable results to be obtained.

[0060] The device can be compressed to its radially maximally loaded state according to process step (D) or (D') into a straight tube with a corresponding inner diameter. The inner diameter of the tube should correspond to the outer diameter of the device in its radially maximally loaded state. The tube is advantageously rigid and does not yield during the expansion of the device. This allows for comparable results.

[0061] In principle, it is also conceivable that the process steps (A) to (E) or (A') to (E') are carried out in a computer simulation, for example using the finite element method (FEM), which models the described real experimental setup.

[0062] The invention accordingly also includes an endovascular device with a coating obtainable by the inventive method.

[0063] The invention further comprises a combination comprising an endovascular device coated according to the invention and a delivery catheter for this device.

[0064] A device according to the invention with the selective coating according to the invention has the advantage over the prior art that the device is almost completely visible in the X-ray image due to an almost complete coating, without the coating affecting important mechanical properties such as RRF and COF to a relevant extent.

[0065] The effectiveness of the proposed selective coating is illustrated below using an example. Example

[0066] In endovascular devices, such as stent systems, made of shape memory alloys, the coefficient of flow (COF) decreases continuously with increasing expansion and a correspondingly larger stent diameter. In such devices made of shape memory alloys that are completely coated with radiopaque materials such as gold, the COF deteriorates significantly, i.e., it decreases. This effect can be minimized by selectively coating the areas that do not contribute significantly to the COF.

[0067] In the examples presented, a selective coating was applied to the areas or sections of the device made of a shape memory alloy which, by definition, exhibited an elongation of less than 1.5% in the radially maximally loaded or radially nominally loaded state.

[0068] Figure 1The graph compares the coefficient of flow (COF) of a fully coated endovascular device made of a shape memory alloy (lower curve) and a fully uncoated endovascular device made of a shape memory alloy (upper curve) as it expands from its radially loaded state (2 mm diameter) to its radially unloaded state (5 mm diameter). It is clearly evident that the COF of the fully coated device is significantly lower than that of the uncoated device, with a loss of between 51% and 97%.

[0069] Figure 2The figure shows a comparison of the COF curve of a device selectively coated according to the invention, made of a shape memory alloy (lower curve), and of a completely uncoated device made of a shape memory alloy (upper curve), expanding from its radially loaded state, where the device diameter is 2 mm, to its radially unloaded state, where the device diameter is 5 mm. It is clearly evident that the COF of the selectively coated device, with a maximum COF loss of only 26%, is significantly lower than that of the uncoated device.

[0070] Figure 3The figure shows a comparison of the increase in radial surface resorption (RRF) between a fully coated endovascular device made of a shape memory alloy (right bar) and an uncoated endovascular device made of a shape memory alloy (left bar), each in the radially nominally loaded condition, which corresponds to a diameter of 2 mm. It is clearly evident that the RRF of the fully coated device, with a percentage increase of 35%, is significantly higher than that of the uncoated device.

[0071] Figure 4The figure shows a comparison of the increase in radial surface area (RRF) between a selectively coated endovascular device made of a shape memory alloy (right bar) and an uncoated endovascular device made of a shape memory alloy (left bar), each in the radially nominally loaded state, which corresponds to a diameter of 2 mm. It is clearly evident that the RRF of the device selectively coated according to the invention, with a percentage increase of only 2%, is only marginally higher than that of the uncoated device.

[0072] Figure 5Figure 1 shows the determination, according to the invention, of the compression-stressed areas of an endovascular device made of a shape-memory alloy. The data for the strain of areas 2 of the device or of the struts 1 were determined in a computer simulation using the finite element method (FEM). The marked areas 2 represent the areas of the device or of the struts 1 whose strain during compression in the microcatheter, i.e., in the radially maximally stressed state, is at least 1.5% compared to the radially unstressed state. These areas 2 are excluded in a coating according to the invention.

[0073] Furthermore, it shows Figure 5 the sections 3 of the struts 1 derived from areas 2, which can alternatively be omitted during selective coating.

[0074] Figure 6Figure 1 shows the determination, according to the invention, of the compression-stressed areas 2 and struts 1 of an endovascular device made of a shape-memory alloy. The data for the strain of the areas 2 and struts 1 of the endovascular device were determined in a computer simulation using the finite element method (FEM). The marked areas 2 represent those areas 2 and struts 1 of the endovascular device whose strain under compression in the vessel, i.e., in the radially nominally loaded state, is at least 1.5% compared to the radially unloaded state. These areas 2 are omitted in a coating according to the invention.

[0075] Furthermore, it shows Figure 6 the sections 3 of the struts 1 derived from areas 2, which can alternatively be omitted during selective coating.

[0076] Figures 1 to 6 each refer to laser-cut endovascular devices.

Claims

1. Endovascular device made of pseudoelastic alloys and comprising a selective coating of radiopaque materials, characterised in that the coating covers only regions or portions of the endovascular device, which regions or portions, when in the radially maximum loaded state, have an elongation of less than 5% compared to the radially non-loaded state of the device.

2. Endovascular device made of pseudoelastic alloys and comprising a selective coating of radiopaque materials according to claim 1, characterised in that the coating covers only regions or portions of the endovascular device, which regions or portions, when in both the radially maximum loaded state and in the radially nominally loaded state, have an elongation of less than 5% compared to the radially non-loaded state of the device.

3. Endovascular device according to claim 1 or 2, characterised in that the elongation in the radially maximum or radially nominally loaded state is less than 3%, preferably less than 1.5% and in particular less than 1% compared to the radially non-loaded state.

4. Endovascular device according to any one of the preceding claims, characterised in that the coating comprises at least one radiopaque material selected from the group of platinum, palladium, platinum iridium, tantalum, gold and tungsten.

5. Endovascular device according to any one of the preceding claims, characterised in that the pseudoelastic material comprises NiTi or NiTiCu.

6. Method for selectively coating an endovascular device made of pseudoelastic alloys comprising the following steps: (A) providing an endovascular device made of pseudoelastic alloys in the radially non-loaded state; (D) compressing the endovascular device to the radially maximum loaded state by radial loading of the device; (E) determining the regions of the endovascular device that have an elongation of at least 5% in the radially maximum loaded state compared to the radially non-loaded expanded state; (F) coating the endovascular device except for the regions determined in step (E).

7. Method for selectively coating an endovascular device made of pseudoelastic alloys according to claim 6, further comprising the following steps: (B) compressing the endovascular device to the radially nominally loaded state by radial loading of the device; (C) determining the regions of the endovascular device that have an elongation of at least 5% in the radially nominally loaded state compared to the device in the radially non-loaded expanded state; wherein the coating according to step (F) is carried out excluding the regions determined in steps (C) and (E).

8. Method for selectively coating an endovascular device made of pseudoelastic alloys according to claim 7, wherein steps (D) and (E) are carried out after step (A) and before steps (B) and (C).

9. Method for selectively coating an endovascular device made of pseudoelastic alloys comprising the following steps: (A') providing an endovascular device made of pseudoelastic alloys in the radially non-loaded state; (D') compressing the endovascular device to the radially maximum loaded state by radial loading the device; (E') determining the regions of the endovascular device that have an elongation of at least 5% in the radially maximum loaded state compared to the radially non-loaded expanded state, and subsequently determining the sections of the endovascular device comprising the corresponding regions of defined elongation; (F') coating the endovascular device except for the sections determined in step (E').

10. Method for selectively coating an endovascular device made of pseudoelastic alloys according to claim 9, further comprising the following steps: (B') compressing the endovascular device to the radially nominally loaded state by radial loading of the device; (C') determining the regions of the endovascular device that have a defined elongation of at least 5% in the radially nominally loaded state compared to the device in the radially non-loaded expanded state, and subsequently determining the sections of the endovascular device comprising the corresponding regions of defined elongation; wherein the coating according to step (F') is carried out excluding the sections determined in steps (C') and (E').

11. Method for selectively coating an endovascular device made of pseudoelastic alloys according to claim 10, wherein steps (D') and (E') are carried out after step (A') and before steps (B') and (C').

12. Method for selectively coating an endovascular device made of pseudoelastic alloys according to any one of claims 6 to 11, characterised in that the device is inserted into a straight tube with a corresponding inner diameter for compression to the radially nominally loaded state according to method step (B) or (B').

13. Method for selectively coating an endovascular device made of pseudoelastic alloys according to any one of claims 6 to 11, characterised in that the device is inserted into a straight tube with a corresponding inner diameter for compression to the radially maximum loaded state according to method step (D) or (D').

14. Method for selectively coating an endovascular device made of pseudoelastic alloys according to any one of claims 6 to 11, characterised in that the elongation according to steps (C) and (E) or (C') and (E') is at least 3%, preferably at least 1.5% and in particular at least 1% compared to the radially non-loaded state.

15. Method for selectively coating an endovascular device made of pseudoelastic alloys according to any one of claims 6 to 14, characterised in that the method steps (A) to (E) or (A') to (E') are carried out in a computer simulation, for example using the finite element method (FEM).

16. Endovascular device having a coating that can be obtained by a method according to any one of claims 6 to 15.

17. Combination comprising an endovascular device according to any one of claims 1 to 5 or 16 and a feed catheter.