MEDICAL IMPLANT FOR TREATING ANEURYSMS

Abstract

The disclosure relates to a medical implant for treating aneurysms, including a support structure, which has a compressible and expansible lattice structure lattice elements that define lattice openings, wherein the lattice structure is covered at least in part with an in particular electrospun membrane of fibres, which membrane includes at least one luminal functional layer and at least one abluminal protective layer, which each have pores, wherein the porosity of the functional layer is less than the porosity of the protective layer. The membrane is so configured that at least the pores of the functional layer open, as a result of a pressure gradient arising between a liquid pressure in an inner through channel of the support structure and a liquid pressure outside the protective layer, so as to increase the throughflow of liquid through the membrane.

Claims

1-18. (canceled)

19. A medical implant for treatment of an aneurysm comprising: a carrier structure having a compressible and expandable mesh structure with mesh elements configured to delimit mesh openings, wherein the mesh structure is covered, at least in one or more sections, with a membrane of fibres including at least one luminal functional layer and at least one abluminal support layer, each layer respectively having pores, wherein a porosity of the functional layer is smaller than the porosity of the support layer, and wherein the membrane is configured such that, as a consequence of a pressure gradient occurring between a first liquid pressure in an inner through channel of the carrier structure and a second liquid pressure outside the support layer, at least the pores of the functional layer open to increase a flow of liquid through the membrane.

20. The medical implant according to claim 19, wherein the fibres of the membrane are arranged loosely on top of one another at points of intersection, so that intersecting fibres are movable with respect to each other at the points of intersection, and wherein at least the fibres of the functional layer of the membrane are elastically or plastically deformable.

21. The medical implant according to claim 19, wherein the fibres of the functional layer of the membrane have a fibre thickness of less than 500 nm and wherein the fibres of the support layer of the membrane have a fibre thickness of at least 500 nm.

22. The medical implant according to claim 19, wherein the functional layer of the membrane has a thickness of less than 10 μm and wherein the support layer of the membrane has a thickness of at least 3 μm.

23. The medical implant according to claim 19, wherein the functional layer of the membrane has a porosity of less than 50% and wherein the support layer of the membrane has a porosity of at least 50%.

24. The medical implant according to claim 19, wherein the functional layer of the membrane comprises at least 10 pores having an inscribed circle diameter of at most 10 μm over a surface area of 100000 μm.sup.2, and wherein the support layer of the membrane comprises at least 5 pores having an inscribed circle diameter of at least 10 μm over a surface area of 100000 μm.sup.2.

25. The medical implant according to claim 19, wherein the fibres of the functional layer have a smaller fibre thickness than the fibres of the support layer, and wherein the functional layer has a higher ductility than the support layer or its fibres.

26. The medical implant according to claim 19, wherein the fibres of the functional layer are formed from a material which has a lower Shore hardness than the material of the fibres of the support layer.

27. The medical implant according to claim 26, wherein the material of the fibres of the functional layer has a Shore hardness of at most 90A and wherein the material of the fibres of the support layer has a Shore hardness of at least 90A.

28. The medical implant according to claim 19, wherein the membrane comprises a thermoplastic polyurethane.

29. The medical implant according to claim 19, wherein the membrane extends around an entire circumference of the carrier structure.

30. The medical implant according to claim 19, wherein the carrier structure is monolithic in configuration, and wherein the mesh elements of the mesh structure form webs configured to delimit the mesh openings of the mesh structure which are formed as cells.

31. The medical implant according to claim 19, wherein the carrier structure has interwoven wires, and wherein the wires form the mesh elements of the mesh structure and delimit the mesh openings of the mesh structure which are formed as interstices.

32. The medical implant according to claim 31, wherein the membrane has a total layer thickness which is at most 40% of a height of the mesh elements.

33. The medical implant according to claim 31, wherein a height of the mesh elements is between 40 μm and 160 μm.

34. The medical implant according to claim 31, wherein a ratio between a thickness of the membrane and a height of the mesh elements is at most 1/3.

35. The medical implant according to claim 19, wherein the functional layer has a perforation in a region of the mesh openings.

36. The medical implant according to claim 35, wherein the perforation is formed by one of holes, straight slits, curved slits, or T-shaped slits.

37. A method for production of a medical implant, the method comprising: providing a carrier structure having a compressible and expandable mesh structure with mesh elements configured to delimit mesh openings; applying a luminal functional layer of a membrane of fibres to the carrier structure; perforating the functional layer by one of a laser cutting process or solvent spraying; and applying an abluminal support layer of the membrane to the functional layer.

Description

[0051] The invention is described in more detail with the aid of exemplary embodiments and with reference to the accompanying schematic drawings, in which:

[0052] FIG. 1 shows a section of a blood vessel system into which a medical implant in accordance with the invention is inserted;

[0053] FIG. 2 shows a detailed section of the implant of FIG. 1 covering an aneurysm;

[0054] FIG. 3 shows a detailed section of the implant of FIG. 1 covering a branching blood vessel; and

[0055] FIGS. 4 to 7 each show a side view of a medical implant in accordance with the invention in preferred exemplary embodiments, each showing a different perforation of the functional layer.

[0056] FIG. 1 shows a section of a blood vessel system with a main vessel MV and three side vessels BV1, BV2, BV3 branching from the main vessel MV. The main vessel MV also has an aneurysm AN, which is arranged between the second side vessel BV2 and the third side vessel BV3. In particular, the aneurysm is positioned close to the third side vessel BV3.

[0057] In order to treat the aneurysm AN, the medical implant in accordance with the invention is inserted. The medical implant comprises a carrier structure 1, which is formed by a mesh structure 10 with mesh elements. The mesh elements may be webs 12, which are interconnected into one piece and therefore form the mesh structure 10. In this regard, the webs 12 delimit cells 13 of the mesh structure 10. As an alternative, the mesh structure 10 may also be formed by interwoven wires. In order to make the mesh structure 10 or the carrier structure 1 visible for radiographic monitoring when inserting the implant into the blood vessel system or into the main vessel MV, radiographic markers 11 are provided on the respective longitudinal ends of the mesh structure 10. Preferably, a plurality of radiographic markers 11 are arranged at each longitudinal end of the mesh structure 10 and are positioned at regular distances in the circumferential direction of the mesh structure 10.

[0058] Furthermore, the implant has a membrane 2, which comprises a luminal functional layer 4 and an abluminal support layer 3. The functional layer 4 and the support layer 3 preferably overlap completely, and therefore have the same length in the longitudinal direction of the mesh structure 10. However, preferably, the support layer 3 protrudes beyond the functional layer 4, at least at the longitudinal ends, preferably by a few millimetres. As can be seen in FIG. 1, the mesh structure 10 may be longer than the membrane 2.

[0059] The implant is arranged in the main vessel MV in a manner such that the implant, in particular the membrane 2, completely covers the neck of the aneurysm AN. In addition, an embolization means 30 may be arranged in the aneurysm AN. Specifically, the medical implant may be supplied by itself or as a set together with an embolization means 30. The embolization means 30 may be a gel, for example. As an alternative, the embolization means 30 may also be formed by coils, i.e. chaotically twisted microwires. The embolization means 30 may be introduced into the aneurysm AN after the implant has been inserted into the main vessel MV. As an example, coils may be fed through the membrane 2 into the aneurysm via a microcatheter. The membrane 2 is or its fibres are so flexible in this regard that the microcatheter expands the pores of the membrane 2 and can therefore channel a path into the aneurysm AN.

[0060] As can also be seen in FIG. 1, the membrane 2 bridges not only the aneurysm AN, but also the second side vessel BV2 and the third side vessel BV3. This is where the benefits of the particular function of the membrane 2 take effect. The membrane 2 comprises the abluminal support layer 3, which has a larger porosity than the luminal functional layer 4. The support layer 3 in this regard is porous in a manner such that it is permanently permeable to blood. In contrast, the functional layer 4 is essentially of low permeability to blood, in particular semi-permeable, and above all less permeable to blood than the support layer 3. At the same time, however, the functional layer 4 is flexible in a manner such that with an appropriate application of force, it becomes permeable to blood or more permeable to blood. A required force of this type may be generated by the pressure gradient, which is set up between the blood pressure in the main vessel MV and the reducing blood pressure in one of the side vessels BV1, BV2, BV3.

[0061] Because the functional layer initially reduces the blood flow in a side vessel BV1, BV2, BV3, a pressure drop or a strong pressure drop is generated between the blood pressure in the main vessel MV and the corresponding side vessel BV1, BV2, BV3. This pressure drop or this pressure gradient generates a force, which is sufficiently high to expand the pores of the functional layer 4. This occurs because the filaments of the functional layer 4 are elastically and/or plastically deformed and/or slide on one another, so that exclusively in the region of the branching blood vessel, i.e. locally in the region of the opening into the corresponding side vessel BV1, BV2, BV3, the functional layer 4 becomes permeable to blood or more permeable to blood. The membrane 2 is “intelligent” insofar as it only allows blood to flow through at those sites at which the pressure gradient between the blood pressure in the main vessel MV and a pressure outside the outer membrane 2 is sufficiently high. This threshold is regularly exceeded at sites of the membrane 2, which cover the side vessels BV1, BV2, BV3 which branch off the main vessel MV. At the site on the membrane 2 which bridges the aneurysm AN which opens from the main vessel MV, the pressure threshold is not exceeded, i.e. the pressure gradient between the blood pressure in the main vessel MV and a pressure inside the aneurysm AN is not sufficiently large to expand the pores of the functional layer 4. Thus, the aneurysm AN remains shielded from the bloodstream, so that blood remaining in the aneurysm AN coagulates within a short period and the aneurysm AN therefore atrophies.

[0062] If an embolization means 30 is additionally arranged in the aneurysm, as can be seen in the exemplary embodiment of FIG. 1, then the support layer 3, which essentially has a stabilizing function, also serves to retain the embolization means 30 in the aneurysm AN, which therefore does not move back into the main vessel MV. This additionally ensures that the aneurysm AN atrophies in a timely manner.

[0063] FIGS. 2 and 3 respectively show a section of the implant with a carrier structure 1 and a membrane 2. The carrier structure 1 is formed by a mesh structure 10, wherein in FIGS. 2 and 3, several webs 12 of the mesh structure 10 are respectively indicated. The webs 12 form cells 13 of the mesh structure 10. In the exemplary embodiment, which is depicted, the webs 12 are monolithically interconnected. As a consequence, the mesh structure 10 is formed as one piece. However, it is also possible for the mesh structure 10 to be formed by wires, which are intertwined or interwoven.

[0064] The cell 13 is bridged by the membrane 2. The membrane 2 comprises at least two layers, which each are formed by electrospun filaments. The layers differ in their thickness and the density of the filaments.

[0065] Specifically, the membrane 2 has a support layer 3, which has a relatively lower density of filaments with a relatively higher filament thickness. The support layer 3 therefore differs from a functional layer 4, the filaments of which have a smaller filament thickness. Furthermore, the density of the filaments of the functional layer 4 is higher than the density of the filaments of the support layer 3. In other words, the support layer 3 and the functional layer 4 have pores 5 which are respectively delimited by the filaments and which are larger in the support layer 3 than in the functional layer 4. This is in any case true for the rest state of the implant, i.e. without any external force being exerted.

[0066] The functional layer 4 is tasked with impeding or at least slowing down the flow of blood through the membrane 2. In this regard, the functional layer 4 works like a flow diverter, i.e. deflecting the flow of blood along its surface. Because of the small filament thickness, the functional layer is relatively flexible. The support layer 3 stabilizes the functional layer 4 and prevents the functional layer 4 from bulging out in the radial direction, or ensures that the functional layer 4 lies tightly against the carrier structure 1.

[0067] FIG. 2 shows the principle of deflection of the blood flow. The membrane 2, which extends over the cell 13, bridges an aneurysm AN. Between the aneurysm AN and the main vessel MV into which the implant has been inserted there is barely any relevant pressure gradient, so that the functional layer 4 remains substantially in its passive state. As a consequence, the functional layer 4 has a small pore size, so that the blood flow is guided mainly along the functional layer 4 and essentially does not penetrate into the aneurysm AN. Thus, the aneurysm AN is substantially uncoupled from the blood flow in the main vessel MV and can atrophy by coagulation of the blood remaining in the aneurysm AN. Nevertheless, a small flow of blood can flow into the aneurysm through the pores of the membrane 2, so that the coagulation process and the formation of a solid thrombus in the aneurysm is not interrupted.

[0068] FIG. 3 shows the function of the functional layer 4 when it bridges a branching blood vessel, for example the second side vessel BV2. Because of the pressure difference which arises between the main vessel MV and the second side vessel BV2, the filaments of the functional layer 4 are deflected or locally deformed. This causes the pores of the functional layer 4 to become enlarged in the region of the mouth of the second side vessel BV2. In contrast, the filaments of the support layer 3 are more stable and largely retain their position. The pores of the support layer 3, however, are still large enough to permit blood to flow through the support layer 3. This is sufficient for the pores of the functional layer 4 to become enlarged in the region of the mouth of the second side vessel BV2 in order to permit a sufficient flow of blood from the main vessel MV into the second side vessel BV2.

[0069] Various exemplary embodiments of medical implants wherein the functional layer 4 is provided with a perforation 14 are shown in FIGS. 4 to 7. For the purposes of clarity, the support layer 3 is not shown in FIGS. 4 to 7.

[0070] Specifically, FIGS. 4 to 7 respectively show a stent with a carrier structure 1 which is configured as a mesh structure 10. The mesh structure 10 comprises a plurality of webs 12 coupled together into one piece which delimit cells 13. Radiographic markers 11 are arranged at the longitudinal ends of the mesh structure 10. A membrane 2 with a functional layer 4 is provided in a central region of the mesh structure 10. The membrane 2 extends over the entire circumference of the mesh structure 10 and completely covers the cells 13. The membrane 2 is connected to the webs 12 of the mesh structure 10.

[0071] The functional layer 4 depicted in FIGS. 4 to 7 has a perforation 14. The perforation 14 is preferably distributed in a pattern over the functional layer 4. In particular, the perforation 14 lies in the region of mesh openings or cells 13 of the carrier structure 1. With regard to the patterned arrangement of the perforation 14 there are commonalities in the exemplary embodiments of FIGS. 4 to 7. Thus, in the exemplary embodiments, which are depicted, the density of the perforations 14 in cells 13 which are arranged close to the longitudinal end of the functional layer 4 is higher than in cells 13 of the central region of the functional layer 4. When positioning the implant in the region of an aneurysm AN, it should be ensured that the flow of blood into the aneurysm AN is interrupted to a certain extent. A local opening of the functional layer 4 in the region of the aneurysm AN is therefore undesirable. Usually, the implant is positioned in a manner such that the central region of the implant, in particular of the functional layer 4, is placed in the region of the aneurysm AN. The fact that perforations 14 are still present in this region, albeit in a lower density, means that the aneurysm AN, for example, could still be well supplied with nutrients compared with branched side vessels BV1, BV2, BV3, because the perforation 14 provides an opening in the functional layer 4. The probability that a side vessel BV1, BV2, BV3 will be covered by the functional layer 4 is higher in the edge regions thereof. The perforation 14 provided there is more permeable.

[0072] The exemplary embodiments 4 to 7 differ in the type of perforation 14 in the functional layer 4. Thus, FIG. 4 shows an exemplary embodiment in which the functional layer 4 has a perforation 14 formed by holes 14a. The holes 14a are substantially in regions of the functional layer 4 which cover the mesh openings or cells 13. The number of holes 14a in the cells 13, which are arranged at the longitudinal ends of the functional layer 4 is greater than in a central region of the functional layer 4.

[0073] In the exemplary embodiment in accordance with FIG. 5, the perforations 14 are formed by straight slits 14b, which extend parallel to the longitudinal axis of the mesh structure 10. A different orientation of the straight slits 14b is possible. In particular, the straight slits 14b may be arranged at an angle of between 0° and 180° with respect to a longitudinal axis of the implant projected into the plane of the wall of the implant.

[0074] In the exemplary embodiment in accordance with FIG. 5, the length of the slits 14b is adjusted to the space, which is available between neighbouring webs 12 in the longitudinal direction of the mesh structure 10, so that the slits 14b are of different lengths. The spacing of the slits 14b in the circumferential direction of the mesh structure 10 also varies, wherein in edge regions of the functional layer 4, the spacing is smaller than in a central region of the functional layer 4.

[0075] The exemplary embodiment in accordance with FIG. 6 shows an implant with a functional layer 4, which has a perforation 14 formed by curved slits 14c. The curved slits 14c extend substantially in the circumferential direction of the mesh structure 10. Two curved slits 14c are arranged in each cell 13 in the edge regions of the functional layer 4, whereas in a central region of the functional layer 4, each cell 13 is associated with one curved slit 14c. A different number and distribution of the perforations 14 is possible.

[0076] The curved slits 14c are preferably orientated in the same direction and in particular in the direction of flow of the blood. In other words, the implant in accordance with FIG. 6 is preferably placed in a blood vessel in a manner such that the blood flows from the longitudinal ends of the curved slits 14c to the apex of its curvature. In the representation of FIG. 6, therefore, the blood would flow from the left end of the mesh structure 10 to the right end of the mesh structure 10. The curved slits 14c therefore form gill-like openings in the functional layer 4.

[0077] In general, for all of the exemplary embodiments in which a perforation 14 is provided, the support layer 3 has a restraining function for the opening of the perforation 14. Particularly in the case of the gill-like embodiment of the openings, the perforation 14 opens by deflection of a portion of the functional layer 4. This deflection is limited by the support layer 3, which in this regard has a restraining function for the valve-like opening of the perforation 14. The restraining function of the support layer 3 and the perforation 14 of the functional layer 4 are therefore matched in a manner such that the perforation 14 then only opens when a predetermined pressure gradient exists between the inside of the membrane 2 and the outside of the membrane 2.

[0078] FIG. 7 shows an exemplary embodiment in which the perforation 14 of the functional layer 4 is formed by T-shaped slits 14d. In this exemplary embodiment as well, more T-shaped slits 14d per cell 13 are provided in the edge regions of the functional layer 4 than in a central region of the functional layer 4. The T-shaped slits 14d are preferably orientated in the same direction. In particular, each T-shaped slit 14d comprises a main slit 14d′ and a cross-slit 14d″, wherein the main slit 14d′ extends parallel to the longitudinal axis of the mesh structure 10 and the cross-slit 14d″ extends perpendicular thereto. The cross-slit 14d″ connects to a distal longitudinal end of the main slit 14d′. Preferably, the implant is placed in the blood vessel in a manner such that blood flows from the proximal end of the main slit 14d′ to the cross-slit 14d″.

LIST OF REFERENCE NUMERALS

[0079] 1 carrier structure [0080] 2 membrane [0081] 3 support layer [0082] 4 functional layer [0083] 5 pore [0084] 10 mesh structure [0085] 11 radiographic marker [0086] 12 web [0087] 13 cell [0088] 14 perforation [0089] 14a hole [0090] 14b straight slit [0091] 14c curved slit [0092] 14d T-shaped slit [0093] 14d′ main slit [0094] 14d″ cross-slit [0095] embolization means [0096] AN aneurysm [0097] BV1 first side vessel [0098] BV2 second side vessel [0099] BV3 third side vessel [0100] MV main vessel