WO1999001087A1

WO1999001087A1 - Vascular support

Info

Publication number: WO1999001087A1
Application number: PCT/EP1998/004081
Authority: WO
Inventors: Wolfgang Ehrfeld; Martin Schmidt; Christoph Schulz; Gregor Feiertag
Original assignee: INSTITUT FüR MIKROTECHNIK MAINZ GMBH
Priority date: 1997-07-03
Filing date: 1998-07-02
Publication date: 1999-01-14
Also published as: DE19728337A1

Abstract

The invention pertains to a vascular support (1) adjustable in different diameters and capable of being stabilized when stretched. Said vascular support (1) presents a reticulate (3) meshed (8) tubular structure which gets tighter in the axial direction (12) when stretched towards the periphery (13). At least one series (17a-g, 18a-k) of meshes arranged in the peripheral direction (13) presents self-locking stop elements which interact when the mesh (8) shape changes. The stop elements (20) can consist of at least one plug-in element (21a, b) and one locating element (22a, b).

Description

Implantable stent

description

The invention relates to an implantable stent with a tubular structure that is extensible in the circumferential direction.

Implantable stents are used in medical applications to maintain the blood or fluid transport in vessels. This applies in particular to the treatment of stenoses by balloon dilation, in which the restenosis rates can be considerably reduced by using stents. In this case, stents are usually applied via a balloon, i.e. when applied, brought into the vessel in a compressed state and then expanded with the help of the balloon. When the balloon is removed, the stent should maintain its expanded state if possible.

For certain applications in the field of pediatric surgery, vascular supports are also required which, in addition to maintaining a certain volume flow, also allow the one-time setting of certain flow rates, i.e. Can take over valve functions.

WO 95/29728 describes a stent made from knitted fiber material. The mesh-like structure is stretched by means of a catheter, the meshes being stretched both in the axial and in the circumferential direction. No means are provided to stabilize the stent in the stretched state. This stent is longer than the previously used stents, which is intended to avoid the repeated insertion of shorter stents. In order to avoid uniform expansion, it is not proposed to use a catheter that is elongated on the inflatable part, but rather to use a conventional inflatable catheter several times. The stent with this mesh-like structure is made from a biocompatible and corrosion-resistant material such as tantalum. The diameter can be 2 - 15 mm and the length 10 - 30 cm. WO 95/29728 also mentions a stent with a self-expanding structure.

No. 5,411,551 describes a stent made from a rolled-up metal foil. The vascular support is inserted into the vessel in the rolled-up state and can expand due to the spring force and thus contact the inner wall of the vessel. Adaptation to irregular surfaces is not possible.

WO 94/13268 describes a tubular, expandable stent, in the structure of which threads are woven which can release an active ingredient. The materials used for the stent graft include Stainless steel, tantalum, gold, titanium, tungsten and platinum as well as polymers. Materials with plastic properties are described that remain in the expanded state due to the deformation that occurred during the expansion. The use of material with elastic properties is also mentioned, with the stent being fixed in the expanded state in that the stent expands itself. Polymers are mentioned as material for the threads carrying the active ingredient, some of which, e.g. Poly lactide, are degradable in the body. Perforated cylinder and wire structures are described as tubular structures.

To fix vascular supports, EP 497 620 proposes a large number of micromechanical barbs on the surface of the vascular support to be provided which penetrate into the tissue when the stent is widened and thus fix the stent at this point. Subsequent removal of the stent is inevitably associated with injury to the vessel.

DE 42 22 380 AI describes an expandable, elongated hollow body which is provided with a coating containing an active ingredient. The cover is stretchy and removable.

Metallic stents generally have the disadvantage that foreign bodies have to be implanted, their explantation, e.g. in the event of later complications, surgery is required, which in most cases involves extreme risks, but is often also impossible. Temporary vascular support application is not possible. Metallic stents also have the disadvantage that a therapy-supporting, local medication application is not possible.

Vascular supports made of biodegradable material have therefore also been developed.

From US 5,443,458 a stent in the form of a tube is known, which is introduced into the vessel in a rolled-up state. In the expanded state, hooks arranged on the outside and distributed over the longitudinal edge engage in corresponding recesses in the overlapping tube section, as a result of which the expanded state of the stent is fixed. The disadvantage is that only a predetermined diameter can be set.

This stent consists of several layers of biodegradable material. The first layer gives the stent strength, while the second layer releases an active ingredient. Poly-lactide and poly-glycolic acid as well as polyorthoesters and polyanhydrides are mentioned as the material of the layer supporting the structure. The production takes place by means of extrusion and stretching. Poly-DL-lactide and poly-caprolactam are mentioned as the material of the second layer. The interconnected layers are cut to the appropriate size by punching or laser cutting.

WO 93/06792 describes a biodegradable stent which contains active substance-containing materials with different breakdown rates in order to enable a controlled release of the active substances. The stent consists of a cylinder provided with a longitudinal slot, which has recesses and transverse fibers on its surface, which are stretched so that they expand the cylinder. The material is also Poly lactide proposed. The fibers are made using known techniques such as melting and spinning.

The previously known solutions for the use of biodegradable materials in the manufacture of stents generally have the disadvantage that a permanent, plastic deformation from the compressed state into the expanded state is excluded by the elastic properties of these materials. A location-stable, gentle application adapted to the surrounding tissue is not possible with these stents. The approach of replacing plastic deformations by spirally rolled up vascular structures with unstructured walls, in which the expanded state is stabilized by suitable structures, as is described in US Pat. No. 5,443,458, is also no longer practicable, since this stent only exists in one predetermined diameter can be fixed and can not adapt to the irregularly shaped surface of the surrounding tissue and thus can not be implanted gently and at the same time stable. All known vascular supports made of biodegradable materials have in common that the dissolution takes place unspecifically and therefore it cannot be ensured at what point in time with what size of the dissolution parts of the stents come into the bloodstream and thus lead to uncontrollable thromboembolic complications. All previously proposed solutions for the construction of stents do not provide any possibility of regulating the flow.

The object of the invention is therefore a vascular support that can be adjusted to different diameters, the vascular support should be stabilized in the expanded state.

This object is achieved with a stent according to the features of claim 1. Advantageous refinements are the subject of the dependent claims.

The tubular structure of the implantable stent is formed by a mesh-like structure with meshes that can be compressed in the axial direction when stretched in the circumferential direction. At least one row of stitches arranged in the axial direction and / or at least one in the circumferential direction has self-locking latching elements which interact when the shape of the stitches changes.

The stent is made in a compressed state and inserted into the vessel. When expanding through a balloon catheter, the stent is expanded in the radial direction and simultaneously compressed in the longitudinal direction. As a result, the stitches are subject to a change in shape, which consists in that each individual stitch is compressed in the axial direction and stretched in the circumferential direction. Due to this change in shape, the position of the self-locking latching elements arranged in the meshes can be changed and can interact in such a way that the shape of the stent is stabilized and fixed in the expanded state.

The detachment of the fixation of the stent structure from the material used and the shift to special locking elements enables the use of different materials for the production of the network structure. Both non-degradable and biodegradable materials are suitable for the production of the stents, preference being given to those materials which can be used directly in the LIGA process using lithography or using impression techniques. For the non-biodegradable materials, biocompatible plastics are preferred.

Net meshes have the advantage that the tubular structure can be built up from recurring elements, each individual mesh can be provided with its own locking elements. This makes it possible to attach the locking elements in each individual mesh or to selectively distribute locking elements over the entire network structure in order to be able to influence the elastic properties of the entire vascular support in this way. Meshes without locking elements are more flexible in the expanded state depending on the type of material used and can better adapt to irregular surfaces of the vessel wall in this way without the entire stent being unstable.

By using different locking elements, different diameters can be set in the expanded state in the same stent. This makes it possible, for example, to create stents with constrictions in order to set a targeted flow rate within the vessel in this way.

The meshes can have an angular, round or oval shape. A diamond-shaped shape of the mesh is preferred. Meshes with a wavy shape are also possible.

In order to be able to set different diameters with one and the same stent, the latching elements preferably have a plurality of latching positions. The locking elements can be designed in different ways, with a distinction being made between expansion-blocking and compression-blocking locking elements in their direction of movement. The strain-blocking locking elements are understood to be those which are designed and arranged in the mesh in such a way that they prevent the mesh from expanding in the axial direction in the expanded state of the stent so that the stent cannot contract again.

The compression blocking locking elements are designed and arranged within the meshes that in the expanded state of the stent a compression of the mesh is prevented in the circumferential direction, so that the vessel support cannot contract again.

Preferably, the locking elements comprise a plug element and a receiving element.

If there are strain-blocking locking elements, these are preferably arranged opposite one another in the axial direction. In the case of compression-blocking locking elements, the plug-in elements and receiving elements are preferably arranged opposite one another in the circumferential direction.

According to a preferred embodiment, the plug-in element and the receiving element each have locking teeth which can be shaped differently depending on whether the locking elements are expansion or compression-blocking.

The locking teeth on the expansion-blocking locking elements are designed such that they block when the plug-in element and the receiving element are pushed apart. Accordingly, the locking teeth on the compression blocking locking elements are shaped so that they Block the plug-in element and the receiving element together. In the direction in which the locking teeth do not block when the plug element and the receiving element move, the locking teeth can slide over one another, so that any diameter can be set when the stent is stretched. Only in the end position, when the vascular support strives to contract again, does the locking effect of the ratchet teeth begin by snagging or bracing.

In order to be able to set predetermined and possibly different diameters of the vascular support when the vascular support is expanded, all or only selected strain-blocking locking elements can be provided with at least one stop element. The stop element is preferably arranged between the locking teeth and the fixed end of the plug element. When inserting plug-in element and receiving element into one another, the end position is thus determined by the stop element.

In order to be able to manufacture vascular supports for flow regulation, locking elements with stop elements are preferably arranged in a central section of the vascular support, so that in this area the expansion-blocking locking elements cannot slide into each other as far as the other locking elements, thereby constricting the vascular support.

The latching elements are preferably arranged at nodes of the network structure. This has the advantage that the network structure is the most stable at these points, so that unintentional breaking of the locking elements during implantation can be avoided.

The regular structure of the vascular support from a large number of meshes also offers the possibility of providing predetermined breaking points at regular intervals. These predetermined breaking points can be in the walls of the mesh or be formed at the nodes of the network structure, which is preferably made of biodegradable material. As a result, the dissolution behavior and the size of the stent parts that are released can be controlled in a simple manner during the degradation process of the material.

Net meshes have the further advantage that, despite the provision of latching elements, there is still sufficient space within the meshes to arrange medicament reservoirs. At least one medicament reservoir is preferably provided on at least one mesh wall. The medicament reservoir can, for example, be molded onto the mesh wall and consist of the same material as the mesh if biodegradable material is used for this. The wall thickness of the medicament reservoir is preferably adapted to the rate of degradation of the biodegradable wall material. This allows the time at which the medication is released into the vascular fluid to be predetermined. Poly-lactide is preferably used as the biodegradable material.

In the manufacture of the stent, a mesh mat is preferably first formed, which has connecting elements on its long side. The LIGA process is preferably used to produce the mesh mat. In the first manufacturing step, flat meshes with integrated latching elements are connected to form a mesh mat. After these flat structures have been detached from the substrate, the mesh mat is rolled and the two open edges are connected to one another, the connection also being able to be fixed again by mechanical structures. It is also possible to weld or glue the two longitudinal edges.

Another preferred method is the direct production of the round stent, which eliminates the step of connecting the mat to a hollow cylinder. This manufacture of the round one-piece stent can for example by laser processing, embossing or injection molding of plastics.

The network structure is preferably produced from at least two layers. Three layers are preferably formed one above the other, a distinction being made between a bottom layer, a middle layer and a cover layer. This structure is particularly suitable when medicament reservoirs are to be arranged within the mesh.

Exemplary embodiments are explained in more detail below with reference to the drawings. Show it:

1 is a perspective view of a stent in the compressed state,

2 the vascular support shown in Figure 1 in the expanded state,

3 shows a section of a mesh mat for the manufacture of the stent shown in FIG. 1,

Fig. 4a u. 4b perspective representations of the stitch from the mesh mat shown in FIG. 3 in the compressed and in the stretched state,

5 shows a perspective illustration of the mesh with medicament reservoir shown in FIG. 4a,

6 is a perspective view of a mesh mat with plug elements according to a further embodiment, Fig. 7 is a perspective view of a stent from the mesh mat shown in Figure 6 and

Fig. 8 is a perspective view of a mesh mat with locking elements according to another embodiment.

In Figure 1, a stent 1 is shown in perspective in the compressed state, i.e. shown in the state not yet inserted into a vessel and thus not yet expanded. The stent 1 has a network structure 3, which consists of a regular arrangement of meshes 8, which in the embodiment shown here have a diamond-shaped shape. The meshes 8 are arranged in such a way that the respective corner points of the diamonds, which form nodes 10, are opposite to the stent 1 in the axial direction 12 or in the circumferential direction 13.

Each stitch 8 forms a parallelogram, so that when the stent 1 is widened, the stitches stretch in the circumferential direction 13 and contract in the axial direction 12 at the same time, as shown in FIG. The radial expansion caused by a balloon catheter, not shown, is indicated in FIG. 2 by the arrows 11. The widening of the stent 1 therefore goes hand in hand with a contraction in length.

In FIG. 1, locking elements 20 in the form of plug-in elements 21a and receiving elements 22a are arranged in part of the meshes 8. Here, longitudinal rows of stitches 8 alternate with locking elements 20 with rows of stitches that have no locking elements. The locking elements 20 are arranged in the axial direction 12 on opposite sides of the mesh, so that when the stent 1 expands, the plug element 21a and the receiving element 22a move towards one another and the plug element is inserted into the receiving element 22a. This means that in the expanded state, as shown in FIG. 2, the latching elements 20 are enabled to work together and to stabilize the expanded network structure 3. The receiving element 22a encompasses the plug element 21a, both latching elements 20 being provided with latching teeth 23a and 24a, which are designed in the form of barbs. The number of locking teeth 23a, 24a defines the number of possible locking positions. After the receptacle element and plug-in element 21a have been plugged together, these locking teeth engage in one another and prevent the meshes 8 from expanding in the axial direction, and thus the entire vascular support 1 from contracting. In this embodiment, the locking elements 20 are therefore expansion-blocking.

In the manufacture of the stent 1, a mesh mat 2 is assumed, as is shown, for example, in FIGS. 3 and 6. On the respective long sides of the net mat 2 8 locking elements 6 and 7 are provided at the corner points of the outer mesh. These are cylindrical plug-in elements 6 and correspondingly designed arc-shaped receiving elements 7, which interlock when the net mat 2 is rolled up into the stent 1 shown in FIG. 1. Instead of these locking elements 6, 7, the net mat 2 can also be welded or glued in the rolled-up state at the corner points of the external stitches.

3 shows that the rows of stitches 17a, 17c, 17e, 17g arranged in the later axial direction 12 alternate with rows of stitches 17b, 17d and 17f in which no latching elements 20 are provided.

Even when viewed in the transverse direction, ie in the circumferential direction 13, rows 18a, c, e, g, i, k can be distinguished from rows of stitches 18b, d, f, h, j in which no latching elements 20 are provided. An external mesh 8 is shown enlarged in FIG. 4a. The locking element 6 is formed on one of the four corner points. Since it is a diamond-shaped mesh 8, four mesh walls 9a, b, c and d are provided. The plug element 21a and the receiving element 22a are fastened at opposite corner points, or are molded on in the embodiment shown. The plug-in element 21a has an essentially rectangular cross-section, 8 locking teeth 23a being formed on opposite sides within the mesh. The top and bottom of the plug element 21a are unstructured.

The receiving element 22a is U-shaped and has a web 25 on which two legs 26a are arranged which extend towards the plug element 21a. At the free end of the legs 26a, 26b spring tongues 27 a, 27b are attached, which extend into the space between the two legs 26a and 26b. On the opposite sides of the spring tongues 27a, 27b, locking teeth 24a complementary to the locking teeth 23a are arranged.

If, as shown in FIG. 4b, the stitch 8 has been stretched in the circumferential direction 13 and the stitch has thus been shortened in the axial direction 12, the plug element 23a pushes into the receiving element 22a, as a result of which the two spring tongues 27a and 27b move outwards are pressed so that the locking teeth 23a and 24a can slide over each other. When the end position is reached, which is defined by the balloon catheter when the stent is widened, and the mesh, due to its elastic material properties, tends to stretch again in the axial direction 12, the locking teeth 23a, 24a interlock and thus block the axial expansion.

5 shows a further stitch 8, which is shown in FIGS. 4a, 4b has locking elements 20 shown. In addition are on the mesh walls 9a, 9b, 9c and 9d medicament reservoirs 30a-d of different sizes arranged. These are cylindrical medicament reservoirs, the height of which corresponds to the height of the mesh walls 9a-9d. The wall thickness of these medicament reservoirs 30a-d is adjusted to the rate of degradation of the wall material used, so that the time of medication delivery can be specified.

The stitch 8 shown in FIG. 5 has a three-layer structure. In order to clarify this structure, the two medicament reservoirs 30c and 30d are partially shown in section. A middle layer 41 is applied to a bottom layer 40, which at the same time forms the bottom plate of the medicament reservoirs, which has corresponding recesses in the region of the medicament reservoirs for receiving the medication. This is followed at the top by a cover layer 42 which closes the cutouts in the middle layer 41 in the region of the medicament reservoirs. Since the walls 9a-9d, the medication reservoirs 30a-30d and the latching elements 20 all have the same thickness, the production of the stitches is possible in a simple manner through the layer structure shown.

6 shows a mesh mat 2 in which the plug-in elements 21a in section 35 are provided with stop elements 28a, b, c of different sizes. These stop elements 28a, b, c are arranged between the fastening point of the plug elements 21a and the locking teeth 23a. When the plug-in element and the receiving element are joined together, the insertion path is limited by the stop elements in that the end face of the legs 26a, 26b abut the end faces of the stop elements 28a, b and c. The length of the insertion path is determined by the thickness or by the arrangement of the stop elements 28a-c. The stop elements 28a are further away from the free end of the plug element 21a than the stop elements 28b or the stop elements 28c. Accordingly, the corresponding plug-in elements 21a have fewer locking teeth 23a, so that overall less Rest positions are possible. The stepped arrangement of the stop elements 28a-28c in the region 35 leads to a constriction when the stent formed from this mesh mat 2 is expanded, as is shown in FIG. 7. Such a vascular support 1 is suitable for setting the vascular flow.

8 shows a mesh mat 2 with latching elements 20 according to a further embodiment. Plug-in elements 21b and receptacle elements 22b are arranged opposite one another in the circumferential direction, in the embodiment shown here being compression-blocking locking elements 20. In the compressed state of the stent, the plug-in elements 21b and the receiving elements 22b are joined together and are pushed apart in the circumferential direction 13 due to the widening of the stent. The locking teeth 23b and 24b slide over one another until the predetermined end state of the stent is reached. Due to the material properties of the stitches 8, the latter endeavor to contract again in the circumferential direction 13, whereupon the locking teeth 23b and 24b interlock and support one another in order to prevent a further contraction in the circumferential direction 13 in this way.

reference numeral

Stent

Mesh mat

Network structure

Long side

Narrow side

Fastener

Mesh a, b, c, d mesh wall 0 node 1 radial direction 2 axial direction 3 circumferential direction 4 predetermined breaking point 7a, b longitudinal row 8a, b transverse row 0 detent element 1a, b plug element 2a, b receiving element 3a, b detent tooth 4a, b detent tooth 5 web 6a , b leg 7a, b spring tongue 8a, bc stop element 0a.b, c, d medicament reservoir 5 constriction 0 bottom layer 1 middle layer

42 top layer

Claims

claims

1. Implantable stent with a tubular structure that is extensible in the circumferential direction, characterized in that

that the tubular structure is a net-like structure (3) with meshes (8) which can be compressed in the axial direction (12) when stretched in the circumferential direction (13), and

that at least one row (17a-g, 18a-k) of stitches (8) arranged in the axial direction (12) and / or at least in the circumferential direction (13) has self-locking latching elements (20) which cooperate when the shape of the stitches (8) changes.

2. Vascular support according to claim 1, characterized in that the meshes (8) have an N-square, round or oval shape.

3. stent according to claim 1 or 2, characterized in that the meshes (8) have a diamond-shaped shape.

4. Vascular support according to claim 1, characterized in that the meshes (8) have a wavy shape.

5. Vascular support according to one of claims 1 to 4, characterized in that the latching elements (20) have a plurality of latching positions.

6. Vascular support according to one of claims 1 to 5, characterized in that the latching elements (20) are designed to block expansion or compression blocking in their direction of movement.

7. vascular support according to one of claims 1 to 6, characterized in that the latching elements (20) comprise a plug-in element (21 a, b) and a receiving element (22 a, b).

8. stent according to claim 7, characterized in that the plug-in element (21 a, b) and the receiving element (22 a, b) in the axial direction (12) or in the circumferential direction (13) are arranged opposite one another.

9. stent according to claim 7 or 8, characterized in that the

Plug element (21a, b) and the receiving element (22a, b) each have locking teeth (23a, b, 24a, b).

10. Vascular support according to claim 9, characterized in that the locking teeth (23 a) on the expansion-blocking locking elements (20) are designed such that they block when pushing apart the plug element (21 a) and receiving element (22 a).

11. stent according to claim 9, characterized in that the

Locking teeth (23b, 24b) on the compression-blocking locking elements (20) are designed such that they block when the plug-in element (21b) and the receiving element (22b) are plugged together.

12. Vascular support according to one of claims 6 to 10, characterized in that the strain-blocking locking elements (20) have at least one stop element (28a, b, c).

13. Vessel support according to claim 12, characterized in that the stop element (28a-c) between the locking teeth (23 a) and the fixed end of the plug element (21a) is arranged.

14. Vascular support according to one of claims 12 or 13, characterized in that the latching elements (20) with stop elements (28a-c) are arranged in a central section (35) of the vascular support (1).

15. Vascular support according to one of claims 1 to 14, characterized in that the latching elements (20) are arranged at nodes (10) of the network structure (3).

16. Vascular support according to one of claims 1 to 15, characterized in that the network structure (3) on the walls (9a-d) of the mesh (8) has predetermined breaking points (14).

17. Vascular support according to one of claims 1 to 16, characterized in that predetermined breaking points (14) are located at the nodes (10) of the network structure (3).

18. Vascular support according to one of claims 1 to 17, characterized in that at least one medicament reservoir (30a-d) is arranged on at least one mesh wall (9a-d).

19. Vascular support according to claim 18, characterized in that the

Medicament reservoir (30a-d) is integrally formed on the mesh wall (9a, b, c, d).

20. Vascular support according to claim 18 or 19, characterized in that the wall thickness of the medicament reservoir (30a-d) is adapted to the rate of degradation of the biodegradable wall material.

21. Vascular support according to one of claims 1 to 20, characterized in that the biodegradable material is polylactide.

22. Vascular support according to one of claims 1 to 21, characterized in that the network structure (3) consists of at least two layers.

23. Vascular support according to claim 22, characterized in that the network structure (3) consists of a bottom layer (40), a middle layer (41) and a cover layer (42).

24. Vascular support according to one of claims 1 to 23, characterized in that the vascular support (1) is formed from a mesh mat (2) which has connecting elements (6, 7) on its long side (4).