Patent Application
20240277499
The present patent application claims the benefit of and priority to German Patent Application No. 10-2023-104170.3, filed Feb. 20, 2023, the entire contents of which are incorporated herein for all purposes by reference.
The invention relates to a medical device for insertion into an organ of the body, with a compressible and expandable mesh structure comprising struts. The struts are connected together by strut connectors and delimit closed cells of the mesh structure. Respectively, two struts of at least one cell are disposed opposite each other and form a first strut pair and a second strut pair.
A medical device of this type is known from EP 1 903 999 B1, for example, which describes a stent which has a closed cell design. In stents of this type, the problem arises that in tightly curved vessels, they do not always have sufficient bending flexibility to remain in good contact with the vessel wall (wall apposition). The measures for improving the bending flexibility taken in the prior art mentioned above are complex.
The objective of the invention is to improve the bending flexibility of the mesh structure of a medical device in a simple manner without relinquishing the closed celled design.
In accordance with the invention, this objective is achieved by a medical device as shown in the drawings and described herein.
A further objective of the invention is to provide a treatment system with a medical device of this type. This objective is achieved as shown in the drawings and described herein.
Specifically, the objective is achieved by a medical device for insertion into an organ of the body, with a compressible and expandable mesh structure comprising struts. The struts are connected together by strut connectors and delimit closed cells of the mesh structure.
Respectively, two struts of at least one cell are disposed opposite each other and form a first strut pair and a second strut pair. One of the two strut pairs is connected together by at least one connecting strut. The connecting strut extends into the cell and bridges it.
The invention has a variety of advantages.
The connecting strut meets the constructional prerequisites for optimizing the mesh structure with closed cells as regards the bending flexibility, without at the same time compromising or at least substantially compromising the supporting force or radial force of the mesh structure. The invention permits very good vessel apposition to be obtained in tortuous vessels with a high supporting force or radial force. Risks which may arise from poor wall apposition, such as migration or negative hemodynamic effects, are considerably mitigated. To this end, at least one connecting strut is provided which connects one of the two strut pairs together, extends into the cell and bridges it. By means of the additional connecting strut, an increased supporting force is obtained, so that other properties or features of the mesh structure can be modified in order to improve the bending flexibility, such as the number of cells on the circumference, for example, without increasing the risk of migration.
The closed cell design has the advantage of good resheathability for repositioning the device in the vessel.
The additional connecting strut is simple to produce, for example by laser cutting. The good re-positionability of the mesh structure is not compromised.
A further advantage of the invention lies in the fact that the basic shape of the mesh structure can be retained. The shape of the cells as a closed cell can be retained. The additional connecting strut supplements the cell design. The “bridging” of the cell by the connecting strut should be understood to mean that the design of the basic cell additionally includes the at least one connecting strut which extends over the entire basic cell between two struts which are disposed opposite each other. The connecting strut bridges or spans the entire cell and connects the two opposite struts of a strut pair.
In general, the opposing struts of a (first) strut pair are not connected together directly, but each to the opposite struts of a further (second) strut pair as well as to the connecting strut.
Together with the further strut pair, the strut pair forms the boundary of the cell. This does not exclude the possibility that the cell could be delimited by further struts. It is also possible for more than one connecting strut to protrude into the cell or into the respective cell and bridge it.
The opposing struts of the strut pairs may be straight and/or curved. Reference should be made to the Applicant's patents in respect of the basic design of the cells.
EP 2 667 831 B1 protects the underlying principle of rotation during expansion via paired opposing struts with different bending stiffnesses. DE 10 2013 104 550 B4 describes a cell design and the shape of the strut connectors, wherein the strut connectors are X-shaped. Because respective adjacent struts have unequal strut widths, twisting of the stent structure occurs during expansion. DE 10 2013 107 258 B4 additionally describes a complete stent construction with edge and transitional cells, cross sectional shapes with flaring as well as edge cells with markers.
The invention is applicable to these protected technologies and is disclosed and claimed in conjunction with the cell designs described in the Applicant's own patents. This does not exclude the fact that the invention is applicable to other cell designs which have not been described here.
The principle of the invention applies to at least one cell of the mesh structure. The principle may be broadened to a plurality of cells of the mesh structure, in particular to a plurality of cells disposed on the circumference of the mesh structure. The present features which are described and claimed in conjunction with at least one cell are also described and claimed in conjunction with a plurality of cells, in particular with a plurality of cells disposed on a segment of the circumference.
The device in accordance with the invention is, for example, suitable as a temporary or permanent vessel implant. It may, for example, be a stent or a thrombectomy device. Other applications are conceivable.
Advantageously, the mesh structure is substantially tubular.
The mesh structure may be self-expanding.
Preferred embodiments of the invention are defined in the dependent claims.
Preferably, the cell is substantially rhomboidal. This has the advantage that the connecting strut is used in conjunction with a well-established closed cell shape which can be optimized well with a view to the bending flexibility. “Rhomboidal” is not used in the strictly geometrical sense in which the struts have to be straight. It is sufficient for the basic shape of the cell to be rhomboidal. The respective strut pairs may each be straight and/or curved opposing struts.
In a preferred embodiment, a plurality of cells are disposed on at least one circumferential segment in which respectively one of the two strut pairs is connected together by at least one connecting strut which extends into the cell and bridges it. Transferring the principle of one cell to a plurality of cells of a circumferential segment has the effect that the supporting force is increased by the additional connecting struts of the respective cells on the entire circumference in the region of the circumferential segment. The number of cells on the circumferential segment is not restricted. It is possible for there to be a plurality of circumferential segments in the axial direction, which respectively have appropriate cells each with at least one connecting strut.
The circumferential segment with the cells with connecting struts can be described as the first circumferential segment.
In a preferred embodiment, the strut connectors of the first circumferential segment are offset on the circumference by an angle which is less than or equal to 180°. This has the advantage that the mesh structure—in the case of a tubular mesh structure—can be compressed to a particularly small diameter when crimped in a catheter. The strut connectors are in a particularly tight arrangement because of the offset disposition, whereupon small diameters of the mesh structure in the crimped state can be obtained.
As an example, three cells disposed on the circumferential segment, in particular the first circumferential segment, are configured in a manner such that the strut connectors-viewed in cross section of the mesh structure—are offset by 120°. The invention or the present exemplary embodiment is not limited to three cells per circumferential segment. The offset arrangement of the strut connectors with respect to the cross section of the mesh structure may also be obtained with another number of cells.
The “cross section” of the mesh structure should be understood to mean a section which runs orthogonally to the longitudinal axis of the mesh structure.
In a particularly preferred embodiment of the invention, the connecting strut bridges the cell diagonally. In this way, a particularly high supporting force is achieved.
The diagonal disposition of the connecting strut is disclosed and claimed in conjunction with at least one cell, in particular in conjunction with all of the cells of the first circumferential segment. A plurality of circumferential segments may be provided in the axial direction which are equipped with diagonal connecting struts corresponding to the first circumferential segment.
In this regard, the “diagonal disposition” means that, with respect to at least one axis of the cell, in particular both axes of the cell, the connecting strut is inclined to, or in general deviates from the position of the axis or the axes, i.e. the connecting strut intersects the axis or the axes. As an example, in the case of a rhomboidal cell, the longitudinal axis of the cells runs between the two tips of the rhomboidal cell which have the larger separation. The normal axis is shorter than the longitudinal axis. The position of the axes may change with respect to the longitudinal axis of the entire device as a function of the state of expansion or compression.
The diagonal disposition means that the connecting strut only connects one of the two strut pairs together. The other strut pair is free having regard to the connecting strut.
The diagonally disposed connecting strut may be straight or curved in configuration. The curved connecting strut is advantageously S-shaped in configuration. Other shapes for the connecting strut are possible.
Preferably, the connecting strut is connected to the strut pair by a respective flexible strut connector, in particular a Z-shaped strut connector. The flexible strut connector, in particular the Z-shaped strut connector, has a greater flexibility than X-shaped strut connectors. This has the advantage that the bending flexibility is further improved.
The flexible strut connector permits relative movement between the connecting strut and the strut pair when the mesh structure is moved, for example curved or expanded/compressed. As an example, the flexible strut connector may be Z-shaped.
In a further advantageous embodiment, the connecting struts of a first cell and the connecting struts of an adjacent second cell in the circumferential direction are offset with respect to each other. An example of how the offset disposition of the connecting struts of two adjacent cells may be obtained is the connection of the respective connecting strut with the associated strut pair via a Z-shaped strut connector.
Other possibilities for the attachment of the connecting struts which cause the connecting struts of two cells which are adjacent in the circumferential direction to be offset with respect to each other are conceivable.
The Z-shaped attachment of the connecting struts ensures that the diagonal connecting struts of two adjacent cells are not aligned, but that their connecting sites with the cell, in particular the rhomboidal cell, are offset with respect to each other in a manner such that in the loaded state, i.e. in the compressed state in the catheter, parts of these adjacent diagonally disposed connecting struts overlap.
In this regard, the offset between the junction sites or connection sites of the diagonally disposed connecting struts to the respective strut pairs, i.e. the length of the overlap, is between 0.1 and 0.9 times the strut length of the cell, in particular of the rhomboidal cell. The offset may be between 0.2 and 0.8 times, in particular between 0.3 and 0.7 times the strut length of the cell, in particular of the rhomboidal cell.
Preferably, the strut width of the connecting strut in the region of its ends is smaller than the strut width in a region which extends between the ends of the connecting strut. In this manner, wall adaptation is further improved, because the diagonal strut of the cell which lies on the inside of a bend in a vessel and is therefore compressed, then has a lower tendency to bend into the interior of the vessel due to the compression.
More preferably, the strut width of the struts of the first and/or second strut pair in a region close to the X-shaped strut connectors is smaller than the strut width in a region close to the Z-shaped strut connectors. The struts of the first and/or second strut pair here preferably taper in configuration in the direction of the X-shaped strut connectors. Good bending flexibility of the struts or of the mesh structure is obtained in this manner.
The ratio of the strut width of the struts in the region close to the X-shaped strut connectors to the strut width close to the Z-shaped strut connectors is preferably between 0.5 and 1.0, in particular approximately 0.75. The ratio of the strut width in the region of the ends of the connecting strut to the strut width in the region between the ends of the connecting strut is between 0.7 and 1.0, in particular approximately 0.95. The struts of the first and/or second strut pair in the region close to the X-shaped strut connectors are consequently more sharply tapered than the ends of the connecting struts.
In a specific embodiment, the circumferential segment has at least 2, in particular 3 cells. In this manner, the bending flexibility is improved compared with an embodiment with more cells on the circumference. Preferably, the mesh structure has a maximum of 5 cells per circumferential segment. The edge regions may have more than 5 cells per circumferential segment, for example 6 cells. Other designs are possible.
The number of cells on the first circumferential segment is advantageously smaller than the number of cells on at least one second circumferential segment which is disposed proximally and/or distally to the first circumferential segment in the axial direction of the mesh structure. In this embodiment, a plurality of circumferential segments are provided in the axial direction of the mesh structure, wherein the circumferential segments which are disposed further outwards relative to the first circumferential segment or a further outwardly disposed circumferential segment has more cells on the circumference than the first circumferential segment.
This embodiment has the advantage that the further inwardly disposed cells in the axial direction of the mesh structure, which may also be described as central cells or inner cells, can be properly optimized with a view to the bending flexibility, because the central cells each have connecting struts, so that in this region, the flexibility is particularly high, but the supportive effect is not especially reduced because the radial force is distributed evenly onto the surface of the vessel.
In contrast to the central cells, the outer cells or outward cells or edge cells which are further out relative to the first circumferential segment or to the central cells do not have any connecting struts. The outward cells may have other functions or properties, such as flaring or radiopacity by means of radiographic markers, for example.
Transposed onto a stent or a thrombectomy device, this embodiment has the advantage that in the central region of the mesh structure, where particularly tight curves occur, the cells of the mesh structure are reinforced by the additional connecting struts so that there, the bending flexibility can be optimized. In this embodiment in accordance with the invention, this is achieved by the fact that the number of rhomboidal cells on the first circumferential segment is smaller than the number of cells on at least one second circumferential segment which is disposed proximally and/or distally to the first circumferential segment in the axial direction of the mesh structure.
The associated poorer distribution of the supporting effect which is usually associated with a smaller number of cells is compensated for by reinforcing these cells by means of the additional connecting struts, so that in this region of the mesh structure, a very good bending flexibility is obtained at the same time as a well-distributed supporting force. The distribution of the supporting force over a larger number of struts compared to the circumferential segment with the same number of cells without connecting struts means that the supporting force is not concentrated onto a few lines of contact, or put another way, it is transferred to a plurality of lines of contact. The connecting struts also contribute to increasing the supporting force.
The ratio of the number of central cells per circumferential segment to the number of outer cells per circumferential segment may be 1:1, 1:2 or 1:3 or 1:4. Other ratios are possible with this embodiment, as long as fewer central cells are provided per circumferential segment than outer cells per circumferential segment.
The basic principle of the invention may also be embodied in an embodiment which has a constant number of cells per circumferential segment along the entire length of the mesh structure.
Here, for the same number of cells, the cell design of the outer cells and the cell design of the central cells may be different. Other differences are possible.
The central cells may also be described as middle cells or inner cells and the outer cells may also be described as outward cells. It is simply a matter of the relative disposition of the cells with respect to each other.
The basic principle of the invention may also be applied to a medical device which has a membrane, wherein the membrane at least partially covers the cells of the mesh structure. The membrane may be configured as an electrospun membrane. In this case, preferably, 9 cells are provided per circumferential segment, because in this manner, the inflow of blood between the vessel wall and the membrane can be substantially prevented or reduced.
The treatment system has a medical device in accordance with the invention or a medical device according to one of the embodiments defined above as well as a catheter in which a guide element is connected to an axial end of the mesh structure.
The invention will now be described in further detail with the aid of exemplary embodiments and with reference to the accompanying diagrammatic drawings, in which:
In use, the mesh structure 10 is tubular.
The struts 11 are connected together by strut connectors 12, which are X-shaped. The struts 11 each delimit a closed cell 13 of the mesh structure 10. In the exemplary embodiment shown here, the cell 13 is rhomboidal in shape. From the figures, it can clearly be seen that this does not mean that a strictly geometrical rhomboidal shape is necessary. The sides of the rhombus could be partially curved and partially straight. The basic shape of the cells 13 is rhomboidal.
The cell 13 is delimited by 4 struts 11 which are each disposed in pairs opposite each other and form two strut pairs 14a, 14b. The opposed struts 11 of the first strut pair 14a are not connected together directly, but with the struts 11 of the second strut pair 14b, they complete the basic rhomboidal shape of the cells 13.
In the example of
The strut width of the struts 11 of the first strut pair 14a is greater than the strut width of the struts 11 of the second strut pair 14b. This means that the struts 11 of the first strut pair 14a have a higher bending strength than the struts 11 of the second strut pair 14b. The rotation of the cell 13 caused by the expansion and compression of the mesh structure 10 leads to an excellent bending flexibility for the entire mesh structure 10 which distinguishes the mesh structure from other closed cell designs significantly. The mechanism is described in detail and protected in the Applicant's patents EP 2 667 831, DE 10 2013 104 550 B4 and DE 10 2013 107 258 B4 and will not be gone into in further detail here.
In general, the features and functions described in conjunction with a cell 13 of the mesh structure 10 are also disclosed and claimed for other cells 13 of the mesh structure 10. In this manner, circumferential segments 16 and axial sections of the mesh structure consisting of a plurality of circumferential segments 16 may have corresponding cells 13. The edge cells of the mesh structure usually have another design because there, they have to have other functions, such as flaring.
The mesh structure 10 overall has a closed cell design. All of the cells 13 of the mesh structure 10 are closed. Other embodiments of the mesh structure 10 are possible.
As can clearly be seen in
The connecting strut 15 divides the cell 13 into two sub-cells or part-cells, in particular into two half-cells, specifically two substantially symmetrical half-cells, which are disposed between the struts 14a, 14b and the connecting strut 15. For its part, each part-cell also forms a closed cell. The divided cell 13 in this regard forms the main cell which determines the design of the mesh structure 13. The main cell is rhomboidal and has the X-shaped strut connectors 12 at the points of the rhomboid. Specifically, four X-shaped strut connectors 12 are provided per main cell.
The connecting strut 15 is curved, in particular S-shaped. Other shapes for the connecting strut 15 are possible.
The term “diagonal” is not intended to indicate a strictly geometrical diagonality.
By means of the diagonal disposition of the connecting strut 15, in sections, specifically in the central region of the connecting strut 15, the connecting strut 15 runs approximately parallel to the struts 11 of the second strut pair 14b. This is the case for the expanded state at least. The S-shaped connecting strut 15 is disposed in a manner such that it approaches the respective strut 11 of the first strut pair 14a substantially tangentially.
In the exemplary embodiment, the struts 11 of the second strut pair 14b are straight. The curved connecting strut 15 extends substantially in the same direction as the straight struts 11 of the second strut pair 14b.
The relative disposition of the connecting strut 15 in the cell 13 may change as a function of the state of compression or expansion of the mesh structure 10.
The strut width of the connecting strut 15 varies. As can be seen in
The strut width in the region of the ends is indicated by S4 and in the central region by S3. By this means, on the one hand, the supporting force of the connecting strut 15 in the region of the strut width S3 is increased and on the other hand, the bending flexibility in the region of the attachment (strut width S4) is improved.
The connecting strut 15 is attached by means of a Z-shaped strut connector 18. The Z-shape of the strut connector 18 means that the end of one connecting strut 15 and the end of the next connecting strut 15 in the adjoining cell together with the strut 11 with which the two strut connectors 15 are connected form a kind of Z. The curvature, in particular the S-shaped curvature of the connecting strut 15, means that there is an almost tangential approach of the end of the connecting strut 15 to the strut 11 in the region of the Z-shaped strut connector 18.
In other words, the two horizontal limbs of the Z are curved and approach the strut 11 approximately tangentially. In doing so, the strut width tapers from S3 in the central region to S4 in the end region of the connecting strut. Then it increases again going towards the connector.
Both the crimping capability as well as the wall apposition can be optimized by means of the position, length and strength of the reduction in the strut width (taper).
The strut width S1 of the strut 11 is larger than the strut width S4 of the connecting strut 15 in the region of the strut connector 18. This is advantageous but not obligatory.
The connecting strut of the strut connector 18 between the two adjoining connecting struts 15 has substantially the same strut width S1 as the remaining strut 11 of the first strut pair 14a to which the connecting strut 15 joins.
The Z-shaped strut connector 18 means that the connecting struts 15 of the two adjacent cells 13 do not align with each other. Rather, their connecting positions with the cell 13 are offset with respect to each other in a manner such that in the compressed state, sections of the immediately adjacent connecting struts 15 overlap. In this manner, the crimping capability of the device or the stent is improved, so that in the compressed state, small diameters for the mesh structure 10 can be obtained.
In addition, the Z-shape of the strut connector 18 contributes to the bending flexibility of the mesh structure 10. Z-shaped strut connectors 18 have a greater flexibility than X-shaped strut connectors 12. The flexible attachment of the connecting strut 15 via the strut connector 18 is particularly advantageous. The advantage is even greater because of the tapered ends of the connecting struts 15.
The overlapping of the connecting struts 15 in the compressed state may be adjusted by the offset between the junction positions or connecting positions of the connecting struts 15 and the strut 11 of the first strut pair 14a. The offset between the junction position or connecting position of the connecting struts 15 (i.e. the length of the overlap) may be between 0.1 and 0.9 times the strut length of the strut 11 of the first strut pair 14a of the cell 13, in particular between 0.2 and 0.8 times, in particular between 0.3 and 0.7 times.
The constructional features and properties described in conjunction with the connecting strut 15 are also disclosed and claimed in conjunction with the correspondingly constructed connecting struts 15 of the other cells 13.
The reinforcement of the cell by the connecting strut 15 enables the mesh structure 10 to be modified to the extent that the bending flexibility can be enhanced without the radial force or supporting force of the mesh structure 10 being compromised in the implanted state. Rather, by means of an appropriate design of the connecting struts 15, the supporting force can be evenly distributed onto the vessel wall along with an increased bending flexibility.
The increase in the bending flexibility may, for example, be achieved by reducing the number of cells 13 per circumferential segment 16. This leads to a configuration of the mesh structure 10 which, as shown in
The function of the diagonal struts consists in the fact that the lost supportive effect due to this reduction in the number of cells is compensated for in the interstices without compromising the bending flexibility, however.
In the initial example of
The effect of the exemplary embodiment in accordance with the invention of
The left hand view of
The wall apposition, i.e. the contact of the closed cell stent C with the vessel wall, therefore reduces both on the inside and also on the outside of the vessel with increasing curvature. In this regard, the curvature is the reciprocal of the radius of the central line. On the outside, the rhomboidal cells are stretched more and more in the axial direction until they cannot stretch any further and lift from the vessel wall. In contrast, on the inside, initially the rhomboids are compressed, and then finally, the structure collapses into the interior of the vessel lumen.
In the right hand view of
When flexed about an axis lying transversely to the longitudinal axis of the stent, the 3-cell design has a better bending flexibility than a 6-cell design of corresponding dimensions. This can best be seen by considering the strut cross sections in a plane which is orthogonal to the longitudinal axis, which lies in a test structure (U-bend) at the point of maximum curvature; see
In the 6-cell design, each connector F has exactly one further connector F diametrically opposite it, see
In contrast, with a 3-cell design, for the same orientation of the strut connector 12 lying on the outer line of the bend, there is no directly opposite strut connector, but the two other strut connectors 12 are respectively offset by 120°, see
The attachment of the connecting struts 15 to the continuous struts 11 of the 3-cell structure is advantageously carried out via Z-shaped strut connectors 18, which permit a further expansion of the mesh structure 10, in particular on the outer line of the bend, than if the neutral lines of adjacent diagonal connecting struts 15 were to be directly aligned. The strut width of the connecting struts 15 may reduce locally in the vicinity of the Z-shaped strut connectors 18 in order to obtain an optimal deformation of the connecting struts 15 for the application. In particular, by this means, the wall apposition of the connecting struts 15 on the inner curve of the bend can be further improved.
Although the cell structure of the exemplary embodiment in accordance with the invention does have wider struts 11, it requires fewer than with a corresponding 6-cell structure with the same radial force, and so comparable stents can be delivered through the same or even through a smaller catheter lumen.
The strut width of the struts 11 of the first and second strut pair 14a, 14b varies. As can be seen in
The ratio of the strut width S1′ to the strut width S1″ as well as the ratio of the strut width S2′ to the strut width S2″ is between 0.5 and 1.0, such as approximately 0.75, for example. The ratio of the strut width S3 to the strut width S4 of the connecting strut 15 is between 0.7 and 1.0, for example 0.95.
The advantages and constructional features described in conjunction with a 3-cell design can in principle also be applied to a mesh structure which has a number other than 3 cells per circumferential segment.
The cell design is in principle suitable for all clinical applications in which a vessel anatomy is to be treated with a permanent implant or a temporarily inserted implant with wall apposition which is as good as possible, without leading to collapse of the structure. These implants, mostly self-expanding, are preferably laser cut from nitinol tubing, brought to their final diameter by heat treatment and electropolished. Other alloys or production processes are conceivable.
In summary, the invention or the exemplary embodiment described here enables a cell to be designed for laser cut stents with closed cells (closed cell design) which reduces the constriction and kinking of the structure in tightly curved vessels which occur in a closed cell design of the prior art beyond a specific curvature. In this regard, the positive properties of the design, capability of crimping to a narrow catheter lumen, resheathability, narrow-mesh covering of the vessel wall are retained to a great extent (covering aneurysm necks), completely retained (resheathability) or even improved (radial force, capability of crimping to a narrow catheter lumen).
| Number | Date | Country | Kind |
|---|---|---|---|
| 102023104170.3 | Feb 2023 | DE | national |
