US20080243230A1 - Stent having radially expandable main body - Google Patents

Abstract

A stent made of a material having a low strength and having a main body circumscribing a cylindrical shape and radially expandable from a contracted starting position into a dilated support position, comprising a) a plurality of support segments disposed around the circumference and arrayed on one another in the axial direction each segment being formed by a strut meandering in its coarse structure in its contracted starting position and having alternately opposing meandering curves expandable into the support position made of flexible material; b) a plurality of axial connectors connecting between zenith points of at least a part of the meandering curves in the axial-parallel direction of the support segments; and c) at least one means for stabilizing the strut coarse structure in its contracted starting position against radial expansion and being automatically detachable upon a radial expansion of the stent.

Description

PRIORITY CLAIM
• This patent application claims priority to German Patent Application No. 10 2007 015 670.9, filed Mar. 31, 2007, the disclosure of which is incorporated herein by reference in its entirety.
FIELD
• The present disclosure relates to expandable vascular stents.
BACKGROUND
• One example of a vascular implant is described in detail in International Patent Publication No. WO 2004/103 215 A1, in particular, in regard to the fundamental areas of application of such stents and the special problems upon use of materials having a low ductile yield and also lower strengths, such as magnesium alloys.
• In the embodiment which may be inferred from this publication, the stent is implemented by a main body circumscribed by a cylindrical shape and radially expandable from a contracted starting position into a dilated support position which, on one hand, comprises multiple support segments running around the circumference and arrayed in the axial direction on one another. The support segments are each formed by a strut which is meandering in coarse structure in its contracted starting position having alternating opposing meandering curves made of flexible material. On the other hand, the main body has axial connectors running in the axial-parallel direction which connect the support segments between zenith points of at least a part of the meandering curves.
• The above-mentioned magnesium alloys as the material for producing stents have significantly lower strength values than typical construction materials for balloon-expandable stents, such as medical steel having the material identifications 316L, MP35N or L 605. These lower strength values cause problems in the practical application of the stents. It is thus necessary for the stent placement to mount the stent on a balloon catheter. For this purpose, the stent, which is structured from a sleeve material by laser cutting, for example, is crimped onto the balloon catheter in its contracted starting position. The stent is also guided on the catheter system through curved areas of the insertion or blood vessel system in this state during the implantation. Individual struts of the stent may open in the corresponding passages, by which the retention forces of the stent on the catheter are reduced. This causes a significant risk of loss of the stent.
• Especially endangered areas of the stent are the terminal strut elements having their meandering curves. In addition, the danger arises due to projecting edge segments, the so-called “flaring,” that, in addition to the mechanical irritation of the internal vascular wall upon passage of the stenosis or the retraction into the insertion catheter, unintended stripping of the stent from the balloon catheter will occur.
SUMMARY
• The present disclosure describes several exemplary embodiments of the present invention.
• One aspect of the present disclosure provides a stent made of a material having a low strength and having a main body circumscribing a cylindrical shape and radially expandable from a contracted starting position into a dilated support position, comprising a) a plurality of support segments disposed around the circumference and arrayed on one another in the axial direction, each segment being formed by a strut meandering in its coarse structure in its contracted starting position and having alternately opposing meandering curves expandable into the support position made of flexible material; and b) a plurality of axial connectors connecting between zenith points of at least a part of the meandering curves in the axial-parallel direction of the support segments; and c) at least one means for stabilizing the strut coarse structure in its contracted starting position against radial expansion and being automatically detachable upon a radial expansion of the stent.
• One feature of the present disclosure provides a stent of the type according to the species in such a manner that unintended expansion of the entire stent or exposed areas thereof, such as the terminal front edges, is reliably prevented during the implantation.
• This feature is achieved according to the present disclosure by a means for stabilizing the strut coarse structure in its contracted starting position against radial expansion which are integrated in the stent design. These stabilization means are then detachable automatically upon the actual radial expansion of the stent.
• These stabilization means advantageously secure radial locking of the stent in its crimped state so that unintended expansion of the stent, even in partial areas, is avoided because of this fixing.
• According to preferred embodiments of the present disclosure, these stabilization means may be implemented in different ways, for example, by detachable glued joints between adjacent meandering curves of a strut or from strut to strut, by catch elements in the stent structure, boundary fixing traverses or by fine structure struts against the cited “flaring.” More detailed explanations may be inferred from the following description, in which exemplary embodiments of the subject matter of the present disclosure are explained in greater detail on the basis of the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• Various aspects of the present disclosure are described hereinbelow with reference to the accompanying figures.
• FIG. 1 is a perspective view of one exemplary embodiment of a stent in its contracted starting position having a terminal glued joint as the stabilization means;
• FIG. 2 is a detail top view of the stent in an unwound view having a glued joint variant;
• FIG. 3 is a detail top view of the stent in an unwound view having a different glued joint variant;
• FIG. 4 is a schematic detail excerpt in an unwound illustration of the stent having catches as the stabilization means;
• FIG. 5 is a schematic detail excerpt in an unwound view of a stent having a boundary fixing traverse;
• FIG. 6 is a schematic detail excerpt in an unwound view of an exemplary embodiment of a stent having a different boundary fixing traverse;
• FIG. 7 is a schematic detail view in an unwound view of an exemplary embodiment of a stent having boundary fine structure struts as the stabilization means;
• FIG. 8 is an enlarged detail excerpt as shown inFIG. 7;
• FIG. 9 is a perspective partial illustration of an exemplary embodiment of a stent having extension struts for removable fastening to a balloon catheter;
• FIG. 10 is a top view of the stent as shown inFIG. 9 in an unwound view;
• FIG. 11 is a detail top view of an exemplary embodiment of a stent in an unwound view having marker projections coupled to one another; and
• FIG. 12 is a detail top view of an exemplary embodiment of a stent in an online view having marker projections coupled in a ring.
DETAILED DESCRIPTION
• FIG. 1 clarifies the structure of the stent in its contracted starting position. The stent is worked out of a cylindrical metal body by laser cutting in such a manner that the stent hasmultiple support segments1 running around the circumference U and arrayed in the axial direction A on one another, which are each formed by one of thestruts2 meandering in their coarse structure in the contracted starting position shown.
• In the direction parallel to the axial direction A, thesupport segments1 are connected to one another byaxial connectors4, which each run between thezenith points5 ofmeandering curves3 to be connected. Theaxial connectors4 always run from the exterior side of ameandering curve3 to the interior side of themeandering curve3 of the adjacent strut due to the offset of theadjacent support segments1 around the circumference U.
• As is not shown in greater detail in the drawings, upon radial expansion of the stent, the sections of themeandering curves3 running between thezenith points5 are deployed around the circumference U. The closer the corresponding sections approach to the circumference U, the greater the so-called collapsing pressure of the stent.
• To achieve the additional radial fixing of the stent desired according to the present disclosure, in the variants shown inFIGS. 1-3, a gluedjoint6 is provided which may be applied between the twoterminal meandering curves3 on diametrically opposite radial positions in the form of a grouting point, for example. This gluedjoint6 is shown schematically inFIG. 2. With this type of gluedjoint6, the adhesive faces are loaded by tension.
• In another exemplary embodiment, it is also possible to attach the gluedjoint6 in such a manner that the adhesive faces are loaded by shear, as indicated inFIG. 3.
• The individual points of the gluedjoint6 may not only be situated terminally, as shown inFIGS. 1-3, but also distributed on the circumference over the length of thestent1. With such multiple positioning, upon radial expansion of the stent, the fixing is detached automatically in chronological sequence in accordance with the retention force. Experiments have shown that in spite of asymmetrical detachment of the individual fixed points, the stent may be open homogeneously if the fixing force is only large enough that theaxial connectors4 are still capable of absorbing it. If gluedjoints6′ are positioned in the area of theparticular strut2 second from the outside, for example, theaxial connectors4 may also act on the gluedjoint6′ from both sides which favors homogeneous opening behavior. In this case, theoutermost strut2 is either to be as short as possible or have the fine structures described in greater detail on the basis ofFIGS. 7 and 8 on the edge to suppress flaring.
• FIG. 4 shows a further exemplary embodiment for the stabilization means for additional radial fixing of the stent. Two neighboringmeandering curves3 of astrut2 are coupled to one another in the contracted starting position at their edges by hookedcatch elements7,8. When the stent is transferred into its contracted starting position, the so-called crimping, thecatch elements7,8 are engaged with one another. The stent is thus held together at its edge, so that the “flaring” cited hereinabove is avoided. During the radial expansion, the engagement betweenelements7,8 is broken open and the stent may open homogeneously.
• In a further exemplary embodiment, the configuration of catch elements in the form of hookedprojections9,10 in the interior of ameandering curve3 is shown by dashed lines inFIG. 4. This fixing is also produced during crimping by hooking of theprojections9,10 and broken upon expansion of the stent. It is recognizable that thehooked projections9,10 may be provided onarbitrary struts2 along the stent.
• FIGS. 5 and 6 show further exemplary embodiments of the stabilization means for the additional radial fixing of the stent in the cramped state. In these embodiments, fixing traverses11 shaped in one piece on the boundary struts2 are provided which connect to the adjacentmeandering curves3 of astrut2 fromzenith point5 tozenith point5. While only one fixingtraverse11 is provided inFIG. 5, in the exemplary embodiment shown inFIG. 6, the boundary of the stent is completely terminated by a row of fixing traverses11.
• Each fixingtraverse11 has a double-arched course having acentral bend12 which acts as the intended breakpoint upon radial expansion of the stent. The stent, as already described in connection with the glued joint6, may expand homogeneously by the tearing of the fixing traverses11.
• A further exemplary embodiment of the stabilization means provided according to the present disclosure is shown inFIGS. 7 and 8. These are peripheral fine structure struts14 on the boundary at theends13 of the stent, which are bound to the exterior sides15 of the meandering curves3. These fine structure struts14 are formed in each case by twostruts16,17 running essentially parallel having coupling struts18 running in the axial direction. The basic configuration of the fine structure struts14 is thus ladder-like, the double struts16,17 being folded in a zigzag in the lateral plane of the stent. Curved groin points19 are shaped into the double struts16,17 in the bend points, via which the coupling struts18 may be fastened in one piece while protecting the material in regard to the radial expansion of the fine structure struts14 at thestruts16,17. The expandability of the fine structure struts14 is improved by the curved shape in these groin points19.
• As schematically indicated inFIG. 8, the fine structure struts14 in the area of the interior groin points19, which are adjacent to one another in the contracted starting position, are additionally fixed by a glued joint6 or also catch means (not shown here), for example. The entire stent is thus stabilized on its front-side boundary in the crimped configuration in such a manner that flaring is kept as small as possible. Due to the fixing at the interior groin points19, the opening forces act on both sides of this fixing, so that higher fixing forces may be overcome without impermissibly distorting the stent structure.
• A further exemplary embodiment of the stabilization means for additional radial fixing of the stent is illustrated inFIGS. 9 and 10. These are extension struts20, which run essentially in the axial direction A and are bound to the strut at one end via an intendedbreakpoint21 to theexternal strut2. Thefree end22 of the extension struts20 is permanently fastened in each case in a suitable maimer to aballoon catheter23, only schematically indicated inFIG. 9.
• The extension struts21 again counteract a radial expansion of themeandering curves3 of theexternal struts2, in particular, which suppresses flaring. Upon dilation of the stent, the intendedbreakpoints21 are torn and the stent is thus released from the extension struts20.
• Exemplary embodiments for stabilization means against flaring shown inFIGS. 11 and 12 use thex-ray marker projections24 often present in stents, which are formed as eye-shaped projections onto themeandering curves3 of theexternal struts2 and are provided with a thermoplastically moldablemarker polymer coating25. To use these elements, which are known in stents, as stabilization means against flaring, thex-ray marker projections24 having theirmarker polymer coating25 are designed in such a manner that thex-ray marker projections24 contact one another after the crimping of the stent and are reshaped into a peripheral ring by a thermal treatment of themarker polymer coating25. The ring formation is supported bytransverse connection elements26 protruding in the peripheral direction from thex-ray marker projections24, which may be designed as either I-shaped or T-shaped in a top view.
• Finally, it is still possible, as shown inFIG. 12, to equip stents with polymer-coatedx-ray marking projections24 against flaring in such a manner that a peripheral ring made of magnesium, for example, is pushed onto theprojections24 having theircoating25 which is embedded therein by heating and brief melting of themarker polymer coating25 and thus fixed. Thering27 may comprise rigid material or wire, and may also be laid on only a partial circumferential length around the stent.
• All patents, patent applications and publications referred to herein are incorporated by reference in their entirety.

Claims (15)

1. A stent made of a material having a low strength and having a main body circumscribing a cylindrical shape and radially expandable from a contracted starting position into a dilated support position, comprising:

a) a plurality of support segments disposed around the circumference and arrayed on one another in the axial direction each segment being formed by a strut meandering in its coarse structure in its contracted starting position and having alternately opposing meandering curves expandable into the support position made of flexible material;

b) a plurality of axial connectors connecting between zenith points of at least a part of the meandering curves in the axial-parallel direction of the support segments; and

c) at least one means for stabilizing the strut coarse structure in its contracted starting position against radial expansion and being automatically detachable upon a radial expansion of the stent.

2. The stent ofclaim 1, wherein the at least one stabilization means is formed by a detachable glued joint between adjacent meandering curves of one or more struts.

3. The stent ofclaim 2, wherein the glued joint is attached to boundary and internal struts.

4. The stent ofclaim 2, wherein the glued joint is attached in such a manner that the glued joint may be loaded upon radial expansion by tension or shear.

5. The stent ofclaim 1, wherein the at least one stabilization means is formed by catch elements which interact with one another on the meandering curves which may be engaged with one another upon transfer of the stent into its contracted starting position and are detachable upon radial expansion of the stent.

6. The stent ofclaim 5, wherein the catch elements are formed by hook projections on the meandering curves.

7. The stent ofclaim 1, wherein the at least one stabilization means is formed by fixing traverses which connect the boundary meandering curves and may be broken open upon radial expansion.

8. The stent ofclaim 7, wherein the fixing traverses run between zenith points of two adjacent meandering curves and have a bend as the intended breakpoint.

9. The stent ofclaim 1, wherein the at least one stabilization means is formed by a plurality of fine structure struts peripherally disposed around the boundary of the stent ends.

10. The stent ofclaim 9, wherein the plurality of fine structure struts are implemented as double struts folded in a zigzag in a lateral plane of the stent which are fixed on one another at their adjacent groin points in the contracted starting position.

11. The stent ofclaim 1, wherein the at least one stabilization means is formed by a plurality of extension struts on the stent which detachably connect the boundary struts to the catheter for placing the stent.

12. The stent ofclaim 11, wherein the plurality of extension struts are each bonded to the stent via an intended breakpoint.

13. The stent ofclaim 1, further comprising a plurality of x-ray marker projections coated via marker polymer on the boundary struts, wherein the at least one stabilization means is formed by x-ray marker projections coupled in a ring via the marker polymer coating in the contracted state.

14. The stent ofclaim 13, wherein the plurality of x-ray marker projections are provided with radially oriented transverse connection elements.

15. The stent ofclaim 13, wherein a ring which is embedded in the marker polymer coating is drawn onto the x-ray marker projections in the contracted stent state.

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