DE10144430A1 - Stent, especially coronary stent, has flexible sections designed to be deformed in tangential plane of stent mantle - Google Patents

Abstract

The flexible sections (4) of the stent (1) are shaped so that they become deformed in the tangential plane of the stent mantle (2), especially when the stent is bent or expands. The stent comprises a tubular mantle with at least one stent component (3) with support sections provided in between flexible sections. The cross-section of the flexible section is different from that of the support section. Independent claims are also included for (a) a balloon catheter with the above stent secured to it, and (b) a method for making the stent.

Description

The present invention relates to a stent, in particular a coronary stent, with a tubular jacket with at least one web element Inflection sections that occur when the stent is deformed, in particular when it is bent or Expanding the stent, experiencing major deformation. Between Flexion sections are arranged support sections. The inflection sections have a flexion cross section that is different from the cross section of the support sections differs. The invention further relates to a method for producing a such stents.

A stent is a so-called intraluminal Expansion element with a generally tubular body, which in a vessel of the human or animal body introduced and expanded there permanently can be used to keep the vessel dilated.

WO 01/00112 A1 describes a generic stent with a meandering shape revolving web elements known, in which in the area of the turning points of the Bridge sections arranged flexion sections a significantly smaller Have cross-sectional area as the support sections. The flexion sections point an essentially rectangular inflection cross-section, the thickness, d. H. its dimension in the radial direction of the stent, some only small Fraction of its width is around a small cross-sectional area and therefore to achieve a high degree of flexibility in this area. The support sections are said to on the one hand by the larger material accumulation for better visibility in the Contribute x-ray. Another aspect is the improved support of the Vessel wall, which is in one version by the increased cover of the Vessel wall is achieved as a result of widened support sections.

With the generic design can be quite flexible stents to reach. However, it has been shown that the known stents have the disadvantage have that their web elements when guiding through narrow, strongly curved Vessel coils tend to deform radially from the tangential plane to step out of the coat. This is the case with balloon-expandable stents that are used for Approach the outside of the implantation site on a corresponding one Balloon catheters sit, extremely disadvantageous because the stent does not only result from this can protrude stent sections on the vessel wall and if necessary, moved on the catheter or even completely withdrawn from it can be. The vessel wall can also be damaged.

Another disadvantage is that it is in the flexion section as soon as the stent is brought up to the implantation site by strong curved vessel sections due to stresses above the yield point local, plastic deformations, which then the Deformation behavior of the stent during expansion at the implantation site disadvantageous influence.

The effects described above occur with the same or at least similar ones Disadvantages also in the deformation of the resulting from other reasons Stents on. This is particularly the case with the expansion of the stent.

The present invention is therefore based on the object of a stent and a method for producing a stent of the type mentioned at the beginning To make available the disadvantages mentioned above not or at least in has a lesser degree and in particular a problem-free deformation of the stent, in particular problem-free guiding of the stent through strong curved vessel sections.

This task is based on a stent according to the preamble of Claim 1 by the specified in the characterizing part of claim 1 Features solved. It will continue to proceed on the basis of a procedure the preamble of claim 11 by the in the characterizing part of Claim 11 specified features solved.

The present invention is based on the technical teaching that one a well and without local plastic deformation due to strongly curved Vessels leading stent or an otherwise deformable, in particular advantageously receives expandable stent if the Flexion cross section is designed so that when deforming the stent, in particular when bending or expanding the stent, one essentially in the Tangential plane of the jacket deformation of the flexion section is ensured. It has been shown that by designing the Flexion cross-section the radial, often also referred to as "out of contour bending" Emigration of the flexion sections from the tangential plane of the jacket at Deforming the stent, for example bending or expanding the stent, can be reduced or even completely prevented.

According to the invention, this can be achieved in that the flexion cross section is designed in such a way that it is often referred to as neutral fiber Stress zero line, which occurs when the stent is deformed, in particular when bending or expanding the stent, prevailing load case in Flexion cross section results in the smallest possible deviation from the radial direction of the stent. In other words, the inflection cross section According to the invention designed such that the zero voltage line, which is in the when deforming the stent, especially when bending or expanding the Stents, prevailing load case in the inflection cross section results in a the smallest possible angle is inclined to the radial direction of the stent.

The angle of inclination of the zero tension line to the radial direction of the stent is preferably less than 15 °, since this means particularly low emigration the flexion sections can be achieved from the tangential plane of the jacket can.

The angle of inclination of the voltage zero line depends, apart from that in Flexion cross section prevailing in the relevant load case Bending moment ratios, decisive from the ratio of the axial surface moments in the Flexion cross section from. The greater the angle of inclination, the smaller the angle Area torque ratio of transverse area torque and radial area torque fails. The radial surface torque should be the axial surface torque of the Flexion cross section around the radial axis pointing in the radial direction of the stent denote, while the transverse surface moment is the axial surface moment of the Flexion cross section around the perpendicular to the radial direction of the stent Cross axis of the inflection cross section designated.

The area torque ratio can in principle be chosen to be of any size, so the inclination of the voltage zero line to the radial direction is as small as possible of the stent. With a view to the most favorable course of the Deformation of the flexion sections during the later expansion of the stent on However, the implantation location is advantageous if the cross-sectional moment is not too large to choose. Otherwise, this works when expanding the stent of the permanent Extension of the regions of the stent curved in the circumferential direction Flexion sections, so that in these areas an undesirably high, elastic reset occurs.

In preferred variants of the stent according to the invention, the The flexion cross section is therefore essentially the same axial with respect to its main axes Surface moments. The main axes correspond essentially to that Radial axis and the transverse axis of the flexion cross section. To do that to obtain the corresponding area torque ratio of about 1 are different Geometries for the flexion cross section possible. So essentially regular polygons with four or more corners can be used. In doing so, regular polygons with an even number of corners, for example one Square, a regular hexagon, a regular octagon, etc. Area torque ratio of 1 achieved.

The stress distribution over the flexion cross section is the more favorable, ever the maximum stress occurring in the flexion cross-section is lower, that is, ever the tension is distributed more evenly over the flexion cross-section. The maximum tensile or compressive stress occurs the furthest from the Stress zero line distant point of the inflection cross section. The Stress distribution is with changing load conditions, as they occur with regular stents, the cheaper the less the variation of the voltage at the edge points of the Is inflection cross section. This is more the case the further the Edge contour of the flexion cross section approximates a circular shape. With preferred Further developments of the stent according to the invention provide that the Flexion cross section is substantially circular.

In further advantageous developments of the stent according to the invention the support sections have a smaller thickness than the flexion sections. Due to the reduced thickness and the reduced area torque achieved that the support sections become more elastic when the stent is bent can be deformed and therefore better adapted to the curved course of the adjust accordingly curved catheter on which the stent at Approaching the implantation site. In other words, this will make one more smoother guiding of the stent achieved by curved vessel sections.

Another advantage of the reduced thickness lies in the area of the support sections in the fact that experience has shown that they have better flow behavior as well as a lower restenosis rate. This is one of the reasons remember that there is a comparatively small thickness in the area of such sections less severe turbulence in the bloodstream, so that a largely unimpeded flow through the expanded vascular area as well in particular, good removal of thrombogenic substances or particles etc. is ensured is.

In other preferred variants of the stent according to the invention provided that the support sections have a greater width than that Flexionsabschnitte. On the one hand, this results in improved coverage and thus Support of the vessel wall achieved. On the other hand, the stent is then more extensive on the catheter with which it is brought to the implantation site, so that there is an improved fit on the catheter.

The web elements of the stent can be arranged in any known manner and be trained. For example, one web element can have one circumscribe closed cell, with several web elements then in Circumferential direction of the stent are connected to one another to form the corresponding support ring. The can be particularly advantageous present invention in connection with preferred variants of Use stents according to the invention in which the jacket of the stent at least one ring section from at least one in the circumferential direction of the Stents encircling meandering web element.

The inflection sections are then preferably in the region of the turning points of the meandering circumferential web elements arranged in the area of Most of the deformation when deforming the stent, for example when The stent is bent or expanded.

The stent according to the invention can be produced in any known manner. For example, its network-like structure can be broken through corresponding cutting or etching techniques from a tubular base body closed jacket are generated. In preferred variants of the Stents according to the invention provide that the web elements at least are formed in sections by a correspondingly shaped wire. in this connection can then the different geometry of the cross sections in the area of Flexion sections and the support sections are done in a simple manner before the wire to the corresponding network-like structure of the stent is formed.

With variants of the stent according to the invention which are particularly easy to produce are the support sections by mechanical deformation of the im Initial condition generated uniform wire over its length.

The present invention further relates to a balloon catheter having a balloon thereon arranged stent according to the invention.

Finally, the present invention also relates to a method for the production of a stent with a tubular jacket with at least one web element with flexion sections, which when deforming the stent, especially when Bending or expanding the stent, the main deformation experienced, and between the flexion sections arranged support sections, wherein the flexion sections have a flexion cross-section that of Cross section of the support sections deviates. According to the invention, that to ensure one when deforming the stent, especially when Curving or expanding the stent, essentially in the tangential plane formed deformation of the flexion section Inflection cross sections are generated. With this you can equally use the above achieve described advantages of the stent according to the invention, so that here reference is made to the above statements.

The stent according to the invention can be produced in any known manner. Thus, as already mentioned above, its network-like openwork structure for example by appropriate cutting or etching techniques from one tubular body with a closed jacket are generated. At a preferred variant of the method according to the invention provides that the cross section of the support sections deviating from the flexion cross section mechanical deformation of the web element is generated.

For this purpose, the corresponding support section can, for example, by Embossing stamps or the like can be processed. It is preferably provided that the cross section of the support sections deviating from the flexion cross section Rolling the web element is generated.

In further, preferred variants of the method according to the invention, the cross section of the support sections deviating from the flexion cross section Manufacture of the tubular jacket generated. This has the advantage that the Production may be carried out in a smaller number of individual steps can. For example, it can be provided that for generating the Support sections a corresponding roller on the circumference of the on a mandrel or such arranged stents rolls to a number of in a single circulation Generate support sections.

Further, preferred embodiments of the invention result from the Subclaims or the description below is more preferred Embodiments which refer to the accompanying drawings. Show it:

Figure 1 is a partial view of a stent according to the invention.

Fig. 2A is a section through a Flexionsabschnitt the embodiment of Figure 1 taken along line AA.

FIG. 2B shows a section through a support section of the embodiment from FIG. 1 along line BB; FIG.

FIG. 2C shows a schematic, perspective view of the section from FIG. 2A; FIG.

. 3A and 3B are sections through a further embodiment preferred of the stent according to the invention;

FIGS. 4A and 4B sections through another preferred embodiment of the inventive stent.

Fig. 1 shows a partial view of a stent 1 according to the invention with a sheath 2 of a meandering manner in the circumferential direction of the stent 1 1.1 extending web members 3; the web elements 3 form support rings which are connected to one another in the longitudinal direction of the stent 1 to form the jacket 2 .

The web elements 3 have flexion sections 4 and support sections 5 . The arcuate flexion sections 4 are arranged in the area of the turning points 3.1 of the web element 3 . The support sections 5 are each arranged between the flexion sections 4 and, in the example shown, run essentially rectilinearly, although it is understood that in the case of other variants of the invention, any other courses can also be implemented.

The stent 1 is usually guided to the implantation site while sitting on a balloon catheter (not shown). Coronary stents in particular must be guided through strongly curved blood vessels. When the stent 1 is passed through such a curved blood vessel, the web elements 3 of the stent 1 on the side facing the center of curvature are compressed in the circumferential direction 1.1 of the stent 1 , the flexion sections 4 being deformed elastically and the support sections 5 approaching one another. On the side facing away from the center of curvature, the web elements 3 are expanded in the circumferential direction 1.1 of the stent 1 , the flexion sections 4 also mainly being elastically deformed and the support sections 5 moving apart.

Fig. 2A shows a section through the Flexionsabschnitt 4 of the stent 1 along the line AA of Fig. 1, while Fig. 2B shows a section through the support portion 5 of the stent 1 along the line BB of FIG. 1.

As can be seen from FIGS. 2A and 2B, the flexion section 4 has a circular flexion cross section 4.1 , while the support section has an essentially rectangular support cross section 5.1 .

FIG. 2C shows a schematic, perspective view of the flexion cross section 4.1 from FIG. 2A in a state in which, when the stent 1 is curved, it is located on the side facing the center of curvature, ie in a state in which the web element 3 extends in the circumferential direction of the Stents 1 compression is applied. The compression of the web element 3 in the circumferential direction in the flexion cross section 4.1 results in a negative bending moment about the axis R, that is to say a bending moment directed against the direction of the axis R. Furthermore, as a result of the course of the web element 3 , which is also curved in the circumferential direction, there is a positive bending moment about the axis Q, that is, a bending moment directed in the direction of the axis Q.

The contour 6 indicates the course of the normal stress at the edge of the flexion cross section 4.1 under the simplifying assumption of a load case with pure bending load. The arrows 6.1 indicate a compressive stress, while the arrows 6.2 represent a tensile stress. As can be seen from FIG. 2C, the circular flexion cross section 4.1 of the flexion section 4 has the effect that the zero tension line 6.3 is only inclined by a small angle α to the radial direction of the stent 1 indicated by the axis R.

• - M_R: Biegemoment um die Achse R in Richtung der Achse R,
• - M_Q: Biegemoment um die Achse Q in Richtung der Achse Q,
• - I_R: axiales Flächenmoment um die Achse R,
• - I_Q: axiales Flächenmoment um die Achse Q.

The angle of inclination α can be determined for the load case described from the following equation:


in which:

• - M _R : bending moment around the axis R in the direction of the axis R,
• - M _Q : bending moment around the axis Q in the direction of the axis Q,
• - I _R : axial area torque about the axis R,
• - I _Q : axial area torque about the axis Q.

Due to the circular flexion cross section 4.1 , the axial area torque I _R and the axial area torque I _{Q are} identical, so that from equation (1) it is clear that the angle of inclination α depends solely on the ratio of the bending moments. This is comparatively large in the present load case, since due to the relatively small curvature in the circumferential direction, only a relatively small bending moment acts about the axis Q. In the present example, the angle of inclination α is approximately 7.5 ° in the load case described.

This slight inclination of the zero tension line to the radial direction of the stent 1 has the effect that the flexion section 4 does not move appreciably radially out of the tangential plane of the jacket 2 when the stent 1 is bent. In other words, the flexion section 4 remains approximately in the curved tubular contour of the jacket 2 and does not protrude beyond it.

It should be noted here that on the side of the stent facing away from the center of curvature, an image of the stress distribution comparable to FIG. 2C results. The only difference is that the voltages have a different sign.

It should also be noted that the action of normal forces in the flexion cross section 4.1 does not affect the inclination of the stress zero line 6.3 . If they were taken into account, this would only experience a parallel displacement along the Q axis.

As can be seen in FIG. 2B, the support section 4 from FIG. 2B has an essentially rectangular support cross section 5.1 . The thickness of the support cross-section 5.1 , ie its dimension in the radial direction 1.2 of the stent 1 , is significantly smaller than the diameter of the flexion cross-section 4.1 , while its width, i.e. its dimension in the transverse direction 1.3 perpendicular to the radial direction 1.2 , is significantly larger than the diameter of the flexion cross-section 4.1 .

The reduced thickness of the respective support section 5 and the thus reduced axial surface moment about the axis of symmetry of the support cross section 5.1 running in the transverse direction 1.3 means that the support sections 5 can be elastically deformed more easily when the stent 1 is bent. They therefore adapt better to the curved course of the correspondingly curved catheter on which the stent 1 sits when it is brought up to the implantation site. In other words, this results in the stent being guided even more smoothly through curved vessel sections.

The increased width of the respective support section 5 leads on the one hand to improved coverage of the vessel wall and thus to better support of the vessel wall. Furthermore, thanks to the increased width, the stent 1 lies on the catheter with a large area, with which it is brought to the implantation site, so that the stent 1 is better seated on the catheter.

The stent 1 is produced in the following way:
a wire with a circular cross-section that is the same over its entire length is first brought into the corresponding zigzag shape by appropriate plastic shaping and shaped into a ring in order to form a support ring from a meandering circumferential web element 3 .

Then this support ring is pushed onto a mandrel, which forms the abutment for a roller. This roller rolls on the circumference of the support ring with a contact force which is selected such that all support sections 5 of the web element 3 receive their flattened shape in one revolution of the roller around the mandrel by plastic deformation of the wire. For this purpose, the roller has a width in its contact area with the web element 3 , which essentially corresponds to the dimension of the support sections 5 in the longitudinal direction of the stent 1 .

The support rings are then connected to one another in the longitudinal direction of the stent 1 , so as to form the jacket 2 of the stent 1 .

It goes without saying that, in other variants of the invention, it can also be provided that the flattened contour of the wire in the region of the support sections 5 is already generated by appropriate stamps etc. before it is formed into a ring or even before it is meandered Is brought into shape.

It is also understood that the processing of the Web elements can also be applied equally to stents in which the mesh-like openwork structure by cutting or etching a initially completely or partially closed outer surface was generated.

Finally, it is understood that the different cross sections of the Flexion sections and the support sections also generated in any other way can be. So it is possible, for example, with a cutting or Etching machining machined the reduced thickness of the support sections by cutting or non-cutting material removal on the jacket of the stent in Generate area of the support sections. It is of course also possible to use the To achieve greater thickness in the area of the flexion sections by applying material.

FIGS. 3A and 3B show sections through a further embodiment preferred of the inventive stent 1 'to be received so that only the differences corresponds in its basic design of the embodiment of Fig. 1,. . The sectional profile of Figure 3A corresponds to that of Fig. 2A; Likewise, the section from FIG. 3B corresponds to that from FIG. 2B.

The difference to the embodiment from FIG. 1 is that the flexion cross section 4.1 'is essentially square. Since the above equation (1) applies regardless of the geometry of the flexion cross section, the substantially square flexion cross section 4.1 'from FIG. 3A also results in the same inclination of the zero stress line to the radial direction of the stent 1 ' for the load case assumed above for FIG. 2C . , This is due to the fact that the axial surface moments are also identical in this flexion cross section 4.1 '.

In other words, a correspondingly favorable deformation behavior can also be achieved with the quadratic flexion cross section 4.1 ', although the stress-strain behavior is somewhat more favorable in the variant with a circular flexion cross section.

In this variant, too, the support sections 5 'again have a lintel cross section 5.1 ' with a reduced thickness and increased width compared to the flexion cross section 4.1 .

Figs. 4A and 4B are sectional views of a further preferred embodiment of the stent 1 "according to the invention, which corresponds in its basic design the embodiment of FIG. 1, is to be such that only received here on the differences. The sectional profile of FIG. 4A corresponds to that from FIG. 2A; likewise the sectional profile from FIG. 4B corresponds to that from FIG. 2B.

The difference is that the flexion cross section 4.1 "of the flexion section 4 " has an axial surface moment about the axis running in the radial direction of the stent 1 ", which is less than that around the perpendicular axis.

As can be seen from equation (1), which also applies here, the angle of inclination of the voltage zero line with respect to the radial direction is further reduced in comparison with the above exemplary embodiments. The tendency to radially migrate the flexion cross sections 4.1 "when the stent 1 is curved" is consequently even lower in this variant.

It is understood that in other variants of the stent according to the invention any other within the limits described above Cross-sectional shapes are used for the flexion sections or the support sections can.

The advantages of the design according to the invention have been described above with reference to Embodiments related to the management of the Stents according to the invention described by curved vessel courses. It goes without saying however, that the deformation behavior described and with it associated advantages of the design according to the invention also in connection with otherwise motivated deformations, in particular in connection with the Expansion of the stent resulted in the same way.

Claims (15)

1. Stent, in particular coronary stent, with a tubular jacket ( 2 ) with at least one web element ( 3 ) with flexion sections ( 4 ; 4 '; 4 "), which undergo the main deformation when deforming, in particular when bending or expanding, the stent and between the flexion sections ( 4 ; 4 '; 4 ") arranged support sections ( 5 ; 5 '; 5 "), the flexion sections ( 4 ; 4 '; 4 ") having a flexion cross-section ( 4.1 ; 4.1 ; 4.1 ") which is from Cross-section of the support sections ( 5 ; 5 '; 5 ") differs, characterized in that the flexion cross-section ( 4.1 ; 4.1 '; 4.1 ") to ensure a substantially in the tangential plane of the sheath when deforming, in particular when bending or expanding the stent ( 2 ) the flexion section ( 4 ; 4 '; 4 ") is formed. 2. Stent according to claim 1, characterized in that the flexion cross-section ( 4.1 ; 4.1 '; 4.1 ") is formed such that the zero tension line ( 6.3 ), which prevails in the load case prevailing during deformation, in particular when the stent is bent or expanded Flexion cross section ( 4.1 ; 4.1 ; 4.1 ") results in an angle as small as possible, preferably less than 15 °, to the radial direction of the stent. 3. Stent according to claim 1 and 2, characterized in that the flexion cross section ( 4.1 ; 4.1 ') has essentially the same axial surface moments with respect to its main axes. 4. Stent according to one of the preceding claims, characterized in that the flexion cross section ( 4.1 ) is substantially circular. 5. Stent according to one of the preceding claims, characterized in that the support sections ( 5 ; 5 '; 5 ") have a smaller thickness than the flexion sections ( 4 ; 4 '; 4 "). 6. Stent according to one of the preceding claims, characterized in that the support sections ( 5 ; 5 '; 5 ") have a greater width than the flexion sections ( 4 ; 4 '; 4 "). 7. Stent according to one of the preceding claims, characterized in that the sheath ( 2 ) comprises at least one ring section made of at least one web element ( 3 ) which meanders in the circumferential direction of the stent. 8. Stent according to claim 7, characterized in that the flexion sections ( 4 ; 4 '; 4 ") are arranged in the region of the turning points ( 3.1 ) of the meandering peripheral web element ( 3 ). 9. Stent according to one of the preceding claims, characterized in that the web elements ( 3 ) are formed at least in sections by a correspondingly shaped wire. 10. Stent according to claim 9, characterized in that the support sections ( 5 ; 5 '; 5 ") are produced by mechanical shaping of the wire which is uniform over its length in the initial state. 11. Balloon catheter with a stent arranged thereon according to one of the previous claims. 12. A method for producing a stent, in particular a stent according to one of claims 1 to 10, with a tubular jacket ( 2 ) with at least one web element ( 3 ) with flexion sections ( 4 ; 4 '; 4 "), which during deformation, in particular undergo the main deformation when the stent is bent or expanded, and support sections ( 5 ; 5 '; 5 ") arranged between the flexion sections ( 4 ; 4 '; 4 "), the flexion sections ( 4 ; 4 ; 4 ") having a flexion cross section ( 4.1 ; 4.1 '; 4.1 "), which deviates from the cross-section of the support sections ( 5 ; 5 ; 5 "), characterized in that to ensure that when the stent is deformed, in particular when it is bent or expanded, it is essentially in the tangential plane of the jacket ( 2 ) deformation of the flexion section ( 4 ; 4 '; 4 ") formed flexion cross sections ( 4.1 ; 4.1 '; 4.1 ") are produced. 13. The method according to claim 12, characterized in that the cross section of the support sections ( 5 ; 5 '; 5 ") deviating from the flexion cross section ( 4.1 ; 4.1 '; 4.1 ") is produced by mechanical reshaping of the web element ( 3 ). 14. The method according to claim 12 or 13, characterized in that the cross-section of the support sections ( 5 ; 5 ; 5 ") deviating from the flexion cross-section ( 4.1 ; 4.1 '; 4.1 ") is produced by rolling the web element ( 3 ). 15. The method according to any one of claims 12 to 14, characterized in that the cross-section of the support sections ( 5 ; 5 ; 5 ") deviating from the flexion cross-section ( 4.1 ; 4.1 '; 4.1 ") is produced after production of the tubular jacket ( 2 ).