DE19653721A1 - Stent - Google Patents

Abstract

The invention relates to a stent, specially a coronary stent, consisting of at least one thin-walled, tubular element with an openly reticular outer surface containing recesses, which are defined by narrow weblike elements. Said weblike elements are formed from the remaining material from the tube wall once the material has been removed from the recess area. The cross section of a weblike element is tapered in the proximity of the connection area with another weblike element in such a way that preferably a deformation comes about therein when the end of the weblike element that is distanced from the connecting area is deviated during expansion.

Description

The invention relates to a stent, in particular coronary stent, as an intraluminal expansion element, accordingly the type mentioned in the preamble of claim 1 and Ver drive to manufacture such a stent.

From European patent specifications EP-B1 0 364 787 and EP-B1 335 341 is an expandable intraluminal element with at least one thin-walled, tubular part (hereinafter referred to as a stent). The mantle surface of the stent is open and reticulated has recesses that are straight in axially and circumferentially extending web-like Elements of low material thickness are limited. The web-like elements consist of the remaining tube wall dung from which the material in the area of the recesses was removed.

Such stents are placed in a surgical procedure Action from inside to outside forces through a hose-shaped pressurized gas Dilator, expanding. The stent remains in spite of Verfor ting its tube shape and widening it through deposits narrowed vessel.

The known stent has the disadvantage that expansion due to the deformation of the axially extending web-like elements can only take place to a limited extent, since the shape change of the individual web-like elements of the stent are set relatively narrow limits. These limits are due to the material stresses associated with the deformation, which - if the deformation becomes too strong - can break one or more of the web-like elements forming the network,
For safety reasons, the deformation must therefore be kept ge far below a possible danger area, since the rupture of a web would lead to the free ends in the area of the fracture protruding into the interior of the vessel provided with the stent. The associated risk of restenosis would not only jeopardize the success of the procedure itself, it would also endanger the patient's life.

Based on the shortcomings of the prior art, the Invention, the object of an expandable stent to specify the genus mentioned at the beginning, which one if possible safe - and therefore also without the risk of chip break caused by overload in the area of the web like elements, is expandable.

The task is characterized by the characteristics of the contractor spell 1 solved.

The invention includes the technical teaching that at fragile, mesh-like made of suitable materials Structural tubular elements which be subjected to deformation due to the application, crit Avoid material loads or even material breaks are, if in such areas, which an increased Verfor tion are already constructive and from the beginning the occurring voltage maxima are limited.

This is not only due to the constructive design with regard to the greatest possible strength by Er  Increase the material cross-sections, but also in that the shape of the webs and connection areas with regard to the expected loads are optimized. this happens in such a way that local maximum stresses occur cannot lead to breakage, but only too wide deformation.

Indeed, it has been found that breaks occur because of this occur because the material used when occurring Deformations (in the stress-strain diagram) do not exist few zone in which a flow occurs, that is, itself Compensate for stresses caused by material shifts. After flowing, a material solidification occurs entry.

In addition, the solution according to the invention closes the Er realizes that by concentrating the deformations on few areas, in each of these the elasticity area is exceeded, so that the expansion of the Deformations occurring in the stent are "permanent", i. H. after Do not remove the balloon catheter to expand it "spring back" again. That way he stays targetable expansion capacity remaining the intended Vasodilation benefits.

In an advantageous development, the invention then closes also the knowledge that after this also occurred further deformation can take place, if in the one following the area of consolidation Area the taper continues to reach the flow permits.  

The stresses that occur during the deformation are minimized according to the invention in such a way that the individual web-like elements are shaped such that the Bending deformation, which is a web-like element in the Expan sion within the hollow cylindrical tube shape is locally does not exceed a predetermined value.

According to the invention, the cross section of a is preferred Bridge elements near the connection to another Web element designed so tapered that there a Ver formation is favored during expansion and the deformation lo cal concentrated.

The taper is designed such that a Ver Forming in adjacent areas one after the other towards increasing distance from the location of the verb dung is made possible with the other web element, so that Even stronger deformations are possible without the risk of breakage are.

If the taper is such that the area the deformation when material solidifies after one state of material flowing in an area that matches the location the connection with another web element closer is shifting to a neighboring area from which If the connection is further away, the flow migrates area on the web-like element during the deformation from a position near the connection area with another stent to a distant one.

The dimensioning is done in such a way that the Wi the resistance to deformation due to bending in the weakening area rich towards increasing distance from the place of  Connection with the other web element also under contact considering the shifting of the bending area shortening lever arm on the one of the connection attacking richly distant area of the land element Forces increases.

The taper is to be designed such that the contra stood against deformation increases less than that according to the state of flow caused by material deformation increasing material consolidation. This can be done by the same permanent cross-sectional dimensions of the deformed web empire, but possibly also in the context of a cross change of cut. Here the changing Lever arm of the attacking deformation force by walking of the flow area are taken into account.

In a preferred further embodiment of the invention there are additional ones near the weakened areas Stops provided that the deformation in the Schwä limit areas of research. The attacks are so before seen that when the stent is expanding, it is near neighboring attacks and are supported on them Zen. In this way there is a further deformation of the bishe area of weakness prevented and the deformation continues in another area. With that then prevents local material overloads without the Deformability of the stent is restricted. By the An the local deformation can be limited so that the risk of breakage is also reduced.

With the invention it is achieved that the deformations controlled local focus so that the expansion of the Stents largely reduced to plastic deformation  becomes. This allows the extension to be very fine check without overstretching which can also adversely affect the vessel wall.

The tapers and stops are preferred by Va riation of the web width with constant material thickness in tangential direction. This comes of generation of the stent from a tube by cutting out the recess against a laser cutter.

According to another cheap embodiment of the invention if the coupling links are essentially the same Shape (s) on how the coupling links between the neighboring ones expandable elements of the individual segments of the Stents, so that there are none at these connection points Form notch peaks when expanding the stent can. Coupling links of this type also have tapered portions according to the aspects described here.

A preferred stent design according to the above is made of tantalum as a material and is with a Coated with amorphous silicon carbide.

Further details of such stents result from a number of patent applications filed simultaneously same applicant.

Other advantageous developments of the invention are characterized in the subclaims and will be described hereinafter together with the description of the preferred embodiments of the invention with reference to FIGS. Closer. Show it:

Fig. 1 shows a preferred embodiment of the invention in side view,

FIGS. 2a to c shows a detail of the embodiment shown in Fig. 1 in different stages during the expansion of the stent,

Fig. 2d the stress-strain curve of pure titanium,

Fig. 3 shows another embodiment of a fiction, modern stents in the processing,

Fig. 3a and 3b, details of FIG. 3,

Fig. 4a shows the embodiment of FIG. 3 in a partially expanded state and

Fig. 4b shows the embodiment of FIG. 3 in fully expanded expanded state.

The stent 1 shown in Fig. 1 has a tubular / hollow cylindrical basic shape with numerous openings, which are surrounded by expansible structural elements which have the shape of compressed rings. These are referred to below as "expandable elements" and are marked with a dash-dotted line 2 using an example. These expandable elements 2 are formed by circumferential narrow web-like areas 4 with a rectangular cross section and are characterized in that they enclose a recess 3 in a ring shape.

In the illustrated embodiment, the cross section of one of the web elements 4 in the vicinity of the connection to another web element is tapered in such a way that ei ne deformation is favored during expansion. These tapered areas are designated 11 and 12, for example.

The taper is designed such that a deformation successively in locally adjacent areas towards increasing distance from the location of the verb with the other web element.

The expandable elements 2 have in the fully expanded state (not shown in the drawing) almost the shape of a polygon. The expansible elements are shaped in such a way that, after the stent has been introduced into a vessel, they are converted into the polygonal shape by dilating with a balloon catheter with minimal deformation.

The embodiment of a stent shown in FIG. 1 is subdivided into several segments which follow one another in the axial direction. These segments are of identical design among themselves and have a lateral surface in which recesses 3 are strung together in the tangential direction and connected to one another by connecting regions.

For the connection between the adjacent segments 2 , web areas are provided which also have tapered portions. This is illustrated by the example of the taper 12.1 . These coupling elements allow the segments to adapt even more to the curvatures or branches of vessels.

The design of the stents described above permits expanding the tubular stents without affecting the Connection points for training to destroy Extreme values of the notch stress leading to the web areas is coming.  

FIGS. 2a to c show how the deformation of a web-like area 10 , which adjoins another web-like area, increases, which - as in the embodiment shown in FIG. 1 - is also an intersection or The area of curvature can act, starting from the stretched state ( FIG. 2a), a deformation first occurs in the region 14 of the taper 13 that is adjacent to the connection with another web portion. The flow area is shown hatched here. After the original flow region 14 has been solidified, the flow region then moves with increasing deformation into a region 15 which is further away from the connection region.

It can be seen that here the taper is made stalten is that the area of deformation in material solidification after a state of flowing material in an area that corresponds to the place of connection with one whose web element is closer to one another beard area shifted from the place of connection is further away. The resistance to deformation by Bending in the weakening area increases towards increasing Distance from the place of connection with the further Ste gelement also taking into account the with the Ver storage of the bending area shortening the lever arm of the the area of the web remote from the connection area elements attacking forces. Resistance to Ver Formation increases less than that after the flow state occurring due to material deformation increasing material consolidation. The taper is le dig by varying the web width with constant mate rial strength formed in the tangential direction.  

The expansion can thus be carried out without local overstretching, which can include the risk of breakage. To illustrate the relationships shown above, the stress-strain diagram (using pure titanium as an example) is shown in FIG. 2d. It is evident that an elastic region with a linear increase in tension ε between 0 and ε ₁ , which corresponds to a "resilient" behavior, adjoins an elastic region until ε _{2 is followed by} a plastic flow region. In this area, a material deformation takes place without springback, so that the stent essentially completely retains the expanded form into which it has been brought through the dilation catheter. The upper stress range ε ₂ should not be exceeded, since the risk of breakage should be taken into account if the stress is increased further. This danger is eliminated by the stops additionally provided in the exemplary embodiment described below.

A stent 1 shown as a further exemplary embodiment in FIG. 3 also has a tubular / hollow cylindrical basic shape with numerous openings which are enclosed by ex pansible structural elements, which in this case have the form of compressed rings. (The reference numerals are used in accordance with the embodiment shown above.) Accordingly, here too, expandable elements 2 are formed by circumferential narrow web-like regions 4 with a rectangular cross section and are distinguished by the fact that they enclose a recess 3 in a ring shape. The expandable elements 2 in this case have almost the shape of a circle or an ellipse in the fully expanded state. It can be seen that the shape in the unexpanded state is derived from the shape of the expanded state, although the stent, when manufactured, never took this state
Has. The shape was found by simulating the compression in a model calculation in a simulated process - starting from an ideal shape to be taken in the expanded state.

The web-like regions 4 enclosing an expandable element 2 are formed several times in an S-shape. They each enclose a recess 3 in such a way that the adjacent web-like regions 4 which are adjacent in the tangential direction are arranged mirror-symmetrically in the same or in an adjacent recess 3 . At their longitudinal ends, the expansible elements 2 have free curved areas 7 and 8 with a greater curvature.

The expansible elements 2 are shaped in such a way that they almost convert into a ring shape after insertion of the stent into a vessel by diatizing with a balloon catheter. It can be seen that the arc 8 occupies a maximum radius. The S-shaped counter arches enable him to suffer as little deformation as possible during expansion.

Between the in the axial (longitudinal) and in the tangential (transverse) direction adjacent to the outer surface of the stent 1 arranged recesses 3 are connecting areas 5 vorgese hen which mechanically couple the respective expandable areas 2 with each other. In the intersecting connecting area 5 , material roundings are provided in such a way that the connection area has an organic shape which reduces the occurrence of increased notch stresses.

The shape of the stent corresponds in the unexpanded direction stood essentially in the form that results if a web structure of regular ger form, in this form from a tubular pattern created in the structure into the unexpanded Form - the later initial form - is compressed. The right regular shape consists of circles, ellipses, rectangles, Squares, polygons, or composed or to these approximate structures.

Branches of webs are designed to avoid jump-like changes in the web width in such a way that the material stresses, particularly in the region of the branching during the deformation, also as a notch stress, do not exceed a predetermined value. The stent reproduced in FIG. 1a is structured substantially homogeneously over its entire length.

It can be seen that in the embodiment shown in the longitudinal direction of the stent, two expansible elements 2 in the transverse direction are connected directly to one another at the end, each of these two expansible elements, in the form of a compressed ring element formed from webs, in the transverse direction in each case web-like element is in each case connected to a further cross-expandable element, which in turn is not directly connected to the front with another expandable element, which in turn is connected to one of the first-mentioned cross-directionally expandable elements with a web-like element, the web-like elements each inclined at such an angle to the transverse direction that this angle decreases with expansion of the stent and thus the non-connected adjacent end faces of transversely expandable elements can also be removed from each other and shorten the stent be avoided in its expansion.

The web-like elements show when not expanded Stent has an inclination to the transverse direction of essentially 45 ° on.

Due to the simultaneous occurrence of the expansion of the stent in the expansion of the expandable elements in the transverse direction of the stent and by the alignment of the inclined connecting elements 10 in the transverse direction, the groups of expandable elements which are not connected to one another are displaced relative to one another in such a way that this movement is performed the shortening of the stent is compensated for by expansion of the flat shapes of the expansible elements into O-rings.

In Fig. 3 - and the enlarged detailed drawings according to Fig. 3a and 3b - it can be seen that additional stops are provided in the vicinity of the weakened areas, which limit the deformation in the weakened areas be. The attacks are provided so that they come in the vicinity of neighboring strikes when expanding stent and are supported on this. In this way, further deformation of the previous weakening area is prevented and the deformation continues in another area. Local mial overloads are then prevented without the deformability of the stent being restricted.

The effect of the stops and weakenings is to be illustrated using the example of the branching in area A, which is shown again enlarged in FIG. 3a. The connecting element 10 branches off from an expandable element 2 . The connection area of the connection element merges into two weakening areas 21 and 22 . The connecting element 10 is also weakened in the transition area. Reinforced stops 23 , 24 and 25 and 26 connect to the weakened areas. The stops 27 and 28 are provided on the connecting element. It can be seen that during the expansion of the stent, the stops 23 and 25 , 26 and 27 as well as 24 and 28 each approach each other and prevent further deformation of the intervening weakening region when they are in contact with one another. The further deformation then concentrates on the areas on the part of the stops formed by the thickenings, which likewise form a type of "weakening" and then absorb the further deformations. In this way, the total deformation can be "divided" into a number of deformation areas, each of which is plastically deformed and thus does not have a "resilient" effect.

The same applies to the weakened areas 32 and 33 in the connection area 5 and the associated stops 34 and 35 . A detailed illustration of this is shown in FIG. 3b (detail B in FIG. 3).

There is also a weakening area 29 in connection with stops 30 and 31 in the external arches of the expansible elements and, in the manner described, localizes the deformations that occur.

In Figs. 4a and b is - using the same reference numerals as in Fig. 3 - see how the structural figure is formed according to tur in an expanded state to a structure having a substantially circular rings, which are connected to webs with each other. The connecting webs between the expandable elements are now largely tangential.

It can be seen from FIGS . 4a and 4b how the deformation takes place “in two stages”, the stops 22 and 23 , for example, initially approaching one another adjacent to the weakening region 21 ( FIG. 4a). Correspondingly, the same applies to the stops 30 and 31 in relation to the weakening 29 and for the stops 34 and 35 in relation to the weakening 33 in the area of the connection point 5 .

Then, in the course of further expansion ( FIG. 4b), further stops 24 and 28 also approach one another or the location of the deformation is transferred to areas which, seen from the weakening, are located beyond the stops.

It can also be seen that branches of webs underneath Avoid abrupt changes in the web width are formed, and that branches are formed in such a way are that the material tensions in particular in the area branching during deformation also as notch stress does not exceed a predetermined value.

The above-described design of the stents 1 permits expansion of the tubular stents without the formation of extreme values of the notch stress leading to the destruction of land areas.

From Fig. 4a and b it can also be seen that in the dilatation not only no shortening, but even a certain elongation of the stent occurs, but this is compensated again with further expansion so that the length of the stent again corresponds to the initial length. This ensures a largely complication-free application. The web-like connecting element 11 'is curved in the embodiment shown in this figure, double S-shaped to minimize the deformations.

From the figures it can also be seen that the stent according to the invention also has very good deformability, since the elements 2 are only connected to one another alternately.

The stent shown here is made of titanium or tantalum as a material, from which a good physical tolerance and excellent ductility results. Others too biocompatible metals or metal alloys are suitable. A micro-coating made of amorphous silicon carbide works against thrombus formation.

The invention is not limited in its execution the preferred embodiments given above games. Rather, a number of variants are favorable, which of the solution shown also in principle makes use of different types.

Claims (17)

1. stent, in particular coronary stent, consisting of at least one thin-walled, tubular element, the circumferential surface of which is perforated in the form of a net and has recesses which are delimited by web-like elements of small width, the web-like elements in particular forming the rest of a tube wall from which the material has been removed in the region of the recesses, characterized in that the cross section of a web element in the vicinity of the connection area is tapered with a further web element in a region of its longitudinal direction in such a way that when a deflection of the stegar term element is removed from the connection region At the end, in the tapered area, only plastic deformation occurs over the entire cross-section of the web. 2. Stent according to claim 1, characterized in that the deformation occurs when the flow state is reached. 3. Stent according to one of the preceding claims, characterized characterized in that the taper is designed such that a deformation in locally adjacent Be range successively towards increasing distance from the place of connection with the other web element. 4. Stent according to one of the preceding claims, characterized characterized that the taper or one of the taper  neighboring area is designed such that the loading range of deformation after a plastic deformation material consolidation occurring in a first area, which is the place of connection with another web element is closer to a neighboring area, that is farther away from the location of the connection than that Area of solidification. 5. Stent according to one of the preceding claims, characterized characterized in that the resistance to deformation is less increases sharply than that due to the material material flow which increases the flow state supply. 6. Stent according to one of the preceding claims, characterized characterized in that the tapering by variation of the Web width with constant material thickness in tangential Direction is formed. 7. Stent according to one of the preceding claims, characterized characterized in that the taper is pre-defined in land areas see which is in the unexpanded state of the stent a position inclined to the longitudinal direction within the occupy the hollow cylindrical surface. 8. Stent according to one of the preceding claims, characterized in that the edges of web-like elements in a crossing or branching area or in the area of a successive stent segments connecting Ver connecting area ( 5 ) have roundings. 9. Stent according to one of the preceding claims, characterized characterized in that means are provided to the plasti limit deformation before a reduction in strength change occurs through cracking or the like. 10. Stent according to claim 9, characterized in that the funds consist of attacks by enlargements the webs, outside of areas of weakness, and / or these adjacent areas formed during deformation the one that deforms with the expansion of the Bring the stents closer together and further deform the Essentially prevent the area of weakness. 11. Stent according to claim 9, characterized in that mechanically after the attacks further areas of weakness are switched, which with further expansion of the stent allow further deformation when the deformation the first weakening area by the attacks in the we is significantly prevented. 12. Stent according to one of the preceding claims, characterized characterized in that further stops are provided, wel the approach of adjacent web-like elements Limit compression or crimping.   13. Stent according to one of the preceding claims, characterized in that several, in the axial direction reihenför mig successive segments ( 2 ) are provided, each of which is connected by a web-like element, which is provided with a taper. 14. Stent according to one of the preceding claims, characterized in that the position of the connecting region ( 6 , 6 ') changes between several segments ( 2 ) from segment to segment in the tangential direction. 15. Stent according to one of the preceding claims, characterized characterized in that outside the weakening areas Ver formation areas are provided in which at Expansi on the stent, at most, deformations occur in which no ver affecting the strength of the structure formations occur. 16. Stent according to one of the preceding claims, characterized by titanium, tantalum or another biocom patible metal or a corresponding metal alloy as Material exists. 17. Stent according to one of the preceding claims, characterized characterized in that a coating of amorphous silicon umcarbid is provided.