DE19653708A1 - Device for intralumenal implantation to expand blood vessel - Google Patents

Abstract

The device comprises a thin walled hollow tubular element whose outer surface has a lattice-like construction with holes bounded by narrow strips made from material removed from the hole area. The strips are connected to neighbouring strips in such a way that when the device is implanted and deforms through expansion, there is a minimal force exerted on the connection areas of the strips. The strips have a cross-over area (5) with the arms (5.1,5.2,5.3,5.4) of the cross so positioned that for a given expansion of the device there is a maximum adjustment in the angles (8,9) between neighbouring strip elements which is not exceeded.

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 Process for producing 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 done not only by the constructive design in relation to the greatest possible strength by increasing the material cross sections, but also by the fact that the shape of the webs and connecting areas is optimized with regard to the expected loads. This happens on the one hand in that the occurring maximum stresses are locally minimized, but on the other hand because that the necessary deformations are minimized
The stresses occurring during the deformation are first minimized according to the invention in such a way that the individual web-like elements are shaped in such a way that the bending deformation to which a web-like element is subjected during expansion within the hollow cylindrical tube shape does not locally exceed a predetermined value tet. The necessary for a deformation to be achieved inte gral of the local angle changes between adjacent connection areas with other web-like elements must - according to the solution described here - be distributed as evenly as possible over the available length.

It is favorable if they are all part of the length the deformations are not significantly larger than it is the ratio of the length of the section concerned to total deformable length. Should be preferred a quarter of a web-like Ele bending deformation occurring during expansion is not great be greater than a third of the total bending deformation, the this web-like element is subjected.

As an advantageous design requirement, it was found that the deformation is favored when the shape of the stent essentially unexpanded Corresponds to form that results when an in expanded Form web structures of regular shape, in this form of mu created from a tubular structure ster, in the unexpanded form - the later exit form - is compressed. So this is a form as out  gait shape that corresponds to the one he is there when you finished one in its expanded form th stent compressed.

Such regular shapes are preferred from circles, Ellipses, rectangles, squares, polygons or from them compound or approximated to these he testifies.

To favor local stress-free deformations locally, it is envisaged that branches of webs under Ver avoiding abrupt changes in the web width are. This will result in notch stresses and avoided the same. This can be achieved that the Material tensions, especially in the area of crossings or branches during deformation also as notch stress does not exceed a predetermined value.

Such a construction leads to the fact that the branch web-like elements are particularly organic Have shape which is essentially the shape of a trunk branches in trees.

In some cases it is convenient if the web-like Ele elements as connections between expandable elements in the are essentially S-shaped, since then areas maximum deformations from the junction or connection areas in the free land areas.

It is also advantageous if there are areas of cross tongues are shaped such that for a given expan sion a maximum change in the angle between adjacent ten web-like elements as arms of a cross or of Branches are not exceeded. This is done before  moves in the meadow that web-like elements as arms of one Cross-shaped or branched from branches are.

If the stent has the edges of web-like elements in an egg a crossing or branching area or in the area nes connecting consecutive stent segments rounding areas that have sharp corners are avoided, the maximum voltages remain here borders.

According to a preferred embodiment of the inven the expandable, essentially hollow cylin drically trained stent with a through recesses, net-like structured surface on the connection score for the web-like Ele that delimits the recesses have an organic shape to create a high, if necessary exclude notch stress leading to breakage eat. A local disruption of the stent leads to night liger way to free, relatively sharp-edged ends inside half the spatial configuration of the stent, which on the one hand the Can pierce the vessel wall or on the other hand the free Cross-section of the vessel through a deflection into the blood reduce track.

This shape is due to a rounding of all connections expansion points relative to each other when expanding the stent web-like elements moving towards each other and ensures in a simple and at the same time advantageous manner, that the extent of the local material deformation to the point of view critical stress points the stent construction when expanding the stent uniform distribution of the deformation work a minima len value.  

To connect the individual, essentially by itself axially extending web and delimiting the recesses like elements are as a cross-shaped web-like element trained coupling elements provided, which the neigh beard arranged recesses in the axial direction each at their ends and in the tangential direction in Mit te of the axially extending web-like elements connect each other.

According to a preferred embodiment of the invention the arms of the cross-shaped coupling elements are arched out forms and arranged such that they are in tangential direction tion the legs of an essentially obtuse angle and a substantially sharp win in the axial direction form. Which attach themselves to the arms of the coupling links closing web-like elements of the recesses are as S formed in the axial direction, the in tangential direction opposite each other the web-like elements arranged mirror-symmetrically are.

In this configuration of the coupling element are after another development of the invention in an advantageous manner Material roundings are provided at the intersection, so that only a relatively minor one when expanding the stent Change in between the neighboring arms of the cross shaped coupling member included angle occurs. Because of this, there is no high notch stress in the Crossing point, especially no local voltage peaks, so that there is no risk of breakage when expanding is.

From the same point of view, those are at the stent ends or at the ends of the segments of the stent of the above described embodiments of the invention  free sections of the recesses are arched, so that even in these areas when expanding the stent only slight mechanical stresses arise and none Notch stress extreme values occur.

The organic forms described above Formation of the lateral surface of the stent according to the invention ensures an essentially even distribution of deformation work done when expanding to the ever sections and delimits recesses thereby extreme stress loads on individual points or Areas on the lateral surface of the stent.

To avoid existing stenoses even in curved blood vessels consequently by expanding stents can, the stent is according to another inexpensive Embodiment of the invention in substantially the same tig trained, arranged in rows in the axial direction divided segments. The above considerations also apply to the connection areas of segmented Stents where the individual segments increase the Deformability are provided with web-like connections. Here, the web-like elements are designed such that the deformations that affect the entire web-like element between connecting areas with other web-like el is subjected to expansion, essentially is minimized. To connect adjacent segments are web-like coupling links provided, the position of which especially from segment to segment in tangential direction tung changes.

As a result, the stent can be advantageous during implantation the shape of the vessel in the area of the Adjust stenosis.  

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.

A preferred stent of the above design consists of Titanium or tantalum as a material and comes with a coating provided with amorphous silicon carbide.

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

FIG. 1b, another advantageous embodiment of the He invention in side view,

Fig. 2 shows a segment as a detail of the embodiment shown in Fig. 1b Darge before expanding and

Fig. 3 shows the detail shown in Fig. 2 in a partially expanded state.

A 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. 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, has never assumed this state. 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. Since the material evenly opposes the mechanical forces acting on it during compression, the local deformations are also evened out. There are no local strong kinks, but even arches, the radii of which are maximum. The shape obtained in this way is used as a basis for the design of the unexpanded shape, which can be converted in the opposite direction into the desired final shape with uniform local deformation.

The web-like areas surrounding an expandable element Be 4 are multiple S-shaped swinging ausgebil det. They each enclose a recess 3 in the Wei se that the adjacent in the tangential direction against opposite web-like areas 4 of the same or an adjacent recess 3 are arranged mirror-symmetrically. At their ends located in the longitudinal direction, the expansible elements 2 have a free arc region 7 with a greater curvature.

The expansible elements are shaped in such a way that after insertion of the stent into a vessel, they are converted into a ring shape by dilatation with a balloon catheter with minimal deformation. It can be seen that the arc 7 occupies a maximum radius. The S-shaped counter arches enable him to suffer the least possible deformation 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. The connection areas 5 are designed in the form of a cross here, the individual arms of the cross (compare positions 5.1 , 5.2 , 5.3 and 5.4 in FIG. 2) having the shape of curved pieces. In the intersecting connection area 5 , material roundings are provided such that the connection area has an organic shape that reduces the occurrence of increased notch stresses.

It can be seen that the individual web-like elements are shaped such that the bending deformation of a web like element in the expansion within the hollow cylin is subject to tubular shape and which results from the integral of the local angular changes during deformation, determined over the length of the web-like Ele elements between adjacent connection areas with other ridge-like elements differ in their length of the element that it also specifies a locally does not exceed a value.  

So it is a quarter of a footbridge long like bending element no longer larger than a third of the total bending deformation that this web-like element is subjected.

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 formed while avoiding sprun-like changes in the web width and in particular designed in such a way that the material stresses in particular in the area of the branching during the deformation also as a notch stress does not exceed a predetermined value. The stent shown in FIG. 1a is structured essentially homogeneously over its entire length.

In Fig. 1b shows a further embodiment of a stent 1 'shown in side view, which is divided into a plurality of successive segments 9 in an axial direction. The segments 9 are formed identically among themselves and have a lateral surface in which recesses 3 are lined up in the tangential direction and are connected to one another in the center by connecting regions 5 .

For the connection between the adjacent segments 2 , coupling elements 6 ( FIG. 1 a ) are provided, which are arranged offset with respect to their position in the tangential direction from segment to segment. These coupling elements allow the segments to adapt even more to the curvatures or branches of vessels.

In order to exclude extreme notch stresses when expanding the stent 1 ″ also in the connection area of the segments 9 , the coupling elements 6 correspond in their design to the connection areas 5 of the individual expandable elements 2 , but are optionally more elongated in the longitudinal direction of the stent, in order to increase the flexibility of the to increase individual segments with each other. .
It can be seen that the individual web-like elements are shaped such that the bending deformation, which a web-like element is subjected to during expansion within the hollow cylindrical tube shape and which results from the integral of the local angular changes during deformation, determined over the length of the respective web-like elements between adjacent connection areas with other web-like elements are distributed over the length of the element in such a way that they do not locally exceed a predetermined value.

It can also be seen from the figures that branching webs avoiding sudden changes are formed towards the web width, and that branches are designed such that the material tensions in particular especially in the area of branching during deformation as a notch stress, do not exceed a specified value tet.  

The above-described design of the stents 1 , 1 'and 1 ''or the design of the connection of the individual elements 3 , 4 and 7 forming the lateral surface allows the tubular stents to be expanded without causing them to be destroyed at the connection points comes from web areas leading extreme values of the notch tension.

In FIGS. 2 and 3, a single segment 9 of the stent 1 shown in Fig. 1b 'in the unexpanded state (Fig. 2) and expanded for comparison in the partially to stand (Fig. 3) shown in schematic form. The intersecting arms 5.1 , 5.2 , 5.3 , 5.4 of the connec tion area 5 are designed such that a maximum change in the intersection angle between the adjacent cross arms is not exceeded at a predetermined degree of expansion.

The arms 5.1 , 5.2 , 5.3 , 5.4 of the cross 5 are arcuate and have rich material roundings at the intersection of the Verbindungsbe. The arms 5.1 , 5.2 , 5.3 , 5.4 form the legs of an essentially obtuse angle in the tangential direction and the legs of an essentially acute angle in the axial direction. The obtuse angle has a value of approximately 120 °, the acute angle accordingly has a value of approximately 60 °.

As can be seen in FIG. 3, the maximum local deformations - and thus the risk of extreme values of the notch stress when the segment 2 expands - remain extremely low. You do not concentrate on a single point of the individual recesses 3 , in particular on the tip of the outer arc pieces 7 , but it extends over the entire area of the S-shaped web-like elements 4 and the arms 5.1 , 5.2 , 5.3 , 5.4 of the Connection areas 5 limited recesses 3rd

The expanded segment 9 'has mutually coupled elliptical or (in the case of further expansion) also circular regions 2 ', the crossing angles between the 5.1 ', 5.2', 5.3 ', 5.4' changing only slightly in comparison with a non-expanded segment . This also reduces the risk of an extremely high material load occurring due to peak loads and notch stresses.

Above all, it can be seen that the Verfor an expansible element formed by web elements ment so that the local deformations as possible stay limited. The arc areas in unexpanded State are chosen as large as possible, so that the Ex pansion all parts of the web-like elements if possible are evenly involved in the forming.

The stent shown here consists of titanium, tantalum or another biocompatible metal or one the metal alloy as a material, from which a good body compatibility and excellent ductility re results. A micro-coating made of amorphous silicon car bid counteracts 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 (22)

1. stent, in particular coronary stent, consisting of at least one thin-walled, tubular element, the outer 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 being formed from the remaining material of the tube wall are, from which the material in the area of the recesses gene was removed, characterized in that the web-like elements are shaped such that the deformation which a web-like element between connecting areas with other web-like elements is subjected to during the expansion as a whole essentially is minimized. 2. Stent according to claim 1, characterized in that the individual web-like elements are shaped such that the bending deformation, which is a web-like element in the Expansion within the hollow cylindrical tube shape below is thrown and results from the integral of the local Chen angular changes in deformation, determined via the Length of the respective web-like element between connecting areas with other web-like elements ten in the way along the length of the element tells that it does not have a given value locally steps. 3. Stent according to claim 1 or 2, characterized in that that the length of a quarter of a web-like Eliminating bending deformation is not greater than  a third of the total bending deformation that this web like element 4. Stent according to one of the preceding claims, characterized characterized that to a length of one fifth of a web-like element eliminating bending deformation is not greater than a quarter of the total bending deformation tion to which this web-like element is subjected 5. Stent according to one of the preceding claims, characterized characterized in that the shape of the stent does not expand state essentially corresponds to the form that arises when a web structure in expanded form of regular shape, in this form of egg a tubular structure created pattern in which not expanded form - the later initial form - compressed becomes. 6. Stent according to claims 5, characterized in that the regular form consists of circles, ellipses, right corners, squares, polygons or composed of these ten or to these approximate structures. 7. Stent according to one of the preceding claims, characterized characterized that branches of webs under avoid training of sudden changes in web width det.   8. Stent according to one of the preceding claims, characterized characterized in that branches are formed in such a way that the material tensions, especially in the area of Ver branching during deformation also as a notch stress does not exceed the specified value. 9. Stent according to one of the preceding claims, characterized characterized that the branches of web-like Ele elements have an organic shape, which essentially Chen corresponds to the shape of trunk branches in trees. 10. Stent according to one of the preceding claims, characterized in that the web-like elements ( 4 ) are substantially S-shaped. 11. Stent according to claim 10, characterized in that adjacent web-like elements ( 4 ) are shaped mirror-symmetrically in the tangential direction. 12. Stent according to claim 11, characterized in that the web-like elements ( 5.1 , 5.2 , 5.3 , 5.4 ) are also shaped in areas of intersections ( 5 ) in such a way that a maximum change in the angle ( 8 , 9 ) between adjacent web-like elements as arms of a cross is not exceeded. 13. Stent according to claim 12, characterized in that the web-like elements as arms of a cross ( 5.1 , 5.2 , 5.3 , 5.4 ) are arcuate. 14. Stent according to one of claims 12 or 13, 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. 15. Stent according to one of the preceding claims, characterized in that several, in the axial direction reihenför mig arranged segments ( 2 ) are provided, each because of a connection area ( 6 , 6 ') are connected to each other ver. 16. Stent according to claim 10, characterized in that the position of the connecting region ( 6 , 6 ') between the individual segments ( 2 ) changes from segment to segment in the tangential direction. 17. Stent according to claim 11, characterized in that a cross-shaped connection area is provided as the connection area ( 6 '). 18. Stent according to one of the preceding claims, characterized in that at the ends of the respective segment Lichen, free sections ( 7 ) of the recesses ( 3 ) are arcuate. 19. Stent according to one of the preceding claims, characterized characterized in that it is made of titanium, tantalum or another biocompatible metal or a corresponding metal government exists. 20. Stent according to claim 14, characterized in that a coating of amorphous silicon carbide is provided is. 21. A method of making a stent, in particular according to one of the preceding claims, characterized records that the shape of the stent in unexpanded Zu was from the form that the stent expanded into State should be determined in such a way that the expanded starting form is made or in a Si simulation model is created, and then on the Diameter of the later unexpanded stent kompri is lubricated, with the resulting shape then being that is, according to the dimensions of the newly manufactured stent is manufactured in an unexpanded state. 22. The method according to claim 21, characterized in that the shape of the expanded stent is determined through uniform shapes, such as contiguous stegar elements in the form of circles, ellipses or polygons.