WO2001037761A2

WO2001037761A2 - Stent and method for the production thereof

Info

Publication number: WO2001037761A2
Application number: PCT/DE2000/004196
Authority: WO
Inventors: Franz Herbst
Original assignee: Franz Herbst
Priority date: 1999-11-26
Filing date: 2000-11-27
Publication date: 2001-05-31
Also published as: DE19957063A1; WO2001037761A3; EP1233727A2; AU2351001A

Abstract

The invention relates to a stent (10) which is made of an expandable netting or of an expandable structure comprised of polygonal basic elements (22), and which has a high degree of flexibility and uniformly favorable properties with regard to stability. The basic elements (22) can be formed into many diverse shapes. They comprise, in particular, symmetrical and/or convex triangular, quadrilateral, hexagonal or octagonal structures that are provided, at least in areas, with curved delimitation segments (24). Preferably, said delimitation segments are alternatively convex and concave (24a or 24b) and/or they themselves have alternating convex and concave areas. The delimitation segments (24) can be, for example, semicircular or can comprise sinusoidal or cosinusoidal curves of the length π or of an integral multiple thereof so that inventive stents (10) preferably have relatively simple, extremely regular, and very symmetrical honeycomb or star-shaped structures. According to the invention, the differently shaped basic elements (22) can also be combined with one another, whereby resulting in the production of stent structures of nearly any degree of complexity. The invention also relates to a method for producing stents (10) of this type during which a data set, which represents the desired stent structure, is firstly generated and is subsequently used for controlling a system for producing stents.

Description

Stent and method for its manufacture

description

The present invention relates to a stent and a method for its production.

Percutaneous transluminal coronary angioplasty (PTCA) is an accepted treatment for arteriosclerotic coronary diseases. The

The success of this method is high. In 2-7% of cases, however, acute or subacute occlusions occur at the site of the angioplasty.

Repeated angioplasty in the affected, diseased vessel can only be remedied in some of the patients. With others

Patients experience a life-threatening circulatory disorder through a number of different mechanisms, including recomposing or collapsing the dilated arteries. Late (chronic) restenosis occurs in these acute or subacute occlusions of coronary angioplasty. The possibility of avoiding acute or subacute restenosis is to prevent the formation of platelet thrombi at the dilation site using appropriate medication.

However, the coronary wall can also be mechanically supported by means of a stent, which usually consists of a cylindrical, expandable metal mesh, which is introduced into the diseased vessel and deployed at the site of the stenosis in order to open the narrowed area and to keep it open by supporting the blood vessel wall. After expansion, stents must therefore have a sufficiently high radial stability to keep diseased vessels open, while at the same time a good one to facilitate implantation

Cross flexibility is required in order to be able to overcome the narrow vascular curves on the way to the narrowed area without damaging the vessel.

To achieve these properties, conventional stents usually consist of both flexible and inflexible units, cells or basic elements, such as differently designed loop elements, which are either direct or are connected to one another via suitable web and / or joint elements.

The flexible basic elements give them the required flexibility, while the basic elements inflexible with respect to the transverse axis provide the required flexibility

Ensure radial stability. Depending on the arrangement, design and size of the flexible and inflexible basic elements used, the stability properties of conventional stents are naturally subject to strong local fluctuations which, for example, lead to impairment of application safety due to uneven expansion. In addition, the design and manufacture of such stents proves to be quite complex.

The object of the present invention is therefore to create a stent with stability properties which are as uniform as possible and which have both high flexibility and good longitudinal and transverse stability. Another part of the

The task is to create a suitable method for producing such stents.

The first part of the task is solved according to the invention by a stent with an expandable braid or an expandable structure made of polygonal or polygonal basic elements with at least regionally curved boundary lines. The basic elements can be shaped in many ways. They include in particular symmetrical and / or convex triangular, quadrangular, hexagonal or octagonal structures, ^• the stents with a high flexibility and uniform good

Form stability properties. However, there are also other polygonal basic elements such as pentagonal, heptagonal or even ten, twelve or four-sided structures conceivable.

To avoid discontinuities or voltage peaks go adjacent

Boundary stretches preferably continuously over each other. They are in particular semicircular or comprise a sine or cosine curve of length π or an integral multiple thereof, so that these stents formed according to the invention have an extremely regular, very symmetrical "honeycomb" or star-shaped structure with correspondingly good ones

Have stability properties of the desired type. Adjacent boundary lines are preferably alternately convex and concave formed and / or the boundary lines themselves already include alternating convex and concave areas.

The basic elements according to the invention can also comprise several differently designed basic elements of the type described. For example, square and hexagonal or octagonal basic elements of the same edge length can be combined with one another in a common stent structure in such a way that the hexagonal or octagonal basic elements each have a common delimiting section alternating with a similar basic element or a square basic element.

Adjacent square basic elements are thus connected to one another by the common delimitation section of two adjacent hexagonal or octagonal basic elements. In a preferred embodiment, at least some basic elements can in turn each comprise at least one smaller identical or alternatively different basic element, whereby these basic elements can both be nested inside one another and arranged next to one another, and the delimitation distances of the smaller and the large basic elements comprising them preferably form a common structure can be connected. The boundary sections of the basic elements here in turn preferably comprise curvilinear boundary sections of the type already described above with continuous transitions between adjacent boundary sections.

The second part of the object is achieved according to the invention by a production method in which a data set representing an expandable braid of polygonal basic elements of the type described is first generated and then used to control a system for stent production which, for example, uses a laser device suitable for laser cutting, comprises a photolithography device suitable for carrying out a photolithographic method or another device suitable for producing a desired stent structure from an output metal tube or other output tube. If necessary, the data record can also be temporarily stored on a suitable data carrier.

Further details, features and advantages of the present invention result not only from the associated claims - individually and / or in combination - but also from the following description of preferred exemplary embodiments in conjunction with the associated drawings. In the Drawings in which the same parts are provided with the same reference numbers show:

1 shows a stent design according to the prior art with conventional loops and joint elements;

Figure 2 shows another stent design according to the prior art with conventional loop and joint elements;

Figure 3a shows a first stent design according to the invention with hexagonal

Basic elements and sinusoidal boundary lines;

FIG. 3b shows an enlarged illustration of a basic element according to FIG. 3a;

4a shows a second stent design according to the invention with hexagonal

Basic elements and sinusoidal boundary lines;

FIG. 4b shows an enlarged partial representation of a basic element according to FIG. 4a;

FIG. 5 shows a partial illustration of a third stent design according to the invention with rectangular basic elements and semicircular boundary sections;

FIG. 6 shows a partial illustration of a fourth stent design according to the invention with a combination of square and octagonal basic elements with 25 semicircular boundary sections;

and

FIG. 7 the stent design according to FIG. 6, the octagonal basic elements 30 each having an additional smaller octagonal basic element with a semicircular shape

Boundaries include.

As already mentioned above, conventional stents usually comprise a combination of differently designed loop and joint elements, which are connected to one another either directly or indirectly via suitable web elements. An exemplary embodiment of this is shown in FIG. 1, in which the developed lateral surface of such a stent is shown. The stent 10 shown comprises one at each of its two outer ends and in the middle Loop segments of different sizes 12 and 14, respectively, consisting of larger loop areas 16. The loop segments 12 and 14 each consist of a large number of similar loop elements 12a and 14a of uniform orientation, which are connected to one another in such a way that they have a meandering or undulating structure form. The

Loop segments 12 and 14 are each arranged in such a way that a larger loop segment 14 in the longitudinal direction of the stent 10 is surrounded by two smaller loop segments 12, the opposite individual "wave crests", bulges or loops of the loop segments 12, 14 each being connected to one another via web elements 18 are. At the outer ends of the stent 10 there is thus in each case a smaller loop segment 12, so that the stent 10 only expands at these points at a higher pressure. This has the consequence that the loop segments 12, 14 expand more evenly and no trumpet-like or tulip-shaped expansion takes place at the ends of the stent 10. To improve flexibility, the three loop areas 16 are each connected to one another by joint elements 20. These are designed and arranged in such a way that every second loop of a loop segment 12 is connected to the two adjacent loops of the respectively opposite loop of the opposite loop element 12 by an S-shaped leg part 20a or 20b of an articulated element 20.

In the exemplary embodiment shown in FIG. 2, the stent 10 comprises four larger loop regions 16 distributed uniformly over its length, each with two loop segments 12, 14 and 14, 14 of the type described above, which in turn are connected to one another by web elements 18 which are located between the opposite loops of the loop segments 12, 14 and 14, 14 extend. Smaller loop segments 12 are in turn arranged at the outer ends of the stent 10, while all other loop segments are larger loop segments 14. The individual loop regions 16 are in each case connected to one another again by articulated elements 20 which extend between two loops of the loop elements 14a or the loop segments 14 which are in each case opposite one another.

In contrast to these conventional combinations of differently designed loop and joint elements 12a, 14a and 20, the stent structure according to the invention shown by way of example in FIG. 3a consists of a large number of interconnected, uniformly shaped, regular hexagonal cell or basic elements 22, each with six alternately convex and concave designs curved boundary sections 24. The basic elements 22 are arranged so that two adjacent basic elements 22 each have a common boundary section 24, so that an extremely regular, honeycomb-like symmetrical structure of high flexibility with uniform excellent flexibility or stability properties in the radial and tangential directions is formed is, which are naturally also transferred to a stent 10 with a suitably designed cylindrical outer surface.

As can be seen in particular from the partial drawing shown in a larger scale in FIG. 3b, the delimitation sections 24 are each designed as essentially sinusoidal curves of length π, successive delimitation sections 24a, 24b corresponding to the first and second half-period of a sine curve, respectively that the already mentioned alternating convex and concave boundary line is created. As a result of the special arrangement of the basic elements 22, three delimitation sections 24 meet at their corner points 26, so that adjacent delimitation sections 24a, 24b each form an angle of 120 ° to one another. To avoid discontinuities or voltage peaks, the transitions between the delimitation sections 24 are each somewhat rounded. For a better illustration of the hexagonal basic element structure, the linear, fictitious delimitation lines 28 of the underlying hexagonal structure, which are not present in the stent structure, are additionally shown in FIGS. 3a and 3b for a basic element 22.

In the embodiment of the invention shown in Figure 4a are the

Boundary sections 24 of the hexagonal basic elements 22 are each formed as sinusoidal curves with a length of 2π, so that the bounding sections 24 themselves already comprise a convex and a concave region, and the basic elements 22 are given an essentially star-shaped appearance. This can be seen particularly well on the basis of the enlarged partial representation of such a basic element 22 in FIG. 4b, in which, for better illustration, as in the case of a basic element 22 in the associated FIG. 4a, the straight fictitious delimitation sections 28 of the same that are not present in the stent structure Basic element 22 underlying hexagon structure are shown.

The two described exemplary embodiments serve only to illustrate the idea according to the invention and it is obvious that Allow stent structures with the desired stability properties to be achieved with other polygonal basic elements 22 and / or with differently configured boundary sections 24. For example, the delimitation sections 24 of the basic elements 22 forming the jacket of a cylinder-shaped or otherwise configured stent 10 can also be semicircular or a sinusoidal curve, the length of which corresponds to another integer multiple of π. In addition, evenly shaped hexagons with unequal side lengths or other regularly or irregularly designed polygons, such as triangles, quadrilaterals or octagons, can be used as basic elements 22.

Thus, the section shown in FIG. 5 from a stent structure according to the invention comprises, for example, rectangular basic elements 22 with semicircular delimitation sections 24, which together form a wave-shaped structure that runs parallel to the longitudinal or transverse axis of the basic elements 22 and, in the unexpanded state, a mesh-like network of dumbbell-shaped Form basic elements 22. For better illustration, the “fictitious” delimitation sections 28 of the rectangular structure on which the basic elements 22 are based are not shown in the stent structure. Of course, here again, differently shaped curved sections or, if necessary, at least in some areas also straight sections 24 are conceivable. In addition, the rectangular basic elements 22 can, for example, also have a different aspect ratio or be square. Furthermore, of course, differently designed quadrilaterals, such as suitable trapezoidal shapes or

Parallelograms, especially diamonds, can be used.

According to the invention, different types or differently designed basic elements 22 can also be combined with one another. A corresponding exemplary embodiment is shown in FIG. 6 on the basis of a section of a stent structure consisting of square and regular octagonal basic elements 22a and 22b of the same side length, in which the basic elements 22a, 22b are arranged such that the octagonal basic elements 22a alternate with an adjacent square basic element 22b or an adjacent octagonal base element 22a have a common boundary section 24.

The square basic elements 22b are thus each arranged in the remaining gaps of a pattern consisting of adjacent octagonal basic elements 22a, so that the opposite corner points 26 Adjacent square basic elements 22b are each separated from one another by the common delimitation section 24 of two adjacent octagonal basic elements 22a.

In the present exemplary embodiment, the delimitation sections 24 are again alternately convex and concave semicircular, so that a braid is formed from a multiplicity of interconnected, equilateral cross-shaped basic elements 22a of different orientation with intermediate "dumbbell-shaped" basic elements 22b. For better illustration, in addition to the actual one in FIG

In addition, the stent structure also shows the delimitation sections 28 of the underlying square and octagonal basic elements 22b and 22a which do not come to light, whereby adjacent basic elements 22 each have common delimiting sections 28. The illustrated exemplary stent structure according to the invention can also be interpreted as a combination of similar, regular octagonal basic elements 22a arranged next to one another with square gaps 22b between them.

In order to form complex shaped larger basic elements 22, some can optionally also be used in the stent structures according to the invention

Boundary sections 24 are omitted, which corresponds to the use of polygonal basic elements 22, such as ten, twelve or four-sided basic elements 22.

For the sake of completeness, it should also be pointed out that boundary sections 24 of the type already mentioned or a different combination of basic elements 22, such as a structure composed of hexagonal and square basic elements, can also be used and to form stent structures with the desired good stability properties to lead. In addition, complex or more extensive combinations of differently designed basic elements 22 are also possible.

In the exemplary embodiment according to the invention shown in FIG. 7, the octagonal basic elements 22a according to FIG. 6 each comprise, for example, a centrally arranged, smaller octagonal basic element 22'a of the same orientation with alternating convex and concave semicircular delimitation lines, which likewise give the basic elements 22a 'a cruciform appearance. The boundaries of the smaller basic elements 22a ' are connected in a suitable manner to the boundary lines of the larger, likewise cruciform base element 22a surrounding them, so that they form a common structure. They are therefore dimensioned in such a way that they at least touch the larger basic elements 22a, but preferably cut them, as shown in FIG. 7, the respectively belonging together

Basic elements 22a, 22a 'either have the same orientation or can be shifted by 90 ° to one another. The octagonal basic elements 22a can, for example, also be replaced by hexagonal basic elements in order to produce a stent structure consisting of hexagonal and square basic elements. A combination of basic elements 22 according to the invention with conventional basic elements is also possible.

To produce the stent structures described or a large number of other stent structures according to the invention, the outer surface of a stent is first filled with polygons of the desired type, so that an initial structure comprising the corner points of the polygons and / or possibly also the associated delimitation distances is created. In this initial structure, the corner points of the polygons are now connected to one another by delimitation sections of the desired type, such as semicircular, sinusoidal or otherwise curved delimitation sections, or the already existing delimitation sections are modified accordingly, so that a mesh of polygonal basic elements according to the invention is finally used as the stent structure Type described above, whose characteristic parameters are used to generate a data set representing the stent structure or the braid. This is then used, if necessary after buffering on a suitable data carrier, to control a conventional system for stent production.

Such a system can, for example, comprise a laser device, with the aid of which stents of the desired type are made from a suitable tube, in particular a

Metal pipe or a plastic pipe of the appropriate size can be cut out. A laser beam from the laser device runs along the longitudinal axis of the rotating tube to be machined clamped on a turntable, the rotational movement of the tube and the movement of the laser beam to generate the desired stent structure being controlled by means of a suitable CAD program representing the stent structure. The system receives the control commands from a DXF file or another CAD-processable file with a corresponding coding of the stent structure. However, the system for producing the stent can, for example, also comprise a photolithographic device for etching out the desired stent structure from an outlet tube made of a suitable material. The output pipe is first covered with a photosensitive paint or

Photoresist coated, then covered with a mask representing the desired stent structure and then exposed to radiation of a suitable wavelength. When using a positive varnish, the varnish is removed from the exposed areas after exposure by means of a suitable solvent, against which the varnish is inert at the unexposed areas, so that a positive image of the mask geometry is formed in the varnish. When using a negative varnish that becomes insoluble through irradiation, the unexposed areas are removed accordingly, so that a negative image of the mask geometry is formed in the varnish. The pipe treated in this way is then treated, for example, by simply immersing it with a suitable etching solution, which dissolves the pipe material at the points at which the lacquer has been removed, while the other points are protected by the lacquer layer, so that one detects the positive or negative Mask image receives corresponding stent structure.

Claims

claims

1. stent (10), comprising an expandable braid or an expandable structure made of basic elements (22), characterized in that the basic elements (22) are polygonal and at least partially include curvilinear boundary sections (24).

2. Stent according to claim 1, characterized in that the basic elements (22) are symmetrical and / or convex.

3. Stent according to claim 1 or 2, characterized in that the basic elements (22) are triangular, quadrangular, hexagonal or octagonal.

4. Stent according to one of the preceding claims, characterized in that the basic elements (22) comprise differently designed basic elements (22a, 22a ', 22b).

5. Stent according to claim 4, characterized in that the basic elements (22) include square and octagonal or hexagonal basic elements (22b or 22a) of the same edge length, which are arranged so that the octagonal (22a) or hexagonal basic elements each alternately with a common basic element (22a) or a square basic element (22b) have a common boundary.

6. Stent according to claim 4 or 5, characterized in that at least some basic elements (22a) each comprise at least one smaller, in particular identical, basic element.

7. Stent according to claim 6, characterized in that that the delimitation distances (24) of the small and the large basic elements (22a 'and 22a) that surround them are connected to one another to form a common structure.

5 8. Stent according to one of the preceding claims, characterized in that adjacent boundary sections (24a, 24b) continuously merge into one another.

9. Stent according to one of the preceding claims, 10 characterized in that adjacent boundary sections (24a, 24b) are alternately convex and concave and / or that the boundary sections (24) comprise alternating convex and concave regions.

15 10. Stent according to one of the preceding claims, characterized in that the boundary sections (24) are semicircular or comprise sinusoidal or cosine-shaped curves of length π or an integral multiple thereof.

20

11. Manufacturing process for stents with the following process steps:

Generation of a data set representing a mesh of polygonal basic elements (22) according to one of the preceding claims and 25 - activation of a system for stent production using the data set.