DE19653708C2 - Stent and method for its manufacture - Google Patents

Description

The invention relates to a stent, in particular a coronary stent, as an intraluminal Expansion element, corresponding to that mentioned in the preamble of claim 1 Art and a method for producing such a stent.

One of the European patent specifications EP-B1 0 364 787 and EP-B1 335 341 expandable intraluminal element with at least one thin-walled, tubular part (hereinafter referred to as a stent). The outer surface of the The stent is openwork and has recesses on, the web extending straight in the axial and circumferential direction like elements of limited material thickness are limited. The bridge-like Elements consist of the remaining pipe wall, of which the material in the Area of the recesses was removed.  

Such stents are surgically operated under the influence of forces directed inside outwards by a pressurized gas tubular dilator, expanded. The stent retains its shape despite the deformation Pipe shape and widens the vessel narrowed by deposits.

Furthermore, from European patent application EP-A2 0 732 088 is a Expandable stent known, in which web-like elements connecting have areas. These connection areas are designed such that the web-like elements that form the arms of an essentially cruciform structure represent, with the arms extending rectilinearly and forming relative sharp edges are merged.

The known stents basically have the disadvantage that the expansion due to the deformation of the axially extending web-like elements only in to a limited extent because the shape change of the individual web-like Elements of the stent are relatively narrow. These limits are conditional due to the material stresses associated with the deformation, which - if the deformation becomes too strong - to break one or more of the mesh can form web-like elements.

For safety reasons, the deformation must therefore usually be far below of a possible danger area, as the breakage of a web is added would lead that its free ends in the area of the fracture into the interior of the would protrude into the stented vessel. Through the associated Not only the success of the procedure itself would risk the formation of restenoses questioned, but also endangered the life of the patient.

Based on the shortcomings of the prior art, the invention lies Task based on an expandable stent of the type mentioned admit which one as safely as possible - and thus also without the risk of a Stress-related break in the area of the web-like elements -  is expandable.

The object is achieved by the characterizing features of claims 1 and 13 solved.

The invention includes the technical teaching that fragile, from suitable Tubular, fabric-like structures made of materials Elements that are subjected to deformation due to the application, crit ce material loads or even material breaks can be avoided if such Areas that are subject to increased deformation are already constructive and the occurring voltage maxima are limited from the outset.

This does not only happen here through the constructive interpretation in relation to a greatest possible strength by increasing the material cross sections, but also in that the shape of the webs and connection areas with regard to the expected loads is optimized. This happens on the one hand in that the occurring maximum stresses are locally minimized, but also in that the necessary deformations are minimized.

The stresses that occur during the deformation are fiction first minimized 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 Expansion within the hollow cylindrical tube shape is subject to a local does not exceed the specified value. For a deformation to be achieved necessary integral of the local angle changes between adjacent Connection areas with other web-like elements must therefore - according to the here described solution - over the available length if possible be evenly distributed.

It is expedient if the deformations related to a length portion are in each case are not significantly greater than the ratio of the length of the subject  Section corresponds to the entire deformable length. It should preferably be on a length of a quarter of a web-like element resulting from expansion Bending deformation should not be greater than a third of the total bending deformation, which is subject to this web-like element. It has proven to be particularly cheap proven here if the length of a fifth of a web-like Eliminating bending deformation is not greater than a quarter of the total Bending deformation to which this web-like element is subjected.

As an advantageous design requirement, it was found that the deformation is favored if the shape of the stent in the unexpanded state in essentially corresponds to the form that results when an in expanded Form web structures of regular shape, in this form from one tubular structure created pattern, in the unexpanded form - the later Initial form - is compressed. So that is a form as a starting form made that corresponds to the one that results when one is in his expanded form manufactured stent compressed.

Such regular shapes are preferred from circles, ellipses, rectangles, Squares, polygons, or composed of these or attached to them approached structures generated.

In order to favor local stress-free deformations locally, that branching of webs while avoiding sudden changes the web width are generated. This will result in notch stresses and the like avoided. It can be achieved that the material tensions especially in the area of crossings or branches during the deformation also as a notch stress does not exceed a predetermined value.

Such a construction leads to the fact that the branches of web-like Elements have a particularly organic shape, which is essentially the Form of rounded branches in trees  corresponds.

In some cases it is convenient if the web-like elements as connections are essentially S-shaped between expandable elements, because then areas of maximum deformation from the junction or joint areas in the free land areas.

It is also advantageous if regions of intersections are also shaped in this way are that for a given expansion a maximum change in angle between adjacent web-like elements as arms of a cross or of Branches are not exceeded. This is preferably done in such a way that the web-like elements as arms of a cross or branching arched are trained.

If the stent meets the edges of web-like elements in a crossing or Branching area or in the area of a successive stent segment connecting connecting area roundings that have sharp corners are avoided, the maximum voltages remain limited here.

According to a preferred embodiment of the invention, the expandable, essentially hollow cylindrical stent with a through Recesses, net-like structured surface at the connection points the web-like elements delimiting the recesses are organic Shaping to a high, possibly leading to breakage Exclude notch stress. A local disruption of the stent leads to night liger way to free, relatively sharp-edged ends within the room configuration of the stent, which on the one hand can pierce the vessel wall or on the other hand, the free cross-section of the vessel by deflecting it into the blood reduce track.

This shape is due to a rounding of all connection points that are in the  Expanding the stent of web-like elements moving relative to one another marked and ensures in a simple and at the same time advantageous manner that the Measure of the local material deformation in relation to the occurring Critical stress points of the stent construction when expanding the Stents have a minimal value due to the even distribution of the deformation work having.

To connect the individual, by extending substantially axially and the web-like elements delimiting the recesses are in the form of a cross-shaped web Like element trained coupling links provided which are adjacent arranged recesses in the axial direction at their ends and in tangential direction in each case in the middle of the axially extending web-like Connect elements together.

According to a preferred embodiment of the invention, the arms are the cruciform coupling links formed arcuate and arranged such that the legs of an essentially obtuse angle in the tangential direction and form a substantially acute angle in the axial direction. The ones at the Arms of the coupling elements connecting web-like elements of the recesses are designed as S stretched in the axial direction, the S in the tangential In the direction of mutually opposing web-like elements mirror-like are arranged metrically.

In this configuration of the coupling element are another training the invention in an advantageous manner at the intersection of material fillets provided so that when expanding the stent only a relatively minor Changing the between the adjacent arms of the cross-shaped paddock link included angle. Because of this, no high kick occurs Notch stress at the crossing point, especially no local stress peaks, so that there is no risk of breakage when expanding.  

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 portions of the recesses arcuate trained so that even in these areas when expanding the stent only slight mechanical stresses and no notch stress Extreme values occur.

The above-described formation of organic forms The outer surface of the stent according to the invention essentially secures one even distribution of the deformation work performed when expanding sections delimiting the respective recesses and thereby avoiding extreme stress loads on individual points or areas on the lateral surface of the stent.

In order to successfully pass stenoses even in curved blood vessels through the To be able to treat expanding stents, the stent is one another favorable embodiment of the invention in substantially the same trained segments arranged in rows in the axial direction. The The above considerations also apply to the connection areas of segmented Stents in which the individual segments are used to increase the deformability web-like connections are provided. Here are the web-like elements designed so that the deformations that affect the entire web-like element between connection areas with other web-like elements in the Expansion is essentially minimized. For connection adjacent segments are provided web-like coupling links, their position changes in particular from segment to segment in the tangential direction.

This allows the stent to easily adhere to the implant Adjust the shape of the vessel in the area of the stenosis.

According to another cheap embodiment of the invention, the coupling has  essentially the same shape (s) as the coupling links between the adjacent expandable elements of the individual segments of the stent, so that there are no notch peaks at these connection points Can expand the stent.

A preferred stent of the above design is made of titanium or tantalum Material and is provided with a coating of amorphous silicon carbide.

The solution to the problem also includes a method for producing a stent with the design features described above.

In terms of process technology, it has proven particularly advantageous if the shape of the stent in the unexpanded state according to the invention from the shape of the Stents in the expanded state is determined in such a way that the expanded Initial form produced or created in a simulation model and then is compressed to the diameter of the unexpanded stent. Form this stent is the one in which the new stent to be manufactured is not expanded state is manufactured.

Other advantageous developments of the invention are in the subclaims are identified or described below together with the description of the preferred embodiment of the invention with reference to the figures.

Show it:

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

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

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

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

A stent 1 shown in FIG. 1 a 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 regions 4 enclosing an expandable element are designed with multiple S-shaped curves. They each enclose a recess 3 in such a way that the web-like regions 4 of the same or an adjacent recess 3 , which are located opposite one another in the tangential direction, are arranged in mirror symmetry. At their longitudinal ends, the expansible elements 2 have a free curved area 7 with an enlarged curvature.

The expandable elements are shaped such that, after insertion of the stent into a vessel, they are converted into a ring shape by dilation with a balloon catheter with minimal deformation. It can be seen that the arc 7 occupies a maximum radius. The S-shaped counterbends enable it to suffer as little deformation as possible during expansion.

Between the recesses 3 arranged in the axial (longitudinal) and in the tangential (transverse) direction adjacent on the lateral surface of the stent 1 , connecting areas 5 are provided which mechanically couple the respective expandable areas 2 to one another. 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 crossing 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, which is a web-like element in the expansion within the is subject to hollow cylindrical tube shape and which results from the integral of local angular changes in deformation, determined over the length of the respective web-like element between adjacent connection areas with others web-like elements are distributed in such a way over the length of the element that it also does not exceed a predetermined value locally.

This is the length of a quarter of a web-like element Bending deformation no greater than one third of the total bending deformation, the this web-like element is subjected.

The shape of the stent essentially corresponds in the unexpanded state the shape that results when a web structure in expanded form from Regular shape, in this form from a tubular structure  created pattern, in the unexpanded form - the later initial form - is compressed. The regular shape consists of circles, ellipses, rectangles, Squares, polygons or composed of or to these approximate structures.

Branches of webs are formed while avoiding abrupt changes in the web width and in particular designed such that the material stresses, in particular in the region of the branching during the deformation, also do not exceed a predetermined value as the notch stress. 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 of identical design and have an outer 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 .

Coupling elements 6 ( FIG. 1 a ) are provided for the connection between the adjacent segments 2 , and 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 design of the coupling elements 6 corresponds 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 allow the flexibility of the individual segments to one another to increase.

It can be seen that the individual web-like elements are shaped such that  the bending deformation, which is a web-like element in the expansion within the is subject to hollow cylindrical tube shape and which results from the integral of local angular changes in deformation, determined over the length of the respective web-like element between adjacent connection areas with others web-like elements are distributed in such a way over the length of the element that it does not locally exceed a predetermined value.

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

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 expand without the formation of the destruction of the connecting points Extremity of the notch stresses leading web areas comes.

In FIGS. 2 and 3, a single segment 9 of the stent 1 shown in Fig. 1b 'in the unexpanded state (Fig. 2) and for comparison in the partially expanded state (Fig. 3) shown in schematic form.

The crossing arms 5.1 , 5.2 , 5.3 , 5.4 of the connection area 5 are designed such that, with a given degree of expansion, a maximum change in the crossing angle between the neighboring crossing arms is not exceeded.

The arms 5.1 , 5.2 , 5.3 , 5.4 of the cross 5 are arched and have material roundings at the point of intersection of the connection area. 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 hence the risk of extreme values of the notch stress when the segment 2 expands - remain extremely low. They do not concentrate on individual points of the individual recesses 3 , in particular on the tip of the outer arch pieces 7 , but extend 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 connecting areas 5 limited recesses 3 .

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 also be seen that the deformation of a web elements formed expandable element so that the local Ver formations remain as limited as possible. The arc areas in unexpanded State are chosen as large as possible, so that all parts of the expansion web-like elements are involved in the forming as evenly as possible.

The stent shown here consists of titanium, tantalum or another biocom patible metal or a corresponding metal alloy as a material, from which good physical tolerance and excellent ductility results. A micro-coating of amorphous silicon carbide acts as a thrombus opposite.

The embodiment of the invention is not limited to the above  specified preferred embodiments. Rather is a number of Variants cheap, which of the solution shown also in principle makes use of different types.

Claims (13)

1. stent ( 1 ), in particular coronary stent, consisting of at least one thin-walled, tubular element of which the circumferential surface is of a perforated, network-like design and has recesses ( 3 ) which form individual segments ( 2 ) through web-like elements ( 4 ) are limited in width, the web-like elements being formed from the remaining material of the tube wall, from which the material in the area of the recesses has been removed, the web-like elements being shaped such that the deformation, which is a web-like element between connecting areas ( 5 ) with other web-like elements is subjected to the expansion as a whole, is essentially minimized, characterized in that the connecting areas as crossing areas ( 5 , 6 ) and the web-like elements as arms of a cross ( 5.1 , 5.2 , 5.3 , 5.4 ) are arched out forms. 2. Stent according to claim 1, characterized in that which is a quarter of a web-like Eliminating bending deformation, which is a web-like Element in the expansion within the hollow cylindrical Tube shape is subjected and which results from the In tegral of the local angular changes in the expansion on, is not greater than a third of the total bend deformation that this web-like element is subjected to is. 3. Stent according to claim 2, characterized in that to a length of a fifth of a web-like Eliminating bending deformation is not greater than a quarter of the total bending deformation that this is subject is subject.   4. Stent according to one of the preceding claims, since characterized in that the intersection areas under Avoid abrupt changes in the web width are trained. 5. Stent according to claim 4, characterized in that the edges of the web-like elements ( 4 ) have fillets in a crossing area. 6. Stent according to one of the preceding claims, characterized in that the web-like elements ( 4 ) are substantially S-shaped. 7. Stent according to claim 6, characterized in that adjacent web-like elements ( 4 ) are shaped mirror-symmetrically in the tangential direction. 8. Stent according to one of the preceding claims, characterized in that a plurality of segments ( 2 ) arranged in rows in the axial direction are provided, which are each connected to one another by a connecting region ( 6 , 6 '). 9. Stent according to claim 8, characterized in that the position of the connecting region ( 6 , 6 ') between the axially aligned segments ( 2 ) changes from segment to segment in the tangential direction. 10. Stent according to one of the preceding claims, characterized in that the sections ( 7 ) of the recesses ( 3 ) located at the free ends of the segments ( 2 ) are arcuate. 11. Stent according to one of the preceding claims, since characterized in that it is made of titanium, tantalum or a  other biocompatible metal or a corresponding one There is a metal alloy. 12. Stent according to claim 10, characterized in that a coating of amorphous silicon carbide is provided is. 13. Method for producing a stent according to a of the preceding claims, characterized in that the shape of the stent in the unexpanded state from the Form of the stent in the expanded state in the way he is averaged that the expanded starting form represents or created in a simulation model concluding on the diameter of the unexpanded Stents is compressed, the shape of which is that in that the new stent to be manufactured in unexpanded Condition is manufactured.