DE102007015994A1 - Stent, has segments formed by meander-shaped rod with opposite meander sheets from flexible material in contracted starting position, where fine structure of rods overlaid basic structure in form of compensation loop formed into sheets - Google Patents

Abstract

The stent has a base body that radially expands from a contracted initial position into an expanded supporting position, and a set of carrier segments (1) are circulated in a circumferential direction and arranged to each other in an axial direction. The segments are formed by a meander-shaped rod (2) with alternating opposite meander sheets (3) from a flexible material in the contracted starting position. A fine structure of the rod overlaid the basic structure in the form of a compensation loop formed into the Meander sheets. The material includes polymers.

Description

The The invention relates to a stent, in particular of a material with a low elongation at break, with the in the preamble of claim 1 specified characteristics.

Such a stent is in the WO 2004/103215 A1 described in detail, in particular with regard to the basic areas of application of such stents and their particular problem when using materials with a low elongation at break, such as magnesium alloys. Such alloys are - as in the DE 197 31 021 A1 and DE 199 45 049 A1 described - biodegradable and dissolve gradually, at least in large parts after their implantation.

such However, materials have at least partly the disadvantage that they - as mentioned - a low elongation at break of, for example, 30% or less, which means all the common ones Stent designs are excluded. This is what medical steel shows the material designation 316 L has an elongation at break of 40 to 50%, determined on a tubular tensile specimen with the parameters Diameter = 1.6 mm, wall thickness = 0.1 mm, sample length = 60 mm and measuring length = 22 mm. A typical biodegradable In contrast, magnesium alloy has an elongation at break of 14%, determined on a tubular tensile specimen with the parameters Diameter = 1.6 mm, wall thickness = 0.2 mm, sample length = 50 mm and measuring length = 30 mm.

At the above WO 2004/103215 A1 removable embodiment, the stent by a cylindrical shape circumscribing realized from a contracted initial position in a dilated support position radially expandable body, on the one hand comprises a plurality of circumferentially encircling, juxtaposed in the axial direction supporting segments, each meandering through a contracted in its starting position in coarse structure Strut with alternating counter-rotating meandering bends of flexible material are formed. On the other hand, the base body has axial connectors extending in an axially parallel direction, which connect the support segments between zenith points of at least part of the meandering arcs.

at The previously known design solution should be more critical Struts areas in terms of the elongation at break of the material thereby can be improved, that in the turning areas of the wavy coarse structure each straight, aligned in the circumferential direction bending sections are provided. These are still supported by the wave structure attached stopper elements that the bend limited in the area of the straight bending sections. In particular by These stoppers make the stent design very delicate and so on consuming in its production.

in principle For the functionality of such stents and the fatigue behavior to be observed in the implanted state. Usually will the fatigue behavior with the help of the so-called Goodman diagram represented and estimated. The representation takes place in a so-called fatigue diagram according to Haigh, which the voltage amplitude over the medium voltage in one applies considered material. In this diagram will be drawn the so-called conservative Goodman line. Lie the points of the Haigh representation in the inscribed triangle is to assume a fatigue strength. In a stent design of degradable material may be due to progressive degradation, despite fulfilling the fatigue criterion, only from Durability be spoken. An improvement in fatigue strength allows for a degradable implant optimized Expect time stability.

Appropriate Analyzes with the stent design according to the aforementioned WO publication disclose that an improvement of the Durability and the time stability behavior desirable is.

Next the fatigue strength or the fatigue strength are also the so-called "Recoil" behavior and the collapse pressure of a stent after its dilation for the practicality relevant parameters.

From that Based on the invention, the object is based basically to further develop a well-known stent design through fine structuring that fatigue behavior, collapse pressure and recoil behavior at a reduced bending stress of the Dilating plastically deforming struts can be improved.

These Task is indicated by the in the characterizing part of claim 1 Fine structure of the struts in the form of in the meandering arches molded compensating loops solved.

The Meander form of the struts should in the broadest sense so be understood that the struts of the support segments in their direction of rotation around the longitudinal axis of the stent a suitable reciprocating Course to "perimeter length" for to provide the dilation of the stent. At these meandering bows can - depending on the stent design - more be formed arcuate structures, so for example by these arches are formed expandable cells.

Further it should be noted that under the indication that the support segments to rotate essentially in the circumferential direction, also helical circumferential support segments are to be understood as these are in the circumferential direction have at least one extension component.

According to one preferred embodiment have these compensation loops an approximately C to double S-shaped curve in the shell plane of the stent. By this shaping, the tasks set according to Achieve goals particularly well.

A flanking measure, in particular with the compensation loops Together, a significant improvement in the expansion behavior and the creep strength involves, are in accordance with a preferred embodiment, provided starting sheets, with which the ends of the axial connectors, each inside at the zenith points of the meandering bows, attached to it. Through these curved lugs the voltage profile within the struts is further equalized and the deformability over the length The maximum utilization of the individual strut sections. This will do that Risk of stress concentrations, especially in the area of Connection of the axial connector to the running in the circumferential direction Aspiration reduced.

According to one preferred embodiment of the lug bows can These are designed so that they will bend during the bending of the stent during the dilation process with its foot points meet. Thus, these form virtually a fulcrum for the bending struts and call thereby a supporting effect out.

Provided the lugs in the over-dilated state a Distance between their feet can they according to another preferred embodiment be designed so that they are elastic at radial pressure in the circumferential direction give in until they meet again with their feet. Such a designed stent then has a two-phase collapse behavior. First, by giving in the lug bows, for example responds gently to vascular passages by giving a soft Collapse from a diameter of 8 mm to 7 mm is allowed. As soon as the footsteps of the lugs meet and thus support each other, becomes a high resistance over the actual struts caused, so a minimum cross-section of the stent and the vessel thus secured is ensured up to a high collapse pressure.

• – Die Dilatationsfähigkeit wird optimiert, das heißt, dass beispielsweise ein Stent mit einem Durchmesser von 2 mm in seiner kontrahierten Ausgangsstellung auf einen Durchmesser von 7 mm anstelle nur 6 mm in seiner dilatierten Stützstellung expandiert werden kann.
• – Das Recoil-Verhalten wird durch einen erhöhten Anteil an sich plastisch verformender Abschnitte der Streben verbessert.
• – Das Stentdesign zeichnet sich ferner dadurch aus, dass die Streben in der dilatierten Stützstellung weitestgehend in Umfangsrichtung durchgestreckt sind, was wiederum weitere Folgeeffekte erzielt:
• – Die Schwingungsamplitude im Hinblick auf die Goodman-Analyse wird reduziert, wodurch die Zeitstandfestigkeit als verbessert nachgewiesen werden kann.
• – Durch die weitestgehende Durchstreckung der Streben in Umfangsrichtung erhöht sich das Stützvermögen des Stents, was zu einer Verbesserung des Kollapsdruckes führt.
• – Die Durchstreckung der Streben verhindert ein asymmetrisches Öffnen, das durch einen niedrigen Verfestigungsmodul in Verbindung mit ungleich breiten/dicken Streben aufgrund der Herstelltoleranzen bedingt wäre.

Due to the inventive design of the stent is in summary ensures that an optimally large proportion of the struts are involved in the deformation. This accommodates the reduced deformability of low elongation materials such as a magnesium alloy. In detail, the following advantageous effects can be achieved:

• - The dilatation ability is optimized, that is, for example, a stent with a diameter of 2 mm in its contracted initial position can be expanded to a diameter of 7 mm instead of only 6 mm in its dilated support position.
• - The Recoil behavior is improved by an increased proportion of plastically deforming sections of the struts.
• - The stent design is further characterized by the fact that the struts in the dilated support position are largely stretched out in the circumferential direction, which in turn achieves further consequences:
• - The oscillation amplitude with respect to the Goodman analysis is reduced, whereby the creep rupture strength can be proved to be improved.
• - By extending the struts in the circumferential direction as far as possible, the support capacity of the stent increases, which leads to an improvement of the collapse pressure.
• - The stretches of the struts prevents asymmetric opening, which would be due to a low solidification module in conjunction with unequal width / thick struts due to the manufacturing tolerances.

The compensating loops provided according to the invention allow a complete stretching of the strut sections by providing the necessary flexibility of the stent structure for the necessary overdilation of the stent. These compensation loops take over the way accordingly the overdilation, which is relatively low. Thus, due to the dilation by the struts an increase in diameter z. B. reached from 2 to 7 mm. The Überdilatation through the compensation loops is then carried out in a diameter range of z. B. 7 mm to 8 mm, so that the compensation loops can be designed to be relatively stiff compared to the strut sections.

Further Features, advantages and details of the invention are the following Description removable, in an embodiment explained in more detail with reference to the accompanying drawings becomes. Show it:

1 2 a schematic view of a stent basic body according to a first embodiment in an unwound configuration in a contracted initial position,

2 an enlarged section of the settlement according to 1 .

3 a corresponding section in dilated support position of the stent,

4 a section analog 3 in the over-sterilized stent position,

5 an enlarged section of the settlement according to 1 in the area of a lug during dilatation,

6 a section analog 5 in the over-sterilized stent position,

7 an enlarged detail of a development of a stent basic body according to a second embodiment in a contracted starting position,

8th an enlarged section of a development of a stent basic body according to a third embodiment in a contracted starting position, as well

9 and 10 Haigh diagrams with Goodman analysis of a stent according to the invention and a stent according to the WO 2004/103215 A1 ,

The 1 and 2 make clear the structure of a stent in its contracted initial position in the form of a development representation. The stent is thereby machined out of a cylindrical metal body by laser cutting in such a way that it has a large number of supporting segments which are circumferential in the circumferential direction U and are lined up in the axial direction A 1 in each case by a contracted in the contracted starting position in its coarse structure meandering strut 2 is formed. Under coarse structure are the in 2 with meandering arcs indicated by solid and dashed lines 3 to understand that have alternately opposite directions of curvature.

In parallel to the axial direction A direction are the support segments 1 by axial connector 4 interconnected, each between the zenith points 5 respectively to be connected Mäanderbögen 3 run. Due to the offset of the adjacent support segments 1 in the circumferential direction U extend the axial connector 4 always from the outside 8th of a meander arch 3 to the inside 10 of the meander arch 3 the adjacent strut 2 ,

How out 1 and particularly 2 becomes clear, is the indicated meander-shaped coarse structure of the strut 2 superimposed on a fine structure, on the one hand from approximately omega or double S-shaped compensation loops 6 in the area between two opposing meandering arcs 3 consists. On the other hand, the axial connectors 4 , the inside at the respective zenith point 5 of a meander arch 3 start, not directly, but over a contrary to Mäanderbogen 3 curved neck bow 7 tethered.

The compensation loops 6 are each in the meandering bows 3 the respective strut 2 molded on the outside 8th the zenith points 5 the attached axial connector 4 exhibit. The compensation loops 6 have directions facing away from each other and are relative to the center plane M of the respective strut 2 arranged off-center.

The bows 7 have the same function as the compensation loops 6 and are each configured substantially omega-shaped, so that the axial connector 4 each outside at the zenith points 9 the signatures 7 are connected. This opens all axial connectors 4 no matter if they are regarding the coarse structure on the outside 8th or inside 10 of a meander arch 3 are scheduled in a stre benbereich, with respect to the respective axial connector 4 then convexly curved.

Like from the 3 and 4 indicates the fine structure of the support segments 1 with the compensation loops 6 and the signatures 7 an optimization of the stent design with respect to the dilatation behavior 3 a stent is shown in partial detail in its nominally dilated configuration. The respective sections are the struts 2 in the meandering arches 3 set up in the circumferential direction U. The between the compensation loops 6 or the signatures 7 lying strut sections 11 ( 3 ) take over the dilation path from the contracted to the nominally dilated configuration according to 3 , The strut sections 11 are set up at an angle C to the axial direction A, compared to the conventional stent design, as for example in the aforementioned WO 2004/103215 A1 is significantly larger. This in turn brings a significant increase in the collapse pressure of the stent with it.

As if from a comparison between 3 and 4 shows, take over the compensation loops 6 and bills 7 the Überdilatationsweg, by the path difference between the in 3 and 4 indicated base lengths L1 and L2 of the compensation loops 6 and bills 7 is represented.

There are the curved lugs 7 a design element that reduces the risk of stress concentrations, as with an acute-angled transition between axial connectors 4 and meander arch 3 would be present, which is the case with the stent according to the cited prior art. The bows 7 ensure as even a voltage as possible and maximum utilization of the deformability of the struts 2 ,

How out 5 becomes clear, the lugs can 7 be designed so that when dilating the stent, so when bending (arrow 12 ) of the struts 2 in a position substantially parallel to the circumferential direction U, act as fulcrums and can develop an additional support effect. This will be the starting sheets 7 so compressed that their feet 13 strike each other and support each other.

Another possible function of the signatures 7 is in 6 shown. There the over-dilated state of the stent is shown, at which the foot points 13 have a clear distance from each other. When applying a radial pressure on the stent, which is implemented in accordance with the circumferential direction U, give the lugs 7 in opposite directions 14 . 15 elastic until they meet again. In this state, they then rely on each other, whereby - if this deformation is carried out in the elastic region of the stent material - a springback is possible. After the meeting of the bases 13 finds another collapse only by a deformation of the extended struts 2 instead of.

Overall, such a stent has a two-phase collapse behavior. As long as the foot points 7 not yet close to each other, the stent yields relatively soft. With further pressure increase, the base points are supported 7 each other and a high resistance is generated over the entire structure of the stent, so that a minimum cross-section of the supported vessel is ensured up to a high collapse pressure.

To clarify the properties of a stent according to the invention, the corresponding parameters of the stent according to the invention and of a stent having the design according to FIG WO 2004/103215 A1 opposite posed. parameter Inventive stent Stent according to WO 2004/103215 A1 Outer diameter (contracted) 2.35 mm 2.25 mm Inside diameter (after dilation) 7 mm 6 mm development ratio 2.98 2.67 Collapse pressure (measured) 0.64 bar 0.5 bar Recoil ratio (calculated) 2.7% 5.1% Recoil ratio (measured) 3.3% 4.8% Wall thickness 0.26 mm 0.26 mm

The improved time stability is illustrated by the so-called Goodman analysis in the Haigh diagram. 5 shows such Haigh diagram of a stent according to the invention, which was dilated to 7 mm. 6 shows a corresponding diagram of a stent according to the aforementioned prior art.

Despite the larger diameter of the stent according to the invention (7 mm instead of 6 mm), the vibration amplitude of 22 MPa is significantly reduced compared with the vibration amplitude of 45 MPa of the stent according to the prior art. Furthermore, in a comparison of the two diagrams according to 5 and 6 This indicates a significant improvement in the creep rupture strength of the stent according to the invention over the prior art.

When Materials are especially metals and metal alloys, in particular from the group comprising iron, magnesium, tungsten and zinc, as well as polymers.

The in the 7 and 8th Illustrated embodiments of stents illustrate that the fine structure according to the invention can be used by formed in the Mäanderbögen compensation loops universal in a variety of stent designs. This is how the stent design works 7 support segments 1 not strictly in the circumferential direction U, but helically around the axial direction A of the stent are formed circumferentially. A component running in the circumferential direction is superimposed on a component running in the axial direction A, so that a spiral design of the stent results, which in the extreme case does not have to have any axial connection elements. At the in 7 Shown embodiment are axial connectors 4 in relatively small numbers about the struts 2 with their meandering bows 3 distributed.

Furthermore, the 7 removable, that the compensation loops 6 For example, a C-shape or an S-shape may have, as the two by the reference numerals " 6C " and " 6S "selected compensation loops 6 make clear.

As is generally to be considered in a configuration of a stent design, care should be taken to ensure that within an in 7 hatched indicated cell Z of the stent, the compensators act symmetrically, for example, by an identical number and shape of the compensation loops 6 is reached. However, if a complex stent structure makes an asymmetrical arrangement of the compensators appear sensible, this can also be achieved.

In the 8th Again, a stent design is shown in which the meandering structure of the struts with their meandering arches 3 less obvious, but still exists. The circumferential in the circumferential direction U supporting segments 1 point here to the meandering arches 3 complementary additional sheets 16 on, which in turn expandable cells are formed.

Furthermore, the 8th clearly that in a stent design with circumferential in the circumferential direction U supporting segments 1 not necessarily directly in the axial direction extending axial connectors must be present. Axial connection elements can also be "head-to-head" meandering arcs 3 be formed, so that nodes 17 form.

The compensation loops in the embodiment according to 8th are both as S-shaped compensation loops 6S into the meandering arches 3 as well as C-shaped compensation loops 6C in the additional sheets 16 formed.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - WO 2004/103215 A1 [0002, 0004, 0028, 0034, 0040, 0040]
• DE 19731021 A1 [0002]
• - DE 19945049 A1 [0002]

Claims (11)

Stent, in particular of a material with a low elongation at break, with a cylindrical shape circumscribing from a contracted initial position in a dilated support position radially expandable base comprising - a plurality substantially in the circumferential direction (U) encircling, in the axial direction (A) juxtaposed support segments ( 1 ), each in its contracted starting position in its coarse structure about meandering strut ( 2 ) with alternating counter-rotating meandering arcs ( 3 ) are formed of flexible material, characterized by - a coarse structure superimposed fine structure of the struts ( 2 ) in the form of in the Mäandbögen ( 3 ) formed compensating loops ( 6 ). Stent according to claim 1, characterized in that the compensation loops ( 6 ) have approximately C to double S-shaped course in the sheath plane of the stent. Stent according to claim 1 or 2, characterized in that the compensation loops ( 6 ) between the respective zenith points ( 5 ) of those meandering sheets ( 3 ) of the respective strut ( 2 ) are formed therein, on the outside ( 8th ) of the zenith points ( 5 ) attaching Axialverbindungselemente ( 4 ) between the support segments ( 1 ) exhibit. Stent according to one of the preceding claims, characterized in that the compensation loops ( 6 ) off-center with respect to the median plane (M) of the respective strut ( 2 ) are arranged. Stent, in particular according to one of the preceding claims, characterized in that in the fine structure of the struts ( 2 ) further strut-shaped axial connectors ( 4 ) as Axialverbindungselemente at their in nenseitig to the respective zenith point ( 5 ) of a meander arc ( 3 ) attaching ends in each case via a counter-rotating to Mäanderbogen ( 3 ) curved lobe ( 7 ) as a further compensation element at the meander arc ( 3 ) are connected. Stent according to claim 5, characterized in that the lugs ( 7 ) are each designed substantially omega-shaped, wherein the axial connector ( 4 ) on the outside at the zenith points ( 9 ) the signatures ( 7 ) are connected. Stent according to claim 5 or 6, characterized in that the lugs ( 7 ) are designed so that they at least temporarily with their feet ( 13 ) come in contact for mutual support. Stent according to one of claims 5-7, characterized in that the lugs ( 7 ) are designed such that in the over-sterilized state of the stent at radial pressure, a preferably elastic yielding of the lugs ( 7 ) takes place until their feet come into contact for mutual support. Stent according to one of the preceding claims 1-8, characterized in that the material with a low elongation at break pure metals, metal alloys and polymers includes. Stent according to claim 9, characterized in that the pure metals from the group comprising iron, magnesium, tungsten and zinc are selectable. Stent according to claim 9, characterized in that the metal alloys comprising a major component of the group Iron, magnesium, tungsten and zinc.