WO2001091669A2 - Stent - Google Patents

Abstract

The invention relates to a stent which can be expanded and transformed from a first state, wherein the inner diameter is narrow, into a second state wherein said diameter is larger and areas devoid of material border on other material elements, in order to define therewith a general stent surface from which elements with material protrude in sections in an expanded state. According to the invention, a first series of sections are provided in order to protrude from the covering surface of the stent in an implanted state in the direction of flow.A second series of sections are also provided in order to protrude from the covering surface of the stent in the direction of a counterflow in an implanted state.

Description

 STENT

description

The present invention relates to a stent.

Stents are implants that are implanted in hollow organs, such as ureters, biliary tract, but above all blood vessels, if these are no longer sufficiently stable due to pathological changes or if they are sufficiently permeable to the required fluid flow, for example blood flow, due to deposits such as calcifications and are therefore dilated Need to become.

Good stents have to meet a number of conflicting requirements.

An implanted stent should be able to follow natural body movements well, which requires a sufficiently high degree of flexibility. It must support the vessel against the external forces, ie it must be sufficiently stable in the radial direction his. It should not move away from the intended location during or after implantation, which is also referred to as "laying", and it should be easy to lay. This implies that it is axially shortened as little as possible during radial expansion it is important to be able to determine its exact position in the hollow vessel well.

In order to place the stent, it is typically pushed with a balloon catheter in a contracted state to the intended location and expanded there. The expansion takes place in that the balloon catheter is inflated to a radial dimension sufficient for the stent expansion at the pathologically changed location. Alternatively, self-expanding stents can be used which are produced from a material with shape memory, for example a so-called memory metal such as Nitinol.

It is known to start from a metal tube for the production of expandable stents, in the edge of which slots are cut with a laser according to predetermined patterns. These slots are arranged relative to one another in such a way that radial enlargement of the stent, that is to say expansion, is possible.

A number of different stent configurations have been proposed to meet some of the objectives discussed above. Attention is drawn in particular to EP 0 800 800 BI, WO-A-95/26695, EP-A-0 709 067, EP-A-0 647 438, EP 0 709 068, EP 0 679 372 and EP 0 541 443.

An expandable stent for implantation in a body lumen such as an artery is known from US Pat. No. 5,514,154. The stent consists of a large number of radially expandable, cylindrical elements, which are arranged on a common axis. mine aligned and connected by one or more connecting elements. The individual, radially expandable cylindrical elements are made of band-like material, which is arranged in a wavy pattern. Portions of the expanded stent engage the outside of the vessel wall to secure the stent to the vessel. It is stated that the connecting, elongated elements, which the expandable cylindrical elements should have a cross-section that is similar to the transverse dimensions of the wave-like components of the expandable stent. It is suggested that all connecting elements of a stent should attach to either the peaks or valleys of the undulating structure of the cylindrical elements. It is mentioned that otherwise a stent shortening can be expected during its expansion.

The aim of the present invention is to provide a novel stent for commercial use. , The aim of this invention is achieved with a stent according to independent claim 1. Preferred embodiments can be found in the subclaims.

It is therefore first proposed a stent, ^'a first state with low internal diameter to a second state which is made expandable, in which the internal width is enlarged and material-free areas together with Mate rial webs define a- general stent sheath surface, via which Material webs protrude in sections in the expanded state, it being provided that a first group of sections is intended to protrude over the stent jacket surface in the direction of flow in the implanted state and a second group of sections is provided in the implant protruded state in the counterflow direction over the stent jacket surface.

A first essential aspect of the invention is thus seen in the fact that a stent jacket surface is provided, over which sections of material webs protrude in opposite directions. This ensures good vascular stabilization through the general stent jacket surface and fixation in the axial vascular direction due to the protruding sections. In this way it is possible to optimally place radially fixed and axially stable expanding stents. It was recognized that the axial stability during positioning increases if fixation takes place via material webs projecting in opposite directions, without a shortening Positioning endangered.

The material webs, which protrude over the general stent jacket surface during expansion, can be grouped in the axial direction, for example in the stent generally circular circumferential groups. The connection between such groups is preferably established via material webs which have a substantially larger cross-section, in particular a larger, preferably approximately twice the width, as the material webs ^' within the group which encircles the stent cylindrically. The material webs can bifurcate at the axial height of the groups encircling the stent, one partial fork being guided to the next group in the axial direction and the other partial fork leading to a material section in the axial group which, in the case of stent expansion, takes place via the general stent man- telflache protrudes. The continuous structure through the bifurcation contributes to a slight stent shortening, typically only in the percentage range. By both the bottom and the top of the circumference of the stent Group of material webs are forked and preferably a partial fork coming from below is connected to a partial fork coming from above, with a particularly small expansion reduction and high radial stability, an alternating change in the flow and counterflow direction via the general one Stent jacket flat protruding areas achieved, which improves the anchorage, especially if the material sections that lead into the groups surrounding the stent are connected via rounded, widened tips. It is advantageous here that a large number of compounds are present.

In a preferred stent, groups of both orientations are thus provided in this way, preferably alternately side by side. A high radial compressive strength is achieved if the sections for one direction are arranged on a generally axially extending line, while the sections alternate radially for the opposite directions.

The alternating change in the radial direction leads to a general zigzag pattern of the sections over the expanded stent, with these repeating in the axial direction. The zigzag areas encircling the stent circumference are preferably connected by sections inclined to the axial direction, which further increases the stability and at the same time ensures good flexibility.

The stent of the present invention will be typically formed integrally ^■, in particular of metal, although it may be as known in the art per se, cut from a one-piece metal tube; cutting can be done with lasers or other suitable, high-precision controllable cutting tools respectively. Cutting in the sense of the invention is understood to mean any suitable method for producing the structures according to the invention. The stent can be made of stainless steel or a nickel-titanium, in particular nitinol, or another memory alloy. In all cases it is preferred to electroplate or otherwise refine the surface in order to ensure a sufficiently smooth and body-compatible surface.

In preferred stents, the stent jacket surface will be generally cylindrical, wherein the stent can have a radial protuberance at one or both axial ends.

The sections can each be formed by two interconnected legs or parts thereof, the two legs preferably being arranged at least approximately and essentially parallel to one another in a non-expanded or only slightly expanded state and being able to be spread out like scissors by the expansion , so that they assume an acute angle to one another when the stent is expanded. In the preferred embodiment, the legs are connected to one another by an enlarged tip, which is preferably rounded on the side facing away from the legs. The arrangement with two legs, which are generally parallel to one another in the unexpanded state and spread apart in the expanded state, leads to the bending of the rounded tip beyond the stent jacket surface due to the mechanical stresses during the expansion, similar to a divining rod. In this case, the tips preferably lead to the material webs connecting circumferential groups to the bifurcations described above. It is particularly preferred if the stent has less than 5%, preferably less than 2% contraction upon expansion. This ensures that the sections serving as general barbs do not move along the vessel wall in a hurtful manner during expansion.

The invention is described below only by way of example with reference to the drawing. In this shows:

Fig.l is a photograph of the expanded stent striped over a non-transparent cylinder according to the present invention; Fig. 2 is a schematic 'enlargement of the photo of Fig. 1. Fig. 3 shows the developed pattern of a stent according to the present invention.

According to FIG. 1, a stent 1, generally designated 1, in its expanded state with a clear width that is larger than that in the non-expanded state, comprises an approximately cylindrical stent jacket surface 2, which is defined in its overall course by the material-free regions 3 and the material webs 4 surrounding them ,

The material webs now have sections 5 which project beyond the stent jacket surface 2. This can be seen particularly well for those sections 5 which are viewed approximately from the side and which are therefore on the edge when viewed from above. It will be appreciated that with the uniform geometry, the slots 5b pointing in the other direction will also protrude.

The stent 1 is cut from the memory alloy Nitinol, starting with a one-piece metal tube continuous wall. The developed wall pattern is shown in Fig. 3.

FIG. 3 shows that the sections 5a and 5b, which protrude beyond the stent jacket surface during expansion, are formed by parallel legs 6a, 6b in the unexpanded state, which are formed by an arc 7 which is wider than the width of the Legs 6a, 6b are connected. The tips pointing radially alternately in the direction of flow and counterflow when the stent is placed form meandering sections around the circumference. These meandering sections are axially connected to one another by the connecting webs 4, the connecting webs 4 being at an alternating angle to the stent axis and bifurcating on the meandering sections as shown, a first partial fork leading into the peripheral group and forming a leg 6a, 6b and the other partial fork is axially continued by the circumferential group.

The stent is manufactured and used as follows:

First, a suitably dimensioned output tube of memory metal in accordance with the unwound ^'shown pattern of FIG. Cut. 3 The expanded metal stent is then impressed into the memory metal in a known manner and the stent is then cooled so that it contracts to the small tube diameter, is placed on a catheter in the cold state and is pushed to the pathological vascular site with a suitable setting device. There the stent is released from the setting device, heated and expanded, whereupon its stent jacket surface lies against the vessel wall. When expanding, the legs 6a, 6b are pulled apart at an acute angle, whereupon the rounded tips zen 7 can be opened over the stent jacket surface. The radial expansion takes place with minimal contraction. The protruding sections 5a, 5b and thus in particular the rounded tips 7 can get caught on the intima of the vascular wall intima without injuring them. The sections in the flow direction and counter-flow direction that protrude after expansion ensure that movement is possible both in the flow direction and in the counter-flow direction. The expanded stent is therefore firmly seated in the vessel, even before it has grown in.

With both materials, the stent of the present invention is able to absorb high radial forces, is secure against wandering and, to facilitate storage, can be twisted in itself.

While it has been described above that a memory alloy is used as the stent material, other variants are possible.

Claims

claims 1. Stent, which is expandable from a first state with a small internal width to a second state, in which the internal width is increased and material-free areas together with material webs define a general stent jacket surface, over which material webs project in sections in the expanded state characterized in that a first group of sections is intended to protrude in the implanted state in the flow direction over the stent jacket surface and a second group of sections is provided in the implanted state to protrude in the counterflow direction over the stent jacket surface. 2. Stent according to claim 1, characterized in that sections of both groups are arranged alternately in the radial direction. 3. Stent according to one of the preceding claims, characterized in that a plurality of sections of a group is arranged on the stent on a generally straight line in the axial direction. 4. Stent according to one of the preceding claims, characterized in that the sections are generally separated from one another via flat webs. 5. Stent according to the preceding claim, characterized in that it is formed in one piece. 6. Stent according to one of the preceding claims, characterized in that it is cut from a metal piece, in particular a metal tube. 7. Stent according to the preceding claim, characterized in that. that it is made from a memory alloy, stainless steel and / or a titanium alloy, in particular nitinol. 8. Stent according to one of the preceding claims, characterized in that the stent jacket surface is generally cylindrical. 9. Stent according to one of the preceding claims, characterized in that it has a radial bulge at its axial ends. 10. Stent after one. of the preceding claims, characterized in that the protruding portions are spaced from the tipped ends. 11. Stent according to one of the preceding claims, characterized in that the sections are each formed by two interconnected legs. 12. Stent according to the preceding claim, characterized in that the two legs ^{' are} at least substantially parallel to one another in an unexpanded or slightly expanded state. 13. Stent according to the preceding claim, characterized in that the legs are arranged at an acute angle to each other in the expanded state. 14. Stent according to one of claims 11 to 13, characterized in that the legs are connected to one another by a, in particular widened, tip. 15. Stent according to the preceding claim, characterized in that the tip is rounded outwards.