Stent

Details Stent Stent

1998-05-22

2001-03-06

Milano, Michael J. (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Arterial prosthesis

Stent structure

C623S001100

Reexamination Certificate

active

06197047

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a stent, particularly a coronary stent, as an intraluminal expansion element, and a method of manufacturing the stent.
An expandable intraluminal element with at least one thin-walled, tubular part (hereinafter referred to as a stent) is known from European patent specifications EP 0 364 787 B1 and
EP 335 341 B1. The surface of the stent is made of net-like open work and contains apertures, which are bounded by strap-like elements of low material thickness extending in straight lines in the longitudinal axial and circumferential directions. The strap-like elements, which can expand in the circumferential direction of the stent, comprise the remains of the tubular wall from which the material in the area of the apertures has been removed.
Another tubular stent, also of net-like structure, is known from international patent application WO 96 03 092 A1. The stent is made up of straps in a meander-shaped arrangement, extending partly in the circumferential and partly in the longitudinal axial direction of the stent. The surface of the stent is similarly made of open-work and has apertures between the straps, in the area of which the material has been removed from the tubular wall.
Stents of this type are expanded during an operation, with outwardly directed forces exerted by a tubular dilator to which high-pressure gas is applied. The stent retains its tubular shape in spite of the deformation, and expands the vessel narrowed by deposits.
For safety reasons deformation of the straps is kept far below a possible danger level, as breakage of a strap would cause its free ends in the region of the breakage to project into the interior of the vessel fitted with the stent. The accompanying risk of the formation of restenosis would not only put the success of the actual operation into question but also endanger the life of the patient.
Thin net structures of the known stent are very susceptible to mechanical damage by exertion of a force, during the period from manufacture to use, and this damage may make them useless of even dangerous. Such damage may not be detected in the non-expanded state and could lead to the final breakage of one or more straps only when the stent is expanded, with the detrimental effects described above.
Known stents also have the drawback that production of their net-like structure is very time-consuming and requires a large outlay on removal of the material cut out of the surface to create the apertures.
SUMMARY OF THE INVENTION
In view of the defects of the state of the art, the invention is based on the problem of providing an expandable stent of the above-mentioned type which is simple to produce and has good stability even in the non-expanded condition, and providing a method of manufacturing the stent.
The problem is solved by a stent with the features of.
The invention includes the technical teaching that, in a stent of the above type, both production costs and susceptibility to damage can be greatly reduced if the surface of the initial tubular body in the non-expanded condition of the stent is substantially free of apertures and is divided into expandable elements which are linked by narrow partition lines.
This teaching has the advantage of considerably reducing the cutting cost because fewer and shorter cuts have to be made in the surface in order to form the dividing partition lines. Secondly far less material has to be taken out in manufacture, thereby reducing both the expenditure on removing the material and the amount of waste to be disposed of.
A further advantage is that the stent surface, which is substantially free of apertures in the non-expanded condition, is far less susceptible to mechanical damage than the previous net-like stents, as forces are directed into the stent structure over a wide area and not concentrated on thin individual components of a net-like structure. Damage to the stent through mechanical strains in production, storage, transportation or even before and during the operation is therefore far more improbable.
Another advantage of the stent according to the invention is that in the expanded condition it covers a considerably larger part of the wall of the vessel than known stents of net-like structure do. The area of the vessel wall which is available for fresh deposits is thereby appreciably reduced, so that the risk of restenosis forming is further diminished.
The feature of the invention that the surface is substantially free of apertures should be understood as meaning that a substantial proportion of the surface has a closed surface, divided only by partition lines. Quite small openings may however be provided, e.g., inside the individual expandable elements, if the total area of the small openings is not significant relative to the surface.
In a preferred embodiment of a stent according to the invention the partition lines are of a width substantially corresponding to that of a clean incision when the surface is severed by means of a cutting beam, e.g. a cutting jet of water preferably a laser beam. Narrow partition lines give the non-expanded stent particularly high stability.
The partition lines are therefore preferably of a width substantially corresponding to the minimum obtainable width of a clean incision when the surface is severed by means of a cutting beam, particularly a laser beam. This not only gives the stent high stability, due to the narrow width of the partition lines, but the production time for the stent may also be shortened, as the width of a clean incision is directly related to the speed at which the cutting beam advances. The minimal partition line width is obtained precisely at the maximum advancing speed of the cutting beam and at which a clean incision is still produced in the severing of the surface by means of the beam.
In another preferred embodiment of the stent according to the invention, the joining straps are inclined to both the longitudinal and the circumferential directions of the stent and are laterally defined substantially over their whole length, between adjacent expandable elements, by the respective partition line defining the external contour of the respective expandable element in that region. The effect of this arrangement, obtained in a simple manner, is that no gaps, i.e. apertures, are formed between the longitudinal sides of the individual expandable elements, and a second effect is that a single partition line defines both part of the contour of the expandable element and half the external contour of the link strap to the adjoining expandable element, so that manufacturing costs are reduced.
An advantage of the stent according to the invention the external contour of the expandable elements is symmetrical with their longitudinal axis. Each element may have a flat first section extending in both the longitudinal and the circumferential direction, and a second section extending at least substantially in the circumferential direction, which sections are linked by an intermediate section extending substantially in the longitudinal direction. This formation of the expandable elements allows a particularly space-saving, tightly packed arrangement thereof, with reduced gaps between them. Thus the expandable elements may, e.g., be structured and arranged so that the second section of an element projects into the constriction formed by the intermediate section, between the first and second sections of the adjacent element, thereby minimizing space between the two elements. This further reduces any possible openings in the surface.
The individual sections, particularly the first and second ones, are preferably produced from regular shapes such as circles, ellipses, rectangles, squares, polygons or formations combining or approximating to these.
In a particularly beneficial embodiment of a stent according to the invention, pairs of expandable elements adjoining each other in the circumferential direction of the stent are turned through 180° from each other. The first section of one element goes into the gap between the firs

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