MXPA96003208A - Endoprotesis that has varied amounts of structural resistance on its longi - Google Patents

Abstract

The present invention relates to an intravascular stent for implantation in a body lumen, characterized in that it comprises: a single-walled tubular body of a biocompatible material having a first end section, a second end section and a central section, being each of the sections defined by the thickness of the material forming the wall of the tubular body, the tubular body further has an open network structure formed of a single piece of metallic alloy and is adapted for radial expansion from a first diameter compressed to a second enlarged diameter, and the thickness of the wall of the first end section is greater than the wall thickness of the central section and the thickness of the wall of the second end section, such that when the stent is expanded to the second enlarged diameter, the first end section is radially stronger and stronger to crush than the section central or the second section of the extre

Description

E DOPROTESIS THAT HAS VARIOUS AMOUNTS OF STRUCTURAL RESISTANCE ON ITS LENGTH BACKGROUND OF THE INVENTION Field of the Invention This invention relates to expandable stent devices, generally referred to as stents, that are adapted to be implanted in a patient's body lumen, such as in a blood vessel or coronary artery, to maintain its opening . These devices are useful in the treatment of atherosclerotic stenosis in blood vessels. Stents in general are tubular shaped devices, which function to keep a segment of a blood vessel or other anatomical lumen open. Stents are particularly convenient for use in supporting and maintaining back a dissected arterial lining, which can occlude the fluid passage and keep a coronary artery open after an angioplasty procedure. Further details of stents of the prior art can be found in U.S. Pat. No. 3,868,956 (Alfidi et al.); the U.S. Patent No. 4,512,338 (Balko et al.); the U.S. Patent No. 4,553,545 (Maas et al.); the U.S. Patent No. 4,733,665 (Palmaz et al.); the U.S. Patent No. 4,762,128 (Rosenbluth), - U.S. Pat. No. 4,800,882 (Gianturco); the U.S. Patent No. 4,856,516 (Hillstead); and the U.S. Patent. No. 4,886,062 (iktor), which are hereby incorporated by reference in their entirety. Various means for supplying and implanting stents have been described. A frequently described method for delivering a stent in a desired intraluminal location includes mounting the expandable stent into an expandable member, such as a balloon, which is provided at the distal end of an intravascular catheter, advancing the catheter to the desired site within the lumen. patient's body, inflate the balloon to expand the stent to a permanent expanded condition and then deflate the balloon and remove the catheter. Prior art stent designs provide a stent that is comprised of wire mesh or fabric having an open network structure or patterns. The open network structure of prior art stents in general provides uniform resistance over the center of the stent, but may be weak at the ends. This configuration may cause prior art stents to be weaker at the ends of the stent because each portion at the ends only has a neighbor support portion. This inherent weakness at the ends of prior art stents may result in the ends decreasing in diameter after implantation in a body lumen.

Therefore it may be important to improve existing stent designs, to provide stronger ends while allowing centers to maintain the radial stiffness required to keep a body lumen open, while at the same time maintaining the longitudinal flexibility of the stent to facilitate its supply to the blood vessel. The present invention satisfies these needs. SUMMARY OF THE INVENTION The present invention is directed to an expandable stent, which is constructed to vary its structural strength over the length of the stent. This variation in structural strength over the length of the stent is achieved in any of several ways, by including adjusting the wall thickness, by varying the geometry of the mesh pattern or open network, or by choosing the particular tempering of the material used. The strength of the stent can be designed to vary substantially or more gradually over the length of the stent. There may be configurations where it is advantageous to reinforce only one end of the endoprosis. This stent will be useful for implantation in a blood vessel where the end of the stent expands to a greater diameter than the other end. This modality will also allow placing the stent in ostial lesions, where higher resistance is required at the ostial interface.

The endoprosthesis of the present invention preferably includes an elongated tubular body having a first end section, a second section and a central section therebetween. The elongated tubular body will have an open network structure or tissue that is adapted for radial expansion from a first compressed diameter to a second expanded diameter, which approximates the inner diameter of the body lumen, where the stent is to be implanted. In one embodiment of the invention, the first end section has an open network structure thicker than the central section or the second end section, such that when the stent is expanded from its first compressed diameter to the enlarged second diameter, The thicker open net structure in the first end section will be stronger and more resistant to crushing forces against backward movement of the body lumen. The central section and the second end section will generally have a uniform structural thickness that is less than the thicker open network structure of the first end section. In other embodiments both the first end section and the second end section may have an open network structure thicker than the center section, such that the center section remains more flexible while the end sections are stronger and more resistant to radial crushing forces imposed by recoil of the body lumen.

In another embodiment of the invention, the first end section has an arcuate section with an open network structure thicker than the central section or the second end section, such that when the stent is expanded from its first compressed diameter to second enlarged diameter, the arched section with the thicker open net structure of the first end section will be stronger and more resistant to the crushing force against recoil of the body lumen. An arched section of the stent is defined as a portion of the circumference of the stent when viewed from one end. Another way to define an arcuate section is to say that it is an arc of the outer surface of the stent when viewed from one end. In this embodiment, the remainder of the first end section, the middle section and the second end section, will generally have a uniform structural thickness, which is smaller than the arched section of the thicker open network structure of the first section of end. In other embodiments, the entire stent network structure may have a thicker arched section of the open network structure than the remaining sections, such that the remaining sections remain more flexible, while the thicker arched sections in the structure Open network of stents are stronger and more resistant to lateral crush forces.

In one embodiment, the endoprosthesis of the invention generally includes a plurality of radially expanding cylindrical elements, which are relatively independent since each has the ability to expand and rub against the others. The individual radially expanding cylindrical elements of the stent are dimensioned so as to be longitudinally shorter than their own diameters. Columns or interconnecting elements extend between adjacent cylindrical elements, provide increased stability and are preferably placed to prevent twisting of the stent before its expansion. The resulting stent structure is an open network having a series of radially expanding cylindrical elements, which are spaced close enough in a longitudinal direction, so that small dissections in the wall of a body lumen can be pressed back into position against each other. the wall of the lumen, but not so closely that they compromise the longitudinal flexibility of the endoprosthesis. The individual cylindrical elements cumulatively provide a stent that is flexible about its longitudinal axis, but that is stronger towards at least one end section to resist crushing in the areas where each portion of the stent alone has a proximal portion of the stent. pattern for cylindrical resistance.

The stent incorporating features of the invention can be easily delivered to the location of the desired body lumen by mounting it on an expandable member, e.g., a balloon, of a delivery catheter and passing the endoprosthesis-catheter assembly through the body lumen to the site. of implant. A variety of means for securing the stent to the expandable member in the catheter to deliver the desired site are available. Currently it is preferred to compress the stent in the balloon. Other means for securing the endoprosthesis in the balloon include providing a retractable liner over the stent, providing ridges or collars in the inflatable member or restricting lateral movement of the stent, or using temporary bioabsorbable adhesives to hold the stent in the balloon. The presently preferred structure for the expandable cylindrical elements forming the stents of the present invention are generally circumferential undulating patterns, for example a generally serpentine pattern. The cross section of the undulating component for the cylindrical element is relatively small and preferably has an approximate expansion ratio of 1.0 to 4.5. The open cross-linked structure of the stent allows perfusion of blood over a large portion of the arterial wall that can accelerate healing and repair of damaged arterial lining.

The cylindrical structures of the stent are plastically deformed when expanded (when nickel-titanium alloys (NiTi) are used to form the stent) such that the stent will remain in the expanded condition. Therefore the cylindrical structures must be sufficiently rigid when they expand to avoid their crushing in use. In addition, because at least one end section of the stent is formed of a material that is thicker than the stent material near the center section, there is less chance that one end (or ends) of the stent is crush after the stent is expanded and placed in the desired body lumen. During expansion of the preferred stent, portions of the undulating pattern will tilt outwards, resulting in projecting members on the outer surface of the expanded stent. These projecting members are inclined radially outwardly from the outer surface of the stent and embed in the vessel wall and thus help hold the expanded stent in such a way that it does not move once it is implanted. When the endoprosthesis is made from super elastic NiTi alloys, expansion occurs when the compression tension is removed, thus allowing the phase transformation of the alloy from the austenitic phase back to the martensitic phase.

The elongate elements interconnecting adjacent cylindrical elements should have a cross section similar to the transverse dimensions of the undulating components of the expandable cylindrical elements, to which elongate elements are connected. In this way, the first and second end sections of the stent are stronger because they are made from thicker material and the elongated elements interconnecting those end sections should be correspondingly thicker and thus correspondingly stronger. than those elongated elements that interconnect adjacent cylindrical elements towards the central section of the endoprosthesis. Other features and advantages of the present invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view in elevation, partially in section of a stent incorporating features of the invention, which is mounted on a delivery catheter and disposed within an artery. FIGURE 2 is an elevation view, partially in section, similar to the view illustrated in FIGURE 1, wherein the stent expands into an artery, depressing the dissected arterial lining against the arterial wall.

FIGURE 3 is an elevation view, partially in section, showing the expanded stent within the artery after the delivery catheter has been removed. FIGURE 4 is a perspective view of a stent incorporating features of the invention in an unexpanded state with one end of the stent shown to illustrate one embodiment of the invention wherein the thicker material is used to reinforce the end of the endoprosthesis. FIGURE 5 is a plan view of a flattened section of an endoprosthesis of the invention, illustrating the undulating pattern of the endoprosthesis illustrated in FIGURE 4, and identifying an embodiment of the invention wherein one end of the endoprosthesis is fabricated from thicker material for added resistance. FIGURE 6 is a schematic representation of laser equipment for selectively cutting pipe in the manufacture of stents. FIGS. 7 to 11 are perspective views schematically illustrating different stent configurations wherein both end sections of the stent have expandable elements that are made of material thicker than the center section. FIGURE 12 is an enlarged partial view of the stent of FIGURE 5 taken over lines 12-12 with the various non-end, slightly expanded members. FIGURE 13 is a perspective view of a non-end portion of the stent of FIGURE 4, after it is fully expanded, illustrating some members projecting radially outwardly. FIGURE 14 is an enlarged partial perspective view of a U-shaped member with its tip projecting outward after expansion. FIGURE 15 is a cross-sectional view illustrating a stent configuration, wherein the thickness of the cylindrical elements is substantially greater at each end of the stent than near the center of the stent. FIGURE 16 is a cross-sectional view illustrating a stent configuration, wherein the thickness of the cylindrical elements gradually increases from the center of the stent toward each end of the stent. FIGURE 17 is a cross-sectional view illustrating a stent configuration, wherein the thickness of the cylindrical elements increases substantially only at one end of the stent and wherein the thickened or thickened area may extend over more than one member. FIGURE 18 is a cross-sectional view illustrating a stent configuration, wherein the thickness of the cylindrical elements gradually increases toward only one end of the stent. FIGURE 19 is an end view illustrating a stent configuration, wherein the thickness of an arcuate section of the open network structure of the stent is substantially thicker than an adjacent arcuate section. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The stent of the present invention is generally delivered intra-luminally, using a conventional balloon catheter, as is known in the art. The endoprosthesis is primarily used to ensure the opening of the body lumen where it is implanted. For example, the endoprosthesis of the present invention will preferably be implanted in the coronary arteries after an angioplasty procedure, to reinforce the artery against recoil or to attach a dissection in the arterial wall. The stent of the present invention is useful for implantation in other body lumens, such as the carotid, iliac, and other peripheral arteries and veins. FIGURE 1 illustrates a stent 10 incorporating features of the invention, mounted on a delivery catheter 11. The stent preferably comprises a plurality of radially expandable cylindrical elements 12., generally arranged coaxially and interconnected by elements 13 arranged between adjacent cylindrical elements. The delivery catheter 11 has an expandable portion or balloon 14 for expanding the stent 10 within the coronary artery 15. The artery 15, as illustrated in FIGURE 1, has a dissected liner 16 that has a portion of arterial passage occluded. The ends of the stent have thicker elements that provide greater resistance and crushing resistance by retraction of the artery or body lumen 15. The delivery catheter 11 in which the stent 10 is mounted, is essentially the same as a dilatation catheter with conventional balloon used for angioplasty procedures. The balloon 14 may be formed of suitable materials such as polyethylene, polyethylene terephthalate, polyvinyl chlorine, nylon and ionomers such as the ionomer manufactured under the trademark "SURLYN" by Polymer Products Division of Dupont Company. Other polymers can also be used. In order for the stent 10 to remain in place in the balloon 14 during delivery to the site of damage within the artery 15, the stent 10 is compressed onto the balloon. A retractable protective supply sleeve 20 may be provided, to further ensure that the stent remains in place in the expandable portion of the delivery catheter 11, and to prevent abrasion of the body lumen by the open surface of the stent 10, during delivery to the location. desired arterial Other means for securing the stent on the balloon 14 can also be employed, such as by providing collars or ridges at the ends of the working portion (i.e. the cylindrical portion) of the balloon. Each radially expandable cylindrical element 12 of the stent 10 can be expanded independently of any other. Therefore, the balloon 14 may be provided with an ated shape that is different from cylindrical, for example an ated tapered shape, to facilitate implanting the stent 10 in a variety of body lumen forms. The delivery of the stent 10 is achieved in the following manner. The stent is first mounted on the atable balloon 14 at the distal end of the delivery catheter 11. The balloon 14 is slightly ated to secure the stent 10 on the outside of the balloon. The catheter-stent assembly is inserted into the vasculature of the patient, with a conventional Seldinger technique through a guide catheter (not shown). A guidewire 18 is disposed through a stenosed area or the damaged arterial section has a detached or dissected liner 16 and then the catheter-stent assembly is advanced over a guidewire 18 within artery 15, until the stent 10 is directly under the detached liner 16. The balloon 14 of the catheter expands, expanding the stent 10 against the artery 15 illustrated in FIGURE 2. While not illustrated in the drawing, artery 15 preferably expands slightly by the expansion of the stent 10 to seat or otherwise secure the stent 10 to prevent movement. In some circumstances during the treatment of the stenosed portion of an artery, the artery may have to expand in order to facilitate passage of blood or other fluid. In a preferred embodiment, the stent 10 serves to hold the artery 15 open after the catheter 11 is removed, as illustrated by FIGURE 3. Due to the formation of the stent 10 of the elongate tubular member, the undulating component of the stent 10 Cylindrical elements of the stent 10 is relatively flat in cross section, such that when the stent is expanded, the cylindrical elements are pressed into the wall of the artery 15 and as a result, do not interfere with the blood flow through the artery 15. The cylindrical elements 12 of the stent 10 that are pressed into the wall of artery 15, eventually they will be covered with endothelial cell growth, this cell growth also minimizes the interference of blood flow. The undulating portion of the cylindrical sections 12 provides good adhesion characteristics to prevent movement of the stent within the artery. In addition, cylindrical elements 12, closely spaced at regular intervals, provide uniform support for the wall of artery 15 and at least one end of the stent has expanded cylindrical elements that are stronger due to the material or design incorporated in the stent, for avoid crushing the stent at those sites in the body lumen. Consequently, the stents of this invention are well adapted to keep a body lumen or artery open against recoil or to adhere and hold in place small fins or dissections in the wall of artery 15, as illustrated in FIGURES 2 and 3. A preferred embodiment of the invention FIGURE 4 illustrates an enlarged perspective view of the stent 10 illustrated in FIGURE 1, with a first end section 36 of the stent having cylindrical elements 12 that are thicker from a point of material view than the central section 37 so as to provide a stronger section in the first end location. The first section 36 is stronger and more resistant to crushing to arterial recession than the central section 37 and the second end section 38 (FIGURES 1 to 3), none of which have increased material thickness. FIGURE 4 further shows a placement of interconnecting elements 13 between radially adjacent expanded cylindrical elements 12. Each pair of the interconnecting elements 13 on one side of the cylindrical element 12, is preferably positioned to achieve maximum flexibility for a stent. In the embodiment illustrated in FIGURE 4, the stent has 3 interconnecting elements 13 between radially adjacent expandable cylindrical elements 12 that are spaced 120 ° apart. Each pair of interconnecting elements 13 on one side of a cylindrical element 12 is radially offset 60 ° from the pair on the other side of the cylindrical element. The alternation of the interconnecting elements results in an endoprosthesis that is longitudinally flexible in essentially all directions, however it is stronger in the first end section 36. FIGURE 5 illustrates the stent of FIGURE 4 in a collapsed condition, to show more clearly the undulating pattern and the thicker cross-section of certain portions of the stent. With reference to FIGS. 7 to 11, alternate embodiments of the stent 10 are illustrated, wherein an open network structure, 37, central section is in the form of a tubular member. Each stent is capable of expanding from a first compressed diameter to a second enlarged diameter within a body lumen, such as within an artery 15 as illustrated in FIGS. 1 to 3. In this manner, such as with the embodiment of The stent of FIGURE 4, the embodiment of the endoprostheses illustrated in FIGS. 7 to 11, is expandable and will deform beyond the elastic limit of each, in order to maintain the opening of the artery or body lumen 15. As illustrated , each of the embodiments shown in FIGS. 7 to 11, has a first section 36 and second section 38 which are of material thicker than the material of the central section 37. The first and second sections 36, 38 are stronger and more resistant to recession of artery 15, and help to hold the stent 10 within the artery. As described herein, the stents of FIGS. 7 to 10 may have either the first end section 36 made of thicker material or both the first and second sections 36, 38 made of thicker material. In addition, the material can be made thicker in a tapered shape, as described with respect to the embodiments of FIGS. 16 to 18. A preferred configuration for the stent 10 is illustrated in FIGURE 4 and FIGURES 12 through 14, in one of the cylindrical elements 12 are arranged in the form of a serpentine pattern 30. As previously mentioned, each cylindrical element 12 is connected to another by interconnection elements 13. The serpentine pattern 30 is constituted by a plurality of U-shaped members 31, W-shaped members 32, and members in shape of Y 33, each with varying radii of curvature, in such a way that the expansion forces have been distributed more homogeneously over the various members. As illustrated in FIGURES 13 and 14, after the cylindrical elements 12 have been radially expandable, the projecting edges outwardly are formed 34. That is, during radial expansion, the U-shaped members 31 will tilt outwardly forming in this way projecting edges outwards. These outwardly projecting edges provide a rough outer wall surface of the stent 10, and are embedded within the arterial wall, thereby facilitating the implant. In other words, edges projecting outward are embedded in the arterial wall, for example within the wall of artery 15, as illustrated in FIGURE 3. Depending on the dimensions of the stent 10, and the thickness of the the various members that make up the serpentine pattern 30, any of the U-shaped members 31, 32-shaped members and Y-shaped members 33, can tilt radially outward to form a projecting edge 34. It is both more likely as It is preferred that the U-shaped members 31 tilt outwardly because these members do not join with any other connecting member 13, which may prevent the U-shaped member from expanding outwardly. As can be seen in FIGURE 13, the first end section 36 has U-shaped, W and Y members thicker than the center section 37. The thicker members in the first end section 36 will provide substantially more support and will resist the crushing by recession of artery 15 than the central section 37. Likewise, when both end sections 36, 38 are illustrated in FIGS. 15 and 16 are thicker, the end sections provide substantially more support in artery 15 and will surely embed. in artery 15 because the projecting edges 34 are tilted outward.

FIGURES 15 and 18 schematically illustrate various preferred embodiments of the stent. Such a configuration provides an endoprosthesis wherein the thickness and thus the resistance of the expandable cylindrical elements 12, are substantially increased in the first and second end sections 36, 38 of the stent 10 as illustrated in FIG. 15. In FIG. In another embodiment, the expandable cylindrical elements 12 gradually increase in thickness toward the first and second end sections 36, 38 and thus gradually increase in strength, moving axially from the central section 37 of the stent to both ends, as shown in FIG. illustrated in FIGURE 16. In another embodiment illustrated in FIGURE 17, the thickness of the expandable cylindrical elements 12 is substantially increased in the first end section 36 of the stent 10, the thickness increased only at the end 36 of the stent 10. it can happen gradually as illustrated in FIGURE 18, FIGURE 19 schematically illustrates another fashion preferred embodiment of the stent of the invention, wherein the thickness, and thus the strength of the expandable cylindrical elements 12, is substantially increased in the arcuate sections 40 of the open network structure of the stent 10. The arched section further thick may be limited to a portion of the first end section 36 or the entire first end section, or may extend longitudinally in a plurality of sections, even to the entire length of the stent. In the preferred embodiment, the endoprosthesis is formed from a metal alloy tube such as a stainless steel pipe, however it can be made from other metal alloys including, but not limited to, tantalum, nickel-tantalum ( NiTi) or from thermoplastic polymers. Currently, a preferred way of producing the stent is by direct laser cutting of a stainless steel tube, as described in U.S. Patent Application. Common property and co-pending No. 08 / 345,501, filed on November 28, 1994 titled "METHOD AND APPARATUS FOR DIRECT LASER CUTTING OF METAL STENTS" (METHOD AND APPARATUS FOR DIRECT CUTTING WITH METAL ENDOPROTESIS LASER) which is incorporated here complete by reference. Other ways of producing the stent of the invention are also contemplated. While the invention has been illustrated here in terms of its use as an intravascular stent in the coronary arteries, it is envisioned that the stent will be useful in other body lumens as well. Due to the high strength characteristics of the stent of the present invention, primarily due to the thicker wall elements at the ends of the stent, they are particularly adapted for use in the coronary arteries, to anchor a graft to repair an aortic aneurysm , and for deployment in peripheral veins and arteries throughout the body. Other modifications and improvements to the invention can be made without departing from its scope.

Claims (22)

1. CLAIMS l.- An intravascular stent to be implanted in a body lumen, characterized in that it comprises: an elongated tubular body having a first end section and a second end section and a central section; the elongate tubular member also has an open network structure and is adapted for radial expansion from a first compressed diameter to a second enlarged diameter; and the first end section and an open network structure thicker than the central section, and the second end section, such that when the stent is expanded to the enlarged second diameter, the thicker open network structure of the first end section is radially stronger and stronger to crush than the middle section and the second end section.
2. 2. The stent according to claim 1, characterized in that both the first end section and the second end section have an open network structure thicker than the central section, making the first and second end sections substantially stronger. than the central section.
3. 3. The stent according to claim 1, characterized in that the thicker open network structure gradually becomes thicker from about the central section toward the first end section.
4. 4. - The stent according to claim 1, characterized in that the thicker open network structure of the first end section is in an arcuate section of the first end section.
5. 5. The stent according to claim 1, characterized in that the thicker open network structure of the endoprosthesis is in an arched section of all sections of the stent.
6. 6. - A longitudinally flexible endoprosthesis for implantation in a body lumen, characterized in that it comprises: a plurality of cylindrical elements that expand independently in the radial direction, and that are interconnected in order to align generally on a common longitudinal axis, at least some of the cylindrical elements have a thicker cross section than other cylindrical elements, - a plurality of connecting elements for interconnecting the cylindrical elements, the connecting elements are configured to interconnect only the cylindrical elements that are adjacent to each other, in such a way that As the stent expands radially outwardly from a first diameter to a second enlarged diameter, the cylindrical elements have the thickest cross section providing substantially more radial support in the body lumen.
7. 7. The stent according to claim 6, characterized in that the plurality of cylindrical elements includes a first cylindrical end element and a second cylindrical end element, the first cylindrical end element has the cross section thicker than the other elements cylindrical
8. 8. - The stent according to claim 7, characterized in that the first and second end cylindrical elements have cross sections thicker than the other cylindrical elements.
9. 9. The stent according to claim 6, characterized in that the endoprosthesis is formed from a biocompatible material selected from the group of materials consisting of: stainless steel, tantalum, NiTi alloys and thermoplastic polymers.
10. 10. The stent according to claim 6, characterized in that the endoprosthesis is formed from a single piece of tubing.
11. 11. The stent according to claim 6, characterized in that the endoprosthesis is coated with a biocompatible coating.
12. 12. - A longitudinally flexible endoprosthesis, characterized in that it comprises: a plurality of cylindrical elements that are independently expandable in the radial direction and that are interconnected to be concentrically aligned on a common longitudinal axis, and which are constructed in such a way that at least one end of the flexible endoprosthesis has cylindrical elements that are radially stronger than the cylindrical elements closest to the center of the endoprosthesis; and a plurality of generally parallel connecting elements for interconnecting the cylindrical elements, the connecting elements are configured to interconnect only the cylindrical elements that are adjacent to each other, such that the stent when it expands radially outwards retains its total length without appreciable shortening .
13. 13. - The stent according to claim 12, characterized in that the cylindrical elements are able to retain their expanded condition to the expander.
14. 14. The stent according to claim 12, characterized in that the radially expandable cylindrical elements in an expanded condition have a length less than their diameter.
15. 15. The stent according to claim 14, characterized in that the endoprosthesis is formed of a biocompatible material selected from the group of materials consisting of: stainless steel, tantalum, NiTi alloys and thermoplastic polymers.
16. 16. The stent according to claim 12, characterized in that the connecting elements between adjacent cylindrical elements are in axial alignment.
17. 17. The stent according to claim 12, characterized in that the connecting elements between adjacent cylindrical elements are displaced circumferentially with respect to the longitudinal axis.
18. 18. The stent according to claim 17, characterized in that the circumferential displacement of the connecting elements between adjacent cylindrical elements is uniform.
19. 19. - The endoprosthesis according to claim 12, characterized in that there are up to 4 connector elements arranged between radially adjacent expandable cylindrical elements.
20. 20. The stent according to claim 12, characterized in that the radially expandable cylindrical elements and the connecting elements are made of the same material.
21. 21. The stent according to claim 12, characterized in that the endoprosthesis is formed from a single piece of tubing.
22. 22. The stent according to claim 12, characterized in that the endoprosthesis is coated with a biocompatible coating.