Patent Publication Number: US-11039902-B2

Title: Marker element and method for the production thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. § 119, of European application EP 18 168 896.1, filed Apr. 24, 2018; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a marker element for an implant, to a scaffold for an implant comprising a marker element, and to a method for producing such a marker element and such a scaffold. 
     The present invention moreover relates to an implant, and in particular to an intraluminal endoprosthesis, comprising a scaffold and a marker element that is attached to the scaffold and comprises, at least in a portion of the volume thereof, a material composition different from the material of the scaffold, which preferably comprises radiopaque and/or X-ray opaque material, and to a method for producing such an implant. 
     The implants are endovascular prostheses (endoprostheses, stents) or other implants that can be used to treat stenoses (vascular constrictions). These usually comprise a scaffold in the form of a hollow cylindrical or tubular base mesh, which is open at the two longitudinal ends of the tubes. Such a scaffold usually comprises a plurality of mutually connected struts, which form the base mesh. The tubular base mesh of such an endoprosthesis is inserted into the vessel requiring treatment and is intended to support the vessel. Other scaffold forms are likewise possible. The present invention further relates to implants that can be used in the field of orthopedics, for example for the skull area, and in particular to implants that, due to the small size and wall thickness thereof, have low X-ray visibility. The invention can likewise be used for stents in the neurovascular field. The important factor here is to keep the blood vessels supplying the brain open with absorbable Mg stents. These systems are used to prevent acute ischemic strokes. 
     Stents or other implants frequently comprise metallic materials in the scaffold thereof. The metallic materials can form a biodegradable substance, wherein polymeric biodegradable materials may also be present. 
     Biodegradation refers to hydrolytic, enzymatic and other metabolic breakdown processes in the living organism, which are caused primarily by the body fluids coming in contact with the endoprosthesis and result in a gradual dissolution of at least major parts of the scaffold or of the implant. A term that is frequently used synonymously with biodegradation is biocorrosion. The term bioresorption encompasses the subsequent resorption of the degradation products by the living organism. The objective of using biodegradable implants is to have these degraded by the organism at a point in time where they are no longer needed, for example with respect to the scaffolding action thereof, and therefore are present in the organism as foreign bodies no longer than is necessary. 
     Substances (base material) suitable for the scaffolds of biodegradable implants can be composed of one material or multiple materials. Examples of suitable polymer compounds include polymers from the group consisting of cellulose, collagen, albumin, casein, polysaccharides (PSAC), polylactide (PLA), poly-L-lactide (PLLA), polyglycol (PGA), poly-D,L-lactide-co-glycolide (PDLLA-PGA), polyhydroxybutyric acid (PHB), polyhydroxyvaleric acid (PHV), polyalkyl carbonates, polyorthoesters, polyethylene terephtalate (PET), polymalonic acid (PML), polyanhydrides, polyphosphazenes, polyamino acids and the copolymers thereof, as well as hyaluronic acid. Depending on the desired properties, the polymers may be present in pure form, in derivatized form, in the form of blends or as copolymers. Metallic biodegradable substances are based on magnesium, iron, zinc and/or tungsten alloys. 
     The position of a stent or other implants is frequently ascertained by imaging methods, such as by an X-ray irradiation device. Due to the small ordinal number and the low density of the biodegradable material, for example magnesium and the alloys thereof, the X-ray visibility of medical implants produced therefrom is very low. To eliminate this drawback, it is known to provide medical devices with marker elements that, at least in a portion of the volume thereof, comprises a material composition different from the material of the scaffold. These so-called (X-ray) markers or marker elements contain, in particular, a material that absorbs X-rays and/or other electromagnetic radiation to a greater degree (hereafter referred to as X-ray opaque or radiopaque material) than the material of the scaffold or the body environment of the patient, thereby becoming visible relative to the surrounding area thereof. Based on the ascertained position of the usually multiple marker elements on the scaffold, it is possible to determine the position and angular position of the implant with respect to the surrounding organs. When a biodegradable scaffold is used, a non-resorbable X-ray opaque or radiopaque material (such as Ta, Au, W) is frequently used for reasons of sufficient X-ray visibility. 
     Such a marker element is frequently cut off or out of a semi-finished product made of the material of the marker element and integrated into an implant in such a way that it is bonded into a corresponding opening (eyelet) provided for this purpose on the scaffold of the implant (for example, at both ends in the axial direction of the implant). Such marker elements and implants are known from the published, European patents or applications EP 2 399 619 B1 (corresponding to U.S. patent publication No. 2011/0319982), EP 3 165 238 A1 (corresponding to U.S. patent publication No. 2017/0119555) and EP 17 150 973.0 (unpublished as of yet), for example. 
     There is a technical requirement with regard to implants comprising integrated marker elements that the marker elements remain in the scaffold combination over a long period of time with a sufficiently high adhesive power. If the marker element is not sufficiently joined to the scaffold of the implant, an undesirable local element may form, or contact corrosion may be caused, as a result of metallic contact between the marker element and the scaffold material. This would result in premature detachment of the marker element from the scaffold of the implant, which would favor undesirable fragmentation and embolization. Moreover, it is to be prevented, in general, that the material of the marker element influences the degradation of the scaffold. With conventional bonding methods, additionally dosing of the adhesive is difficult since very small adhesive quantities are used for each marker element. It is also difficult the position the adhesive required for bonding, making this process often imprecise. 
     SUMMARY OF THE INVENTION 
     It is thus the object of the present invention to create an implant or a scaffold for an implant in which local element formation and corrosion are at least reduced. Accordingly, a marker element was to be created, which does not form a local element and avoids corrosion after integration into the implant. Moreover, cost-effective, simple and automatable methods for producing such a marker element, a scaffold comprising such an integrated marker element or an implant comprising such a scaffold are to be provided. In particular, the handling of the adhesive is to be improved. 
     The object is achieved by the method for producing a marker element described in the independent method claim. 
     The object is achieved, in particular, by a method for producing a marker element for an implant made of a layered or wire-shaped semi-finished product, comprising an X-ray opaque or a radiopaque material, wherein a respective adhesive layer is attached to or on at least one side of the semi-finished product, or a plurality of sections of the semi-finished product, so that a layer composite is formed at least in sections, and wherein subsequently a plurality of marker elements are cut out of the layer composite, or are detached from the layer composite, by appropriately cutting or appropriately severing (such as breaking away a web) in a direction transversely, and preferably perpendicularly, to the layers of the layer composite. The adhesive layer can be attached to the semi-finished product by use of coating (e.g. dip coating or spray coating), for example. It is possible for one or more further layers comprising an X-ray opaque or a radiopaque material to be provided in the layer composite. 
     The method according to the invention has the advantage that dosing of the adhesive for individual marker elements is eliminated. Marker elements that already comprise an adhesive layer which is exactly metered for the particular application and ideally positioned can be produced effectively by means of an automated method. 
     As an alternative, the individual marker elements can be coated as bulk material. 
     The resultant marker element can then be inserted into an opening (eyelet) of the scaffold and bonded thereto. If necessary, further treatments and/or coatings of the layer composite are carried out prior to detaching the marker element from the layer composite (see below). 
     The layered semi-finished product is formed, for example, by a film, a plate, a hollow cylinder (tube) or a three-sided, four-sided or more than four-sided, preferably straight, hollow prism, which is open at the two ends in the direction of a longitudinal axis. 
     The semi-finished product comprises an X-ray opaque or a radiopaque material in the form of a metal or a metal alloy, containing at least one metal or noble metal selected from the group consisting of the elements gold, platinum, tungsten, tantalum and titanium, or consists of such a metal or such a metal alloy. The semi-finished product is particularly preferably made of tantalum or a tantalum alloy. The described materials of the marker element have good X-ray absorption properties and can be provided, on the surface thereof, very easily with a dense, passivating and insulating (i.e., electrically non-conducting) oxide layer, e.g. by plasmaelectrolytic oxidation or other passivation methods (such as the use of a passivating coating comprising a polymer or parylene when using gold as the radiopaque material). In this way, they allow a marker element having a minimal size to be configured. The semi-finished product is preferably produced by drawing from the respective material. 
     The detachment of the at least one section from the semi-finished product (for example after cleaning (pickling) and/or passivation treatment) takes place by cutting (e.g., by means of laser), breaking away a web or mechanical cutting from the semi-finished product. If necessary, the section can be detached from the semi-finished product along a portion of the contour, so that the section is still connected to the semi-finished product by at least one web. Afterwards, cleaning (pickling) and/or a passivation treatment can take place. Thereafter, the section is completely detached from the semi-finished product by means of severing (e.g., by use of laser or by use of a mechanical cutting tool). 
     The adhesive layer preferably comprises a thermoplastic elastomer (TPE) or consists of a TPE. TPEs (also referred to as elastoplasts on occasion) are plastic materials that behave similarly to the traditional elastomers at room temperature, but can be plastically deformed when heat is supplied and thus exhibit thermoplastic behavior. TPE encompasses the following material classes, for example: 
     a) PE-A or TPA (thermoplastic copolyamides, e.g. PEBAX (Arkema)); 
     b) TPE-E or TPC (thermoplastic polyester elastomers/thermoplastic copolyesters, e.g. Keyflex (LG Chem)); 
     c) TPE-O or TPO (olefin-based thermoplastic elastomers, primarily PP/EPDM); 
     d) TPE-S or TPS (styrene block copolymers (SBS, SEBS, SEPS, SEEPS and MBS), e.g. Kraton (Kraton Polymers), Septon (Kuraray), Styroflex (BASF), Thermolast (Kraiburg TPE) or Saxomer (PCW)); 
     e) TPE-U or TPU (urethane-based thermoplastic elastomers, e.g. Elastollan (BASF) or Desmopan, Texin, Utechllan (Bayer)); and 
     f) TPE-V or TPV (thermoplastic vulkanizates or cross-linked olefin-based thermoplastic elastomers, predominantly PP/EPDM, e.g. Sarlink (DSM)). 
     Elastic adhesives have the advantage that they contribute to improved trackability, i.e., to the adaptation to the surrounding tissue as the implant is advanced during insertion, whereby premature loss of a marker element is avoided. 
     For example, polyurethane dissolved in dimethylformamide can be used as a TPE adhesive. Alternative adhesives from the above material classes are likewise conceivable, preferably together with a suitable solvent, which evaporates under the action of heat so as to effect curing of the adhesive. 
     As an alternative or in addition, the adhesive layer can comprise a resin and/or shellac and/or a low viscosity adhesive. 
     In addition to polyurethane, a degradable polymer (e.g. PLLA L210, PLLA L214), for example, can be used as an advantageous polymer-based adhesive. These adhesives are particularly biocompatible and also provide good electrical insulation. 
     In a preferred exemplary embodiment, in the method for producing the marker element using a layered (i.e., film-like, plate-shaped or hollow body-shaped) semi-finished product a continuous first layer or a plurality of sections of a first layer of the semi-finished product is/are arranged on a first side of the adhesive layer, and a continuous second layer or a plurality of sections of a second layer of the semi-finished product is/are arranged on a second side of the adhesive layer located opposite the first side, and are attached thereto, whereby these form the layer composite at least in sections. 
     With the method described in this exemplary embodiment, a marker element having a sandwich design is created, which has the advantages described below when bonded into an opening of the scaffold. 
     The above exemplary embodiment of a method for producing a marker element can be automated well, in particular, when a continuous first layer of a film-like semi-finished product, comprising an X-ray opaque or a radiopaque material, is arranged on a first side of the adhesive layer, and a continuous second layer of a film-like semi-finished product, comprising an X-ray opaque or radiopaque material, is arranged on the second side of the adhesive layer located opposite the first side, and are attached thereto, whereby these form the layer composite at least in sections. 
     The above object is further achieved by a method for producing a scaffold, preferably made of a magnesium alloy, and in particular of a rare earth-containing magnesium alloy, a magnesium zinc aluminum alloy or a magnesium zinc calcium alloy, for an implant including a marker element, comprising a layer composite including at least one layer comprising an X-ray opaque or a radiopaque material and an adhesive layer. The marker element is introduced into an opening of the scaffold and, using a heat source, the marker element is heated in such a way that the adhesive layer of the marker element becomes softened or liquefied, so that the adhesive of the adhesive layer creates an adhesive joint with the inner surface of the opening. 
     In the method according to the invention, the marker element preferably has a composition different from the material of the scaffold. 
     According to the invention, the at least one marker element is attached to the scaffold by means of an adhesive, and preferably by means of an adhesive comprising or consisting of TPE. This is because it was found that, in particular, an integral joint achieves a simple and mechanical joint that does not strain the filigree scaffold. In addition, by adapting the shape of the marker element to the shape of the opening (eyelet, receptacle) on the scaffold of the implant into which the marker is introduced, or conversely, a form fit can be achieved. However, the inside dimensions (e.g. the inner width and length) of the opening are slightly larger than the outside dimensions of the marker element, whereby a gap still remains between the marker element and the inner edge of the opening around the outer edge of the marker element after having introduction into the opening, the adhesive being able to flow into this gap after softening or liquefying so as to establish an integral joint between the marker element and the opening. 
     In one exemplary embodiment, the opening is configured as a through-opening. 
     In one refinement of the invention, using a marker element comprising a layer composite including at least one first layer and one second layer, each comprising an X-ray opaque or a radiopaque material, and an interposed adhesive layer, the marker element, after having been introduced into an opening of the scaffold, is subjected to a pressure force in a direction transversely to the layers of the layer composite, and preferably perpendicularly to the layers of the layer composite, in such a way that the adhesive exits on the lateral face of the marker element and creates an adhesive joint with the inner surface of the opening. The pressure force can be applied, for example, by means of appropriate crimping pliers or an appropriate crimping tool and causes the adhesive to be distributed in the gap between the marker element and the inner edge of the opening. Compressing the first layer and the second layer comprising the X-ray opaque or radiopaque material reduces the space available for the adhesive between these layers, causing the adhesive to ooze out on the side of the marker element into the adhesive gap between the marker element and the opening. In the case of a hollow cylindrical scaffold, the pressure force preferably extends in the radial direction. This exemplary embodiment is particularly well-suited for further automation of the method and achieves particularly good results with respect to the bond to the scaffold and the avoidance of the formation of local elements. Advantageously, no capillary action is required with this exemplary embodiment to distribute the adhesive in the adhesive gap. 
     In a preferred exemplary embodiment, the scaffold is placed on a mandrel, which fills the inner volume of the scaffold, before the marker element is introduced into the opening. In the case of a hollow cylindrical scaffold, the mandrel can have the shape of a cylinder, for example. The mandrel forms an abutment for applying the pressure force and can be removed again after the at least one marker element has been attached by bonding. 
     In a further exemplary embodiment, the marker element is heated by the heat source, before or after the pressure force is applied to the marker element, in such a way that the adhesive layer of the marker element is softened or liquefied. In this exemplary embodiment, the lateral exiting (oozing) of the adhesive out of the sandwich layer composite is particularly favored. 
     In a further exemplary embodiment, the scaffold is provided, at least in a predefined area, with a coating containing a pharmaceutically active substance before the marker element is bonded in. 
     A “pharmaceutically active substance” (or therapeutically active or effective substance) shall be understood to mean a plant, animal or synthetic active ingredient (drug) or a hormone, which is used in a suitable dose as a therapeutic agent for influencing states or functions of the body, for substituting active ingredients produced naturally by humans or the animal body, such as insulin, and for eliminating or rendering harmless pathogens, tumors, cancer cells or substances foreign to the body. An antiproliferative active ingredient, such as paclitaxel, sirolimus or everolimus, is preferably used as the pharmaceutically active substance. 
     As an alternative or in addition, the scaffold is provided, at least in a predefined area, with a coating containing a pharmaceutically active substance after the at least one marker element has been bonded in. 
     The above object is further achieved by a disk-shaped marker element for an implant comprising a layer composite including at least one first layer comprising an X-ray opaque or a radiopaque material and an adhesive layer that is joined to the first layer and arranged so as to adjoin the first layer. The first layer and the adhesive layer are separated from the semi-finished product by means of a cut extending through the first layer and the adhesive layer. 
     By arranging the adhesive layer on the X-ray opaque or radiopaque first layer and cutting the layer composite as a whole out of these layers of the semi-finished product, dosing and positioning of the adhesive before the marker element is bonded into the scaffold or the opening thereof are eliminated. 
     The disk-shaped marker element is preferably made of tantalum, tungsten, gold, platinum or another material having similarly high radiodensity. 
     The above object is further achieved by a scaffold for an implant comprising an above-described marker element, wherein the marker element is bonded into an opening (eyelet) of the scaffold. The bonding method was already described above in detail. 
     The above object is also achieved by an implant comprising an above-described scaffold with the same advantages. 
     The invention will be described hereafter based on exemplary embodiments and with reference to the figures. All described and/or illustrated features, either alone or in any arbitrary combination, form the subject matter of the invention, independently of their combination in the claims or their dependency references. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a marker element and a method for the production thereof, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a top plan view of a section of a scaffold of an implant; 
         FIG. 2  shows a marker element in a view from above; 
         FIGS. 3A-3E  are illustrations of a first exemplary embodiment of a method according to the invention for producing a marker element in a respective sectional view ( FIGS. 3A-3C ) and the marker element produced thereby in a view from the side ( FIG. 3D ) and in a perspective view from the side ( FIG. 3E ); 
         FIGS. 4A-4D  show a second exemplary embodiment of a method according to the invention for producing a marker element in a respective sectional view ( FIGS. 4A-4B ) and the marker element produced thereby in a view from the side ( FIG. 4C ) and a perspective view from the side ( FIG. 4D ); 
         FIG. 5  is a diagrammatic, a cross-sectional view of a second exemplary embodiment of a marker element; 
         FIG. 6  is a side view of a third exemplary embodiment of a marker element; 
         FIGS. 7A-7D  show a third exemplary embodiment of a method according to the invention for producing a marker element ( FIG. 7A ) and the marker element produced thereby in a cross-sectional view ( FIG. 7B ), a view from above ( FIG. 7C ) and a perspective view from the side ( FIG. 7D ); 
         FIGS. 8A-8D  are sectional views showing an exemplary embodiment of a method according to the invention for producing a scaffold for an implant in individual steps; 
         FIG. 9  is a side, perspective view of a tool for producing the scaffold; 
         FIGS. 10A-10C  show an exemplary embodiment of a method according to the invention for producing a scaffold for an implant comprising a marker element according to  FIG. 7  in individual steps, each in a sectional illustration; 
         FIGS. 11A-11D  show an exemplary embodiment of a method according to the invention for producing a scaffold for an implant comprising a marker element according to  FIG. 6  in individual steps, each in a sectional illustration; 
       and 
         FIGS. 12A-12D  show an exemplary embodiment analogous to  FIGS. 11A-11D , wherein the opening for the marker element is designed as a pocket here. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a section of a scaffold  10  of an implant according to the invention in the form of a medical stent, for example made of the degradable magnesium alloy WE43.  FIG. 1  shows a through-opening (hereafter eyelet)  20  having an elliptic basic shape, which is provided at the distal or proximal end of the scaffold  10 , for example. At the distal and/or at the proximal end of the scaffold  10  of the implant, a respective eyelet  20  is, or three eyelets  20  offset by 120° are, provided as components of the scaffold, for example on a strut. The scaffold is preferably formed as a hollow cylindrical mesh comprising a plurality of struts. For example, the dimensions of the eyelets  20  are 800 μm (dimension  20   a  in  FIG. 1 )×350 μm (dimension  20   b  in  FIG. 1 ). 
     An X-ray opaque marker element  30  (see  FIG. 2 ), which, as is described hereafter, can be attached to the eyelet  20  by means of an adhesive layer, can be arranged in the eyelet  20 . 
     The X-ray opaque material used in the marker element  30  can be predominantly made of tantalum (e.g. having a purity of 99.9%) or a tantalum alloy. The thickness of the marker element  30  is 100 μm, for example. The wall thickness of the scaffold  10  can be 100 μm, for example. The dimensions of the marker are, for example, 750 μm (dimension  30   a  in  FIG. 2 )×300 μm (dimension  30   b  in  FIG. 2 ). 
     In the first exemplary embodiment shown in  FIG. 3  for producing a marker element  30 , initially a semi-finished product in the form of a film-like first layer  31  made of the X-ray opaque or radiopaque material, for example tantalum (e.g. having a purity of 99.9%) or a tantalum alloy, is provided with an adhesive coating  33 , made of a TPE for example. The adhesive coating is made of polyurethane dissolved in dimethylformamide, for example, and has a thickness of approximately 0.025 mm. On the side located opposite the first layer  31 , a second layer  32  made of the X-ray opaque or radiopaque material, for example tantalum or a tantalum alloy, is then applied to the adhesive coating  33 . The resultant layer composite is shown in  FIG. 3A . 
     In the second step, individual marker elements  30  are now cut out of the layer composite by means of a cutting method, for example by means of laser cutting or another mechanical cutting method. The cutting is illustrated in  FIG. 3B  by dotted lines  34 . The cut extends perpendicularly to the layers  31 ,  32 ,  33  of the layer composite. The marker elements  30  thus separated each comprise a layer composite including three layers, wherein the adhesive layer  33  is arranged in a sandwich-like manner between the first layer  31  and the second layer  32  comprising the X-ray opaque or radiopaque material. This is also apparent in  FIGS. 3D and 3E , which each show an individual marker element  30 . 
     As an alternative, a semi-finished product in the form of a film-like first layer  31  comprising an X-ray opaque or a radiopaque material, including partially cut-out sections  31   a  for the marker element, can be provided on one side with an adhesive layer  33  (for example, made of a TPE) (see  FIG. 4A ). Afterwards, a further semi-finished product in the form of a film-like second layer  32  comprising an X-ray opaque or a radiopaque material, including partially cut-out sections  32   a , is applied to the second side of the adhesive layer  33  located opposite the first layer  31  (see  FIG. 4B ). The surfaces of the layers  31   a  and  32   a  can have been passivated before the adhesive coating is applied. Such passivation can take place, for example, by means of plasmaelectrolytic treatment (plasmaelectrolytic oxidation). The respective sections  31   a ,  32   a  are located on top of one another. Here, “partially cut-out” shall be understood to mean that the respective section  31   a ,  32   a  is still connected to the remaining material of the respective layer  31 ,  32  by at least one web (not shown). Afterwards, as is shown in  FIG. 4B , the marker element is separated (pushed out) by means of a force in a direction perpendicular to the layers  31 ,  32 ,  33  (see arrow  36 ) by severing the at least one web of the sections  31   a ,  32   a . The interposed adhesive layer  33  is likewise severed. The separation can also take place by means of laser cutting or another mechanical cutting method. The individual marker element  30 , which is shown in  FIGS. 4C and 4D , has the same composition as a marker element  30  produced according to  FIGS. 3A-3D . 
       FIG. 5  shows a marker element  37  comprising a plate-shaped first layer  31  made of an X-ray opaque or a radiopaque material, for example tantalum or a tantalum alloy, which in an already cut (separated) state was provided on the entire surface thereof with an adhesive layer  39 . Such a coating can be implemented, for example, by means of dipping in an appropriate solution or by means of spraying as bulk material consisting of a plurality of plate-shaped first layers  31 . 
       FIG. 6  shows a marker element  41  comprising a plate-shaped first layer  31  made of an X-ray opaque or a radiopaque material, for example tantalum or a tantalum alloy, which on a portion of the surface thereof was provided with an adhesive coating  43 . 
       FIG. 7  shows a method for producing a marker element in which a cylindrical wire  45  made of the X-ray opaque or radiopaque material, for example tantalum or a tantalum alloy, was initially provided on the lateral surface thereof with an adhesive layer  47 , and in particular a TPE material. The surface of the wire  45  can have been passivated before the adhesive coating  47  is applied. 
     Afterwards, the wire is cut in a direction transversely (e.g. perpendicularly) to the longitudinal axis thereof so as to form individual marker elements  48 . The progression of the cuts is illustrated with dotted lines  49  in  FIG. 7A . The cutting can take place by means of laser cutting or other known cutting methods, for example. The resultant marker elements  48  are shown in different views in  FIGS. 7B to 7D . The marker elements  48  are characterized by comprising a small cylindrical plate  45   a , which on the circumference thereof is provided with the adhesive coating  47  (see  FIGS. 7B to 7D ). 
     Based on  FIGS. 8A-8D , it will now be described how a marker element  30  produced according to  FIGS. 3A-4D  or is introduced into an opening (eyelet)  20  of a scaffold  10  and joined thereto. 
     Before the marker element  30  is placed into the eyelet  20 , the scaffold  10  which is to be provided with at least one marker element is threaded onto a mandrel  50 . This means that the substantially hollow cylindrical scaffold  10  is placed on a cylindrical mandrel  50  in such a way that the mandrel  50  takes up the entire inside volume of the hollow cylindrical scaffold  10 , and that the lateral surface of the mandrel  50  rests directly against the inside of the struts of the scaffold  10 . 
     After the scaffold  10  has been placed on the mandrel  50 , the marker element  30  is now inserted into an appropriate eyelet  20  (see  FIG. 8A ). It is apparent from the figure that an adhesive gap  21  is formed between the lateral surface of the marker element  30  and the inner edge of the opening  20  in that the outside dimensions of the marker elements  30  are slightly smaller than the inside dimensions of the opening  20 . Afterwards, the marker element  30  is heated under the action of an appropriate heat source  53 , whereby the adhesive layer  33  is softened. This is shown in  FIG. 8B .  FIG. 8C  illustrates that, in the following step, the marker element  30  protruding slightly in height h beyond the eyelet  20  is pressed together, for example by means of a crimping tool  60  shown in  FIG. 9 . The direction of the compression force is a direction transversely (e.g. perpendicularly) to the progression of the layers or of the longitudinal axis of the scaffold  10 . The direction of the force is illustrated in  FIG. 8C  by an arrow  55 . 
     The introduction of the mechanical force causes the two layers  31 ,  32  of the marker element  30  to be compressed, whereby the available volume is reduced for the softened adhesive of the adhesive layer. Consequently, the softened adhesive  33   a  from the adhesive layer  33  is pushed out of the side of the marker element  30 , so that the adhesive flows into the empty volume of the adhesive gap  21  between the marker element  30  and the inner edge of the eyelet  20  of the scaffold  30  and bonds to the inner edge of the eyelet  20 . In this way, good joining between the marker element  30  and the scaffold  10  by means of adhesive can be achieved using a method that can be carried out automatically. The adhesive  33   a  completely fills the adhesive gap  21 . This state is shown in  FIG. 8D . 
     The crimping tool  60  shown in  FIG. 9  has a cylindrical opening  62 , into which the scaffold  10  threaded onto the mandrel  50  is introduced together with the marker element  30 , which is not fully attached yet. A number of jaws  63  are arranged around the circumference of the opening  62 , which when the handle  64  connected to the jaws  63  is pressed down are guided in such a way that the diameter of the opening  62  is decreased. In this way, the above-described force can be applied to the marker element  30  perpendicularly to the layers of the marker element  30  so as to laterally push out the adhesive  33   a  from the adhesive layer  33  to bond with the eyelet  20 . 
     After the pressing in the crimping tool  60  and curing by cooling of the adhesive  33   a , the scaffold  10  is removed from the crimping tool  60  again. Afterwards, the mandrel  50  can be removed from the scaffold  10  again. 
     Using a simple method that is simple to automate, a permanent joint can thus be created between the marker element  30  and the scaffold  10 , in which the dosing of the adhesive and the application thereof can be achieved without difficulty and with precision. 
     The mounting of a marker  48  ( FIGS. 10A-10C ), in principle, does not differ from a marker  30 . The adhesive is already present on the circumference of the marker. Since the adhesive is liquefied before the marker  48  is pressed in, it is possible to compensate for shape tolerances of the eyelet. Accordingly, a smaller adhesive gap is provided here than in the embodiment according to FIGS.  8 A- 8 D. The heated adhesive automatically fills the gap between the marker  48  and the stent  10 . 
       FIGS. 11A-12D  show the mounting of a marker  41 . This variant is advantageous in particular when the eyelet is not formed as a through-opening, but as a pocket (see  FIGS. 12A-12D ). 
     In general, identical components are denoted by identical reference numerals within the scope of the drawings.