Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent in combination with graft
Reexamination Certificate
1997-12-05
2001-11-06
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent in combination with graft
C623S001340
Reexamination Certificate
active
06312456
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a stent, in particular a coronary stent, as an intraluminal expansion element comprising a thin-walled, hollow-cylindrical base body of an X-ray transparent material having a surface area which has an open-worked, net shaped design owing to recesses and comprising at least one X-ray opaque element or region.
European patent document EP-B1 0 364 787 discloses an expandable, intraluminal element with at least one thin-walled, tube-shaped segment (in the following called a stent). The surface area of the stent has an open-worked, net-shaped design and comprises recesses, which are limited by web-like elements with low material strength that extend in a straight-line in the axial and circumferential directions. The web-like elements consist of the remaining tube wall where the material was removed in the region of the recesses. Four of these web-like elements, together with the connecting pieces provided at their ends, form a so-called “expansible region” of the stent surface area.
Such stents are expanded during an operation, e.g. to remove a stenosis, under the effect of forces that act from the inside toward the outside and by using a tubular dilator admitted with compressed gas. Despite the deformation, the stent retains its tubular shape and dilates the vessel that is restricted as a result of deposits.
The above-described stents are produced from biocompatible materials such as stainless steel, titanium or other metals. Titanium stents have proven to be particularly useful with respect to physical tolerance, options for medical use and mechanical workability.
However, for the wall thicknesses used for stents, the metals used most often are essentially X-ray transparent, and stents fashioned from these cannot be seen by the physician when using X-rays. Nevertheless, the identification of the stent position with the aid of a suitable monitor has proven to be very critical for the correct handling.
A stent visible in an X-ray is disclosed in European patent document EP-A-O 709 068, for which the visibility in the X-ray is achieved through a coating with a metal having a high atomic weight or through expanded, e.g. ring-shaped, extensions on the individual ends of the meshes.
German patent document DE-U-296 07 916 discloses a stent with a segment visible in the X-ray, which is produced in particular by welding together two prefabricated hollow cylinders made of X-ray transparent or X-ray reflecting material.
The accuracy of the stent position determination can still be improved for both of the aforementioned arrangements.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to specify a stent of the aforementioned generic type, for which the position inside the body of a patient can be determined very precisely with the aid of X-rays.
The above and other objects are accomplished in accordance with the invention by the provision of a stent comprising a thin-walled, hollow-cylindrical base body of an X-ray transparent material having a surface area which has an open-worked, net shaped design owing to recesses and comprising at least one X-ray opaque element or region which extends essentially in a linear direction over at least a portion of the stent circumference located at least one end region of the stent while the rest of the stent remains X-ray transparent.
The invention includes the technical teaching that for the identification with X-rays of a stent, a sufficient contrast can be achieved and simultaneously a very precise determination of the angular position of the stent inside the body is possible, even if only a very limited region or a single element, which is essential to the determination of the angular position, is designed to be visible in the X-ray. In particular, this is a linear region adapted to the circumferential outline of the stent and even more specifically a ring or ring-shaped segment, for which the projection in the X-ray picture provides exact information not only concerning the location, but also the orientation of the stent.
The end regions of the stent in particular are suitable for providing this region or element. If the stent length is known, the exact stent position can be determined even with a single, X-ray opaque element.
It is important that the X-ray opaque modification does not essentially impair the expansion capability of the stent.
The X-ray opaque or reflecting element or the corresponding region is designed to have an “expansion reserve” for this. It is also possible to provide a coating for a regularly deformable, X-ray transparent stent segment, which reflects the X-rays. This coating preferably is applied with a vapor-deposit or vacuum-HF-coating method (sputtering etc). X-ray optical identifiers of almost any shape can be generated in this way, so that the physician can securely control position, direction and form of the stent. In accordance with a different embodiment, the curved, rounded connecting pieces for the web-like elements at the end of the stent are themselves composed of X-ray opaque material.
Gold, silver or tantalum in particular are provided as material for the X-ray opaque element for the above-described embodiments of the stent according to the invention, which is preferably produced from titanium, since these metals have the required biocompatibility in the X-ray range, in addition to a relatively high reflection factor.
The use of laser technology is provided for the necessary soldering connections and removal operations in the stent production and for the hollow-cylindrical tube rounds, required for the stent production, necessitated in particular by the small dimensions of the parts.
In order to design the linear or the rounded segments (in the not-expanded state) to be X-ray opaque at the ends or in the center of the stent, a meandering, curved thread (e.g. of Ta) of a X-ray opaque material is welded onto or welded into a thin-wall stent hollow cylinder (for example of Ti) The material pairing Ti-Ta is particularly favorable because these metals are soluble into each other and can therefore be easily welded together.
This embodiment of the stent according to the invention is very compatible with the body and exhibits excellent deformability. An outer micro-coating of amorphous silicon carbide additionally counteracts a thrombosis formation.
Owing to the fact that during the expansion of the axially extending web-like elements due to deformation, the stent can adapt only to a limited at the stent end to the shape of the tissue for a blood vessel to be expanded in this area, where the effectiveness of the stent ends, the material cross section of the web-like elements of the stent is reduced at the stent end in accordance with one advantageous modification In a favorable manner, this ensures that a “flowing” transition with variable, compensating change in the cross section occurs, if possible, from a vessel area expanded by the stent to the adjoining vessel area that is free of a stenosis.
This reduction in the cross section is preferably created while maintaining the radial dimensions in tangential direction, so that the stent can be produced from tube rounds by means of a laser cutting tool and by cutting out the recessed regions. With the rigidity of the stents reduced in this way toward the end region, it is particularly important that this reduced rigidity is not increased again by adapting the design of the X-ray opaque regions or elements.
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Kranz Curt
Mueller Heinz
Biotronik Mass-und Therapiegeraete GmbH & Co. Ingenieurbuero Ber
Kinberg Robert
McDermott Corrine
Phan Hieu
Venable Baetjer
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