Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1998-05-12
2001-09-11
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001110
Reexamination Certificate
active
06287331
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to tubular endoprostheses to be used inside the body.
BACKGROUND OF THE INVENTION
Tubular endoprostheses such as medical stents are placed within the body to perform a function such as maintaining a body lumen open, for example, a passageway occluded by a tumor or a blood vessel restricted by plaque. Tubular endoprostheses in the form of grafts are used to substitute for or reinforce a lumen, such as the aorta or other blood vessels which have been weakened, e.g., by an aneurysm.
Typically, these endoprostheses are delivered inside the body by a catheter that supports the device in a compacted or otherwise reduced-size form as it is transported to the desired site. The size is particularly small when a percutaneous insertion technique is employed. Upon reaching the site, the endoprosthesis is expanded so that it engages the walls of the lumen.
The expansion mechanism may involve forcing the endoprosthesis to expand radially outwardly, for example, by inflation of a balloon carried by the catheter, to plastically deform and fix the device at a predetermined expanded position in contact with the lumen wall. The expanding means, the balloon, can then be deflated and the catheter removed.
In another technique, the endoprosthesis is formed of a highly elastic material that can be reversibly compacted and expanded. During introduction into the body, the endoprosthesis is restrained in the compacted condition and upon reaching the desired site for implantation, the restraint is removed, enabling the device to self-expand by its own internal elastic restoring force.
In many cases, X-ray fluoroscopy is used to view an endoprosthesis within the body cavity to monitor placement and operation. The device may also be viewed by X-ray film after placement for medical follow-up evaluation. To date, the requirement for radiopacity has limited the construction of devices to certain materials which in turn has limited the features attainable for particular applications and the available insertion techniques.
SUMMARY OF THE INVENTION
In the invention, metal such as in the form of wire or filament or the like is used for constructing tubular medical endoprosthesis such as stents. Desirable attributes of these wires vary with the stent application, but include properties such as stiffness, tensile strength, elasticity, radiopacity, weldability, flexural life, conductivity, etc. These properties are hard to find in conventional wires. According to the invention, desired properties are achieved by creating a multiple metal coaxial construction. For example, it may be very desirable to have high radiopacity along with elasticity and strength. This is accomplished by combining a radiopaque metal with an elastic metal. Although it is possible to put either metal on the inside or outside, it is preferable to put the dense radiopaque material (e.g., tantalum) on the inside (core) since dense materials are generally less elastic and the elastic material (e.g., titanium or nickel-titanium alloy) on the outside (clad). The clad or “skin” of the wire will undergo more deformation in bending than the core, so the elastic component is best positioned at the skin.
Thus, an aspect of the invention is a metal stent device with at least a portion to be used within the body having properties that can be tailored to a particular application. The portion within the body is formed of preferably two or more dissimilar metals joined together to form a unitary member. Typically, each metal contributes a desirable property to the device which is not substantially impaired by the presence of the other metal. In particularly preferred devices, one metal provides enhanced radiopacity. In these embodiments, the stent is comprised of a metal outer member having a predetermined density and an exposed outer surface and a core including a metal having a density greater than the outer member to enhance radiopacity. The core is secured within and substantially enclosed by the outer member. Preferably, the stent is configured such that the mechanical properties, for example, the elastic properties, of the metal forming the outer member are affected by the core to a desired degree so that the stent has a desired overall performance suitable for its intended use. Preferably, the mechanical properties of the outer member dominate the properties of the stent yet the radiopacity of the member is substantially enhanced by the denser core. The invention also allows increased radiopacity of the stent without adversely affecting and in some cases improving other important properties such as the biocompatibility, small size or other performance characteristics. These performance advantages can be realized by proper selection of the material of the outer member and core, their relative size, and geometrical configuration. The particular performance characteristics to be achieved are dictated by the stent application.
The term “metal” as used herein includes electropositive chemical elements characterized by ductility, malleability, luster, and conductivity of heat and electricity, which can replace the hydrogen of an acid and forms bases with the hydroxyl radical and including mixtures including these elements and alloys. Many examples are given below.
An aspect of the invention features a tubular prosthesis device for use within the body. Forming the tubular endoprosthesis is a metal filament material comprised of a metal outer member of extended length having an exposed outer surface and a core within the extended outer member formed of a different metal than the outer member. The core is secured within and substantially enclosed by the outer member. The device is capable of reduction to a small size for introduction into the body lumen and expandable to a sufficiently large size to engage the wall of the body lumen.
In some preferred embodiments, the outer member and core are such that the endoprosthesis is elastic and capable of radial reduction in size without plastic deformation to the small size for introduction to the body and self-expandable by an internal elastic self-restoring force to the large size for engaging the wail of the lumen.
In other embodiments, the outer member and core are such that the endoprosthesis is plastically deformable; it is formed of small size for introduction into the body and expandable by plastic deformation to the large size for engaging the wall of the lumen.
Various embodiments of the invention may also include one or more of the following features. The device is formed into the tubular shape by knitting of the wire or filament into loosely interlocked loops of the filament. The metal of the core has a density greater than the metal of the outer member of the device. The cross sectional dimension of the filament is about 0.015 inch or less. The cross-sectional dimension of the filament is about 0.006 to about 0.0045 inch and the core has a cross-sectional dimension of about 0.0014 to about 0.00195 inch. The core has a density of about 9.9 g/cc or greater. The core is selected form the group consisting of tungsten, tantalum, rhenium, iridium, silver, gold, bismuth and platinum. The outer member is selected from superelastic alloys and precursors of superelastic alloys and stainless steel. The outer member is nitinol. The core is tantalum.
Another, particular aspect of the invention features a self-expanding tubular prosthesis device for use within the body formed of loosely interlocked knitted loops of a metal filament material. The filament is formed of an elastic metal capable of deflection without plastic deformation to produce a self-restoring force. The filament material is formed of an elastic metal outer member of extended length having high elasticity and an exposed outer surface, and a core of a different metal than the outer member, which core is secured within and substantially enclosed by the outer member. The device is capable of reduction to a small size for introduction into the body lumen and expandable by the internal restoring force to a su
Boston Scientific Corporation
Fish & Richardson P.C.
McDermott Corrine
Phan Hieu
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