Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent combined with surgical delivery system
Reexamination Certificate
2000-11-03
2002-10-29
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent combined with surgical delivery system
C623S901000
Reexamination Certificate
active
06471719
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to medical technology. The present invention particularly relates to expandable cardiovascular stents which are intended for radial arterial lumen recovery with subsequent restoration of normal blood flow.
BACKGROUND OF THE INVENTION
One of the most perspective tendencies in the development of stents is the design with improved antithrombotic properties to lessen the necessity of systematic anti-coagulation therapy and to reduce bleeding and vascular complications. However, all the currently available stents are executed from metal, and in each model there is a compromise between the constructive elements of radial strength and flexibility, to safely support the deformed walls of the artery and, with the least resistance, to prevent the normal pulsation of the vessel.
The variety of stent designs is determined, on the one hand, by the fact that the metal intravascular scaffolding must perform the vessel dilation and, on the other hand, must safely avoid penetration of the vessel wall or causing stenotic particles or thrombi to enter the blood flow. The stent should not injure the surrounding tissues that could take place during placement of the stent in the desired location of the pathological formation in the vessel, should not crumple upon the effect of blood pressure and the muscular influence, and should not deform and slide off the uninflated or not fully inflated dilatation balloon during delivery.
But the most important desired characteristic of a stent is that the stent should, as much as possible, have properties similar to the properties of the vessel itself. More particularly, the stent should not substantially correct the vessel hemodynamics, limit the vascular tissue pulsation, interfere with its blood flow, etc.
P. Ruygrok and P. Serruys, generalizing the results of the accumulated observations and the necessity of systematic increase in antithrombotic properties, recommend that the optimal stent design be provided with the following properties: flexibility, trackability, low profile, visibility, thromboresistance, biocompatability, reliable expandability (see “Calculation”, Vol. 94, No. 5, Sep. 1, 1996). Presumably, the creation of a stent meeting the above-mentioned requirements, as well as its equipment by a temporary constructive element for local drug delivery, is an efficient means for the reducing a systematic anticoagulation therapy, bleeding and vascular complications after a significant traumatic influence to which the deforming scaffolding of the vessel belongs.
The above enumerated recommendations for stent design are generally recognized. However, these recommendations cannot alone be used for stent design since they are devoid of criterion evaluations. It is natural that the clinical practice requires the specification and quantification of some stent basic properties that are to a considerable extent suitable for their use by the creators of new designs.
A number of requirements, adopted from the clinical practice and, in particular, formulated by Dr. Martin E. Leon (Cardiology Research Foundation, New York) could be stated as follows:
1. There should be sufficient metal coverage by the stent of the vessel lesion parts. For the vessels with a diameter of 3 to 4 mm, the metal coverage should be about 15 to 25%, reaching 30% in SVG segments with a diameter of about 5 mm.
2. The stent must have areas of differing qualitative properties, along its longitudinal axis. In particular, along the edges the stent struts should be more rigid, while in the stent middle part the stent struts should be more flexible.
3. It is necessary to ensure the axis perpendicularity and sufficient rigidity of the stent end face surfaces.
4. Preferably a stent will behave like a closed stent, but have the flexibility of an open stent.
5. In the stent, after expansion, the relatively small distances between the struts, about 1 mm, should be preserved.
6. The stent should operationally preserve invariable the radial sizes. This is connected with the non-admission of stent metal relaxation after expansion (no recoil).
7. It is desirable to have the stent length of from about 8 to 40 mm. A stent length less than 8 mm makes it difficult to ensure its stable location in a vessel, and a stent length more than 40 mm makes it difficult to place it effectively due to complicated anatomical outlines of the vessel. For example, if long coverage by a stent of the vessel lesion is needed, it will be better to implant several stents of a shorter length in consecutive order.
8. It is undesirable to change a stent's axial sizes upon its final expansion in a vessel.
9. Upon the stent expansion in a vessel the operational pressure of the guiding catheter balloon should not exceed 8 atm.
10. The stents of the considered class should have the necessary diameters from 2.0 mm to 5 mm.
11. The overall stent design should be capable of creating specialized models, such as, for example, a V-shaped stent with a special protection of pair vessels carina area, etc.
It is supposed that in the near future the number of various stent designs will become unlimited, though the expediency of the problem solution requires the creation of no more than ten different modifications, sufficiently universal and efficient models according to the generalized operational characteristics.
A balloon expandable sheet stent, in which the constructive elements are preliminarily formed in a shape of a stencil on the thin sheet metallic blank surface, is known (see the patent request PCT/IL 98/00189 from Apr. 21, 1998), as shown in
FIG. 1. A
stencil comprises two relatively rigid bands (
2
,
3
) whose branches form periodically repeating winding outlines (
4
) which, in the stent expandable shape, take the form of the semicircles, placed one after another oppositively in relation to the relatively rigid bands (
2
,
3
) in an alternative sequence along the stent longitudinal axis.
Such a location of the stent semicircles (
5
,
7
) with a side view on the relatively rigid bands (
6
) location plane is schematically shown in FIG.
2
. The prototype-stent has high functional properties and, in general, corresponds to the requirements demanded from such designs. The stent constructive elements, circular in the light, allow to register its diameter with precision. Besides, the semicircles arch-shape possesses a heightened stability that makes it possible to use thin blanks in a stent metal cover that can stand pressures, including extreme ones, from the side of the pulsating vessel, and at the same time the semicircles arch-shape has a good capacity of shape-retention after the removal of the guiding catheter balloon pressure (no recoil).
The relatively rigid bands (
2
,
3
) reliably ensure the stent axial lengths. Also, such a stent design has high technological possibilities that are determined by the capacities of creating a volumetric device from the thin sheet metallic blank without applying the known connecting means (welding, soldering, lock connections, etc.).
However, the prototype-stent has some essential drawbacks. To create a stent tube form the neighboring semicircles are folded into opposite sides, thus making the clearance between the neighboring semicircles (
5
,
7
), but folded into one side, an increased one. For a number of cases this fact limits the use of a stent in the clinical practice. Moreover, the semicircles alternation along the longitudinal axis, shown in
FIG. 2
, creates on the stent end faces some “steps”, contrary to the notion that the stent axis end will be perpendicular.
This stent design, as well as the majority of the known clinical models, possesses the same monotonous properties along its entire extent. This does not always correspond in its extent to the anatomical properties of a vessel, especially to that with the pathological changes, requiring correction of the angioplasty. In addition there are some definite differences in the hemodynamics inside the stenting and those sections of the vessel that adjoin it. The co
Boldyrev Romul
Voinov Valerian
Jackson Suzette J.
McDermott Corrine
Reed Smith LLP
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