Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
1999-02-16
2002-11-26
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001150
Reexamination Certificate
active
06485524
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a stent for the treatment of pathological body vessels, which can be introduced into the body vessel in the form of at least two longitudinally extended filaments by means of an implantation device and assumes its predetermined form only at the site of implantation after the implantation has been carried out.
The introduction of spiral stents of metal or plastic into a diseased body vessel for treating pathological body and blood vessels is known. Such treatments are considered for diseased vessel occlusions or aneurysms, particularly of the aorta. The implantation of such vessel prostheses is made difficult due to the considerable diameter of these prosthesis. For the most part, only one surgical implantation of the vessel prostheses is possible in combination with an opening of the vessel and a subsequent vessel closure by means of a vessel suture. In the case of treatment of an aortic aneurysm, stents are introduced by means of the pelvic arteries. This treatment is made difficult or is completely obstructed by stenoses occurring principally in combination with aortic aneurysms and by the serpentine course of the pelvic arteries.
In the named cases, but also in the case of treatment of small vessels, such as intracranial vessels, it is advantageous to use stents, which can be widened from a small diameter present during the implantation to a larger diameter at the implantation site. It is provided accordingly to implant balloon-expandable and self-widening stents with a suitable catheter in the vessels to be treated. However, up to the present time, the named stents have still not fulfilled the technical prerequisites for a problem-free insertion.
Thus, for example, in the case of the so-called IN stent, this involves an elastic spiral, which is kept at a smaller diameter during introduction in the body vessel by the catheter, is released from the catheter at the site of implantation by means of a special mechanism, and then widens to its diameter of use.
Here, there is the disadvantage that the diameter of the spiral stent is at most double in the widened state when compared with the initial state, whereby relatively large puncture openings are necessary for introducing this type of stent. In this connection, the use of a thermo-memory wire has already been described in the paper “Transluminally placed coil spring endarterial tube grafts”, Invest. Radiol. (1969) No. 4, pages 329 ff. by Charles Dotter.
Thermo-memory wires are for the most part Nitinol wires, i.e., thus nickel-titanium alloys, which are brought to a predetermined form at temperatures between 400° and 500° Celsius, and keep this form up to a determined transformation temperature below body temperature.
The “thermo-memory property” is understood to mean that these wires lose their previous form and elasticity by an appropriate subsequent cooling, for example by means of ice water, and then are freely movable as longitudinally extended wire and are flexible. As soon as the wire has again warmed up to a temperature approximately corresponding to body temperature, such a wire springs back in a fully elastic manner into the spatial form impressed during the heat treatment.
Charles Dotter has proposed to implant a spiral stent from cooled thermo-memory wire in the form of a longitudinally extended wire, which then springs into the desired spiral and prosthetic form at the site of implantation, due to its described thermo-memory property. It has been shown that such simple coiled stents in their predetermined state have law stability and are also difficult to introduce and to place exactly.
A stent is known from WO 94/03127, in which several wire filaments that are longitudinally extended in an introductory shape assume in their predetermined state an undulating form that conforms to the vessel wall, whereby the wavy lines of two filaments are shaped each time such that a network comprised of approximately oval elements is formed. The stability of this network can be increased further in that wavy lines lying opposite one another are joined together at sites where they approach one another.
It is a disadvantage in this network-type stent that the implantation of such a complicated structure leads in particular to considerable difficulties in the case of greatly curved vessels. In addition, the construction of such a stent made of a multiple number of individual filaments requires a catheter with a relatively wide introduction diameter. Further, in this above-described stent, each time there is only one single predetermined diameter in the expanded or widened state. It is thus difficult to adapt the stent diameter to the diameter of the artery to be treated.
SUMMARY
The object of the present invention is thus to create a stent of the above-named type and functional purpose, which is characterized by a high stability as well as a simple handling during implantation and, in addition, has a high rate of expansion, i.e., a particularly high ratio of stent diameter in the expanded state to stent diameter in the introduction state.
This object is resolved in a stent having at least two filaments in the form of opposing spirals over at least one part of the longitudinal extent of the stent. The stent according to the invention thus exists in its predetermined state of at least two spirals, which are arranged opposite one another, thus in opposite rotational direction, and has the outer form of a tube. It is this double-spiral stent with filaments in the extended state, thus with a nearly one-dimensional structure, which is introduced.
A stent formed in this way has a high stability with a simultaneous high flexibility. The pitch of the individual spiral loops can thus be greatly modified over the entire length of the stent. This makes possible, in particular, a placement of the stent in greatly curved body vessels, without having to contend with adversely affecting the stability of the stent or damaging the lumen of the body vessel, if it becomes constricted, even if only in segments. The entire length of the stent body can also be modified due to the variability of the pitches of the individual spirals. In this way, for example, an improved anchoring of the stent within the body vessel can be achieved. Further, a varying load capacity or support capacity of the stent each time adapted to the vessel can be achieved in the treatment of vessel disorders, such as, for example, aneurysms. Spiral loops with smaller pitch, thus of higher density, are required roughly at the ends of an aneurysm stent in order to anchor the stent here, while in the region of the aneurysm itself, fewer spiral loops are required.
A particularly careful and simple implantation of the stent is then possible, if the filament is produced from a thermo-memory wire. In this connection, in particular, the use of Nitinol® wires is recommended. However, plastic filaments with suitable thermo-memory properties can also be used. Instead of the filaments produced from thermo-memory wire, high-elastic to super-elastic wires may also be selected as filaments, which arrive at the site of implantation in their predetermined spiral form, due to their special elastic properties. Such a filament can also be produced from Nitinol, from special steel, or also from suitable plastics.
Appropriately, there are two filaments, each time forming a coil of a single filament wire, which has a sharp bend, an arc-shaped piece or a loop roughly at the distal end of the stent, such that the configuration of two opposed spirals is made possible. Such a design has a high stability.
Instead of producing the double-spiral structure of the stent according to the invention from one filament wire, which is bent correspondingly into the shape of opposed spirals, it is also possible to cut the double-spiral structure of the stent from a tube-shaped workpiece. The cutting out can be produced very efficiently by means of a laser. The particular advantage of this configuration lies in the fact that the opposed spirals are already joined with o
McDermott Corrine
Pellegrino Brian E.
RatnerPrestia
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