Catheter for producing a stent containing plastic

In order to create a stent, which despite being simple to guide in the relevant body conduit allows flexible adaptability to the body conduit in a simple manner while avoiding undesirably high expansion forces on the wall of the body conduit, in accordance with the invention a catheter is provided, with an essentially tubular filling area surrounding the part of the catheter which can be introduced into the body conduit, which can be filled with a plastic mass which forms the stent by a process of hardening; there is provision for positioning the filling area at the position intended for the stent in the body conduit, for hardening the plastic mass in the filling area, for creating the stent and for removing the catheter from the body conduit with the stent remaining in the body conduit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German application No. 10 2005 024 626.5 filed May 30, 2005, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to a catheter for producing a stent containing plastic, with simultaneous positioning of this stent in body conduit, especially in the form of a blood vessel.

BACKGROUND OF THE INVENTION

A stent is a tubular implant which provides radial outwards support for the wall of a body conduit, e.g. a blood vessel, bile duct, an air conduit or an esophagus. The stent usually consists of the elastic material, e.g. a metal or metal alloy or a polymer and frequently has a mesh or network or spiral-type structure, with stents in the form of a metal mesh being the most widely used. The stent is introduced into the relevant body conduit with the aid of a catheter and once in place, is bought into adhesive contact with the wall of the body conduit. Stents are used in particular with blood vessels as endoluminal vessel prostheses in the vessel wall for artherosclerotic stenosis therapy.

Contracting the stent to make it easier to introduce into the body conduit, introducing it in the contracted state with the aid of a catheter into the relevant body conduit and expanding the stent there with a balloon end of the catheter or by self-expansion into an expanded diameter is known from DE 199 51 279 A. The use of the high-grade elastic nickel titanium alloy Nitinol as a stent material is additionally known from DE 199 51 279 A1.

The stent used in each case must be precisely tailored in its length and in its expansion diameter to the characteristics of the relevant body conduit, in order on the one hand to sufficiently expand this conduit or support it and on the other hand so as not to slip within the body conduit, without however exercising such high expansion forces on the wall of the relevant body conduct that the result is an undesirably great expansion of the body conduit or even an injury to it. It is also known from the previously mentioned DE 199 51 279 A1, in order to avoid expansion forces which are too high, to provide the stent body at least partly with a covering which essentially prevents the stent body expanding fully in the direction of its free diameter.

A device for producing a stent, especially one containing a polymer material, is known from DE 69202308 T2. The stent consists of a cylindrical body which, when positioned at the desired location in the body conduit, can be expanded radially so that it delimits a hollow cylindrical cavity. This cylindrical body is filled before being used in the body conduit with a material which can be hardened so that after its radial expansion the device is hardened.

SUMMARY OF THE INVENTION

The underlying object of the present invention is to create a stent, which despite being simple to guide in the relevant body conduit, allows flexible adaptability to the body conduit in a simple manner while avoiding undesirably high expansion forces on the wall of the body conduit.

This object is achieved by a catheter in accordance with the independent claim; Advantageous embodiments of the invention are the subject of the assigned subclaims.

By filling the inventive, essentially tubular filling area surrounding a part of the catheter introduced into the body conduit with a plastic mass which can be hardened into the stent it is possible to produce the stent directly at a position in the body conduit intended for the stent, in order on the one hand to avoid an elastic expansion in accordance with the previous positioning methods and in this case any undesirably high expansion forces which may occur, and on the other hand to adapt the stent in its form to the relevant structure of the body conduit, especially avoiding sharp edges which can injure the body conduit; Through this adaptation the stent is also especially safely secured against slippage within the body conduit through a close-fitting adhesive contact with the wall of the body conduit. In addition this flexible adaptability avoids the otherwise necessary stockpiling of a large number of stents which differ for example in their form, their expansion diameter and their length. The invention also makes it possible to produce and position stents in a particularly cost-effective manner.

It is useful for the plastic material used for the plastic mass to be bio-compatible, with polymers, especially elastomers such as silicon or rubber elastomers being especially suitable as a result of their elastic properties.

Through an inner chamber connected, especially via a closable opening, to the filling area for temporarily accepting the plastic mass it is possible, for simple introduction of the catheter into the body conduit, to fill the filling area with the plastic mass only once the stent has reached its intended position. To tailor the stent particularly well to the body conduit, a filling area expandable in an attachable form by filling it with the plastic mass especially temporarily accommodated in the inner chamber, is provided. Usefully the filling area is filled by a pressure exerted on the plastic mass.

In order on the one hand to securely prevent the plastic mass from escaping into the rest of the body conduit by keeping it in the filling area, and on the other hand to enable the form of the stent to be influenced, a delimiting means is provided on the catheter which restricts the filling area and at least partly defines the form of the stent. The delimitation is particularly successful with a delimiting means in the form of an envelope completely surrounding the filling area; especially by providing a method of releasing the envelope from the catheter it is possible in a simple manner to separate the catheter from the stent, with the envelope remaining in the body conduit as a component of the stent.

In an especially simple manner the delimitation means is embodied in the form of two seals delimiting the filling area at one of the two ends in each case from the rest of the body conduit; an embodiment of the seals whereby the catheter can at least partly expand and retract them or fold them in and out makes it possible on the one hand to retract the seals for an especially simple introduction of a catheter into the body conduit and only on reaching the position intended for the stent to extend them or fold them out again and on the other hand to retract the seals or fold them in to make it especially easy to release the stent from the catheter after the hardening of the plastic mass. The extension or retraction of the seals can for example be undertaken by an expansion or by a contraction of the seals.

In accordance with an advantageous embodiment of the invention a closable capsule which only extends over part of the length of the catheter is provided as a part of the inner chamber; This makes it possible in a simple manner to introduce the plastic mass in the capsule together with the catheter into the body conduit and there to fill the filling area with the especially liquefied plastic mass from the capsule.

In accordance with a further advantageous embodiment of the invention, a tube leading to an operating end of the catheter which remains outside the relevant body conduit is provided as part of the inner chamber; This makes it possible in a simple manner to fill the filling area located at the position intended the stent with the plastic mass, especially in a liquefied form, from outside through the operating end.

Advantageously a means for liquefying and/or for hardening the plastic mass is provided by a temperature variation; this makes it possible for the plastic mass, because of its particularly good malleability in the liquid state, to be adapted especially well to any characteristics of the body conduit and makes the filling area particularly easily to fill.

To enable the internal diameter of the stent be adapted, an inflatable balloon section is provided arranged within the tubular filling area; this is inflated after positioning of the filling area in accordance with the desired internal diameter, e.g. by introducing fluid into it.

In order to additionally stabilize the stent, an embodiment of the filling area is provided for accommodating a wire mesh which can be encapsulated with the plastic mass. This wire mesh is encapsulated with the plastic mass when the filling area is filled. When a self-expanding wire mesh is used it is worthwhile to force this initially into an unexpanded form with an additional removable sheath over the wire mesh and only let it expand by removing the sheath once the intended position is reached.

An embodiment of the filling area to accept markers which can be encapsulated by the plastic mass and are impermeable to x-radiation makes it possible to create a stent of which the position and/or the sizes can be detected on an x-ray image of the relevant body conduit on the basis of the markers encapsulated into the stent; Such markers are for example rings made of gold arranged on the end of the stent.

As an alternative or in addition to the markers encapsulated into the stent, the position and/or size of the stent can be made visible by an image created by an imaging method especially on an x-ray image, by the plastic mass being mixed with either a positive or a negative contrast means. Since the mixing covers the entire stent, this stent, by contrast with the stent known from DE 199 51 279 A1 with a simple coating, can be more easily seen on the relevant image.

For an imaging process based on x-radiation for example, substances containing iodine and substances containing iron ox-ide particles for an imaging system based on magnetic resonance are suitable as a positive contrast means. The positive con-trast means can be mixed into the plastic mass especially sim-ply in powder or crystalline form, e.g. as a salt of triiodo-benzoic acid.

For an imaging method based on x-radiation and for sonography, gases such as carbon dioxide are suitable as negative contrast means for example. These gases can be mixed especially simply with the plastic mass in the form of gas bubbles encapsulated in plastic. In a practical application this mixing can be undertaken by foaming the gas through the plastic mass or by adding small plastic balls which each have the gas inside them in a hollow cavity.

To expand the body conduit to a desired diameter it is useful, before positioning the stent, to perform a balloon dilatation of the body conduit.

FIGS. 1-4illustrate the inventive method for producing a stent with reference to an exemplary embodiment of an inventive catheter.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows, in a longitudinal section, a part of a catheter2introduced into a body conduit1, with the catheter2being surrounded by an essentially tubular-shaped filling area3which is enclosed within an envelope4and which is connected via two openings5or6to an inner chamber, in this exemplary embodiment in the form of a cylindrical capsule8, arranged in the catheter2, containing a liquefied and hardenable plastic mass7. The plastic mass7is mixed with a substance impermeable to x-radiation, e.g. a crystalline salt of triiodobenzoic acid. The envelope4is held onto the catheter2at its front and rear end by a clamping ring9or10which can be expanded and retracted, which encloses the entire circumference of the catheter2in each case, so that the filling area3is completely sealed from the body conduit1. The two openings5and6each have an opening slider11or12, with which the openings5or6are each closed. To fill the filling area3with the plastic mass7from the capsule8a piston13which can be moved within the capsule is provided. The clamping rings9or10, the opening sliders11or12and also the piston13are remotely operated or at least partly controlled by a person operating the catheter2. The catheter2is already positioned with its filling area3at the position intended for the stent.

FIG. 2shows the catheter2fromFIG. 1, with on the one hand the openings5and6being opened by moving one of the sliders11or12in each case and on the other hand the piston13being pushed into the capsule, so that the filling area3is filled with the plastic mass7from the capsule8and is thereby expanded towards the wall of the body conduit1. This expansion does not create any undesired expansion forces since the viscous plastic mass7can distribute itself to adapt to the wall of the body conduit1.

After the openings5or6have closed once more, the plastic mass7is hardened to produce a stent14, depending on the plastic e.g. simply by a hardening period elapsing.

FIG. 3shows the catheter2fromFIG. 2, with the openings5or6closed again, the plastic mass7already hardened into a stent14and in addition the envelope5released from the catheter2by retraction of the clamping rings9or10. In this state it is possible to remove the catheter2from the body conduit1with the stent14simultaneously remaining in the body conduit1.

To adapt the stent14in respect of its internal diameter, an inflatable balloon section arranged within the tubular filling area3is provided, which is inflated after the positioning of the filling area3at the position intended for the stent14. To make the diagram as easy to understand as possible this balloon section is not included as part of the drawing in this exemplary embodiment.

FIG. 4shows the body conduit1fromFIGS. 1-3with the stent14produced by the catheter2after the removal of the catheter2from the body conduit, with the envelope4released from the catheter2remaining with it in the body conduit1as part of the stent14. Mixing-in a substance impermeable to x-radiation with the plastic mass7, enables the stent14produced from the plastic mass7to be easily recognized on an x-ray image of the body conduit1.

To enable stents of different lengths to be produced with the same catheter, further clamping rings can be provided between the clamping rings9or10. The envelope4is accordingly held by one of its ends with clamping ring10and with its other end by one of the other clamping rings.

FIG. 5shows in a longitudinal cross section such as that shown inFIG. 2, a catheter2introduced into a body conduit1with an essentially tubular filling area3surrounding the catheter2, which is delimited by two seals in the form of two elastic expansion rings16or17expanded by application of force, each of which takes in the entire circumference of the catheter2, from the rest of the body conduit1and which is connected via the two openings5or6with an inner chamber arranged in the catheter2containing a viscous and hardenable plastic mass7, in this exemplary embodiment in the form of a tube15leading to an operating end arranged outside the body conduit1. As in the previous exemplary embodiment, in this embodiment too the two openings5and6each have an opening slider11or12, with which the openings5or6can be closed in each case. In addition two markers impermeable to x-radiation in the form of two gold rings29and30are arranged around the catheter2, which each enclose the entire circumference of the catheter2and are held in their position by four retaining bolts31-34or35-38arranged in pairs on opposite sides of the catheter2and able to be withdrawn completely into the catheter2.

In the drawing the filling area3is already positioned at the position intended for the stent and is filled by introducing the plastic mass7via the end of the tube arranged at the operating end of the catheter2. To simplify the filling it is useful to liquefy the plastic mass7, e.g. by heating it beforehand. After the plastic mass7has hardened into the stent the next steps provided are to close the openings5or6with the opening sliders11or12, to harden the part of the plastic mass located in the filling area7into a stent, to release the stent from the catheter2by retracting the rings16or17by means of a pressure reduction, to retract the retaining bolts31-38fully into the catheter and to remove the catheter2from the body conduit1, with the stent remaining as intended in the body conduit1.

It is also possible to retract the retaining bolts31-34or35-38before the filling of the filling area3or at least before the hardening-off of the plastic mass7, if nec. coupled with the closing of the openings5or6by the opening sliders11or12, in order to avoid the retaining bolts31-34or35-38pressing into the hardening plastic mass7and causing unevenness in the stent.

FIG. 6shows, in a longitudinal cross section such as that shown inFIG. 2or5, a catheter2introduced into the body conduit1with a filling area3which is enclosed by an envelope4and is already filled with a plastic mass7on introduction of the catheter2into the body conduit1. The filling area3is embodied so that, in addition to the plastic mass7, it can also accommodate a wire mesh28encapsulated by the plastic mass7, which is provided for additional stabilization of the stent formed later by the hardening of the plastic mass7. Within the essentially tubular filling area3is arranged a balloon section18belonging to the catheter2, of which the balloon envelope19—like the envelope4of the filling area3in FIGS.1and2—is held onto the catheter2at its front and rear end by an expandable and retractable clamping ring9or10in each case, so that the inner area of the balloon section18is completely closed off from the body conduit1. The filling area3is completely surrounded by the envelope4and the balloon envelope19together. The balloon section18is connected via two line openings21or22with a line20arranged in the catheter2which leads to the operating end of the catheter2and to which a fluid27, e.g. in the form of a cooking salt solution, can be fed to the balloon section18. The line openings21and22can be closed off with the aid of a flap23or24by hinging the flaps in the direction25or26.

In the drawing the filling area3is already positioned at the position intended for the stent and the balloon section18is inflated by feeding the fluid27into it, so that the filling area3is pressed with the plastic mass4onto the wall of the body conduit1. The internal diameter of the stent which can be made from plastic is determined by the volume of the fluid27fed into the balloon section18. After the plastic mass7hardens into the stent, the next steps provided are to close off the line openings21or22with the flaps23or24, to release the balloon envelope19and thus also the envelope4of the filling area3and the stent from the catheter2by retracting the clamping rings9or10and finally to remove the catheter2from the body conduit, with the balloon envelope19and the envelope3remaining with the stent as components of it in the body conduit1. Usefully the non-functioning free ends of the balloon envelope19consist of a material which can be broken down by the body, so that after a time necessary to break down the free ends, only the hardened plastic mass4of the stent, if necessary with an encapsulation surrounding the plastic mass, remains behind.

It is possible, for hardening the plastic mass by heating it up, to arrange a heating element in the catheter2, e.g. in its balloon section18. In addition the plastic mass can be heated up indirectly by a heating means arranged at the operating end of the catheter, from which the heat is transported to the plastic mass7via the fluid27circulating in the tube15; to this end a conduit for feeding in the heated fluid27and a further conduit for taking away the fluid cooled by the heat dissipation to the plastic mass7can be provided in the tube15.

It is further possible not to leave the balloon envelope18—permanently connected to the catheter2—in the body conduit1, but to remove it together with the catheter2from the body conduit1.

The invention can be summarized as follows: In order to create a stent, which despite being simple to guide in the relevant body conduit allows flexible adaptability to the body conduit while avoiding undesirably high expansion forces on the wall of the body conduit, in accordance with the invention, a catheter is provided with an essentially tubular filling area surrounding the part of the catheter which can be introduced into the body conduit, which can be filled with a plastic mass which forms the stent by a process of hardening; there is provision for positioning the filling area at the position intended for the stent in the body conduit, for hardening the plastic mass in the filling area for creating the stent and removing the catheter from the body conduit with the stent remaining in the body conduit.