Device for inserting an implant

p0001The invention relates to a device comprising an endovascular implant which is intended for introduction into blood vessels or body cavities of the human or animal body, and an insertion aid, wherein the implant and the insertion aid are connected to each other by means of a detachment element which is electrolytically corrodible After implantation of the implant into the body, a minimum partial dissolution of the detachment element and a detachment of the implant from the insertion aid takes place by applying a voltage.

p0002The use of endovascular techniques for the occlusion of body cavities or vessels such as arteries, veins, fallopian tubes, or vascular malformations (eg, vascular aneurysms) is known in the art. In this case, for example, so-called occlusion coils are inserted through a catheter into the cavity to be occluded and deposited there by means of an endovascular guide wire serving as an introduction aid. The implantation of other implants, for example stents, is also known.

p0003Various methods for isolating the implant from the insertion aid are known from the prior art. In addition to mechanical methods, the electrolytic detachment of stainless steel wire spikes, such as those described for the first time in electrocoagulation by Thompson et al. And McAlister et al. In 1979 (<nplcit id="ncit0001" npl-type="s"><text>Radiology 133: 335-340, Nov. 1979</text></nplcit>; <nplcit id="ncit0002" npl-type="s"><text>AJR 132: 998-1000, June 1979</text></nplcit>). Based on this, the<patcit id="pcit0001" dnum="EP0484468B1"><text>EP 0 484 468 B1</text></patcit> A device for implanting occlusion coils based on electrolytic detachment.

p0004Similar devices also disclose the <patcit id="pcit0002" dnum="US20060282112A1"><text>US 2006/0 282 112 A1</text></patcit>. In addition, various materials for the catheter, including MP35-M, of an alloy containing 35% N: 35% Co, 20% Cr and 9.75% Mo, can be found in this document.

p0005Irrespective of the type of the implant to be inserted, it is always important for the treating physician to keep the peeling time as short as possible so that, for example, there is no displacement of the implant or other unpredictable things during the detachment. For this reason, different materials have been used in the past for the separation element arranged between the implant and the insertion aid, which enable a rapid resolution when a voltage is applied. In the<patcit id="pcit0003" dnum="WO03017852A1"><text>WO 03/017852 A1</text></patcit> For example, a stainless steel which has been subjected to a pre-corrosion process by a heat treatment is used.

p0006The <patcit id="pcit0004" dnum="US2006082112A1"><text>US 2006/082 112 A1</text></patcit> Forms the preamble of claim 1.

p0007SUMMARY OF THE INVENTION The object of the invention is therefore to provide a device of the initially described type with means which further reduce the removal times of the implant from the insertion aid.

p0008This object is achieved according to the invention by a device comprising an endovascular implant which is provided for introduction into blood vessels or body cavities of the human or animal body and an insertion aid, the implant and the insertion aid being connected to one another via a detachment element which is electrolytically corrodible , So that, after introduction of the implant into the body, at least a partial dissolution of the detachment element and a detachment of the implant from the insertion aid takes place by applying a voltage, the detachment element being made of a cobalt chromium alloy containing at least 20% by weight of cobalt And 10 to 40% by weight of chromium.

p0009It has surprisingly become apparent that detaching elements based on cobalt-chromium alloys allow extraordinarily short peeling times when a voltage is applied. These are generally less than 30 s (2 V, 2 mA). Peel-off times of only 5 s are also possible, whereby the peel-off times also depend, of course, on the thickness of the peel element. Compared to the prior art, which is described, for example, in the<patcit id="pcit0005" dnum="WO2005070308A2"><text>WO 2005/070308 A2</text></patcit> Of 20 to 40 s under otherwise identical conditions, this represents a significant improvement.

p0010Cobalt-chromium alloys can be used as they are known as stellite^® By the company Deloro. These are cobalt-chromium alloys, which can have fractions of tungsten, nickel, molybdenum, iron and other elements. Stellite^® Are very resistant to wear, which is why they are used in particular for components which are exposed to high loads. All the more surprising was the realization that from Stelliten^® Can be dissolved electrolytically particularly rapidly.

p0011The content of cobalt is preferably at max. 70% by weight, in particular a content between 30 and 60% by weight is advantageous. The chromium content can in particular be 15 to 30% by weight.

p0012Further elements can improve the properties of the release element. Thus, an alloy with 4 to 12% by weight of molybdenum and / or 5 to 20% by weight of tungsten is advantageous.

p0013The content of nickel, manganese or iron can be significantly higher if necessary and, in the case of manganese and iron, up to 30% by weight. The nickel content can be between 8 and 40% by weight.

p0014Examples of useful cobalt-chromium alloys are those as described under the names Elgiloy^® or Phynox^® to be expelled. The German material number is 2.4711. The alloy contains 40% by weight of cobalt, 20% by weight of chromium, 16% by weight of iron, 15% by weight of nickel and 7% by weight of molybdenum and optionally in small amounts of manganese, carbon, silicon, phosphorus , Sulfur and beryllium.

p0015Another suitable alloy is Stellite^®25. This alloy contains, inter alia, approximately 50% by weight of cobalt, 20% by weight of chromium, 10% by weight of nickel and 15% by weight of tungsten. Another example is Stellite^®21 with about 63% by weight of cobalt, 28% by weight of chromium and 6% by weight of molybdenum.

p0016The introducer aid is preferably a conventional guide wire, as has proven itself to bring occlusion helixes or stents to their destination through a catheter. The insertion aid closes proximally to the implant, ie in the direction from which the doctor advances the implant.

p0017The implant may be an occlusive helix or a stent. In addition, the implant can also be a stent-like system for influencing the blood flow, which is either braided, laser-cut from a metal or plastic film, or through suitable plastic membranes. In principle, however, the invention can be used for all types of endovascular implants which are brought to their destination by means of an introductory aid and are to be detached there from the insertion aid. Implants are also understood to mean objects which are designed to be detachable only in an optional manner and remain in the body or are removed again depending on the course of the treatment. An example of this are detachable stent retriever systems for removing or displacing thrombi.

p0018Advantageously, the detachment element consists of one or more wires. The thrust or tensile forces can be passed on well over the wires so that the treating physician is able to perform both simple feeding and retraction of the implant. Simple positioning is important for the physician to bring the implant exactly to the desired destination.

p0019The wire or wires may have a round, square, oval, or tubular cross-section. Any desired combinations, for example of round and square wires, are also possible. The wires are usually produced by pulling the raw material onto the corresponding end cross-section. The structure of the microstructure and thus the peel-off properties of the peeling element can be controlled by the drawing process. By varying the cross-section and the shape of the wires, these can be optimally adapted to the application purpose.

p0020In order to further simplify the detachment, it is possible to perform a surface treatment on the detachment elements. A roughening of the surface, for example, results in a faster resolution as the surface area of ​​the detachment element is increased. Also known are further possibilities for moving a detachment element to a faster resolution by means of an additional treatment, for example from the already mentioned one<patcit id="pcit0006" dnum="WO03017852A1"><text>WO 03/017852 A1</text></patcit>, To which reference is hereby made. For example, the detaching element can be subjected to a heat treatment in the sense of a precipitation process, by means of which the metal in its structure is modified in such a way that it decomposes particularly rapidly upon application of an electrical voltage in an electrolyte. Such a heat treatment is possible with the aid of a laser, in a furnace or by means of an induction coil. The cooling is advantageously relatively quickly in the form of a repelle kung. In this way, microstructural states are generated which promote the electrolytic dissolution.

p0021Cobalt shows a reversible allotropic phase transformation during heating and cooling. At high temperatures, the cubic-surface-centered phase (α-cobalt) is stable, which, when cooled at about 420 ° C., transitions into the hexagonal ε-cobalt. While ε-cobalt is very poorly formable, the metastable α-phase is more ductile. The transformation temperature between the two phases can be varied by the choice of different alloying additives. In principle, additions of chromium, molybdenum or tungsten stabilize the hexagonal phase and reduce the stacking energy, while the elements iron, nickel and manganese favor the cubic phase and increase the stacking energy. After the solution annealing, the alloy normally consists mainly of α-cobalt, then the content of ε-cobalt is increased by cold forming (eg wire drawing) and / or precipitation processes. By means of a precipitation hardening, intermetallic phases can be precipitated from the alloy, which increases the corrosion susceptibility of the alloy. Ultimately, the alloy should predominantly be metastable as α-cobalt but also have a certain content of ε-cobalt.

p0022Also possible are other types of additional treatment, such as pre-corrosion, for example by means of an etching. Furthermore, it is possible to passively detach the detachment by construction-induced formation of local corrosion elements. Corrosion elements of this type are formed in the adjacent arrangement of different noble metals, ie the detachment element is made of a less noble metal than the implant and / or the insertion aid.

p0023The dissolution of the detachment element is effected by applying an electrical voltage. This can be either alternating current or direct current, with a small current intensity (&lt;3 mA) being sufficient. The detachment element is the anode at which the oxidation and dissolution of the metal takes place.

p0024In order to improve the active influence on the resolution, it may be useful to construct the detachment element in such a way that the local corrosion elements described above are avoided. This can be done, for example, by insulating the detachment element against adjacent regions of the device, for example by means of insulating adhesive connections between the detachment element and the implant.

p0025The electrolytic detachment takes place by applying an electrical voltage to the detachment element by means of a voltage source. The detachment element serves as an anode, while the cathode is positioned on the body surface. Of course, the detachment element has to be electrically connected, in particular via the insertion aid, to the voltage source. In this case, the insertion aid must also be electrically conductive. Since the corrosion current which is produced is controlled by the area of ​​the cathode, the area of ​​the cathode should be selected to be significantly greater than the area of ​​the anode. To a certain extent, the resolution speed of the detachment element can be controlled by adjusting the cathode area relative to the anode area. The invention accordingly also relates to a device which comprises a voltage source and optionally an electrode which can be placed on the body surface.

p0026Alternatively or additionally, further measures can be taken to assist the detachment of the detachment element. In this context, the use of light waves, sound (ultrasound) or magnetic forces is mentioned.

p0027In addition, it is expedient if a securing means runs through the implant. Such securing means have the advantage that, in the event of incorrect positioning of the implant, the necessary retraction into the catheter becomes significantly safer. The retraction, for example, of an occlusion helix without securing means entails the risk that parts of the helix are pulled apart by tensile or torsional stress and thus irreversibly plastically deformed. In an extreme case, the helix can tear or break, which can lead to a life-threatening embolism. Both fuses of flexible polymer filaments and materials with shape memory properties have been described.

p0028Devices have already been described in which several detachment elements are provided so that, if necessary, variable-dimensioned lengths of the implant can be placed at the intended location. This makes it possible, for example, to deposit occlusive coils in precisely the right length in the aneurysm. In this context,<patcit id="pcit0007" dnum="WO0132085A1"><text>WO 01/32085 A1</text></patcit> Respectively.

p0029The use of such implants, which can be electrolytically corroded in several places, is based on the recognition that, when a current is applied to such a device, the detachment point nearest to the distal end of the catheter is specifically dissolved by electrolysis. This is because, on the one hand, the detachment points located in the catheter are isolated from the ionic medium through the catheter and therefore can not be subjected to electrolysis, and on the other hand the current density decreases from proximal to distal as a result of the distally increasing resistance. The electrolytically corrodible position adjoining the distal end of the catheter distal to the distal end of the catheter is therefore subject to the strongest electrolytic processes and preferably dissolves.

p0030The use of platinum or platinum alloys has proved particularly suitable for the formation of the implants. These have, inter alia, the advantage that they are X-rayed and thus the introduction of the implant can be easily visualized. The cobalt-chromium alloys used for the detachment element are generally MR compatible and therefore also permit visualization.

p0031The device according to the invention can also be present directly in combination with a microcatheter, by means of which the implant is brought to its intended location by means of the insertion aid. The catheter and the implant used should be matched in terms of their dimensions. If necessary, The catheter can also exert a constraint on the implant, which causes the implant to assume a secondary structure which has previously been impressed upon it after release from the constraint. In addition, the catheter is additionally provided with X-ray markings, which enable positioning in the target region by means of known imaging methods.

p0032Typically, the detachment element has a length of 0.05 to 0.5 mm, in particular about 0.2 mm, and a diameter of 0.04 to 0.5 mm, in particular about 0.1 mm.

p0033The invention is described with reference to the appended claims <figref idrefs="f0001">FIG</figref> In more detail. This shows the schematic structure of the device according to the invention.

p0034The device is composed of an implant 1, an insertion aid 2 and a detachment element 3. The insertion aid 2 is located at the proximal end, the implant 1 at the distal end, ie, in the feed direction of the device. The implant 1 is brought to its intended location by advancing the insertion aid 2 in a catheter not shown here.