Patent Description:
Rapidly biodegradable vascular supports for sealing vulnerable plaques or biodegradable vascular supports as temporary flow diverters for treating aneurysms are not available in the market.

If permanent or slowly degradable vascular supports are used for this purpose, even though an implant is only required for a very short period of time, the implant (for example, due to potential thromboses) or necessary long-term medication (for example, additional hemorrhage due to the administration of thrombocyte aggregation inhibitors) poses a potential longer-term or permanent risk in the least favorable case, for example in the case of intracranial aneurysms with permanent implants.

The biodegradable vascular supports/scaffolds available in the market were primarily developed to preserve as great a radial force as possible for the longest possible time, which is not even required for the above-described applications.

The disadvantages of these implants, which are predominantly made of plastic (PLLA), are, in principle, high wall thicknesses, in many instances poor adaptation to the shape of the vessel (malapposition), very long degradation times and, resulting from all these factors, a relative high risk of thrombosis.

Mg-based vascular supports additionally result in a permanent degradation product; however, the tendency to cause thrombosis appears to be drastically reduced compared to permanent metals and plastic materials, regardless of the wall thickness.

<CIT> is directed to a stent made of a magnesium alloy degradable under physiological conditions and an outer polymeric coating that allows to control the degradation of the stent. The biologically degradable magnesium alloy contains <NUM>-<NUM> wt% dysprosium, <NUM>-<NUM> wt% neodynium and/or europium, <NUM>-<NUM> wt% zinc, <NUM>-<NUM> wt% zirconium , balance to <NUM> wt% magnesium wherein the stent has a polymeric coating. The polymer coating comprises or consists of one or several substances selected from the group consisting of one of several substances selected from a list including polylactides, polyglycolides, polyanhydrides, polyhydroxybutyrate, polycaprolactone, polydioxanone. After the entire dissolution of the inner basic scaffold, the polymeric coating can also be degraded biologically, so that after a few months the stent has entirely dissolved.

Proceeding from this, the object underlying the invention is to provide an implant or a vascular support that is at least partially improved with respect to the aforementioned disadvantages, and additionally shows substantially residue-free degradation. In particular, a rapidly biodegradable vascular support is to be provided, which has mechanical integrity that is limited in terms of time and which can be degraded after the mechanical integrity has been lost, and preferably is used to seal vulnerable plaques or as a temporary flow diverter for treating aneurysms.

This object is achieved by an implant, in particular a vascular support, having the features of claim <NUM>. Advantageous embodiments of the invention will be described hereafter.

According to claim <NUM>, an implant is disclosed, in particular a vascular support, in particular for implantation into a vulnerable plaque or for disrupting the flow into an aneurysm, wherein the implant can be fully biodegraded within a time period of less than <NUM> days, in particular of less than <NUM> days, preferably of less than <NUM> days, wherein the implant in particular comprises a magnesium alloy or is made thereof, including Zn (zinc) and Ca (calcium).

The invention thus in particular provides an implant or a scaffold/vascular support that can be implanted into an existing vulnerable plaque, so that uncontrolled rupturing of the plaques, and a potentially subsequent thrombotic event, can be prevented, and the implant can, thereafter, be completely biodegraded within a time period of less than <NUM> days, preferably of less than <NUM> days, and ideally in less than <NUM> days.

Furthermore, one embodiment of the invention relates to an implant or a vascular support/scaffold that, when an aneurysm exists, disrupts the flow into the arising cavity which maintains this aneurysm from a fluid point of view, so that a flow-free zone can arise in the space of the former aneurysm and the cavity can be incrementally closed by coagulation and cell colonization. In the process, depending on the requirements of the therapy, the implant is to be completely dissolved after a time period of less than <NUM> days, less than <NUM> days, or even less than <NUM> days, so that the risk of thrombosis caused by a foreign object or a degradation product is avoided, especially in intracranial vessels. The invention relates in particular to an implant for treating local vascular diseases that require only short-term mechanical stabilization (for example vulnerable plaques or aneurysms). According to one embodiment of the invention, it is provided that the implant is made of or comprises a biodegradable magnesium alloy, in which the time until full biodegradation can be varied by way of the content of the involved alloying elements. The implant (for example vascular support) can be coated with a polymer, and this polymer can contain a pharmaceutical drug.

As a result of rapid degradation of an implant in the two applications mentioned above, the time during which a patient has to be treated with thrombocyte aggregation inhibitors (dual antiplatelet therapy, DAPT) is also decreased. A shorter therapy duration reduces the risk of undesirable hemorrhage. In addition, minimal and only brief mechanical loading of the vessel decreases a provocation of the excess proliferation of neointima and potential stenosing of the affected vascular section associated therewith.

According to the invention, a biodegradable vascular support is provided, which can be implanted into the vascular wall at the appropriate location by way of a balloon. Such a vascular support is made of a biodegradable metal. To achieve complete dissolution after less than <NUM> days, a magnesium alloy (Mg alloy for short) is used for this purpose. The Mg alloys are those alloys that contain Zn and optionally Ca.

Surprisingly, it was additionally shown in animal experiments that this group of alloys can be degraded to a very large degree after a comparatively shorter implantation duration, and can be fully degraded in the case of the more rapidly degrading alloys that have higher Zn contents, without leaving behind a degradation product or a relevant amount of residues.

This finding was not to be expected insofar as other previously examined alloys, specifically magnesium alloys, that contain rare earths or aluminum as the alloying elements have a longer degradation time, and leave a degradation product behind.

The degradation kinetics can be set by way of the Zn content or by way of the Zn/Ca ratio, in general the following applying:.

According to the invention, it is provided that the Mg alloy is a Mg alloy having a Zn content between <NUM> wt. % and <NUM> wt. % Zn and comprising <NUM> wt. % to <NUM> wt.

According to a further embodiment, preferably Mg alloys comprising between <NUM> wt. % and <NUM> wt. % Zn are to be selected, in particular for full thermomechanical processability, since all the Zn can be brought into solution at up to <NUM> wt.

According to a further embodiment, Mg alloys having a Zn content of ≥ <NUM> wt. % and a Ca content of < <NUM> wt. % are preferred, in particular for rapid and substantially reliable full dissolution.

According to a further embodiment of the invention, it is provided that Mg alloys comprising more than <NUM> wt. % Zn are to be selected, in particular for the high strength possible, since here a permanently precipitated intermetallic phase of Mg and Zn is present, and very strong particle hardening is also achieved at room temperature due to the high percent by volume.

The above-described Mg alloys are also referred to as high Zn alloys hereafter. These alloys are in particular suitable for achieving as complete a degradation as possible in less than <NUM> days, possible also in considerably less time, as was able to be demonstrated in animal experiments.

If it is desired that an implant according to the invention is to be stable initially for a certain period of time, but is to degrade as rapidly as possible thereafter, it is provided, according to a further embodiment, to additionally coat the respective high Zn alloy or the implant made thereof with a biodegradable polymer. In this case, for example, an implant in the form of a vascular support is initially protected by the polymer against corrosion. Following degradation of the polymer, which has progressed far enough for the physiological medium to penetrate the layer, the vascular support or the implant degrades, which takes place particularly rapidly in the case of the high Zn alloys. Suitable biodegradable polymers are listed below.

If it is desired to optimize the mechanical properties of one of the aforementioned metal alloys (for example by way of grain refinement) or to further expedite the degradation kinetics thereof, for example for reasons related to the mechanical properties, when the composition being is fixedly defined, this can be achieved, according to a further embodiment of the invention, by adding one or more micro-alloying elements.

According to one embodiment, such micro-alloying elements are typically used in contents of less than <NUM> wt. %, preferably in contents of <NUM> wt. % to <NUM> wt.

This can preferably involve the addition of one or more of the elements Ag, Fe, Mn, Si, for example, wherein in particular Mn and Si, preferably in combination, can be used to generate specific, strength-enhancing and corrosion-expediting intermetallic phases.

This definition of limits for the contents of possible micro-alloying elements applies to both alloy types.

To obtain particularly advantageous mechanical properties, one embodiment of the implant according to the invention is provided, which has a fine-grained microstructure, having a grain size of no more than <NUM>, preferably < <NUM>, and in particular preferably < <NUM>. During the dilatation of plaques, particles (for example components of the soft, fat-like plaques or also small, fully or partially calcified particles) can be released. To additionally offer particularly high protection against such a possible release of particles, the vascular support is additionally provided with a net. This net can be attached to the inside or outside.

According to one embodiment, the net is made of one of the aforementioned biodegradable metal alloys, wherein a preferred diameter of the wires that are used ranges between <NUM> and <NUM>, and/or wherein the preferred size of the mesh (distance between the wires) ranges between <NUM> and <NUM>.

According to one embodiment, the net is made of one of the aforementioned biodegradable metal alloys, wherein a preferred diameter of the wires that are used ranges between <NUM> and <NUM>, and/or wherein the preferred size of the mesh (distance between the wires) ranges between <NUM> and <NUM>, wherein the net is additionally coated with a biodegradable polymer.

At least one of the following polymers can be used as the biodegradable polymer, which can be used as a coating on the resorbable base body of the implant, in particular of the vascular support, within the above-described meaning: polylactide, polyglycolide, polyanhydride, polyhydroxybutyrate, polycaprolactone, polydioxanone, a poly(trimethylene carbonate)-based polymer, polyphosphazene, polyhydroxyalkonates, polyanhydride, polyacetal, polycarbonate, poly(ether ester); a copolymer of the aforementioned polymers, a mixture of the aforementioned polymers, or a blend of the aforementioned polymers.

The following are considered to be particularly suitable: poly(L-lactide), poly)D,L-lactide), poly(D,L-lactide-co-glycolide), polyhydroxybutyrate, polycaprolactone, copolymers of the aforementioned polymers.

According to one embodiment of the invention, the layer thickness of the polymer layers can be <NUM> to <NUM>, layer thicknesses of <NUM> to <NUM> being preferred, and those of <NUM> to <NUM> being particularly preferred.

To be able to achieve as effective covering of a vulnerable plaque or of an aneurysm as possible by way of the base body of the vascular support, additional designs can optionally be preferred for the vascular supports which have an increased so-called "metal to artery ratio" compared to conventional vascular supports. The metal to artery ratio describes the percentage of the vessel wall that is covered over the length across which the implant extends in the vessel. Suitable metal to artery ratios for implants or vascular supports according to the invention are in a range of above <NUM>%, preferably above <NUM>%, and in cases in which the greatest possible coverage is desired, up to <NUM>%. (The information always relates to the coverage in percent after implantation).

Further examples of the invention using high Zn alloys.

Claim 1:
An implant, in the form of a vascular support, in particular for implantation into a vulnerable plaque or for disrupting flow to an aneurysm, wherein the implant can be fully biodegraded within a time period of less than <NUM> days, in particular less than <NUM> days, preferably less than <NUM> days, and wherein the implant in particular comprises a magnesium alloy or is made thereof, wherein the Mg alloy is a Mg alloy having a Zn content between <NUM> wt.% and <NUM> wt.% Zn and comprising <NUM> wt.% to <NUM> wt.% Ca, characterized in that the implant is provided with a net being made of one of the aforementioned biodegradable metal alloys and having wires, wherein the diameter of the wires that are used ranges between <NUM> and <NUM>.