EP1633281A1

EP1633281A1 - Stents

Info

Publication number: EP1633281A1
Application number: EP04739765A
Authority: EP
Inventors: Peter Simon; Karl Kratz; Andreas Lendlein; Birgit Schnitter
Original assignee: MnemoScience GmbH
Current assignee: MnemoScience GmbH
Priority date: 2003-06-13
Filing date: 2004-06-09
Publication date: 2006-03-15
Also published as: WO2004110313A1; CA2527976C; BRPI0411437B8; US20070129784A1; BRPI0411437B1; BRPI0411437A; CA2527976A1

Abstract

The invention relates to stents for non-vascular or vascular use, said stents comprising a shape-memory polymer.

Description

stents

The invention relates to a temporary stent made of shape memory polymers (SMP) for use in the non-vascular or vascular area. The stent can be reduced in size by the shape memory effect and can be removed in a minimally invasive manner. Another object of the invention is a method for implanting and removing the stent and for producing and programming the stent.

State of the art

Tubular tissue supports (stents) are inserted into the hollow organ for the treatment of blocked or narrowed hollow organs or after surgical interventions. They serve to stop the constricted area or to take over the function of the injured hollow organ in order to enable normal flow or drainage of body fluids again. For the treatment of clogged or narrowed blood vessels, stents are inserted into the blood vessel, which stop the narrowed area and allow normal blood flow again.

Stents are usually cylindrical structures made of a kind of wire mesh (wire coil design) or tubes that can be perforated or not perforated (slottet tube design). Common stents are between 1 and 12 cm long and about 1-12 mm in diameter.

The mechanical requirements for a stent are contradictory. On the one hand, a stent must exert high radial forces on the hollow organ to be supported. On the other hand, it is necessary that the stent can be radially compressed in order to be able to easily insert it into a hollow organ without thereby damaging the vessel wall or the surrounding tissue.

This problem was solved by inserting the stents in compressed form and only stretching them in the right place. The diameter is smaller in the compressed state than in the expanded state. In principle, this process can also be used for minimally invasive removal of the stent. One possible problem is however, the fact that the usually used metallic materials cannot always be stretched out completely or folded up again, which represents a potential risk of injury to the adjacent tissue.

There are two different ways to insert a stent minimally invasively

Technologies established (Market report "US peripheral and vascular stent and AAA stent graft market" (Frost & Sullivan), 2001):

Balloon expandable stents (system consists of balloon, catheter, stent) Self-expandable stents (system consists of sleeve for insertion

(protective sheeth), catheter, stent);

Self-expanding stents consist of a shape memory material (SM material), whereby metallic SM materials such as Nitinol are in the foreground. The shape memory effect is an effect that has been studied with great interest in recent years and enables a targeted change in shape by applying an external stimulus (for details in this regard reference is made to the literature already published, for example “Shape Memory Alloys”, Scientific American, Vol. 281 (1979), pages 74 - 82). The materials are able to change their shape in a targeted manner when the temperature rises. The shape memory effect is triggered in order to enlarge the diameter of the stent "on its own" and to fix it in place.

As already indicated above, the removal of expanded stents is problematic. If the stent has to be pulled out of a tubular cavity, there is a risk that the surrounding tissue will be damaged by abrasion because the stent is too large and has sharp edges. The shape memory effect is therefore also used to reduce the diameter of the stent again when a stent is to be removed again. Examples of removable implants (stents) made of shape memory metals are known in the prior art: US 6413273 "Method and system for temporarily supporting a tubular organ"; US 6348067 "Method and system with shape memory heating apparatus for temporarily supporting a tubular organ"; US 5037427 "Method of implanting a stent within a tubular organ of a living body and of removing same"; US 5197978 "Removable heat-recoverable tissue supporting device". Nitinol cannot be used for a nickel allergy. The material is also very expensive and can only be programmed using complex processes. This programming method requires comparatively high temperatures, so that programming in the body is not possible. The SM material is therefore programmed outside the body, ie brought into its temporary form. After the implantation, the shape memory effect is triggered and the stent expands, ie regains its permanent shape. Removal of the stent by reusing the shape memory effect is then not possible. A common problem with metallic stents, not only in the vascular area, is the occurrence of restenosis.

In contrast, other metallic stents made of SM materials, for example from US Pat. No. 5,197,978, also allow the shape memory effect to be used to remove the stent. However, these metallic materials are very complex to manufacture and tissue compatibility is not always guaranteed. Due to the poorly adapted mechanical properties of the stents, inflammation and pain occur again and again.

The temporary stent described in US 5716410 "Temporary stent and method of use" is a spiral made of a shape memory plastic (SMP). The SMP material contains an embedded heating wire. The heating wire is connected to an electrical controller via a catheter shaft, the shaft end being placed as a hollow tube over one end of the spiral. If the implanted stent, which is in its expanded, temporary form, is heated above the switching temperature T _trans , the diameter of the spiral is reduced. This should make it easy to remove the stent. A disadvantage of the spiral structure is that the radial forces are too small to expand tubular cavities. The radial forces of the spiral are only distributed over a small contact area with the tissue; there is a risk of local mechanical overloading due to pressure, possibly even cutting into the tissue. In addition, the attachment of the catheter shaft (heating element) to the heating wire of the implanted spiral is difficult because the catheter shaft only has to be put over one end of the spiral. Further examples in the prior art relate to stents made of shape memory polymers which can be implanted in compressed, temporary form, the desired permanent size being generated by the shape memory effect at the place of use (US 4950258, US 6245103, US 6569191, EP 1033145). The stent is removed either by another surgical procedure or by breaking down the material in the body. A disadvantage of the materials used is their embrittlement during degradation and the formation of particles that, when detached from the device, can lead to blockages. In addition, degradation can also change the structure / nature of an implant so that there is an incompatibility with blood and / or tissue.

Pain that is caused by the inadequate mechanical adaptation of the stent to the surrounding tissue and slipping of the stent are further problems that occur again and again.

Object of the invention

However, since stents have conquered an ever wider range of uses in medicine, efforts are necessary to overcome the disadvantages described above. Stents are therefore needed for non-vascular or vascular use, which enable minimally invasive implantation as well as gentle removal. The materials for the stent should also be adaptable to the respective place of use, e.g. with regard to varying mechanical loads. The materials should preferably allow further functionalization of the stent, e.g. by embedding other medically useful substances.

To the disadvantages of St. d. Techniques to overcome are required: a simple procedure that enables minimally invasive implantation and removal of a stent, a stent that can be removed minimally invasively and atraumatically, preferably using the shape memory effect, a stent that does not enter the vascular wall during vascular or non-vascular use ingrown, a stent that has a surface that is hemocompatible, a stent that has sufficient mechanical strength / integrity during use so that the function is not impaired despite any biodegradation that may occur, a stent that does not grow together with the tissue to be supported so that it can easily be removed again, and which also inhibits the formation of a biofilm or the encapsulation of germs, a method for producing and programming such a stent.

Brief description of the invention

This object is achieved by the subject matter of the present invention as defined in the claims. These stents comprise a shape memory material (SMP material), preferably an SMP material, which exhibits a thermally induced or light-induced shape memory effect. The SMP materials to be used according to the invention can have one or two forms in mind.

Such stents solve the problems mentioned above, either overall or at least partially. Thus, the present invention provides stents comprising an SMP material which can be minimally invasively and atraumatically removed using the shape memory effect, which are tissue compatible and have sufficient strength / stability so that after the desired time of use during which they are used Function without loss of mechanical stability, can be removed again.

In particular to prevent the formation of a biofilm and to prevent ingrowth, the stent can be modified for non-vascular use, by a suitable selection of segments for the SMP material, by a surface modification, in particular a microstructuring, or by suitable coatings or by use of disinfectants that are released from the stent after implantation.

Furthermore, depending on the place of use, the stent can be adapted to the respective requirements by suitable modifications, for example because of different pH conditions, the presence of specific enzymes or generally the microbial environment make special demands. A corresponding selection of segments for the SMP materials can take these requirements into account.

Brief description of the figures

Figure 1 shows schematically the size difference between the permanent and the temporary form of the stent of the invention.

Figure 2 shows a schematic representation of the steps for inserting and removing the stent. The light gray part represents the stent, the dark gray part the balloon of the catheter and the black part the catheter.

Figure 3 shows schematically the principle of operation of a stent with two shapes in memory.

Detailed description of the invention

In preferred embodiments, the object is achieved by a stent made of SMP, characterized in that the stent is preassembled in its permanent form on a balloon catheter which can be tempered or provided with a suitable light source (in particular UV), the diameter of the temporary form being larger than in the permanent form (see FIG. 1), the temporary form acts as a tissue support, the SMP has a switching temperature of 40 ° C and higher or a switching wavelength of 260 nm or more, through which the SM effect of the implanted stent takes the permanent, compressed form so that it can be easily removed with minimal invasiveness.

A possible method for minimally invasive insertion and removal of a stent comprises the following steps (FIG. 2):

Deploy: 1. the stent, which is preassembled on a balloon catheter that can be heated or provided with a suitable light source, is inserted minimally invasively into the tubular, non-vascular organ,

2. the stent is placed, if necessary, by means of the catheter about its Ttrans (at least 40 ⁰ C.) (balloon filled with warm water or gas),

3. The stent is brought into the temporary shape (stretched) by inflating the balloon catheter with warm water or gas until it has reached the desired shape / expansion; i.e. the stent is only programmed directly at the implantation site,

4. The expanded stent is cooled by means of a catheter under Ttrans (balloon fills with cold water or gas) or irradiated with light of a wavelength greater than 260 nm in order to fix the temporary shape

5. the balloon is contracted or the radiation is stopped and the balloon catheter is removed,

Remove:

1. the balloon catheter is inserted into the stent area for removal,

2. the balloon is stretched with liquid (water) or gas in order to make direct contact with the stent and to ensure heat transport or to ensure irradiation with light,

3. the stent is heated by means of a catheter via T _trans or irradiated with light of a wavelength of less than 260 nm in order to trigger the shape memory effect in order to bring the stent back into its permanent (smaller) shape,

4. The balloon is slowly released (discharge of liquid (water) or gas), whereby the stent contracts (SM effect) and automatically attaches itself to the balloon.

5. The compressed stent is cooled if necessary and removed together with the balloon catheter.

Alternatively, this procedure can also be described as follows:

Deploy: I. the stent, pre-assembled on a temperature-controlled balloon catheter, is inserted into the tubular organ in a minimally invasive manner,

6. the placed stent is heated by means of a catheter over its Tt _rans (at least 40 ⁰ C) (balloon fills with warm water or gas),

7. The stent is brought into the temporary shape (stretched) by inflating the balloon catheter further with warm water or gas until it has reached the desired shape / expansion; i.e. the stent is only programmed directly at the implantation site,

8. The stretched stent is cooled by means of a catheter under T _tran s (balloon fills with cold water or gas) in order to fix the temporary shape,

9. The balloon is contracted and the balloon catheter is removed. Remove:

10. The balloon catheter is inserted into the stent area for removal.

I I. the balloon is expanded with liquid (water) or gas in order to make direct contact with the stent and to ensure heat transfer,

12. the stent is heated by means of a catheter over _tran s (balloon fills with warm water or gas) in order to trigger the shape memory effect in order to bring the stent back into its permanent (smaller) shape,

13. The balloon is slowly released (discharge of liquid (water) or gas), whereby the stent contracts (SM effect) and automatically attaches itself to the balloon.

14. If necessary, the compressed stent is cooled and removed together with the balloon catheter.

A possible method for minimally invasive insertion and removal of a stent with light-induced shape memory comprises the following steps (FIG. 2):

Deploy:

1. the stent preassembled on a balloon catheter provided with a suitable light source is inserted minimally invasively into the tubular organ,

2. The stent is brought into the temporary shape (stretched) by further inflating the balloon catheter with (warm) water or gas until it has reached the desired shape / expansion; ie the stent is only programmed directly at the implantation site, 3. the expanded stent is irradiated with light of a wavelength greater than 260 nm in order to fix the temporary shape,

4. The balloon is contracted or the radiation is stopped and the balloon catheter is removed.

Remove:

5. the balloon catheter is inserted into the stent area for removal,

6. the balloon is stretched with liquid (water) or gas in order to make direct contact with the stent and to ensure irradiation with light,

7. the stent is irradiated with light of a wavelength of less than 260 nm in order to trigger the shape memory effect in order to bring the stent back into its permanent (smaller) shape,

8. The balloon is slowly released (discharge of liquid (water) or gas), whereby the stent contracts (SM effect) and automatically attaches itself to the balloon.

9. The compressed stent is removed along with the balloon catheter.

In this context, it is particularly preferred if the stents, which are only programmed at the place of use, since they are then brought into the temporary form there, are heated above their transition temperatures before they are introduced into the body outside the body. Since there are no forces acting on the stent, there is no change in the expansion of the stent. However, this heating allows the stent's SMP material to become elastic and flexible. This makes it easier and easier to insert the preheated stents compared to the more rigid stents before heating. Especially when it comes to large stents and / or stents that have to be pushed through tightly wound vessels or the like, this preheating offers a significant improvement in terms of the insertion of the stent.

In many applications in which stents are placed, it is very important that the actual position of the stent corresponds exactly to the desired location. This is particularly important when two stents are used in succession, since precise placement is extremely important to ensure the desired success. With conventional stents, however, it is difficult to correct the placement of stents because the stent has to be folded again at the place of use is often problematic. The stents according to the invention, which are only programmed directly on site, offer a clear advantage here. Since the stents according to the invention are present in their expanded form in the temporary state in this embodiment, a simple downsizing of the stent can be achieved by triggering the SM effect, so that the stent which has been downsized again can be placed again, which means a simple correction of the placement allows. After the correction, the stent according to the invention is then reprogrammed using the method steps already described above and left in the temporary state as a tissue support.

The insertion with correction can be outlined by the following procedural steps:

1. The stent preassembled on a temperature-controllable balloon catheter is inserted into the tubular organ.

2. The placed stent is heated above the transition temperature by means of a catheter.

3. The stent is brought into the temporary shape (stretched) until it has reached the desired shape (expansion).

4. The stretched stent is cooled below the transition temperature by means of a catheter and thus fixed in the temporary state.

If it is subsequently determined that the stent has not yet been placed correctly, the following correction steps are also carried out:

5. The stent is heated to the transition temperature by means of a catheter in order to trigger the shape-memory effect and to bring the stent back into its smaller shape.

6. The balloon is slowly released, causing the stent to contract.

7. The stent sitting on the balloon can now be placed correctly. Then steps 3 and 4 are repeated to reposition the stent. The catheter is then removed.

The correction method described here can of course also be carried out in an analogous manner with the shape-memory materials which have a light-induced shape-memory effect.

Stents with two forms in memory

The advantage of a dual-programmed stent is that it can be implanted in a minimally invasive manner in a compressed form and that it is fixed at the site by heating. The first change in shape (e.g. diameter increase) is carried out. After the desired residence time at the place of use, the stent can be removed minimally invasively by heating it again to bring about the second change in shape (e.g. reduction in diameter).

Stents with two shapes in memory can be produced from SMP, which are characterized by covalent network points and two switching segments or two transition temperatures T _trans , where: T _trans 1 <T _trans 2 and both switching temperatures are above body temperature. The covalent network points determine the permanent shape of the stent, the switching segments each determine a temporary shape.

In one embodiment, a stent in the form of a tube is characterized in that the diameter of the permanent shape D _{perm is} small, the diameter of the first temporary shape D _temp 1 is larger than D _perm , and the diameter of the second temporary shape D _te mp2 is smaller than D _te m _P 1 is: D _pe r _m <D _temp 1> D _temp 2.

The diameter of the second temporary shape can be identical or different from the permanent shape: D _pe rm = D _te mp2 or D _per m ≠ D _temp 2.

Programming the stent twice consists of the following process steps: 1. heating the stent above T _tr ans 2, 2. Expansion of the stent from D _per m to D _temp 2,

3. cooling below T _tra ns2 and above _{T tran} s1,

4. Compression of the stent to D _te mp1.

5. cooling under Tt _ran s1 •

When the double-programmed stent is heated via T _trans 1, the shape changes from D _te mp1 to D _te mp2, ie the diameter increases. With further heating via T _trans 2, D _{pΘrm is} taken, ie the diameter decreases again (FIG. 3).

The present invention will be further described below.

The stent of the present invention comprises an SMP material. Thermoplastics, blends and networks are suitable. Composites made of SMP with inorganic nanoparticles are also suitable. No heating element is preferably embedded in the SMP material. The shape memory effect can be triggered thermally with the aid of a heatable medium, by using IR or NIR radiation, by applying an oscillating electric field or by UV radiation.

With the definition that the stent according to the invention comprises an SMP material, it should be defined that the stent on the one hand essentially consists of an SMP material, but that on the other hand the stent can also be a conventional stent, embedded or coated with an SMP material. Material. These two main constructions offer the following advantages.

Stents that consist essentially of SMP materials use the SMP material to determine the mechanical properties of the stent. The fact that the materials described below are used ensures good tissue compatibility. Furthermore, such stents, as described above, can be implanted minimally invasively and removed again. The SMP materials can still be processed relatively easily, which facilitates their manufacture. Finally, the SMP materials can be compounded or coated with other substances so that further functionalization is possible. In this context, reference is made to the following explanations. The second embodiment which is possible in principle is a stent which comprises a conventional basic structure, such as, for example, a “wire mesh construction” or a deformable tube. These basic structures are coated with or embedded in an SMP material. In particular with wire mesh structures, it has been shown that the SMP materials can exert a sufficiently large force to deform the basic structure when the shape memory effect is triggered, so this embodiment allows the positive properties of the conventional stents to be combined with the positive effects of the SMP materials described above Stents with a very high mechanical resistance can be obtained since this is supported by a conventional basic structure, which is why this embodiment is particularly suitable for stents which are exposed to high mechanical stress.

The surface of the stent is. designed to be compatible with the physiological environment at the place of use, using a suitable coating (e.g. hydrogel coating) or surface microstructuring. With the stent design, the general conditions such as pH value and bacterial count must be taken into account depending on the place of use.

Suitable materials for the stents of the present invention are described below.

SMP materials in the sense of the present invention are materials which, due to their chemical-physical structure, are able to carry out targeted changes in shape. In addition to their actual permanent shape, the materials have another shape that can be temporarily imprinted on the material. Such materials are characterized by two structural features: network points (physical or covalent) and switching segments.

SMPs with a thermally induced shape memory effect have at least one switching segment with a transition temperature as the switching temperature. The switching segments form temporary cross-linking points, which dissolve when heated above the transition temperature and form again when they cool down. The Transition temperature can be a glass temperature T ₉ amorphous areas or melting temperature T _m crystalline areas. It is generally referred to as T _trans in the following. At this temperature, the SMP show a change in shape.

Above T _tr ans the material is in the amorphous state and is elastic. If a sample is heated above the transition temperature TVans, then deformed in the flexible state and cooled again below the transition temperature, the chain segments are fixed in the deformed state by freezing degrees of freedom (programming). Temporary cross-linking points (non-covalent) are formed so that the sample can no longer return to its original shape even without external load. When heated again to a temperature above the transition temperature, these temporary crosslinking points are dissolved again and the sample returns to its original shape. The temporary shape can be restored by programming again. The accuracy with which the original shape is restored is called the recovery ratio.

In photo-switchable SMPs, photoreactive groups, which can be reversibly linked by irradiation with light, take over the function of the switching segment. In this case, the programming of a temporary shape and restoration of the permanent shape is carried out by irradiation without a change in temperature being necessary.

In principle, all SMP materials can be used to manufacture stents. By way of example, reference can be made here to the materials and the production processes which are described in the following applications, which by reference directly belong to the content of the present application:

German patent applications: 10208211.1, 10215858.4, 10217351.4, 10217350.8, 10228120.3, 10253391.1, 10300271.5, 10316573.8

European patent applications: 99934294.2, 99908402.3 Two shape memory SMP materials are described in US Patent 6,388,043, which is incorporated herein by reference.

Conventional materials for stents that can be used in the context of the present invention, in particular in the above-mentioned second embodiment, are as follows:

In principle, suitable biostable materials for use in the medical field are polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), PVC, polycarbonate (PC), polyamides (PA), polytetrafluoroethylene (PTFE), polymethacrylates, polymethyl methacrylate (PMMA), Polyhydroxyethyl methacrylate (PHEMA), polyacrylates, polyurethanes (PUR), polysiloxanes, polyether ether ketone (PEEK), polysulfone (PSU), polyethers, polyolefins, polystyrene.

Established materials for use in the non-vascular area are e.g. Polysiloxanes (catheter and tube probes, bladder prostheses), PHEMA (urinary bladder catheters) and PA (catheter tubes).

Already established materials for use in the vascular area are e.g. PUR (artificial blood vessels, heart valves), PET (artificial blood vessels, blood vessel coatings), PA (heart mitral valves), polysiloxanes (heart valves), PTFE (vascular implants).

Thermoplastic elastomers can be used to produce the stents according to the invention. Suitable thermoplastic elastomers are characterized by at least two transition temperatures. The higher transition temperature can be assigned to the physical network points that determine the permanent shape of the stent. The lower transition temperature at which the shape memory effect can be triggered can be assigned to the switching segments (switching temperature, T _tra ns). With suitable thermoplastic elastomers, the switching temperature is typically about 3 to 20 ^° C. above body temperature.

Examples of thermoplastic elastomers are multiblock copolymers. Preferred multiblock copolymers are composed of the blocks (macrodiols) from α, ω-diol polymers of poly (ε-caprolactone) (PCL), poly (ethylene glycol) (PEG), poly (pentadecalactone), poly (ethylene oxide), poly (propylene oxide), poly (propylene glycol), poly ( tetrahydrofuran), poly (dioxaπon), poly (lactide), poly (glycolide), poly (lactide-raπ-glycolide), polycarbonates and polyethers or from α, ω-diol copolymers of the monomers on which the above-mentioned compounds are based, in a molecular weight range M _n of 250 to 500,000 g / mol. Two different macrodiols are linked using a suitable bifunctional coupling reagent (in particular an aliphatic or aromatic diisocyanate or diacid chloride or phosgene) to form a thermoplastic elastomer with molecular weights M _n in the range from 500 to 50,000,000 g / mol. In a phase-segregated polymer, a phase with at least one thermal transition (glass or melt transition) can be assigned to each of the blocks of the above-mentioned polymer independently of the other block.

Multiblock copolymers of macrodiols based on pentadecalactone (PDL) and D-caprolactone (PCL) and a diisocyanate are particularly preferred. The switching temperature - here a melting temperature - can be set in the range between approx. 30 and 55 ° C via the block length of the PCL. The physical network points for fixing the permanent shape of the stent are of a second crystalline phase having a melting point in the range of 87 - 95 ⁰ C formed. Blends made of multiblock copolymers are also suitable. The transition temperatures can be specifically set using the mixing ratio.

Polymer networks can also be used to produce the stents according to the invention. Suitable polymer networks are characterized by covalent network points and at least one switching segment with at least one transition temperature. The covalent network points determine the permanent shape of the stent. In suitable polymer networks, the switching temperature at which the shape memory effect can be triggered is typically about 3 to 20 ^° C. above the body temperature.

To produce a covalent polymer network, one of the macrodiols described in the section above is crosslinked using a multifunctional coupling reagent. This coupling reagent can be an at least trifunctional, low molecular weight Compound or a multifunctional polymer. In the case of the polymer, it can be a star polymer with at least three arms, a graft polymer with at least two side chains, a hyperbranched polymer or a dendritic structure. In the case of both the low molecular weight and the polymeric compounds, the end groups must be capable of reacting with the diols. In particular, isocyanate groups can be used for this (polyurethane networks).

Amorphous polyurethane networks made from triols and / or tetrols and diisocyanate are particularly preferred. Star-shaped prepolymers such as oligo [(rac ~ lactate) -co-glycolate] triol or -tetrol are produced by the ring-opening copolymerization of rac-dilactide and diglycolide in the melt of the monomers with hydroxy-functional initiators with the addition of the catalyst dibutyltin (IV) oxide ( DBTO). Ethylene glycol, 1, 1, 1-tris (hydroxymethyl) ethane or pentaerythritol are used as initiators of the ring-opening polymerization. Oligo (lactate-co-hydroxycaproate) tetrols and oligo (lactate-hydroxyethoxyacetate) tetrols and [oligo (propylene glycol) -b! Ock-oligo (rac-lactate) -co-glycolate)] triols are prepared analogously. The networks according to the invention can be obtained simply by reacting the prepolymers with diisocyanate, e.g. a mixture of isomers of 2,2,4- and 2,4,4-trimethylhexane-1,6-diisocyanate (TMDI), in solution, e.g. in dichloromethane, and subsequent drying.

Furthermore, the macrodiols described in the section above can be functionalized to corresponding α, ω-divinyl compounds which can be crosslinked thermally or photochemically. The functionalization preferably allows the macromonomers to be covalently linked by reactions which do not result in any by-products. This functionalization is preferably provided by ethylenically unsaturated units, particularly preferably by acrylate groups and methacrylate groups, the latter being particularly preferred. In particular, the conversion to α.ω-macrodimethacrylates or macrodiacrylates can be carried out by the reaction with the corresponding acid chlorides in the presence of a suitable base. The networks are obtained by cross-linking the end group functionalized macromonomers. This crosslinking can be achieved by irradiating the melt, comprising the end group-functionalized macromonomer component and, if appropriate, a low molecular weight comonomer, as will be explained below. Suitable process conditions for this are Irradiating the mixture in the melt, preferably at temperatures in the range of 40 bisi OO ⁰ C, with light having a wavelength of preferably 308 nm. Alternatively, a heat crosslinking is possible when an appropriate initiator system is used.

If the macromonomers described above are crosslinked, networks are created with a uniform structure if only one type of macromonomer is used. If two types of monomers are used, networks of the AB type are obtained. Such AB-type networks can also be obtained if the functionalized macromonomers are copolymerized with suitable low-molecular or oligomeric compounds. If the macromonomers are functionalized with acrylate groups or methacrylate groups, suitable compounds that can be copolymerized are low molecular weight acrylates, methacrylates, diacrylates or dimethacrylates. Preferred compounds of this type are acrylates, such as butyl acrylate or hexyl acrylate, and methacrylates, such as methyl methacrylate and hydroxyethyl methacrylate.

These compounds, which can be copolymerized with the macromonomers, can be present in an amount of 5 to 70% by weight, based on the network of macromonomer and the low molecular weight compound, preferably in an amount of 15 to 60% by weight. Varying amounts of the low molecular weight compound are incorporated by adding appropriate amounts of the compound to the mixture to be crosslinked. The low molecular weight compound is incorporated into the network in an amount which corresponds to the amount contained in the crosslinking mixture.

The macromonomers to be used according to the invention are described in detail below.

By varying the molecular weight of the macrodiols, networks with different crosslinking densities (or segment lengths) and mechanical properties can be achieved. The macromonomers to be covalently crosslinked preferably have a number average molecular weight, determined by GPC analysis, from 2,000 to 30,000 g / mol, preferably from 5,000 to 20,000 g / mol and particularly preferably from 7,500 to 15,000 g / mol. The macromonomers to be covalently crosslinked preferably has a methacrylate group at both ends of the macromonomer chain. Such functionalization allows the macromonomers to be cross-linked by simple photoinitiation (irradiation).

The macromonomers are preferably biostable or very slowly degradable polyester macromonomers, particularly preferably polyester macromonomers based on D-caprolactone or pentadecalactone. Other possible polyester macromonomers are based on lactide units, glycolide units, p-dioxanone units and their mixtures and mixtures with D-caprolactone units, polyester macromonomers with caprolactone units or

Pentadecalactone units are particularly preferred. Preferred polyester macromonomers are also poly (caprolactone-co-glycolide) and poly (caprolactone-co-lactide). The transition temperature can be set via the quantitative ratio of the comonomers. Biostable macromonomers based on polyethers, polycarbonates, polyamides, polystyrene, polybutylene terephthalate and polyethylene terephthalate are also particularly preferred.

The macromonomers to be used according to the invention are particularly preferably polyesters, polyethers or polycarbonates, comprising the crosslinkable end groups. A particularly preferred polyester to be used according to the invention is a polyester based on D-caprolactone or pentadecalactone, for which the above-mentioned information about the molecular weight applies. The preparation of such a polyester macromonomer, functionalized at the ends, preferably with methacrylate groups, can be prepared by simple syntheses which are known to the person skilled in the art. These networks, without taking into account the further essential polymeric component of the present invention, show semicrystalline properties and have a melting point of the polyester component (can be determined by DSC measurements), which is dependent on the type of polyester component used and is therefore also controllable. It is known that this temperature (T _m 1) for segments based on caprolactone between 30 and 60 ⁰ C, depending on the molecular weight of the macromonomer.

A preferred network with a melting temperature as the switching temperature is based on the macromonomer poly (caprolactone-co-glycolide) dimethacrylate. The Macromonomer can be reacted as such or copolymerized with n-butyl acrylate to form the AB network. The permanent shape of the stent is determined by covalent network points. The network is characterized by a crystalline phase, the melting temperature of which can be set in the range from 20 to 57 ° C., for example by the comonomer ratio of caprolactone to glycolide. For example, n-butyl acrylate as a comonomer can be used to optimize the mechanical properties of the stent.

Another preferred network with a glass transition temperature is obtained from an ABA triblock dimethacrylate as a macromonomer, characterized by a central block B made of polypropylene oxide and end blocks A made of poly (rac-lactide). The amorphous networks have a very wide switching temperature range.

Networks with two transition temperatures, such as interpenetrating networks (IPNs), are suitable for producing stents with two shapes in memory. The covalent network is based on poly (caprolactone) dimethacrylate as a macromonomer; the interpenetrating component is a multiblock copolymer made from macrodiols based on pentadecalactone (PDL) and D-caprolactone (PCL) and a diisocyanate. The permanent shape of the material is determined by the covalent network points. The two transition temperatures - melting temperatures of the crystalline phases - can be used as switching temperatures for a temporary form. The lower switching temperature T _trans 1 can be set in the range between approx. 30 and 55 ° C over the block length of the PCL. The upper switching temperature T _trans 2 is in the range from 87 to 95 ⁰ C.

The SMP materials described above are essentially based on poly or oligoester segments. These SMP materials therefore sometimes show inadequate stability in a physiological environment, since the ester bonds can be degraded hydrolytically relatively easily, although the stability is sufficient for most applications, in particular for stents which do not remain at the place of use for a very long period of time. Such problems can, however, be overcome by the SMP materials instead comprising segments based on poly or oligoether units or poly or oligocarbonate units. Such segments can for example be based on poly (ethylene oxide), poly (propylene oxide) or poly (tetramethylene oxide).

Furthermore, photosensitive networks can be used to produce the stents according to the invention. Suitable photosensitive networks are amorphous and are characterized by covalent network points that determine the permanent shape of the stent. Another feature is a photoreactive component or a unit which can be reversibly switched by light and which determines the temporary shape of the stent.

In the case of photosensitive polymers, a suitable network is used which contains photosensitive substituents along the amorphous chain segments. When exposed to UV radiation, these groups are able to form covalent bonds with one another. If the material is deformed and irradiated with light of a suitable wavelength λ1, the original network is additionally cross-linked. Due to the networking, the material is temporarily fixed in the deformed state (programming). Since the photocrosslinking is reversible, the crosslinking can be released again by re-irradiation with light of a different wavelength λ2 and the original shape of the material can thus be called up again (restoration). Such a photomechanical cycle can be repeated any number of times. The basis of the photosensitive materials is a wide-meshed polymer network which, as stated above, is transparent with regard to the radiation intended to trigger the change in shape, i.e. preferably forms a UV-transparent matrix. Networks of the present invention based on low molecular weight acrylates and methacrylates which can be polymerized by free radicals, in particular C1-C6- (meth) acrylates and hydroxy derivatives, wherein hydroxyethyl acrylate,

Hydroxypropyl methacrylate, hydroxypropyl acrylate, poly (ethylene glycol) methacrylate and n-butyl acrylate are preferred; n-butyl acrylate and hydroxyethyl methacrylate are preferably used.

A component that is responsible for the crosslinking of the segments is used as the comonomer for producing the polymeric networks of the present invention. The chemical nature of this component naturally depends on the nature of the monomers. Suitable crosslinkers for the preferred networks based on the acrylate monomers described above as preferred are bifunctional acrylate compounds which are suitably reactive with the starting materials for the chain segments, so that they can be reacted together. Such crosslinkers include short, bifunctional crosslinkers, such as ethylene diacrylate, low molecular weight bi- or polyfunctional crosslinkers, oligomeric, linear diacrylate crosslinkers, such as poly (oxyethylene) diacrylates or poly (oxypropylene) diacrylates, and branched oligomers or polymers with acrylate end groups.

As a further component, the network according to the invention comprises a photoreactive component (group) which is jointly responsible for triggering the specifically controllable shape change. This photoreactive group is a unit which, by excitation with a suitable light radiation, preferably UV radiation, is capable of a reversible reaction (with a second photoreactive group) which leads to the generation or dissolution of covalent bonds. Preferred photoreactive groups are those which are capable of reversible photodimerization. Various cinnamic acid esters (cinnamate, CA) and cinnamic acid esters (cinnamylacylate, CAA) are preferably used as photoreactive components in the photosensitive networks according to the invention.

It is known that cinnamic acid and its derivatives dimerize under UV light of approximately 300 nm to form a cyclobutane. The dimers can be cleaved again when irradiated with UV light of a smaller wavelength of approximately 240 nm. The absorption maxima can be shifted by substituents on the phenyl ring, but always remain in the UV range. Other derivatives that can be photodimerized are 1, 3-diphenyl-2-propen-1-one (chalcone), cinnamic acyl acid, A-methylcoumarin, various ortho-substituted cinnamic acids, cinammyloxysilanes (silyl ether of cinnamon alcohol).

The photodimerization of cinnamic acid and similar derivatives is a [2 + 2] cycloaddition of the double bonds to a cyclobutane derivative. Both the E and Z isomers are able to undergo this reaction. When irradiated, the E / Z isomerization competes with the cycloaddition. In the crystalline state however, E / Z isomerization is hindered. Due to the different arrangement possibilities of the isomers to one another, 11 different stereoisomeric products (truxillic acids, truxic acids) are theoretically possible. The distance between the double bonds of two cinnamic acid groups required for the reaction is about 4 Å.

The networks are characterized by the following properties:

Overall, the networks are good SMP materials with high reset values, i.e. the original shape is retained again to a high percentage, usually above 90%, even if a cycle of shape changes is carried out several times. There is also no disadvantageous loss of mechanical property values.

To increase the hemocompatibility, the chemical structure of the SMP materials used according to the invention can be modified, e.g. by installing the above-mentioned poly or oligoether units.

Processing of the polymers into stents

For processing thermoplastic elastomers into stents, for example in the form of a hollow tube or the like (FIG. 1), all customary polymer-technical methods such as injection molding, extrusion, rapid prototyping, etc. can be used. are used, which are known to the expert, in addition, manufacturing processes such as laser cutting can be used. In the case of thermoplastic elastomers, different designs can be realized by spinning in mono- or multifilament threads with subsequent weaving into a cylindrical network with a mesh structure.

When producing stents from polymer networks, it must be noted that the form in which the crosslinking reaction of the macromonomers takes place corresponds to the permanent form of the stent (casting process with subsequent hardening). The network materials according to the invention therefore require special milling and cutting methods for further processing. Perforation or cutting of a tube using LASER light of a suitable wavelength is recommended. With the help of this technology - especially when combining CAD and pulsed CO ₂ or YAG lasers - molds can be worked down to a size of 20 μm without exposing the material to high thermal stress (and thus undesirable side reactions on the surface). Alternatively, it is recommended to further process it into an operational stent.

The second embodiment is obtained by coating or embedding a conventional material (see above) in an SMP material by a suitable method.

The required mechanical properties of a stent depend on the place of use and require an adapted design. If the implanted stent is exposed to strong mechanical deformations, a very high degree of flexibility is required without the stent collapsing during the movements. In principle, the "wire coil design" is more suitable here. In other areas of lower organs, the stent is less mechanically stressed by deformations, but rather by a relatively high external pressure. A suitable stent must be characterized by high radial forces on the surrounding tissue The "slotted tube design" seems more suitable here. Tubes with perforations allow liquids to flow from the surrounding tissue into the stent (drainage).

In the prior art, in particular, there have always been problems with blood vessels with small diameters, since the known stents are not sufficiently flexible and adaptable for such vessels. However, the stents of the present invention also allow for safe use in such vessels because the superior elastic properties of the SMP materials, i.e. high elasticity with small deflections and high strength with large expansion, the vessel protects, for example in the case of pulsatile movements of the arteries.

Since drainage effects are in the foreground for stents that are to be used in the non-vascular area, a design with an embedded conventional basic structure is particularly suitable for such stents, or a design essentially made of SMP material (perforated tube or mesh body) because the easiest of these is the permeability to liquids required for drainage, while at the same time having sufficient mechanical strength. Functionalization of the stents

To make the stent easier to insert, it can be equipped with a coating that increases its lubricity (e.g. silicones or hydrogels).

Further possibilities for improving the hemocompatibility include the possibility that a coating is provided (the materials required for this are known to the person skilled in the art) or the surface can be microstructured. Suitable methods for surface modification are, for example, plasma polymerization and graft polymerization.

For easier localization of the stent using imaging diagnostic methods, the shape memory plastic can be veneered with a suitable X-ray contrast medium (e.g. BaSO ₄ ). Another possibility is to install metal threads (e.g. stainless steel) in the stent. These metal threads are not used for stabilization (but for localization); it is their exclusive task to increase the x-ray contrast. A third possibility is veneering with metals which, in addition to their high X-ray contrast, also have virostatic, fungicidal or bactericidal properties (for example nano-silver). Another alternative in this regard is the incorporation of radiopaque chromophores such as triiodobenzene derivatives into the SMP materials themselves.

In a further embodiment, the SMP can be compounded with inorganic nanoparticles. Examples are particles made of magnesium or magnesium alloys or magnetite. Particles made of carbon are also suitable. SMPs functionalized in this way can be heated in an oscillating electric field in order to trigger the shape memory effect.

The stent according to the invention can furthermore be loaded with a number of therapeutically active substances which support the healing process, suppress the restenosis of the stent or also prevent secondary diseases. In particular, the following can be used: • Anti-inflammatory agents (e.g. ethacridine lactate) • Pain-relieving active ingredients (e.g. acetylsalicylic acid)

• Antibiotic active ingredients (e.g. enoxacin, nitrofurantoin)

Active substances against viruses, fungi (for example elemental silver)

• Antithrombic agents (for example AAS, clopidogrel, hirudin, lepirudin, desirudin)

Cytostatic active ingredients (for example sirolimus, rapamycin or rapamune)

• Immunosuppressive agents (for example ABT-578)

• Active ingredients to reduce restenosis (e.g. taxol, paclitaxel, sirolimus, actinomycin D)

The stent according to the invention can be loaded with active substances in different ways.

The active ingredients can either be veneered directly with the plastic or applied to the stent as a coating.

Such stents can also be used in the field of gene therapy.

If the material of the stent is veneered directly with the active ingredients, the active ingredient can either be released in a degradation-controlled or diffusion-controlled manner. In the case of degradation-controlled release, the rate of diffusion of the active ingredient from the matrix is slower than the rate of degradation of the polymer. If this is the case, the active ingredient is advantageously either embedded in a degradable coating which surrounds the stent or directly in the polymer material. In the case of diffusion-controlled release, the rate of diffusion of the active ingredient from the matrix is faster than the rate of degradation of the polymer. The active ingredient is continuously released from the matrix over time.

As a third possibility, the active ingredient can be introduced into the pores of a porous shape memory plastic. After loading with the active ingredient, the pores of the material are closed and the stent is brought to the site of action as described above. A suitable external stimulus (heat or radiation of light) opens the pores and the active substance is suddenly released. For this application there is a shape memory plastic in particular suitable, which has two forms in memory; one of the forms is responsible for the change in shape of the stent, the second form of the stent is responsible for the opening of the pores.

If the active substances are introduced into the material of the stent according to the invention, the active substances are released after the stent has been implanted. The release of the active ingredient is associated with the breakdown of the stent; It should therefore be noted that the rate of diffusion of the active ingredient from the stent must be lower than the rate of degradation of the material of the stent and that the mechanical stability of the stent is not impaired by this degradation.

In such embodiments, for example, the stent can include multiple SMP materials, e.g. one to ensure the stability / integrity of the stent and one coated on the surface of the stent and containing the active ingredients.

The following areas of application come into question in particular

Iliac stents

These are 10-120 mm long, usually 40-60 mm. Are used in the abdominal area. Two stents are often used because the use of long stents is difficult. However, the stents of the present invention are distinguished by good flexibility and enable very gentle minimally invasive application and removal, so that the stents of the present invention can also be used in lengths which are not considered feasible in the prior art.

Renal stents

A high radial strength is required here because of the high elastic loading in the kidney artery, which may require increased mechanical strengthening of the stent. Either the "slotted tube design" is suitable here or the use of conventional stents coated with or embedded in the SMP materials. Both embodiments allow the use of radio-opaque markers. It is also important to ensure that the stent is securely installed on the balloon of the catheter and that it is precisely inserted. Due to the different anatomy of living things, there are adjusted, variable lengths and Diameter necessary. Combination with a distal protection device or a plaque filter is also recommended.

Carotid stents (carotid artery)

• A long stent can be used here to avoid the previous technique of combining two stents.

• Can also be used on vascular crotches

• Optimal adaptation to different diameters possible

• Network with tight meshes desirable and feasible (see above), because filter function u. This may be necessary to prevent blood clots from entering the brain (plaque filter function).

• Stent must be pressure stable, which may LJ. pressure could be built up from the outside, the stent should not collapse;

Femoral-poplietal stents (hip-knee)

Here is a high radial strength due to high elastic loading in the blood vessel, which may require increased mechanical reinforcement. Here, the "slotted tube design" is more suitable (possibly using a conventional framework), in particular the use of two long stents can also be considered here.

Coronal stents

• Wire coil design.

• Atraumatic insertion without abrasive effects is an essential condition here and is possible with the stents of the present invention.

Design of non-vascular stents

The main areas of application are the entire gastrointestinal tract, trachea and esophagus, bile duct, ureter, urethra and fallopian tube. Accordingly, stents in various sizes are used. The different pH values of the body fluids and the appearance of germs must be taken into account individually in the stent design. Regardless of the place of use, non-vascular stents are mainly used to drain body fluids such as bile, pancreatic juice or urine. A design of a perforated hose is therefore recommended, which on the one hand can safely discharge the liquid to be removed from the cavity, but on the other hand absorbs the liquid over the entire distance. Furthermore, the polymer material used must have a high degree of flexibility in order to ensure wearing comfort. For better identification in X-ray analysis, the starting material can be blended with X-ray contrast agents such as barium sulfate or X-ray-opaque chromophores are built into the SMP materials, for example by polymerizing in suitable monomers. If stents are to be used in areas where germs occur, the incorporation of antibiotic active ingredients into the material can make sense.

The crusting of the stents, which occurs particularly frequently in the uretheral area, can be reduced by suitable coating or surface modification.

The fixation of the stent essentially depends on the place of use. In the case of a urethral stent, the proximal end is in the renal pelvis, the distal end in the bladder or outside the body. The proximal end forms a loop in the kidney pelvis after expansion has been completed, thus ensuring a secure hold.

Another possibility for fixing stents is that the stent presses firmly against the surrounding tissue outward via radial forces or contains anchor elements which serve for fixing.

In the case of biliary or kidney stents, atraumatic placement and removal is an essential condition. In particular, it must be ensured when placing that the tissue is not affected by abrasive effects and thus inflammation is caused. Therefore, a stent used in this area has no restraining elements that could injure the tissue. Examples of suitable materials that can be used in the context of the present invention are set out below by way of example:

Examples of multiblock copolymers

The multiblock copolymer was made from macrodiols based on pentadecalactone (PDL) and D-caprolactone (PCL) and a diisocyanate. PDL specifies the proportion of pentadecalactone in the multiblock copolymer (without taking diisocyanate bridges into account) and the molecular weight of the polypentadecalactone segments. PCL provides the corresponding information for caprolactone units.

The mechanical properties depending on the temperature for Example 8 are as follows:

Examples of polymer networks

Suitable polymeric networks are obtained by copolymerizing a macrodimethacrylate based on glycolide and D-caprolactone units with n-butyl acrylate. The proportion by weight of glycolide in the macrodimethacrylate is 9% by weight (or 11% by weight in Example 13). The molecular weights of the macrodimethacrylates are around 10,000 - 11,000 g / mol.

Examples of amorphous polymer networks

The amorphous networks were made from ABA triblock dimethacrylates, where A stands for segments made of poly (rac-lactide) and B for segments made of atactic poly (propylene oxide) (M _n = 4000 g / mol).

PD = polydispersity

* Sample polymerized during DSC measurement

** Values above 100 are due to contamination

The polymeric amorphous networks were examined with regard to their further thermal and mechanical properties. The results of these tests are summarized in the following tables.

Example T _g 1 T _g 2 modulus of elasticity at break elongation tensile stress (° C) ("C) 22 ° C (MPa) at 22 ° C (%) at 22 ° C (MPa)

14 -51 7 1, 24 128 1, 43

15 -60 (-43 ^* ) 4 (1 1 ^* ) 2.02 71 0.94

16-46 AD 1, 38 218 2.18

17 -50 15 4.17 334 5.44

18 -59 (-45 *) 7 (33 ^* ) 4.54 110 1.89

19 -62 (-49 *) 29 (43 ^* ) 6.37 210 3.92 determined by DMTA; nd - undetectable

thermal transition at T _g 2

Examples of photosensitive networks

10 mmol of n-butyl acrylate (BA), a cinnamic acid ester (0.1 - 3 mmol) and possibly 2 mmol of hydroxyethyl methacrylate (HEMA) are mixed in a glass flask. 1 mol% AiBN and 0.3 mol% poly (propylene glycol) dimethacrylate (M _n = 560) are added to the mixture. The mixture is filled with a syringe into a mold made of two silylated slides, between which there is a Teflon sealing ring with a thickness of 0.5 mm. The mixture is polymerized at 80 ^° C. for 18 hours.

The form in which networking takes place corresponds to the permanent form. The mixture can also be networked in any other form.

After the polymerization, the network is released from the mold and covered with 150 mL hexane fraction. Then chloroform is gradually added. This solvent mixture is exchanged several times within 24 hours in order to remove low-molecular and non-crosslinked components. Finally, the network is cleaned with hexane fraction and dried in vacuo at 30 ^° C. overnight. The weight of the extracted sample relative to the previous weight corresponds to the gel content. The two tables below show the amounts of the monomers used, the swelling Q of the networks in chloroform and their gel content G.

BA = butyl acrylate; mts urees er: = mts ure; A = hydroxyethyl methacrylate; HEA = hydroxyethyl acrylate; HPMA = hydroxypropyl methacrylate; HPA = hydroxypropyl acrylate; PEGMA = poly (ethylene glycol) methacrylate

In a further series, a proportion of 2 mmol of hydroxyethyl methacrylate (HEMA) is additionally added to the binary polymer systems, since a further possibility for controlling the mechanical properties of the polymer networks is to be expected through this comonomer.

Preparation of the interpenetrating networks IPN n-butyl acrylate is crosslinked with 3% by weight (0.6 mol%) of poly (propylene glycol) dimethacrylate (molecular weight 560 g / mol) in the presence of 0.1% by weight of AiBN as described above. The film is then swollen in THF to remove unused monomer and then dried again. The film is then allowed to swell in a solution of the star-shaped photoreactive macromonomer in THF (10% by weight) and then dried again. The loading of the network with the photoreactive component is then about 30% by weight. Production of the star-shaped photosensitive macromonomers

Star-shaped poly (ethylene glycol) with 4 arms (molecular weight 2000 g / mol) is dissolved in dry THF and triethylamine. For this, cinnamylidene acetyl chloride dissolved in dry THF is slowly added dropwise. The reaction mixture is stirred for 12 hours at room temperature, then for 3 days at 50 ° C. Precipitated salts are filtered off, the filtrate is concentrated and the product obtained is washed with diethyl ether. H-NMR measurements show a conversion of 85%. UV-spectroscopically, the macromonomer has an absorption maximum at 310 nm before the photoreaction and at 254 nm after the photoreaction.

The polymeric amorphous networks were examined with regard to their further thermal and mechanical properties. The results of these tests are summarized in the following table.

* Network of n-butyl acrylate; 0.3 mol% crosslinker; without photoreactive component ** IPN; 0.6 mol% crosslinker, physically loaded with photoreactive component

The shape memory properties were determined in cyclic photomechanical experiments. Die-cut, dumbbell-shaped 0.5 mm thick pieces of film with a length of 10 mm and a width of 3 mm were used.

Claims

claims

1. Stent, comprising an SMP material, for use in the non-vascular or vascular area.

2. Stent according to claim 1, wherein the stent has a basic structure made of a metal, coated with the SMP material, preferably an SMP material with one or two shapes in memory.

3. Stent according to one of the preceding claims, further comprising additional additives selected from X-ray contrast materials and medically active compounds.

4. Stent according to at least one of the preceding claims, wherein the SMP material is selected from polymer networks, thermoplastic SMP materials, composite materials or blends.

5. Stent according to one of the preceding claims, wherein the SMP material is selected from SMP materials in which the SMP effect is thermally induced, photoinduced and / or wherein the SMP material is biocompatible and / or hemocompatible.

6. Stent according to one of the preceding claims, wherein the SMP material has values for modulus of elasticity of 0.5 to 50 MPa and / or an elongation at break of 100 to 1200% and / or a retention fixation of more than 90%, preferably more than 92%, more preferably more than 95% and particularly preferably more than 98%, and / or a recovery ratio after 5 cycles in the thermomechanical experiment of more than 90%, preferably more than 92%, more preferably more than 95% and particularly preferred more than 98%.

7. The stent according to claim 5, wherein the network contains caprolatcon units, pentadecalactone units, ethylene glycol units, propylene glycol units, lactic acid units and / or glycolic acid units.

8. The stent of claim 6, wherein the network consists of cross-linked caprolactone macromonomers.

9. A method for producing a stent according to one of the preceding claims, comprising processing the SMP material into a stent by extrusion processes, coating processes, die casting processes or spinning and weaving processes.

10. Kit comprising a stent according to at least one of claims 1 to 6 and additionally a temperature-controllable balloon catheter and / or a balloon catheter with a light guide.

11. A method for minimally invasive stent implantation comprising the following steps:

Placing a stent according to one of claims 1 to 7 onto a temperature-controllable balloon catheter or a balloon catheter with a light guide,

Insertion of the stent placed in this way into the desired location,

Heating the stent by introducing a heating medium into the catheter,

Stretching the stent to program the SMP material,

Introducing a cooling medium into the catheter in order to fix the stent in the stretched state, or introducing light (preferably UV light) of a suitable wavelength in order to fix the stent in the stretched state,

- Remove the balloon catheter.

12. A method for removing an implanted stent according to one of claims 1 to 7, comprising the following steps, preferably after the implantation according to claim 10:

Insertion of a balloon catheter at the implantation site,

Introducing a heating medium into the balloon catheter to heat the stent or introducing light of a suitable wavelength, Triggering the shape-memory effect by heating or exposure to light, so that the stent is converted from its temporary shape to the permanent shape,

- Perform the balloon catheter together with the stent.

13. The method of claim 11, further comprising the step of introducing a cooling medium after the introduction of the heating medium to cool the stent in the permanent form prior to execution.

14. A method for minimally invasive implantation of a stent, the stent being an SMP material with two shapes in memory, comprising the following steps:

Placing a stent according to one of claims 1 to 7 on a temperature-controllable balloon catheter or a balloon catheter with a light guide, the SMP material being in the first temporary form,

Insertion of the stent placed in this way into the desired location,

Heating the stent by introducing a heating medium into the catheter or introducing light of a suitable wavelength to obtain the second temporary shape,

- Remove the balloon catheter.

15. A method for removing an implanted stent, the stent comprising an SMP material with two shapes in memory, comprising the following steps, preferably after the implantation according to claim 13:

Insertion of a balloon catheter at the implantation site,

Introducing a heating medium into the balloon catheter to heat the stent or introducing light of a suitable wavelength,

Triggering the shape-memory effect by heating or exposure to light, so that the stent is converted from its second temporary shape to the permanent shape,

- Perform the balloon catheter together with the stent.