WO2003082149A2

WO2003082149A2 - Stent

Info

Publication number: WO2003082149A2
Application number: PCT/EP2003/003106
Authority: WO
Inventors: Ralph Kienzler
Original assignee: Ralph Kienzler
Priority date: 2002-03-28
Filing date: 2003-03-26
Publication date: 2003-10-09
Also published as: AU2003221521A1; DE10214281A1; WO2003082149A3

Abstract

Disclosed is a stent (10) used for a recanalizing treatment of a stenosis-affected vessel, particularly an artery, comprising a shell that has the basic shape of a tubular cylinder and is provided with a grid structure or mesh structure which makes it possible to radially and axially modify the form of the stent at a defined correlation. Said stent is made of a nitinol material which is superelastic or elastic in a form-maintaining manner depending on the ambient temperature, i.e. said material develops restoring forces resulting in the stent returning to a form that had been impressed thereupon at an elevated temperature after being deformed in the superelastic range of temperature. The inventive stent comprises at least one anchoring section, the hub of which achieves a force-fitting or force-form-fitting fixing of the stent in the treated vessel, and a lining section used for recanalizing the stenosis. The part of the stent (10) forming the anchoring section (10/2, 10/3) develops a significantly higher restoring force than the lining section (10/1) at a given radial deformation, i.e. the stent returns to the form that has been impressed thereupon at a high temperature.

Description

stent

description

The invention relates to a stent for a re-canalizing treatment of a stenosis-containing vessel, in particular an artery, with a basic cylindrical-tubular jacket that has a lattice or mesh structure that enables radial and axial changes in shape of the stent in a defined correlation, and with the further generic features mentioned in the preamble of patent claim 1.

Stents of the aforementioned type are manufactured, inter alia, from Nitinol, a nickel-titanium alloy which, below a transition temperature T _{Af, is} in a super-elastic phase with a martensitic structure in which the stent is very easily deformable, in particular into an elongated one with a small diameter Can be brought into a configuration in which it can be relatively easily brought into its position in the vessel required for treatment by means of a guidewire of a catheter, and is present at an elevated temperature "above" the transition temperature in an austenitic phase in which the material has a "shape memory "in that the stent has a form elasticity after the transition temperature has been exceeded in such a way that it resumes the shape given before the cold deformation. The transition temperature T _Af depends significantly on the ratio of the alloy components Ni and Ti and is set by specifying the alloy ratio in such a way that the transition temperature is somewhat lower than the body temperature, so that the stent is based on the body temperature and the shape memory property of the nitinol " by itself "in its configuration suitable for therapy.

The reliable anchoring of the stent at the treatment site, which is important for long-term therapeutic success, is described in DE 44 18 336 A1 known stent achieved by designing end sections of the stent such that these in the radially expanded state achieved by the shape-memory of the material have a larger diameter than that between; lining section which extends to them and which is essentially associated with the recanalization of the stenosis. In the known stent, this is achieved by suitably specifying the length of the webs delimiting the grid openings which are connected in pairs in free corners of an overall zigzag-shaped edge region which penetrate somewhat into the vessel wall and, as it were, when the stent moves in alternative directions erect and penetrate deeper into the vessel wall, which ensures that the stent is securely anchored.

However, this type of stent anchoring has the disadvantage that the free end tips, in which the terminal lattice webs converge, can cause punctures of a pulsating artery. The known stent can therefore itself pose a danger to the vessel lined with.

It is therefore the object of the invention to improve a stent of the type mentioned at the outset in such a way that with good anchoring in the vessel to be recanalized, extensive security against traumatization of the vessel is achieved and a risk of thrombosis is largely ruled out.

This object is achieved, according to the basic idea of the invention, by designing the stent in such a way that a part of the stent forming an anchoring section of the stent with a predetermined radial expansion, which it unfolds when inserted into the vessel to be treated, in the sense of taking back its embossed shape develops a significantly higher restoring force than the subsequent lining section of the Stents, which, however, "remember" the same diameter and strive to expand.

A major advantage of the stent according to the invention is that it is securely anchored immediately after its insertion into the vessel to be treated and that its lining section, due to its weaker restoring force, only "slowly" - later in time - to its intended target Widened diameter, generated only moderate expansion force in the lining area, under the effect of which the original stenosis, eg. B. stenosis due to fat deposits tending to calcification. The anchoring section can in turn be designed as a cylindrical tube, so that the risk of injury to the vessel can be largely excluded. The stent according to the invention is not only suitable for providing effective recanalization of a stenosis-afflicted area of an artery or another vessel, but also in cases in which the end positions in the vessel wall can gradually recede due to the moderate application of force. also suitable to bring about a cure in the sense of eliminating the dangers cause.

In principle, an anchoring section is sufficient for a sufficiently secure fixation of the stent according to the invention. However, it may then be necessary to position the stent with a defined orientation in the vessel to be recanalized, e.g. B. to introduce an artery, expediently so that the anchoring section is arranged downstream of the lining section.

Orientation errors can be excluded from the outset by designing the stent such that its lining section is arranged between two terminal anchoring sections, between which the stenosis-afflicted part of the artery is arranged when the stent is inserted. With this design of the stent, the lining covering Cut the same be designed for a particularly low form restoring force, which is favorable for a "slow" breakdown of the stenosis and counteracts the risk that relatively large embedding particles get into the vascular canal across the stent ends and can cause thrombosis ,

Within the meaning of the inventive concept, relatively increased restoring forces of a stent in the region of the respective anchoring section, regardless of whether the stent is made of a Nitinol material with "shape memory" or is made of another suitable, biologically compatible material, can be achieved in that the lattice structure of the Stents forming stents have a smaller material cross section in the area of the lining section than in the adjacent anchoring section (s).

In the case of a stent according to the invention based on a nitinol material, the aforementioned property can also be achieved in that the lining section and the anchoring section (s) of the stent have different alloy ratios, with the differently alloyed stent sections being expediently connected to one another welded, preferably joined together in a laser welding process.

For a production of the stent according to the invention from a nitinol material, the features of claim 6 indicate a procedure according to which the desired stent properties can be achieved essentially solely by thermal treatment of stent sections at different times, preferably by cooling the anchoring sections more quickly are arranged as a support section of the stent adjacent to such a stent section or between such stent sections, which can be achieved in a simple manner in that during the cooling of the stent the extension adjacent to an anchoring section thereof clothing section is further heated in such a way that its cooling rate is lower than that of the more rapidly cooled anchoring section, in addition to the fact that the anchoring section (s) of the stent is / are quenched with a high cooling rate to a temperature which is significantly lower than the transition _temperature T _Af , whereby significant differences in the elastic properties of the anchoring sections and the respective lining section of the stent can be achieved.

This applies in particular when the cooling phase is ended as soon as the temperature of the lining section has "just" _fallen below the transition temperature J _Af , so that its "impressed" restoring force corresponds to only a minimal value and a favorable extension of the period of time that the stent is achieved after being exposed to the body temperature of the treated patient, it takes until it has taken on its impressed shape.

A stent according to the invention can be created according to the features of claim 11 by a sequence of tempering processes, by means of which the desired shape memory behavior is achieved successively, which would not be achievable in a single tempering and cooling process.

A tempering device suitable for the production of stents according to the invention and corresponding to the features of claim 12, by means of which various sections of a stent can extract heat with a different rate of temperature decrease, such that a temperature profile with an upper and a one is seen over the length of the stent results in the lower extreme value, is realized in a preferred embodiment in such a way that at least one section of the stent can be supplied with heat while another section is being cooled, these functions being able to be implemented in a simple manner according to the features of claims 14 and 15. In combination with this, the heating or cooling thermal treatment is promoted by an outer shape enveloping the outside of the stent, the multi-part design of the outer shape according to claim 17 being particularly advantageous if a section of the stent to be cooled is e.g. B. to be cooled by means of a cooling gas stream. In connection with this, the multi-part design also enables the core according to claim 18 to have a particularly efficient thermal treatment of the stent.

Further details of the invention will become apparent from the following descriptions thereof with reference to the drawing. Show it

1a to 1c embodiments of the stent according to the invention, used as endoprostheses for stenosis therapy of an artery, in a schematically simplified partial representation and

2 a temperature control device suitable for the thermal pretreatment of stents according to FIGS. 1a-1c, in a representation corresponding to FIGS. 1a to 1c

In FIGS. 1a, 1b and 1c, a total of 10 each denotes a stent which can be inserted into an artery 12 in the sense of minimally invasive therapy for preventing and removing a vascular occlusion threatened by a stenosis 11.

The stent 10 is inserted into the area 12/1 of the artery 12 which is affected by the stenosis by means of a catheter device (not shown) with a guide wire and guide tube which guides the stent 12 and which is connected to an artery which runs close to the surface, e.g. B. one of the inguinal arteries is inserted into the vascular system and can be advanced to the area to be treated. The relevant - minimally invasive - surgical technique is generally known and is not itself the subject of the invention. It essentially consists of inserting the stent 10 in a state of minimal diameter into the stenotic region of the artery 12 and bringing it there in an expanded state in which it is anchored sufficiently securely on the one hand and on the other hand to ensure that a defined one Lumen of the blood vessel 12 remains open. The expansion of the stent required for this takes place, depending on the material from which it is made, with the aid of an inflatable balloon and / or due to a shape elasticity of the stent, which leads to a self-expansion of the stent to the required dimensions after an outer shell has been peeled off, which had previously kept it in the state of minimal diameter.

The stent 10 shown in FIGS. 1a to 1c in its state inserted into the artery 12 has a "central" lining section 10/1 and anchoring sections 10/2 and 10/3 arranged on both sides thereof, each of which is in one piece in the exemplary embodiment according to FIGS. 1a to 1c are executed with the lining section 10/1.

For the purpose of explaining the basic shape, the stent 10 is assumed to be cylindrical-tubular or tubular, with its jacket having a lattice structure with diamond-shaped lattice openings which are bordered by thin webs 13 which are formed contiguously at intersection points 14. The structure of the stent sheath corresponds in principle to that of an expanded metal.

For the stent 10, it is further assumed that it consists of a nickel / titanium alloy (Nitinol) which develops a "shape memory" (memory effect), in that a Nitinol part that is cold at a temperature below a transition temperature has been deformed, when the temperature rises above the transformation temperature, it returns to the shape that existed before the cold working. The The transformation _temperature T _Af can be specified by a precise specification of the alloy ratio, defined as the proportion of nickel as the base material and the titanium as an addition to the alloy, whereby, according to the purpose of the stent, this transition temperature is selected to be slightly lower than that usually given in the field of use of the stent Body temperature, so that the stent can be reminded of a shape previously impressed on it by warming it up to the body temperature.

The memory capacity, understood as the restoring force which the stent is able to develop after deformation below the transition temperature after the temperature has risen above the transition temperature, can be achieved by thermal pretreatment of the stent and influenced by the choice of the treatment boundary conditions, in that the stent is brought into its desired shape at an elevated temperature, and the stent is then rapidly cooled to a temperature below the transition temperature.

The stamping of the stent shape is usually carried out in that it is expanded with radial expansion onto a core determining its inner shape and then at a temperature which is substantially higher than the transition temperature T _Af , for. B. is annealed at a temperature around 560 ° C until its nitinol material has completely reached an austenitic phase in which the shape that it will later "remember" - should "approach" again - "breathed in" - is impressed.

Then the stent is rapidly reduced to a temperature below the transition temperature in the assumed example of use. B. cooled to a temperature which is significantly below the transition temperature and the stent material is in a martensitic phase in which it is "cold" elastic deformable and the stent "axially" is stretchable to the extent that a diameter reduction can be achieved in which the stent is placed in a blood vessel can be introduced. In order to bring the stent to a predetermined nominal diameter suitable for its use, which essentially corresponds to the required lumen of a vessel to be expanded, it may be necessary to carry out several tempering processes in which the stent is successively attached to it the shape required for vascular therapy is approximated and brought into it.

The shape-memory capacity impressed on the stent 10 by the tempering and subsequent cooling under a predetermined shape has an effect, of course within predetermined limits, in such a way that the stent, even if in its martensitic state, has been given a shape which it martensitic Phase would be retained, after heating to or above the transition temperature "remembers" the shape impressed by thermal pretreatment and tries to take it again - elastic in shape.

Utilizing these previously explained properties of the stent material, the stent 10 is designed in such a way that the end sections of the stent forming the anchoring sections 10/210/3 have a significantly higher restoring force in the sense of the return to the one impressed at high temperature given the radial deformation The shape of the stent unfolds as the lining section 10/1, so that after the stent has been brought into an arrangement penetrating into the stenotic region 12/1 of the artery 12, it has a much weaker restoring force in terms of shape memory than the anchoring sections 10/2 and 10/3, which are accordingly much faster than the lining section 10/1 of the stent, as it were spontaneously, reach their largest diameter in particular in such a way that the anchoring sections 10/2 and 10/3 reach their maximum inside diameter D / i just a few seconds or minutes after the conversion is exceeded reach temperature Taf, but the lining section 10/1 much later, e.g. B. only after days or weeks. A stenosis 11 can therefore, as by the Figures 1a to 1c illustrated, slowly and gently break down for the artery 12. The risk of thrombosis formation is considerably reduced.

The characteristic feature of the stent 10 is that the anchoring sections 10/2 and 10/3, compared to the lining section 10/1, develop higher "form-elastic" restoring forces at values higher than the transition temperature and therefore also develop in a short time As shown schematically in FIG. 1 a, the diameter required for anchoring them in the artery 12 can be implemented in such a way that, given the thickness of the grid webs 13, the lengths of the webs measured between adjacent crossing points in the lining section 10/1 are greater than in the anchoring sections 10/2 and 10/3.

The desired effect can also be achieved in that, as shown schematically in FIG. 1b, the webs 13 of the stent jacket in the anchoring sections 10/2 and 10/3 are thicker than the webs 13 of the anchoring section 10/1, but the lattice structure is the same in all stent sections.

The stent shapes represented by FIGS. 1a and 1b can be achieved by suitably specifying the lengths and widths of longitudinal slots which are cut in a laser cutting process into a nitinol tube provided as a blank for manufacturing the stent.

Different restoring properties of the lining section and the anchoring sections can also be achieved by thermally different treatments of the lining section 10/1 and the anchoring sections 10/2, given the uniform design of the lattice structure of the stent sheath as seen in the length of the stent 10, as shown in FIG. 1c and 10/3 can be achieved because the shape-memory of the Nitinol material can be influenced by its thermal pretreatment. Aspects to be considered for thermal pretreatment are at least the following:

The shape-memory of nitinol is more pronounced the more perfect and complete the austenitic phase of nitinol is before the material is cooled. The tempering of the stent at high temperature serves to meet this requirement.

The shape memory is also more pronounced the faster the cooling from the austenitic to the martensitic phase of the nithinol has taken place, so that a different elastic recovery force can be implemented by a different rate of cooling.

The properties of the stents corresponding to the concept of the invention, which have been shaken up to now essentially with reference to FIGS. 1a and 1b, can therefore also in the case of stents which, as shown in FIG Pretreatment of their functional sections - the lining section and the anchoring section (s) - can be implemented, in particular by the fact that their anchoring sections 10/2 and 10/3 are cooled more rapidly than the lining section 10/1 arranged therebetween at high temperature.

For an exemplary explanation of possible procedures in this regard, reference is now made to FIG. 2, in which 20 denotes a tempering device, which can be used to carry out the last shaping phase of the stent, by means of which the stent has its final shape and also Shape memory is impressed.

The stent 10 is mounted on an essentially cylindrical-tubular core 10, on the conical core pieces 21/1 and 22/2 in the from FIG. 2nd apparent arrangement are set that facilitate the mounting of the stent 10 on the core to increase the diameter.

The core 21 consists of a thermally highly conductive, chemically inert stainless steel material that does not react with the stent material or enables diffusion processes that could have a significant influence on the stent material.

An electric resistance heater represented by a heating coil 22 is installed in the core 21, the heating power of which can be controlled. The heat given off by the heating coil 22 is transferred to the stent 10 by heat conduction. In the outer region of the central stent section, the length of which corresponds to that of the lining section of the stent, rod-shaped radiation heating elements 24 are provided in axially symmetrical grouping with respect to the central longitudinal axis 23 of the core 21, by means of which the stent 10 can be heated "from the outside" by heat radiation.

Viewed in the direction of the central longitudinal axis 23 of the core 21 or the stent 10, a pair of semi-cylindrical outer mold halves 26/1 and 26/2 or 26/3 and 26/4 are arranged on both sides of the central arrangement of the rod-shaped heating elements are from an open configuration shown in the left part of FIG. 2, in which they are located at a large radial distance from the respective end section 10/2 or 10/3 of the stent 10, which is intended to form an anchoring section of the stent 10, into which the right part of FIG. 2 indicated closed position are displaceable, in which they enclose the respective end section, form-fitting and are in good thermal contact with this.

For the sake of simplicity, the closing and opening drives required for this, which can be implemented using conventional technology, are not shown. The outer mold halves 26/1 to 26/4 are provided with cooling systems schematically indicated by cooling coils 27, by means of which they can be cooled to temperatures far below the conversion temperature T _Af , by passing a precooled heat transport medium stream through these cooling coils 27.

The outer mold halves 26/1 to 26/4 are expediently designed in such a way that their overall heat capacity is substantially - e.g. B. 5 times - larger than that of the core and the stent, taken together, so that their temperature after the stent heating has been switched off and the mold halves have been brought into thermal contact with the stent, at most to 1/5 of the temperature that the stent 10 had before the mold halves were closed.

The total heat capacity of the outer shape used for cooling and the temperature to which the stent is to be quenched, at least in the area of its anchoring sections, can be easily coordinated with one another and with that of the stent and core so that water is used as the coolant can, d. H. whose boiling point is not reached even if it does not circulate in the cooling coils 27.

Appropriate modifications of the tempering device 20 or alternative designs to it, which are not shown for the sake of simplicity, can be the following:

The rod-shaped heating elements can be integrated into an outer mold divided into two mold halves, the mold halves for cooling the stent, for. B. by introducing cooling gas into a previously evacuated chamber in which the tempering device is located, apart. The core carrying the stent can be formed in several parts, for. B. in that the end portions of the stent supporting core parts are removable and the end portions of the stent are exposed to a coolant flow on the inside.

The core and / or an outer shape of the stent can also be designed such that liquid nitrogen can be used as the coolant.

Further, the purpose of being able to cool different functional sections of the stent at different rates, serving tempering device designs, in particular also the realization of an electronic control unit for controlling the tempering process, can be easily realized by a person skilled in the art if the purpose is known and are not considered in detail to require explanation.

Claims

claims

1. Stent for a re-canalizing treatment of a vessel with stenosis, in particular an artery, with a basic shape according to the cylindrical-raw shell, which has a lattice or mesh structure that allows radial and axial changes in shape of the stent in a defined correlation, the stent consists of a metal alloy which, depending on the ambient temperature, is super-elastic or shape-retaining elastic in the sense of the development of restoring forces which, after deformation of the stent in the super-elastic temperature range, lead to the taking back of a shape which had been impressed on the stent at elevated temperature, the stent has at least one anchoring section, the widening of which enables the stent to be fixed in the treated vessel in a force-locking or force-locking manner, and a lining section which serves to recanalize the stenosis, characterized in that the anchoring section (10/2, 1 0/3) forming part of the stent (10) with a given radial deformation develops a significantly higher restoring force in the sense of the return to the shape of the stent imprinted at high temperature than the lining section (10/1).

2. Stent according to claim 1, characterized in that the stent (10) has two anchoring sections (10/2 and 10/3), between which a lining section extends.

3. Stent according to claim 1 or claim 2, characterized in that the lattice structure of the stent casing-forming webs (13) in the region of the lining section have a smaller material cross section than in the adjacent anchoring section (s) (10/2 or 10/3 ).

4. Stent according to one of claims 1 to 3, characterized in that the lining section (10/1) and the anchoring section (s) (10/2, 10/3) of the stent consist of nitinol material of different alloy ratios ,

5. Stent according to claim 4, characterized in that the differently alloyed stent sections are welded to one another, preferably joined to one another in a laser welding process.

6. A process for producing a stent from a nitinol (Ni (i- ₀ , _X ) Ti ₀ , x) material, which is brought into an austenitic phase by annealing at a temperature which is significantly higher than a transition temperature T _Af , in which the stent (10) is brought into a form intended for its intended use, and after cooling below the transformation temperature T _Af enters a martensitic phase in which the stent is compressed to the minimum diameter in the configuration intended for its use Can be brought into a position in which, at a further increased temperature T (T> T _Af ), it develops an elastic restoring force for resuming the shape impressed during tempering above the temperature T _Af , characterized in that the stent sections (10/1 or 10/2 and 10/3) with significantly different rates of temperature reduction to the temperature below the transition temperature T _Af be held.

7. The method according to claim 6, characterized in that anchoring sections (10/2 and 10/3) are cooled more rapidly than a lining section of the stent (10) arranged adjacent to or between such sending sections.

8. The method according to claim 7, characterized in that during the cooling of the stent of the same anchoring section adjacent liner section is further heated such that its cooling rate is less than that of the faster cooled anchoring section.

9. The method according to claim 7 or 8, characterized in that the anchoring portion (s) of the stent is / are quenched with a high cooling rate to a temperature which is significantly lower than the transition temperature T _Af .

10. The method according to any one of claims 7 to 9, characterized in that the cooling phase is ended as soon as the temperature of the lining section _falls below the transition temperature T _Af .

11. The method according to any one of claims 7-10, characterized by a sequence of treatment cycles of the stent (10) comprising cold forming, tempering and cooling phases, for gradual expansion from its use form.

12. Device for the thermal treatment of a stent according to one of claims 1 to 5 and using the procedures according to at least one of claims 6 to 10, with a tempering device, in which the stent on the one hand at temperatures that are significantly higher than the transition temperature T _{Af can be} tempered and, on the other hand, can be cooled to a temperature below the transition temperature T _Af , the stent being pulled onto a core (24), the shape of which is predetermined by the outer shape and which can be impressed on the stent by the thermal treatment, characterized in that a cooling device (26 / 1-4, 27) is provided, by means of which different sections of the stent can remove heat at a different rate of temperature decrease, such that over seen the length of the stent 10 results in a temperature profile with an upper and a lower extreme value.

13. Device according to claim 12, characterized in that the tempering device comprises a heating device by means of which heat can be supplied to at least one section (10/1) of the stent (10), while another section (10/2, 3) is cooled ,

14. Device according to claim 12 or claim 13, characterized in that the core (21) carrying the stent can be heated by means of a radiant heater, preferably an electrical resistance heater (22) with controllable heating power.

15. Device according to claim 14, characterized in that at least one end section of the stent can be cooled by means of a cooling medium flow.

16. Device according to one of claims 12 to 15, characterized in that an outer shape is provided which surrounds the stent and is in thermally conductive contact therewith, which can be heated in sections and cooled in sections.

17. The device according to claim 16, characterized in that the outer shape is formed in several parts, such that a part of the outer shape enveloping the coolable section is removable in the cooling phase from the section of the stent to be cooled.

18. Device according to one of claims 12 to 17, characterized in that the core carrying the stent is constructed in several parts, such that a part of the core carrying a coolable section of the stent can be disengaged from the stent.