A METHOD FOR MAKING AN EXTENSIBLE STENT FROM SHEET MATERIAL

Abstract: Method for making an extensible stent from a sheet-shaped material used therein, and a stent obtained by using this material, in which method one starts from a template with an outer configuration corresponding with the desired final configuration, winds this with the sheet-shaped material which comprises coherent fibers and which is, either earlier or after the winding, soaked with a controlled curable plastics.

Description: Title : A METHOD FOR MAKING AN EXTENSIBLE STENT FROM SHEET MATERIAL The invention relates to a method for making an extensible stent which is to be brought into a form- retaining state by curing. Vasculair stents for locally reinforcing a body vessel, to be introduced by means of a catheter are brought into their final configuration by means of an extensible element at the distal end of this catheter whereafter irridiation with UV radiation initiates the curing of the plastics material are known from the prior art. Mentioned are the patent publications US-5.344.444 , US-5.464.419 , EP- 0 521 573 Bl en EP-0 617 930, all haviang the same inventor as the present one. Despite the ongoing development in the field of such stents there as is yet no method by means of which stents can be made quickly and cheaply, if necessary even shortly before the introduction thereof into a body vessel in each desired final configuration, meeting all requirements. The invention aims to provide such a ethode. To this end the invention proposes a method for making an extensible stent which is brought in a form retaining state with predetermined final configuration by curing, in which one starts from a template with an outer configuration corresponding with the desired final configuration, winds this with sheet-shaped material made from coherent fibers which is either before or after the winding soaked with a plastics with a controlled initiated curing. This plastics can be dissolved in a solvent whichthereafter is evaporated controllable by heating. Making a template, which, after winding it in the way as proposed by the invention results into a stent which is completely suited to a specifiek situation, particularly a situation which is evaluated on the hand of X-ray images of a body vessel which is to be treated, can be done cheaply. It is possible, after making the template, to 2 compare the dimensions and configurations thereof with X- ray images of the body vessel in question, whereafter, if possible, configuration and dimensions of the template can be corrected. Thereafter, the stent is made in the way as proposed by the invention and this stent is then fit to be introduced into the body vessel. If necessary the making of the final stent can be preceded by making a trial model. Preferred embodiments of the method according to the invention are described in the claims 2 up to and including 7. The fact that the method according to the invention is excellently suited to provide thereon a therapeutic active for a radiation emitting substance leads to the advantage that it is possible to implant it into a patient directly after the determination of shape and configuration of such a stent, so that the treatment can be started without any delay. In a preferred embodiment of the method according to the invention one will use a sheet-shaped base material with metallic reinforcing fibers distributed therein. With these simple measures which can be integrated simply in the fabrication process of the base material an increased strength of the material is obtained so that for a particular use it can have smaller dimensions, particularly a smaller thickness, in combination with a certain opaqueness for X-ray radiation so that not only the positioning but also the detection of a stent made from this material at a later moment becomes very easy. Length, diameter and configuration of the fibers will, in a certain practical embodiment, be adapted to the use one has in view. Preferred embodiments are given in the claims 9 and 10. Further preferred embodiments for using this material are described in the claims 11 up to and including 16. The measure according to claim 17 gives the possiblity for a local treatment with radio-active radiation. The starting material for the fibers can be made radioactive by introducing a radio-active isotope in the melt thereof. Of course then when handling and using the material the necessary safety measures must be taken but as the intensitivity of the radiation is only low - this 3 as a result of the short distance between stent and tissue to be treated - this will not result into any insurmountable problems in practice. The sheet-shaped starting material which comprises the fibers is preferrably made in the way as described in the claims 19-21. The claimed exclusive rights also include a stent such as is subject of the claims 22-26. The invention is elucidated on the hand of a drawing. Therein show: fig. 1 schematically the use of a template in the method according to the invention; fig. 2 in cross-section a preferred embodiment of a stent, obtained therewith; fig. 3 the use of a template to execute the method according to the invention in combination with the provision of openings in the surface of the stent obtained therewith; fig. 4 a side view of a stent, obtained in this way; fig. 5 a side view of a template and the stent formed thereon, having a tapering configuration; fig. 6 a side view of a template with a stent made thereon in a configuration in which the ends of the stent have a greater diameter than the middle part thereof; fig. 7 schematically and in top view sheet-shaped material to be used in the method according to the invention; fig. 8 schematically and in perspective a stent made from this material; fig. 9 schematically and in top view sheet-shaped material to be used in the method according to the invention according to a second embodiment; fig. 10 schematically and in perspective view another embodiment of a stent obtained by using this material; fig. 12 in top view a third embodiment of sheet-shaped starting material; fig. 13 a fourth embodiment of the sheet-shaped starting material according to the invention; and fig. 15 in perspective view a stent made therefrom. The method according to the invention will be elucidated on the hand of the schematic fig. 1. On a template 2 with, 4 in this example, a cylindrical outer surface a strip of flexible material 4 is wound which is made from mutually coherent fibers; a good starting material for executing the method according to the invention is thin and pure paper. It is clear that the drawing of fig. 1 is not on scale; this also goes for the other drawings to be discussed hereinafter. After winding such a length of material on the template 2 that the wound cylinder 5 has obtained the desired thickness the material is cut-off and thereafter soaked in a plastics, which can be dissolved in a solvent of the kind known as such, the curing ofo the plastics can be initiated controllably by irradiation with UV-radiation. One can also use a fiber material which is soaked in such a plastics before it is wound, but handling thereof is somewhat more difficult. After removal of the template 2 and, if necessary, heating in an oven, one obtains a stent 5 with the cylindrical configuration as shown in fig. 2 in cross- section. Thereafter this stent, of which the outer surface is still somewhat sticky, can be rolled in a therapeutic substance (aspirin, heparin, cocain) in powder form, which adheres to the outer surface and can easily be provided thereon in a controlled quantity. Controlled powdering is also possible. For many uses it is desired that the ends of a stent are more flexible than the middle part and according to the invention this can be obtained very simply by chosing a higher concentration of the plastics material in the end zones, indicated in fig. 2 with 6a and 6b, than in the middle zone 8. In some cases it is desired that a substance with a therapeutic action, or a substance emitting radio-active radiation is provided not over the entire surface of the stent but only in a certain part thereof. The method of the invention makes it easy to coat the, still sticky, outer surface of the stent with a substance with therapeutic action, not equally, but only selectively on certain surface parts. The invention also gives the possibility to form openings on certain preferred places in the stent, said openings being filled with a substance with therapeutic action later-on. 5 To this end one can, as fig. 3 shows, use a template 10 in which the stent 12, wound thereon, is pierced by pins, placed in rings, as indicated by 14, 16 en 18. After curing of the stent and the removal of the pins the stent 20 results within its body three rings of openings 14', 16', 18', corresponding with the rings of pins 14, 16 and 18. One is, of course, totally free in chosing the shape of the stent as this is completely determined by the outer shape of the template. Fig. 5 shows a somewhat tapering template 22 of which the left hand end 24a has a smaller diameter than the right hand end 24b; corresponding therewith the stent 26, obtained with this template, is also tapering; the left hand end 28a has a smaller diameter than the right hand end 28b. This stent can be removed easily from the template 22. Making a stent of which the outer ends have a greater diameter than the middle part poses no problem. Fig. 6 shows in side view such an embodiment of the method according to the invention: the template 30, as used, has ends 32a, 32b with a greater diameter than the middle part and corresponding therewith the stent 34, formed thereon, has ends 36a, 36b with a greater diameter than the middle part 38. Of course one will use in this case a template with two aligned parts which are removed to the left and right respectively from the stent 38. According to a advantageous embodiment of the invention it is proposed to introduce and distribute metallic reinforcing fibers into the sheet-shaped starting material. These fibers are preferably made from titanium, generally from a "biocompatible" material . This introducing can be done during the grinding of the fibers or also during the intensive mixing of the pulp. The length and the diameter of the fibers to be added can be chosen in dependance on the final use one has in mind. The fibers can be supplied individually and incoherently but it is also possible to introduce them more or less coherently into the pulp, as will be described later on. As a value for the minimum diameter to be used one thinks of 5 μm and as minimum length 1-2 mm, although the 6 dimensions are certainly not restrictive and particularly the minimum dimensions are only set by the possibility of handling the fibers. The weight percentage of the fibers can be chosen independant from the aim one has in mind: a weight percentage of 10-20% is possible. Other values are also possible. It is, of course, possible to mix the fibers with the plastics material before the sheet material is soaked with it. The introduced metallic fibers are of course impervious to UV radiation, which could result in the problem that the curing of the plastics, being started by irradation with UV radiation will not proceed evenly in a stent made from the material according to the invention. In order to ensure that in any case an important part of the stent, made from the material according to the invention is directly irradiated with UV radiation it is proposed not to introduce the fibers equally into the starting material but according to a certain stripe pattern. Fig. 7 shows a part of sheet material 42 with equally distributed metallic fibers 44 therein, which are, of course, shown only schematically. The sheet 42 is cut up along the perpendicular crossing vertical cutting lines 46a, 46b, 46c to individual sheets 4a, from which the stent 50, shown in perspective view in fig. 8, is made. Preferably however, the fibers are not distributed equally but according to a pattern of mutual parallel lines which include an angle with the boundaries of the sheet 44, such as shown in fig. 9, according to which the sheet 42 is provided with a pattern of strips 54 in which metallic fibers are embedded in the starting material. So a stent as shown in fig. 10 and indicated therein with reference numeral 56, made from such a sheet 54, has strips 60 which run obliquely over the outer surface 58 and in which the metallic fibers, which give the stent 56 its strength, are embedded in the material. In order to initiate the curing the sleeve is irradiated from within with UV radiation and practically the whole inner surface will then be irradiated equally. 7 When the fibers are prepared in such a way that they emit radio-active radiation the stent also has a therapeutic action. According to the invention it is furthermore possible to wind a stent in the way as shown schematically and in perspective view in fig. 11: a sleeve 62 from normal fiber material which has none or only a very small percentage of metallic fibers supports, on the outer surface 64 thereof, a helically wound strip 66 which is made of sheet material, soaked with curing plastics and having therein a certain concentration metallic fibers. Here, too, the irradiation of the curing plastics will take place starting from the center of the core so that the base layer 64 will cure swiftly and uniformly; however after this layer 24 sufficient UV radiation reaches the strip 26 to initiate the curing thereof. This embodiment has the advantage that one can choose the composition of the plastics present in the strips 66 in such a way that the curing of the basic core 64 and the strips 66 occurs equally fast. The aspect discussed above according to which the fibers are distributed strip-like in the basic material can also be realised in the way as shown in fig. 12. The fibers will be made generally by drawing wire-shaped starting material and in the known manner they are then available in bundles; from such a bundle of fibers smaller bundles are made which are embedded with predetermined mutual distances in the pulp material. Fig. 12 shows a part of a pulp bed indicated with reference numeral 90 ; with predetermined mutual distances d fiber bundles 92 are embedded therein. Finally one obtains a starting material which is reinforced in a strip-like manner and from which stents having the configuration according to fig. 4 can be made. Fig. 13 shows a fiber material 80 having therein elongate fibers 82 which are all directed in the same direction indicated by the arrow 84. When a part 80a is separated therefrom, from which part finally a cylindrical stent 86 according to fig. 8 is made, all fibers 88 therein will be oriented in the circumferential direction. In this way this element has an increased radial strength. After making the stent as described hereabove this stent can be coated with the commercially available 8 "chronoflex" ® , whereafter the whole is baked at a suitable temperature. This results in a biocompatible outer surface so that the material can be used without problems in a body vessel.

Claims: 9 CLAIMS 1. Method for making an extensible stent which is brought in a form retaining state with predetermined final configuration by curing, in which one starts from a template with an outer configuration corresponding with the desired final configuration, winds this with sheet-shaped material made from coherent fibers which is either before or after the winding soaked with a plastics with a controlled initiated curing. 2. Method according to claim 1, characterised in that one supplies the plastics dissolved in a solvent and removes this solvent by heating the soaked sheet-material. 3. Method according to claims 1-2 in which one provides on the still sticky, outer surface of the stent, either by powdering or by rolling, a therapeutically active or radioactive radiation emitting substance. 4. Method according to claims 1-3 in which one provides in the surface holes destined to be filled with a substance which is therapeutically active or emits radio-active radiation. 5. Method according to claim 4 , in which one forms the holes by piercing the wound material with pins with a configuration corresponding to the desired holes. 6. Method according to claims 1-5, in which one distributes the plastics inhomogenously over the stent. 7. Method according to claim 6 , in which one choses a smaller concentration of the plastics in the fiber material at the ends of the stent than in the middle part thereof. 8. Method according to claims 1-7, in which one uses a sheet-shaped starting material with metallic reinforcing fibers distributed therein. 9. Method according to claim 8, in which the diameter of the reinforcing fibers is chosen to lie between 2 μm and 500 μ. 10. Method according to claims 8-9, in which the length of the reinforcing fibers is chosen to lie between 2 mm and 10 ram. 11. Method according to claims 8-9, in which one uses elongate reinforcing fibers. 12. Method according to claims 8-10, in which one uses curved reinforcing fibers. 10 13. Method according to claims 8-12, in which one uses titanium reinforcing fibers. 14. Method according to claims 8-13, in which one concentrates the reinforcing fibers according to a predetermined stripe pattern. 15. Method according to claim 14, in which one brings the reinforcing fibers in bundles in the base-layer. 16. Method according to claims 8-15, in which one uses elongate, essentially equally directed, fibers. 17. Method according to claims 8-12, in which one uses fibers prepared to emit radio-active radiation. 18. Method according to claims 8-17, in which the obtained stent is coated with a coating of chrono lex. 19. Method for making sheet-shaped material comprising coherent fibers and destined to be used in a method according to one or more of the claims 8-18 in which one adds the reinforcing fibers during the step of the grinding of the fibers. 20. Method for making sheet-shaped material to be used in the method according to one or more of the claims 8-18 in which one adds the reinforcing fibers during the mixing of the pulp of the starting material. 21. Method for making sheet-shaped material according to claim 20 in which one introduces the reinforcing fibers in bundles and according to a predetermined pattern into the pulp. 22. Stent obtained by using the method according to one or more of the claims 1-20. 23. Stent according to claim 22, characterised in that the configuration thereof differs from a cylindrical configuration. 24. Stent according to claim 22, characterised in that the diameter at the outer ends thereof is greater than same of the middle part. 25. Stent according to claims 22-24, characterised by openings, formed in the surface thereof, to contain a material which is therapeutically active and/or emits radio-active radiation. 26. Stent according to claims 22-25, characterised in that the concentration of curing plastics matarial is at 11 the outer end thereof smaller than in the middle part thereof .

Inventors: GLASTRA HENDRIK, GLASTRA, HENDRIK
Applicants: GLASTRA HENDRIK, RIGITEC B V, GLASTRA, HENDRIK, RIGITEC B.V.
Application year: 1999
Main classification: A61F2
IPC codes: A61F2, A61L27, B29C35, B29C53, B29C70, F16L11