Stent graft and method for manufacturing the same

Abstract

The present invention relates to a stent graft comprising a base stent having first and second longitudinal ends, a lumen extending longitudinally through the base stent, and a covering material provided for lining the base stent, the base stent having a roughened surface that is at least partially infiltrated by the covering material to form a form fitting connection.

Description

[Technical field]

[0001] The present invention relates to a stent graft and a method for its manufacture. [Background technology]

[0002] Stent grafts, or covered stents, are frequently used in medicine for a range of endovascular repairs and other procedures, such as the placement of a transjugular intrahepatic portosystemic shunt (TIPS). Often used to keep blocked or restricted blood vessels open, compared to uncovered stents, which have walls that are easily permeable by blood, stent grafts are themselves tubular conduits and can partially replace the blood-conducting function of blood vessels.

[0003] A typical stent graft consists of three layers: a base stent, which is a stent that provides structural integrity and defines the shape of the stent graft. Such a base stent may be made of a self-expanding material such as Nitinol, and expands to a delivery configuration upon implantation within the body by warming to the patient's body temperature. The base stent may itself be balloon expandable, and may be expanded to the stent's final delivery configuration by a balloon that is inserted within the stent and then inflated.

[0004] In the prior art, stent grafts are often covered on the inside and outside with a covering layer made of a biocompatible backing material (e.g., expanded polytetrafluoroethylene (ePTFE) or fluorinated ethylene propylene (FEP)) that turns the scaffold formed by the base stent into a tubular structure that can function as a blood conduit.

[0005] A common challenge for such stent grafts is the desire to improve the flexibility of the stent graft and reduce its delivery profile. In short, high flexibility is advantageous for implanting the stent graft in vessels that may be tortuous. A small delivery profile makes it easier to deliver the stent graft in narrow vessels, reducing vessel damage and patient discomfort. In prior art devices, these two objectives have been achieved by constructing the outer covering layer as a ribbon band spirally wound around the outer surface of the base stent rather than as a single complete layer, or by reducing the thickness of both layers to some extent, both of which entail disadvantages during processing. The effective wall thickness of the outer wall is accordingly reduced, making the stent graft more flexible and reducing its delivery profile. However, in such stent grafts, it is necessary to ensure that the covering material is securely attached to the stent graft. Furthermore, a structure in which covering layers are provided on both the inside and outside of the base stent can lead to wear, corrosion, and fatigue at the joints.

[0006] Enhancing the adhesion of the coating to the base stent is also a general concern. It is important to ensure that the coating is securely attached to the base stent; if this cannot be ensured, the stent graft is not suitable for implantation and must be discarded. Summary of the Invention

[0007] The present invention aims to solve or alleviate one or more of the problems mentioned above, and in particular to provide a stent graft which improves adhesion of a covering material to a base stent while also allowing for improved flexibility and a smaller delivery profile. It is also an object of the present invention to provide a method for producing a stent graft having such advantages.

[0008] The invention is defined by claims 1 and 7. Embodiments are defined in the dependent claims. According to the invention, the stent graft comprises a base stent, which may be a self-expanding base stent or a balloon-expandable base stent, having first and second longitudinal ends, a lumen extending longitudinally between the first and second longitudinal ends of the base stent, such that the base stent as a whole is tubular.

[0009] A covering is provided to line the base stent, the covering transforming the base stent into a stent-graft capable of functioning to conduct blood therethrough, and the covering is secured to the base stent such that the base stent and covering can be treated as a single mechanical unit.

[0010] According to the invention, the base stent has a roughened surface that is at least partially infiltrated by the coating material to form a positive fit, i.e. there are recesses and / or protrusions formed by the material of the base stent with which the coating material engages and helps to hold the coating material on the base stent. Having such a roughened surface improves the adhesion of the coating material to the base stent. By roughened surface, we mean that the surface is not smooth and is therefore structured with shaped features that allow the coating material to penetrate therein. The roughened surface can be provided on all parts of the base stent, i.e. both the struts and the connectors.

[0011] In an embodiment, the covering material is provided only on the inside of the base stent, without covering the outside of the base stent. It cannot be excluded that a small amount of covering material is extruded onto the outside of the base stent during manufacturing, but most of the outside of the base stent is not covered. When the covering material is provided only on the inside of the base stent, such an arrangement improves both the flexibility of the stent graft and the delivery shape of the stent graft. This is because the cross-sectional area of ​​the stent graft is reduced, which improves flexibility (because bending stiffness is reduced) and at the same time reduces the cross-sectional area, improving the delivery shape.

[0012] Similarly, in other embodiments, the coating material is only applied to the outside of the base stent, without covering the inside of the base stent. Again, it cannot be excluded that a small amount of coating material is extruded to the inside of the stent during manufacturing, but most of the inside of the base stent is not covered. Again, such a configuration improves flexibility and delivery shape. Furthermore, compared to a configuration in which the coating material is only applied to the inside of the base stent, such a stent graft is easier to manufacture, since it is generally easier to provide microcavities for bonding the coating material on the outside of the base stent rather than on the inside. For example, it is easier to sandblast the base stent from the outside rather than from the inside to create microcavities, and the same applies to other methods of creating microcavities, such as using a laser (it is easier to irradiate the outside surface of the base stent).

[0013] In embodiments, the covering material forms a tube, and in some embodiments, the tube extends along the entire length of the base stent. Because the tube extends along the entire length of the base stent, no portion of the base stent is exposed, i.e., there are no uncovered portions of the base stent that could impede blood flow. Thus, the usable length of the base stent is maximized.

[0014] In an embodiment, the roughened surface is roughened by sandblasting. Such a roughened surface is particularly advantageous for bonding a base stent. Such a method is also relatively easy to implement.

[0015] In embodiments, the roughened surface comprises microcavities. These microcavities are particularly good for adhering the coating material. Such microcavities can be understood as pores or holes in the surface with a length scale significantly smaller than the thickness of the component on which they are placed. For example, the length scale (diameter) of such irregularities can be less than 50% of their thickness, preferably less than 20% of their thickness. In some embodiments, these microcavities are blind holes. By providing blind holes, the coating material does not have to penetrate the entire base stent, avoiding weakening the coating material at the point where it flows into the base stent (as the amount of coating material that flows into the holes is limited).

[0016] In an embodiment, the stent graft comprises holes that penetrate the entire base stent material. Such through holes, i.e. holes that extend from the inside to the outside of the base stent, allow the coating material to completely penetrate the base stent and reach the other surface. This results in a particularly strong adhesion of the coating material to the base stent, as the coating material flows through these holes, resulting in a riveting effect. Such through holes can also be combined with blind holes (i.e. some of the holes in the base stent can be blind holes and others can be through holes).

[0017] In another aspect of the invention, a method of making a stent graft is provided by providing a base stent having first and second longitudinal ends and a lumen extending longitudinally therethrough, the stent having a roughened surface facing the lumen.

[0018] A tubular covering is then placed on the stent. The tubular covering can be slid inside the stent, but can also be slid onto the stent, so that the covering lines the inner lumen of the base stent, or at least theoretically the outer periphery of the base stent. The tubular covering is then at least partially infiltrated into the rough surface to form a form-fitting connection, thereby fixing the covering to the base stent. To infiltrate the covering, pressure is applied to the covering to force it into the microcavities. For example, a ribbon can be tightly wrapped around the covering to apply pressure, or an inflatable balloon can be introduced into the lumen of the base stent and inflated in place. If the covering is one that softens when heated, it is generally desirable to heat it above the temperature at which the covering softens. For coverings such as ePTFE, a temperature of about 335°C, slightly above its melting point of 327°C, has been found to provide good results. This method provides a stent graft with improved adhesion of the covering to the base stent. The delivery profile and flexibility of the produced stent graft is also improved when the covering is provided only on the inside or only on the outside of the base stent.

[0019] In an embodiment, the step of providing a base stent includes a step of intentionally roughening the surface facing the lumen. That is, a previously smooth stent is roughened. A roughening method can be selected that results in improved permeability of the coating material, which can improve adhesion. It should be noted that the roughening step can also be used on a prefabricated base stent that is already rough, so it does not mean that the surface of the base stent before roughening is smooth.

[0020] In embodiments, the roughening step includes one or more steps of microgrinding, pressing and / or sandblasting the lumen-facing surface, such steps resulting in a particularly roughened surface.

[0021] In an embodiment, the roughening step comprises irradiating the surface to be roughened with a laser. Using such a laser, the surface can be roughened in a very controlled manner, such that one can have sufficient control over how the surface is roughened so that the resulting adhesive properties can be precisely tailored.

[0022] In an embodiment, the roughened surface comprises blind holes through which the coating material at least partially penetrates. Such blind holes limit the amount of coating material that can penetrate into them. This prevents the coating material from being overly weakened at those holes.

[0023] In an embodiment, the roughened surface comprises holes that penetrate the entire material of the base stent from the luminal side to the abluminal side of the base stent. As previously mentioned, such a configuration is used to improve adhesion. [Brief description of the drawings]

[0024] [Figure 1] 1 shows a stent graft according to one embodiment of the present invention. [Diagram 2] 1 illustrates a method of manufacturing a stent graft according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 1 shows in perspective view a stent graft according to an embodiment of the invention. The stent graft 10 comprises a base stent 12 having three rings 13 made of zigzag struts 15. The rings 13 are connected by connectors 17. On the inside of the base stent 12 is provided an inner covering 14 which lines the lumen 16 of the stent graft 10.

[0026] As can be seen in the drawing, the base stent 12 further comprises through holes 18 arranged to extend radially from the luminal surface of the base stent 12 to the abluminal surface of the base stent 12 and at least partially permeated by the coating material 14. The coating material, which may be ePTFE, flows into the holes during sintering, thus providing adhesion and mechanical grip between the stent graft 12 and the coating material 14. The through holes 18 are provided in both the connectors 17 and the struts 15 of the rings 13.

[0027] FIG. 2 illustrates in a flow chart a method of manufacturing the stent graft 10 shown in FIG. In step S10, a base stent 12 is provided. The base stent 12 is then roughened in step S12. This roughening can be performed using microgrinding, which adds a roughness greater than that of a base stent that has been previously polished (the standard surface treatment for such stents). One option would be to use a porous Nitinol material before cutting the stent. Another method would be to sandblast the surface of the base stent or use other mechanical surface treatment techniques such as pressing. Alternatively, laser microcavities can be made or blind holes can be created using a laser. It is also possible to create through-holes 18 that run completely through the base stent 12 from the luminal side to the abluminal side, as shown in FIG. 1. If microgrinding is used and a porous Nitinol material is used, steps S10 and S12 can be a single step, and therefore no separate roughening step is required other than providing a sufficiently porous base stent 12.

[0028] In the next step S14 of placing the covering material 14, the covering material 14 is placed on the base stent. The covering material may be placed in the lumen 16 of the base stent 12 or may be placed so as to surround the base stent.

[0029] Finally, the coating 14 is bonded to the base stent 12 (step S16) through a sintering process similar to that performed in the prior art. In this step, in an embodiment, a sufficiently high pressure can be used to force the coating 14, such as ePTFE, onto the roughened surface and into holes in the base stent surface, if present, to increase the grip of the coating 14. This improves mechanical fixation, and if holes are present, the coating will flow through the holes 18 onto the opposite surface, resulting in a particularly strong mechanical fixation of the coating to the base stent. This bonding step is otherwise similar to the bonding steps performed in prior art stent graft manufacturing processes.

Claims

1. a base stent (12) having first and second longitudinal ends and a lumen (16) extending longitudinally through said base stent (12); a covering material (14) provided to line said base stent (12); A stent graft comprising: The base stent (12) has a roughened surface that is at least partially infiltrated by the covering material (14) to form a form-fitting connection; the roughened surface comprises microcavities which are blind holes; Stent graft.

2. The stent graft according to claim 1, wherein the covering material (14) is provided on the inside of the base stent (12) without covering the outside of the base stent (12).

3. The stent graft of claim 1, wherein the covering material (14) is provided on the outside of the base stent (12) without covering the inside of the base stent (12).

4. A stent graft according to any one of claims 1 to 3, wherein the covering (14) forms a tube extending along the entire length of the base stent (12).

5. A stent graft according to any one of claims 1 to 4, wherein the roughened surface is roughened by sandblasting.

6. A stent graft according to any one of claims 1 to 5, wherein the stent graft comprises holes (18) passing through the base stent (12).

7. A method for manufacturing a stent graft, comprising: - providing a base stent (12), said base stent (12) having first and second longitudinal ends and a lumen (16) extending longitudinally therethrough, said base stent (12) having a roughened surface facing said lumen (16), said roughened surface comprising microcavities that are blind holes; - placing a tubular covering (14) inside said base stent (12) and allowing said covering (14) to at least partially penetrate into said roughened surface to form a form-fitting connection; A method for manufacturing a stent graft, comprising:

8. The method of claim 7, wherein the step of providing a base stent (12) includes the step of roughening a surface to be infiltrated by the coating material (14).

9. The method of claim 8 , wherein the step of roughening comprises microgrinding, pressing and / or sandblasting the surface to be roughened.

10. 10. The method of claim 8 or 9, wherein the step of roughening comprises irradiating the surface to be roughened with a laser.

11. The method according to any one of claims 7 to 10, wherein the roughened surface comprises through holes (18) extending through the base stent (12).

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