Endovascular prosthesis

Description

FIELD OF INVENTION

[0001] The invention falls within the field of vascular endoprostheses, more particularly intended to be implemented in the case of aortic aneurysms.

[0002] The invention relates more particularly to such vascular endoprostheses incorporating a textile tubular structure and at least one filamentary element of the shape memory alloy type. EARLIER ART

[0003] An aneurysm is a dilation of a segment of an artery. Rupture of this pathological area can lead to hemorrhage, sometimes fatal. When such an aneurysm is detected, two solutions can be implemented by the medical team: the first consists of resolving the aneurysm through open surgery, a particularly complex and invasive technique. The second consists of bypassing the aneurysm by inserting an endoprosthesis, implanted within the artery upstream and downstream of the aneurysm; this is called endovascular surgery. This bypass allows blood flow within the endoprosthesis and, consequently, reduces blood pressure within the aneurysm and, therefore, the risk of its rupture. The main advantage of this second solution is that it significantly reduces the length of the procedure itself.

[0004] Such endoprostheses typically consist of a textile body attached to an exoskeleton, usually made of steel or a metal alloy, and advantageously exhibiting superelastic or shape-memory properties. This exoskeleton is usually sutured to the textile body, or attached to the stent during a procedure known as electrospinning in the relevant field. The textile body is, for example, made of PET (polyethylene terephthalate).

[0005] Shape memory materials are now widely known and used. They are characterized by their ability to undergo relatively significant deformation reversibly. This phenomenon is due to a crystallographic phase transformation within the material when it is subjected to mechanical loading—stress—and / or temperature variations. Thus, shape memory materials are capable of developing several particularly interesting properties, such as superelasticity and ferroelasticity (shape memory). Among shape memory alloys, those based on nickel and titanium are well-known, such as those marketed under the brand name Nitinol.

[0006] For example, in documents US 2006 / 058862 A1 and US 6,814,747, such an endoprosthesis has been described, comprising a tubular textile envelope, on the outside of which are attached, more or less periodically, rings made of shape-memory alloy, capable of expanding under the effect of temperature, and in this case typically under the effect of human body temperature, so as to give the endoprosthesis the tubular shape required to perform its shunt function, and consequently, to give the endoprosthesis a shape sufficiently reduced to allow its introduction into the artery in question, for example by means of a catheter.

[0007] While this type of endoprosthesis has undoubtedly enabled significant progress in the treatment of aneurysms by endovascular surgery, it nevertheless presents a number of disadvantages.

[0008] Among these, the first case to mention is endoleaks, which are leaks of the implanted endoprosthesis. These endoleaks are inherent to the structure of the tubular sheath itself, typically woven, in addition to the suture zones of the shape-memory alloy exoskeleton on the sheath. These zones can create areas of weakness in the tubular sheath, and consequently, openings through which blood flow can escape. When such an endoprosthesis is implanted, for example, in the aorta, particularly the abdominal aorta, and given the high blood flow pressure at this level, these leaks can quickly become a problem, notably preventing the resorption of the aneurysm that the endoprosthesis is specifically designed to reduce.

[0009] Another inherent difficulty in using anterior artery stents lies in poor positioning and unsatisfactory behavior at the kinking stage, that is, the twisting and turning the stent may undergo to adapt to the meanders of the artery into which it is to be implanted. Such kinking of the stent can lead to at least partial occlusion, resulting in significant complications requiring further surgery.

[0010] Another difficulty arising from anterior artery endoprostheses lies in their heterogeneity. Indeed, due to the suturing or fixation method of the rings or equivalent system, and more generally the exoskeleton on the tissue structure, the endoprosthesis exhibits mechanical behavior that differs from that of native tissues. This leads to more or less rapid endoprosthesis rejection, necessitating periodic replacement due to the increased risk of occlusion and preventing the desired effect, namely, aneurysm resorption. Furthermore, the heterogeneity of the anterior artery endoprosthetic structures can lead to potential slippage of the structure within the artery—migration—inevitably resulting in the need for a second, highly invasive operation. BRIEF DESCRIPTION OF THE INVENTION

[0011] The invention aims to provide a vascular endoprosthesis designed to overcome these various drawbacks.

[0012] It therefore has as its object a vascular endoprosthesis consisting of a tubular knitted textile structure, integrating within the meshes of said knitted textile structure at least one continuous helical weft yarn, extending along the entire main dimension of the endoprosthesis, said at least one yarn made of a shape memory alloy having previously undergone such training, and in particular such thermomechanical treatment, that it gives it super-elastic properties or during the austenitic transformation resulting from the temperature of the human body, so that said yarn gives the structure its tubular shape.

[0013] In other words, the invention consists of eliminating any form of exoskeleton and any sutures thereof on the textile structure of the prior art, giving the endoprosthesis optimal homogeneity, and developing, due to the optimization of the mesh of the knitted textile structure and the thermomechanical behavior of the weft, the most advanced biomimetic behavior possible.

[0014] Due to the integration within its structure and more specifically within the mesh of the knitted textile structure of a continuous shape memory alloy yarn, it therefore gives, once the endoprosthesis is in place, the desired tubular shape, in order to allow it to fulfill its primary function, namely to allow the circulation of blood flow within it.

[0015] According to the invention, the knitted textile structure is obtained on a Rachel double bed knitting machine, or on a hook knitting machine, according to a Charmeuse weave, or other similar bonds of the double knit type, weft chain, or any other weave allowing good biomimetic characteristics of the implanted structure, and according to the mechanical characteristics sought, in particular elasticity, extensibility or other behavior.

[0016] It should also be noted that, due to the electronic controls of the knitting machines used, it is possible to change the weave during manufacturing, and for example to have areas of different density or characteristics.

[0017] The textile structure in question is made from PET (polyethylene terephthalate) or any other biocompatible polymer yarn (polypropylene, ePTFE - expanded polytetrafluoroethylene, for example) and / or absorbable or biodegradable (for example of the PGA type - polyglycolic acid).

[0018] The weft yarn, made of shape-memory material and advantageously of Ni-Ti, is continuously inserted into the mesh of the knitted textile structure. The insertion occurs at the double bed, offset in the direction of production. This continuous weft is conveyed to the two beds by rotating around them, and thus simultaneously with the creation of the two textile layers resulting from the knitting at the two beds. The primary objective of the Ni-Ti weft is to ensure the main functions of the endoprosthesis, and in particular, optimal deployment of the structure within the aneurysm during endovascular surgery.

[0019] This can result in a helical arrangement of the weft thread. The metal skeleton is therefore directly and continuously integrated within the textile structure, in a particularly homogeneous manner and without any sutures, unlike previous endoprostheses, which have exoskeletons that are generally sutured to the textile, leading to heterogeneous structures.

[0020] According to the invention, the weft yarn, typically made of nickel-titanium alloy, can itself undergo a preliminary corrugation before its insertion into the double bed. This particular corrugation of the weft yarn, the amplitude and pitch of which are controlled and imposed during the specific heat treatment of said yarn, provides greater flexibility to the structure and aids in the final crimping phase, better known in the field by the Anglo-Saxon term "crimping," necessary to allow the insertion of said structure into its catheter for in situ implantation.

[0021] The weft wire, made of nickel-titanium alloy, has a diameter between 50 and 200 micrometers. If the wire diameter is less than 50 micrometers, experience shows that the wire's primary function—giving the endoprosthesis its tubular shape after austenitic transformation—is insufficient, and there is a risk of occlusion.

[0022] If, on the other hand, the diameter of the wire constituting the frame is greater than 200 micrometers, the endoprosthesis becomes too rigid and its behavior deviates too much from the desired biomimicry, which may lead to a risk of migration of the endoprosthesis within the artery into which it is introduced and, consequently, to risks of leakage.

[0023] According to another feature of the invention, the longitudinal deformation of the endoprosthesis, that is, along its principal dimension, is between 0 and 30%. This deformation may be necessary to maintain a close biomimetic behavior and thus ensure optimal and homogeneous blood flow, reducing the risk of disruption to other areas of the arteries. It is inherent to the unique knitted textile structure that allows for these adjustments to the resistance-elongation curve.

[0024] According to an advantageous feature of the invention, the endoprosthesis, once made, is subjected to compaction of its walls by a mechanical action, then coated with a specific surface coating (composed mainly of collagen, albumin or gelatin, this coating solution being advantageously supplemented with components necessary for the biocompatibility of the structure, such as heparin, carbon or fluoropolymers), so as to give said endoprosthesis the level of permeability required with regard to the viscosity of the blood flow, and therefore corollarily avoid leaks, and typically a permeability close to 0.1ml / cm2 / min determined according to ISO 25539-2.

[0025] The invention also relates to a method for manufacturing this vascular endoprosthesis. This method consists of: ▪ to be made by knitting with dropped stitches on a double bed loom, two sheets joined together at their respective production-direction edges to ultimately define a tubular structure; ▪ and to insert a continuous weft made of shape-memory yarn at the double bed, inserted into the stitches on said two sheets with an offset in the production direction, the continuous weft being conveyed to the bed by revolution around said bed, typically in a helical manner with respect to the production direction of the structure.

[0026] According to an advantageous feature of the invention, the helix pitch is constant and, in order to achieve the required compactness and optimize the seal of the endoprosthesis, this pitch is 1:1, meaning that the weft yarn made of shape-memory material makes one turn of the tubular textile structure around every mesh. However, depending on the desired characteristics, this pitch can be from 1:2 to 1:10. BRIEF DESCRIPTION OF THE FIGURES

[0027] Other features and advantages of the invention will become clear from the description given below, by way of example and not limitation, with reference to the accompanying drawings, in which: There figure 1 is a schematic view illustrating an endoprosthesis according to the invention placed within the abdominal aorta. figure 2is a schematic view of two types of endoprosthesis according to the invention, illustrating respectively an endoprosthesis with a constant diameter (left part), and an endoprosthesis with a stem obtained directly during fabrication (right part), the two types of endoprosthesis being able to be assembled during implantation on the patient. figure 3 is a schematic view of an endoprosthesis according to the invention during its fabrication phase on a double-bed loom, showing the weft yarn with super-elastic properties. figure 4 is a schematic representation of a detail of the figure 3 . There Figure 5 This is a schematic, top-view representation of the principle implemented by the method for manufacturing the endoprosthesis of the invention. figure 6 is a schematic top-view representation of a double bed, showing the insertion of the shape-memory weft yarn that forms the weft at the bed level. figure 7 is a schematic perspective representation of a device capable of implementing the process of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] We have schematically described in relation to the figure 1 The implantation of an endoprosthesis (1) according to the invention within the abdominal aorta (2). For simplicity of illustration, only the continuous weft wire (3) made of shape-memory alloy, and in this case of a nickel-titanium alloy, such as Nitinol, is shown. Its helical path, resulting from the method of embodiment of said prosthesis, can be clearly observed and is, moreover, described in more detail later.

[0029] In this example, the main endoprosthesis, intended to bypass the aneurysm (4), splits at a junction zone (5) into two secondary endoprostheses (6, 7), intended to be implanted in the beginning of the two femoral arteries (8, 9).

[0030] The upper zone of the endoprosthesis is fixed to the aortic arch. In this case, experience shows that the fixation zone (10) to the aortic necks must be reinforced relative to the body of the structure in order to avoid any risk of migration once the structure is implanted. in-vivo. The nickel-titanium weft wire can therefore, in said area, have a different diameter or thermomechanical behavior in order to ensure the retention of the endoprosthesis.

[0031] There figure 3 The diagram illustrates the fabrication of the endoprosthesis according to the invention on the two beds (11, 12) of a Rachel loom with the meshing yarn bars (13) and the continuous nickel-titanium alloy weft yarn (14). The latter passes alternately over each of the two beds while being integrated into the meshes on each side (needles (15) and loops (16)) by means of a rotating device (see Figures 5 And 7), according to a step of 1 / 1 or from 1 / 2 to 1 / 10 by stopping said rotary device. The rotation of the weft yarn (14) around the two bed frames is illustrated by the arrow.

[0032] We were represented within the figure 4 a detail of the figure 3 More precisely, the mesh within the wefts has been schematically represented. This shows the threads (17) constituting the structure, and for example made of PET, which are woven around the weft thread (14).

[0033] This embodiment also allows, through programming, the reduction of the tube width ultimately defined by the 3D textile structure during the manufacturing cycle, in order to produce one of the secondary legs or endoprostheses (6, 7) of an aortic aneurysm prosthesis, intended to be inserted into one or both femoral arteries (see figure 2 ).

[0034] According to this particular form of realization ( figure 2(right side), the second leg (6, 7) is produced separately on the knitting machine, with a diameter smaller than that of the main endoprosthesis. Assembly is performed during placement on the patient by interlocking and securing the prosthesis according to the requirements of the endoprosthesis.

[0035] The junction zone (5) between the different portions (3, 6 and 7) is made by knitting, weaving or any other means of assembly, according to a geometry specific to the desired configuration, and allows the whole structure to be linked continuously.

[0036] This secondary endoprosthesis is introduced in situ using a second catheter, as is standard practice for endoprostheses. In this case, during placement, the narrower portion hooks into the first portion as the catheter exits. The diameter of the stem is slightly larger than that of the receiving portion, allowing it to exert sufficient force on the first portion to ensure its stability in vivo. If necessary, additional hooks or clips can be added to eliminate any risk of slippage or separation of the different sections.

[0037] The in situ placement of this endoprosthesis is performed using one or more catheters, into which the endoprosthesis is inserted. This insertion generally follows a crimping step, more commonly known as "crimping," of the 3D structure of the endoprosthesis. Once in place, in this case within the abdominal aorta, the superelasticity of the nickel-titanium alloy wire causes the structure to return (after being crimped to allow its insertion into the catheter) to its initial, tubular shape, enabling the endoprosthesis to perform its intended function, specifically allowing blood flow and thus resolving the aneurysm.

[0038] We have represented in relation to the Figure 5The principle of the method for making the endoprosthesis of the invention. Fundamentally, a 3D structure is generated using a Rachel loom or double bed hook loom (20) (for which, for the sake of simplicity of understanding, the wire feed modules have not been shown).

[0039] Around this double-bed loom, a bobbin (21) feeds the weft yarn (22) made of nickel-titanium alloy, which has previously undergone heat treatment to optimize its thermomechanical behavior. This bobbin is mounted on a support (23). As a result, the weft yarn is woven at the needles (24) and the heddles (25) mounted on the RACHEL loom beds as the 3D structure is built at this point.

[0040] For this purpose, the weft yarn supply reel (21) is arranged in a plane perpendicular to that receiving the double beds and passing through the cooperation zone of the needles and the loops of said beds.

[0041] The rotational movement of the bobbin around the two bed frames is achieved by any means, and in any case, by a mechanism synchronized with the mesh formation cycle of the 3D structure on the double bed loom. This bobbin delivers the weft yarn after it has passed through a braking device (26), in order to ensure correct tension of the weft yarn. This braking is carried out either directly on the weft yarn or on the bobbin itself. Such braking systems are known per se. They can be, in particular, mechanical, electrical, or even electromagnetic in nature.

[0042] The programming of the helix pitch described by the weft yarn relative to the production direction of the 3D structure can be managed directly in conjunction with the knitting program of the 3D background structure. Typically, this programming is such that after impregnation or coating, a permeability of approximately 0.1 ml / cm² / min is obtained, in any case conforming to the applicable standard for the said determined 3D structure, and in particular capable of fulfilling its most appropriate sealing function to contain the blood flow intended to pass through it.

[0043] The diameter of the tube resulting from the 3D structure is typically 20 millimeters. However, this diameter can vary between 5 and 40 millimeters, depending on the patient and the areas of application of the endoprosthesis, whose use is not limited to aortic aneurysms alone, but also in other vascular pathologies, particularly when internal replacement or reinforcement is necessary.

[0044] Furthermore, the helix pitch of the weft yarn is fixed so that each time the weft yarn makes one turn of the tubular textile structure, it completes all the constituent meshes, or every 2 to 10 meshes (typically with a mesh density of approximately 7 to 20 meshes / cm). The resulting structure ensures optimal thermomechanical behavior and prevents the risks of kinking, endoleaks, and migration once the endoprosthesis is inserted into the pathological arterial segment.

[0045] The double bed was also schematically represented in top view on the figure 6 The front (F1) and rear (F2) bed frames were thus materialized, at which the knitting yarns (27) of the 3D support structure appear, as well as the schematic arrangement of the weft yarn inserted by means of a device, as illustrated on the figure 7 .

[0046] Such a device typically comprises a weft yarn feeder (21) mounted on a circular ring (28). This circular ring is thus mounted around the double-bed loom. It is driven in rotation, for example, by means of toothed gears (29), which are driven by electric motors (not shown). These toothed gears mesh with the toothed peripheral edge (30) of said ring. A belt drive system or any other means of drive can be used to ensure rotation. The operation of the electric motor(s) driving the toothed gears is synchronized with the operating cycle of the double-bed loom, so as to introduce the weft yarn at the appropriate time at each bed.

[0047] Thus, the weft yarn completes a revolution, and in the example described, a rotation, around the bed frames in the area where the 3D textile structure is created by the interplay of knitting elements mounted on bed frames, namely needles and needles. The needles themselves are moved on support bars (31), according to the selected yarn binding program.

[0048] Also shown in this figure is the braking device (32) positioned at the output of the reel, in order to regulate the tension of the weft yarn.

[0049] According to the invention, after fabrication of the endoprosthesis, it is fully coated with a solution, for example, of collagen. This optimizes the permeability level, measured according to the applicable ISO 25539-2 standard for the endoprosthesis, which proves sufficient and meets current requirements. This coating can also be performed using other available techniques, such as spraying.

[0050] The advantages of the endoprosthesis of the invention are readily apparent. Firstly, its biomimetic nature should be emphasized, resulting from its homogeneous structure and manufacturing process, which eliminates the need for an exoskeleton and sutures, and from the mesh pattern of the 3D knitted structure. This design promotes the durability of its implantation, as the risks of in-vivo migration are limited, and consequently, the risk of rejection is reduced. Secondly, the risk of occlusion is eliminated, regardless of the tortuosity of the arteries the endoprosthesis may encounter, allowing it to conform to the specific anatomy of certain blood vessels. Finally, any risk of leakage is prevented, particularly due to the mesh structure of the 3D structure.

Claims

1. A vascular stent graft (1) formed of a tubular knitted textile structure, integrating within the meshes of said knitted textile structure at least one helical continuous weft yarn (3, 14, 22), extending all along the major dimension of the stent graft, said at least one yarn (3, 14, 22) made of a shape memory alloy having previously been submitted to such an education, and particularly such a thermomechanical treatment, that, at the human body temperature, said yarn gives the structure its tubular shape by superelasticity or shape memory effect.

2. The vascular stent graft according to claim 1, characterized in that the knitted textile structure is obtained on a double needle bed Rachel loom or on a hook loom, according to a weave selected from the Charmeuse, double knit, or weft chain group.

3. The vascular stent graft according to any of claims 1 and 2, characterized in that the diameter of the knitted textile structure is in the range from 5 to 40 millimeters.

4. The vascular stent graft according to any of claims 1 and 2, characterized in that it comprises a limb obtained after reduction of the diameter of the knitted textile structure, said limb being configured to form a secondary stent graft (6, 7).

5. The vascular stent graft according to any of claims 1 to 4, characterized in that the knitted textile structure is made of a biocompatible material selected from the group comprising PET (polyethylene terephthalate), polypropylene, ePTFE, and biodegradable or bioresorbable materials of PGA type.

6. The vascular stent graft according to any of claims 1 to 5, characterized in that the weft yarn (3, 14, 22), made of a shape memory material is made of nickel-titanium, and in that it is continuously inserted into the meshes of said knitted textile structure.

7. The vascular stent graft according to any of claims 1 to 6, characterized in that the weft yarn has a diameter in the range from 50 to 200 micrometers.

8. The vascular stent graft according to any of claims 1 to 7, characterized in that the longitudinal deformation of the stent graft, that is, along its major dimension, is in the range from 0 to 30%.

9. The vascular stent graft according to any of claims 1 to 8, characterized in that it is coated with collagen, albumin, or gelatin, to provide said stent graft with a permeability close to 0.1 ml / cm2 / min regarding the viscosity of the blood flow, and thus as a corollary to avoid leaks while respecting the biocompatibility of the stent graft.

10. The vascular stent graft according to claim 9, characterized in that the collagen, albumin, or gelatin coating also comprises heparin, carbon, or a fluoropolymer.

11. A method of forming a vascular stent graft, comprising: ▪ forming by warp stitch knitting on a double needle bed loom two layers joined together at the level of their respective edges in the production direction to eventually define a tubular structure; ▪ and inserting a continuous weft made of a shape memory yarn at the level of the double needle bed, inserting into the meshes on said two layers with an offset in the production direction, the continuous weft being conveyed to the level of the needle beds by revolution around said beds, typically helically with respect to the production direction of the structure.

12. The method of forming a vascular stent graft according to claim 11, characterized in that the pitch of the helix followed by the shape memory yarn is constant and 1 / 1, that is, the weft yarn makes turns around the tubular textile structure once for every stitch.

13. The method of forming a vascular stent graft according to claim 11, characterized in that the pitch of the helix followed by the shape memory yarn is constant and is in the range from 1 / 2 to 1 / 10.

14. The method of forming a vascular stent graft according to any of claims 11 to 13, characterized in that the double needle bed loom is a RACHEL loom or a hook loom, wherein the weft yarn (3, 14, 22) is inserted at the level of the double needle bed of said loom with an offset of this insertion in the production direction, this continuous weft being conveyed to the level of the two needle beds by revolution around the latter and thus concomitantly to the forming of the two textile layers resulting from the knitting at the level of the two needle beds.

15. The method of forming a vascular stent graft according to claim 14, characterized in that the weft yarn itself undergoes a previous corrugation before its insertion into the double needle bed of the RACHEL loom or of the hook loom.