CH639841A5 - Fabric for cardiovascular prosthesis and prosthesis for cardiac valve - Google Patents

Description

The present invention relates to a tissue for cardiovascular prostheses and more particularly to replacement heart valves which are made of fabrics supported by armatures and which have the shape of a triple sheet, as well as a prosthesis for heart valve.

It relates to long-lasting replacement heart valves which can withstand many flexion cycles, which offer as faithfully as possible the same mechanical characteristics as natural valves and which avoid conditions promoting the formation of blood clots.

The replacement of heart valves with prostheses has become a common surgical technique. However, the prostheses currently implemented do not fully meet the requirements indicated above. It is common that the closure of most heart valve prostheses is based on the seal of a ball or a flap that bears against an annular seal. In such a form of prosthesis, the ball (or flap) is disposed in the blood channel when it is moved away from the joint in the flow position. This arrangement is disadvantageous from two important points of view. First, the pressure drop across the valve, when in the open or flow position, is greater than that which occurs in a natural valve and therefore imposes a slight, but continuous and cumulative overload on the heart. . Second, the presence of the ball or flap results in regions where the turbulent flow tends to deteriorate red blood cells.

With these drawbacks in mind, attempts have been made to produce leaflet valves whose structure and function are more closely related to those of a human valve. The latter comprises thin and flexible membranes which fold flat against the wall of the blood vessel which surrounds them when they are in the open position, so as to cause only a minimum of disturbance to the blood flow. In the closed position of the valve, the sheets constitute three contiguous pockets which are held tightly in tight contact by blood pressure. Due to the extreme lightness and flexibility of the leaflets, the valve, whose response time is short, rapidly changes from its fully closed position to its fully open position, so that the loss of energy from the blood which s flow is weak and its annoying reflux is minimal.

These functional features of the human valve are due to the composite structure of the natural leaflet. The latter com-50 takes bundles of collagen fibers that are embedded in softer tissue. This composite structure gives the sheets a good load bearing capacity, a high tear resistance as well as sufficient flexibility and softness so that they ensure a good seal in the closed position. At the tip of the pressure spray, the sheet supports a load which is greater than 150 g / cm along a line which is perpendicular to the load.

The tissue of the heart valve also offers an elastic characteristic which is anisotropic in that its deformation under load in one direction is different from its deformation in another direction. It has been found useful to define two particular directions in the present thesis. These directions are parallel and perpendicular to the free edge of the sheet and correspond to the circumferential and radial directions commonly indicated in the literature.

65 In addition to its free edge, the natural sheet lengthens very easily when the load increases, until it has reached an elongation of 10 to 12% for a load of 1 to 2 g per centimeter of width. If the load increases further, its resistance to an extension

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additional increase considerably. Perpendicularly to its free edge, the region where the load is exerted easily elongates when it increases, up to an elongation of approximately 20% for a load of approximately 2 g / cm. If the load continues to increase, the resistance to further elongation, although greater than the initial resistance of the region, is not as great as in a direction parallel to its free edge.

Recent progress has been to use stabilized pig heart valves to replace failing human valves. These valves have certain characteristics of the human valves which have been described above. However, the removal, calibration, sterilization, fixation and storage of pork valves is complicated and expensive. Consequently, it would be desirable to have a triple-leaf heart valve which is entirely of synthetic material.

To this end, the invention is defined as indicated in claims 1 and 11.

Preferably, the fabrics are woven in the form of a ribbon which includes an edge of uncut threads which constitutes the free edge of the sheet of the heart valve. The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which:

fig. 1 is a photograph representing a fabric of multifilament polymers with plain weave before it shrinks by compression,

fig. 2 is a photograph representing the fabric of FIG. 1 after compression shrinkage in the warp and weft directions,

fig. 3 is a perspective view of the main frame of an advantageous embodiment of the heart valve of the invention,

fig. 4 represents a ribbon of fabric in the form it takes when it is introduced into the main frame between the rods of its branches,

fig. 5 is a perspective view of the second frame,

fig. 6 is a plan view of the frame of FIG. 3,

fig. 7 is a plan view of the frame of FIG. 5,

fig. 8 represents the heart valve at an intermediate stage of its production, the fabric being introduced into the main frame and having been cut to open it in order to prepare its bonding to the frame,

fig. 9 is a developed view corresponding to that of FIG. 8 of the heart valve, in the intermediate stage of its production, fig. 10 is a section along line 10-10 of FIG. 9, and fig. 11 shows the configuration of a flat braided fabric.

Fig. 1 shows a form of starting fabric 12 which comprises warp threads 14 and weft threads 16. The warp and weft threads each consist of twisted filaments 18 of a polyester, for example polyethylene terephthalate. By way of illustration, the fabric can be woven with approximately 40 threads per centimeter in each direction, the threads measuring approximately 30 denier. Each thread contains 30 filaments 18, each with a diameter of about 10 (i.

Because the wires are untwisted, as shown in fig. 1 on which they are woven, they have a flat shape. As a result, the thickness of the fabric is only about 3 to 4 diameters of a filament. In addition, as explained below, it is preferable that the fabric is woven with at least one selvedge which does not have any cut thread. For this reason, it is advantageous for the fabric to be woven in the form of a ribbon, although this shape is not compulsory.

Polyester yarns which exist in the industry generally contain many impurities which may be harmful to the human body if they remain in the prostheses which are implanted. These impurities include the residual catalyst of the polymerization process, oligomers, antioxidants and other materials for stabilizing, depainting and finishing surfaces. Therefore, it is important to use only pure polymeric material.

As shown in fig. 1, the wires 14 and 15 are woven so as to form interstices 20. These interstices play a role in the subsequent stages of shrinking and crimping of the process described below, which are carried out on the fabric of FIG. 1 to give it the curly shape bilaterally shown in FIG. 2. During successive stages, the fabric is shrunk in two directions by compaction while it is subjected to compressive forces which are exerted in a plane, each stage being substantially that which is described, for example, in United States Patent No. 3001262. It is possible to use a machine similar to that described in United States Patent Nos. 2765513 and 2765514. The shrinking operations produce crimps on the wires and force them to flourish or spread out in the interstices of the armor.

To give it the desired elongation characteristics in two directions, similar to those of a natural valve leaflet, the same fabric is compacted successively both in the direction of the warp threads and in that of the weft threads. From this point of view, the process differs from the technique described by the aforementioned patent of the United States of America No. 3001262, according to which the threads of a first woven fabric are crimped in the warp direction, the fabric being then frayed and the warp threads used as the weft threads of a subsequently woven fabric, which is later crimped in the warp direction to give it the desired characteristics of elongation in both directions. In the process described here, the threads of both warp and weft are crimped and heat fixed so that the crimps are situated in planes parallel to the fabric, and the threads flourish in the interstices so as to give open interstitial spaces of variable dimensions and orientation between the filaments. A large number of these latter spaces have dimensions between 20 and 40 | x which are advantageous for rapid growth of natural fabrics and they are distributed regularly throughout the fabric. Therefore, the finished fabric is relatively thin compared to the final fabric produced by the technique of the aforementioned United States patent in which, finally, the crimps and the open filaments of the weft threads are necessarily displaced and reoriented during the second weaving with respect to the plane of the fabric and the locations of the interstices in the final weave.

We have realized the advantage presented by a thin fabric compared to a thicker fabric, due to the desired functional characteristics, in particular its flexibility and its possibilities of elongation, the fact that it does not cause the formation clot and its ability to withstand millions of flexion cycles without fatigue failure. The characteristic of not causing a clot is given to the tissue described herein by the fact that it facilitates the growth of natural tissue, so that the flowing blood is only in contact with compatible surfaces produced naturally. The filaments of the fabric thus become similar to the bundles of collagen fibers of a natural sheet and constitute a support or lattice of textile material on which and in which the body can deposit fabrics which fulfill the function of membrane of the sheet and offer the characteristics of sealing required. If a clot forms on the separation surface between tissue and blood, natural tissue grows so that the clot is firmly anchored to the tissue from which it does not separate to enter the blood stream. The tissue is therefore completely embedded in a layer of living tissue which is thin enough to be nourished by diffusion processes.

It is evident from the above description that the process of tissue growth has an influence on the thickness and, therefore, on the flexibility and stiffness of the sheet when in operation. These characteristics, in turn, influence the susceptibility to fatigue rupture and the ability to minimize regurgitation in the closed position. In addition, in order for it to be used effectively as a leaflet to a heart valve, the tissue must include a region which very easily elongates to degrees between 10 and 20%. In particular, as will be seen from

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the description which follows fig. 3 to 10 in the closed position, each sheet undergoes a bending of a relatively short radius of curvature along a line perpendicular to its free edge. A region of high stress concentration is located along this line.

An additional advantage of the process described here is indicated in FIG. 2, on which it should be noted that the individual wires flourish in the interstices 20, that is to say that the filaments deviate locally in the latter so as to constitute a matrix of smaller interstitial spaces distributed , of various dimensions and orientation. This arrangement facilitates the growth of natural tissue. On the contrary, a tissue such as that of FIG. 1, which includes a regular configuration of spaced openings of predetermined dimensions and relatively large, does not facilitate the growth of natural tissues as much.

A fabric according to the invention has been subjected to natural tissue growth tests and has behaved much better from this point of view, than other existing fabrics. The fabric of the invention can be produced with the particular elongation characteristics which are necessary for its application as a sheet and which can be different in two directions such as those of the warp and the weft.

The crimping or compaction process will be described below in more detail. The machine described by the patents of the United States of America Nos. 2765513 and 2765514 mentioned above is used. A woven canvas ribbon such as that shown in FIG. 1, about 300 mm wide, between two sheets of paper and passed it in the warp direction in the nip between upper and lower rollers. The peripheral speed of the upper roller is 1.6 m / s and that of the lower roller 0.33 m / s. During this compaction phase, the warp threads are narrowed or compacted so as to form crimps that the pressure exerted by the rollers forces them to be placed in the planes parallel to the fabric. At the same time, the filaments of the warp threads spread out in the interstices situated between the weft threads, that is to say that the threads flourish in these interstices so as to produce spaces of dimensions and various orientations, as shown in fig. 2. At the end of this compaction phase, the fabric is removed from the sheets of paper.

A second compaction phase is then carried out in a manner substantially identical to that described above, with the exception of the fact that the piece of fabric is passed in the direction of the weft in the pinching zone of the rollers.

Each of the packing phases described above can be optionally repeated and, in this case, it is preferable to rotate the ribbon by 90 ° after each phase.

It is possible to vary the number and the degree of compaction operations in the two directions so as to produce the desired characteristics of elongation under load in each of the two directions and thus approach the corresponding characteristics of a natural sheet. In all cases, the compaction operations are carried out so as to allow very easy elongation which can reach degrees of between 10 and 20%.

After undergoing compression phases, the fabric is fixed hot while it is relaxed at a temperature below the melting temperature. For polyethylene terephthalate, a temperature of 210 ° C. can be provided, for example. The hot fixing is preferably carried out in an oven with circulation of hot air for a period the duration of which is, for example, A min.

In some cases, it is advantageous to treat the yarn before weaving it to avoid damaging the filaments during the weaving operation. A suitable treatment method consists in coating the threads with a 5% solution of polyvinyl alcohol. After weaving, this additive is removed by washing the fabric in an aqueous bath.

An advantageous form of a triple-sheet prosthesis for the replacement of a heart valve will be described below. As shown in fig. 3, a main frame 22 consists of a round polypropylene rod in one piece with a diameter of 0.1 cm which is curved so as to give it a configuration comprising three parallel and equidistant branches 24, 26, 28 , each of which comprises two slightly spaced parts which are connected at one end and which diverge at the other. The divergent parts constitute three lobes 30, 32 and 34. The connected ends of the parts of each pair constitute handles 36, 38 and 40. FIG. 6 5 is a plan view of the main frame 22.

A second frame 42 (FIGS. 5 and 7) comprises a section of round polypropylene rod with a diameter of 0.1 cm which is bent in a configuration comprising three lobes 44, 46 and 48 which generally correspond to the lobes 30, 32 and 34 of io so as to fit tightly against the latter, as shown in fig. 9.

The assembly is started by threading a ribbon 50 produced by the method described above and shown in FIG. 2, by the three pairs of branches, so as to produce the device, the shape of which is shown in FIG. 4. To make the figure clearer, the frame 22 is shown in exploded perspective in FIG. 3 with respect to FIG. 4. The upper edge which does not include any cut thread constitutes the free edges 52, 54 and 56 of the leaflets of the valve.

A double layer of fabric is thus passed between the 20 parts of the rod, the pair of which constitutes one of the branches 24, 26 and 28. The fabric must be firmly fixed to these branches as well as to the junction lobes 30, 32 and 34. To facilitate this fixing, the fabric is preferably cut longitudinally outside each branch, as shown in fig. 8.

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As seen in fig. 8, an adhesive such as polyurethane dissolved in tetrahydrofuran is used to fix the fabric to each branch, as described below. The flaps 58 and 60 are spaced from one another and the adhesive is applied at the external point of their junction at the point where they penetrate between the parts of the rod, along a continuous line disposed between points a and b. The adhesive reaches the outer surfaces of the frame by crossing the fabric flaps along this line, i.e. it only comes into contact with the outside surfaces of the parts of the frame rod . The sheets only include the parts of the fabric which are located inside the frame and which are not crossed by the adhesive. This avoids local stiffening and the resulting flexural break which could be caused by the penetration of this adhesive.

The method of applying the adhesive described above also makes it possible to regularly distribute the bending forces along the edges of the sheets and to avoid stress concentrations. These edges can move with each bending on the rounded surfaces of the parts of the rod which are located inside the frame 45 and which the adhesive does not reach.

In addition, the adhesive application process reduces the contact that the blood could have with this product.

The fabric is then fixed to the lobes 30, 32 and 34 by first placing the second frame 42 in the vicinity of the lobes between which the jaws of tissue pass, as shown in FIGS. 9 and 10. An adhesive 61 is then applied through the fabric to the surfaces of the main frame 22 and of the second frame 42 both along a continuous line disposed between the points b of the branches and connecting these three points. As in the previous operation, it is preferable that the adhesive does not penetrate any part of the material of the sheets which is located inside the main frame 22 and that it cannot come on contact with blood passing through the valve.

The operations described above essentially terminate the production of the parts of the valve which are constituted by the leaves-6o lets. The remaining operations are intended to facilitate the suturing of the prosthesis inside the blood vessel. The excess fabric on the outside of the frame can be rolled up and consolidated along the junction line between the main frame and the second frame so as to constitute fasteners for stitches during setting. surgical place of the valve.

Preferably, the material of the frame is polypropylene, although other materials have also been used with success. Polypropylene provides flexural endurance and chemical stability

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excellent, but difficult to stick to other materials. To facilitate bonding, the main frame 22 and the second frame 42 can be coated with polyurethane by coating them with multiple dipping. The resulting coated elements of the reinforcements have shown that they have the advantageous characteristics of polypropylene without structural failure or failure at the bonded junctions.

The valves made with the tissue described above were tested in an accelerated fatigue machine to determine their long-term endurance characteristics. The fatigue fractures thus caused generally occurred in the region where the tissue is subjected to the greatest flexion, that is, in each sheet, along a line which is perpendicular to its free edge and which is substantially at equal distance between the contiguous branches. The ruptures generally occurred by breaking of the filaments of the wires arranged parallel to the free edge of the sheets. To give greater resistance to the fabric along these lines, woven fabrics may have a greater number of threads supporting the load in this direction. However, the increase in the number of threads that it is possible to bring to a woven canvas weave, such as that of FIG. 1, is limited, if one does not want to bring serious disturbances to the geometric shape of the interstices of the tissue.

Another weave of a fabric which is more resistant to such fatigue failure is shown in FIG. 11. The fabric represented is a ribbon 62 braided flat, which includes three sets of threads, that is to say a 25

first set 64 arranged diagonally, a second set 66 arranged diagonally and a third longitudinal set 68 which is arranged internally. The yarns of each of these three sets are preferably twisted multiple filament yarns similar to those shown in FIG. 1. The ribbon 62 is braided on a conventional flat braiding machine. It should be noted that no wire is cut in each edge, one of which becomes the free edge of each sheet. This avoids fraying the free edges of the sheets as in the example described above. In this embodiment, the two sets 64 and 66 fulfill the function of supporting the load which was assumed by a single set of threads in the fabric described above. This results in an increase in the number of wires which are an important component of load support oriented parallel to the free edge.

Preferably, the fabric 62 of FIG. 11 is formed by braiding the sets of threads 64 and 66 and by internally arranging the longitudinal threads 68, in a well known manner, in order to produce a fabric of the triaxial type. An additional advantage of such flat braided fabrics compared to conventional woven fabrics is the fact that, in a clean manner, they are extremely extensible in the transverse direction to the machine, that is to say perpendicular to the threads 68. Such fabrics can be provided with stretching characteristics in two directions by any desired combination of stretching possibilities produced by packing them only in the direction of the threads 68.

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Claims (17)

639,841 1. Tissue for cardiovascular prosthesis, characterized in that it comprises threads with multiple filaments woven in polymer material which extend in two directions arranged angularly and that it has open interstitial spaces of dimensions between 20 and 40 n distributed evenly, and its elongation ability is such that part of the fabric can lengthen by at least 10% in at least one of the two directions. 2. Fabric according to claim 1, characterized in that the threads have, in each direction, crimps situated in planes parallel to the fabric and that they open out in the interstices of the crimps to form the open interstitial spaces. 2 3. Fabric according to one of claims 1 or 2, characterized in that its flexibility and elasticity are different in both directions. 4. Fabric according to one of the preceding claims, characterized in that the threads have a flat shape and are essentially untwisted. 5. Fabric according to claim 4, characterized in that it has a thickness less than 4 diameters of a filament. 6. Fabric according to one of the preceding claims, characterized in that the angle formed by the two directions of the son is a right angle. 7. Fabric according to one of the preceding claims, characterized in that the diameters of the filaments are 10 (i. 8. Fabric according to one of the preceding claims, characterized in that it has the shape of a ribbon having an edge of uncut threads. 9. Fabric according to claim 8, characterized in that the ribbon is braided flat. 10. Fabric according to claim 9, characterized in that it has longitudinal threads arranged parallel to the selvedge, and braided carrier threads arranged at an acute angle relative to the selvedge. 11. Prosthesis for heart valve, characterized in that it comprises an armature, which comprises three parallel and equidistant branches each consisting of two parts of a rod connected by a first end and diverging from the other, which are in the form of lobe connected to said stem parts of the other branches, the lobes forming an opening between them, and three sheets of fabric according to claim 1, which are each introduced between the stem parts of two of said branches and are hermetically bonded thereto and at the junction lobes, each sheet comprising a free edge disposed between said branches, the free edges of said sheets being deformable so as to come into contact with each other, in order to hermetically seal said opening. 12. Prosthesis according to claim 11, characterized in that each sheet is elastic and flexible in directions parallel and perpendicular to its free edge. 13. Prosthesis according to claim 12, characterized in that the flexibility and the elasticity of each sheet parallel to its free edge are different from its elasticity and its flexibility perpendicular to this free edge. 14. Prosthesis according to claim 11, characterized in that the parts of the rod of each pair are spaced from each other. 15. Prosthesis according to claim 11, characterized in that a second frame consists of a rod and has a shape which corresponds substantially to said junction lobes of the first, the sheets arranged between said frames being hermetically bonded thereto. . 16. Prosthesis according to claim 11, characterized in that the sheets are hermetically bonded to the frames by an adhesive which is applied from the outside of the opening. 17. Prosthesis according to claim 11, characterized in that said parts of the rod have rounded contours on which the sheets roll when they are deformed, the sheets being hermetically glued to said parts of the rod by an adhesive applied to their surface located outside of said rounded contours.