GB1600506A

GB1600506A - Bio-prosthetic valves

Info

Publication number: GB1600506A
Application number: GB3470277A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-05-25
Filing date: 1978-05-25
Publication date: 1981-10-14

Description

(54) BIO-PROSTHETIC VALVES (71) We, DONALD NIXON ROSS of 25 Upper Wimpole Street, London W.1., of British nationality; and ENDRE BODNAR c/o 9 West End Court, West End Avenue, Pinner, Middlesex, of Hungarian nationality, do hereby declare the invention, for which we pray that a patent may be granted to us, and the the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to bio-prosthetic valves.

Aortic and pulmonary valves of human or animal origin can be used for the replacement of defective cardiac valves. If the transplanted valve is non-viable, i.e. has been fixed and preserved in chemicals, it has to be supported in a frame, which is known as a stent. Hitherto such stents, whether com- mercial or not, have comprised a metal or synthetic resin material structure having a cloth covering.

Great effort has been devoted to developing the shape of such stents, with a view to making the shape such that it will cause the least possible change in the morphological shape of the valve when it is mounted on the stent, because any distortion of the original shape of the valve resulting when the valve is mounted on a stent can result in a substantial increase in the stress to which the valve will be subject in operation, and can make the valve grossly incompetent.

As no two aortic or pulmonary valves are of identical geometric configuration (in much the same way as no two human faces are of identical geometric configuration), it will be appreciated that the problem of suitably matching aortic and pulmonary valves to stents is a difficut one.

According to the present invention, there is provided a method of making a bioprosthetic valve, the method comprising forming a stent around the outer surface of a natural valve (preferably an aortic or pulmonary valve) by a process comprising depositing onto the said surface a structural material or a material which is capable of producing such a material, using the said outer surface as a form.

Thus, it is possible in accordance with the present invention to make a stented bioprosthetic valve in which the original morphological shape of the valve can be preserved, without having to undertake any selection procedure to try to match the valve to its stent.

The process used to form the stent can comprise applying at least one coating of liquid which is capable of setting to form a coating of structural material, for example protein or a synthetic resin. In such embodiments, the liquid which is applied, when in its liquid form, generally is not a structural material, but is capable of producing such a material. Examples of such liquids are solutions which form a structural material upon evaporation of solvent, for example resin solutions and protein solutions; liquids which form a structural material by chemical reaction, for example a mixture of a resinous liquid and a chemical hardener for the resin; liquids which can form a structural material by a combination of chemical reaction and solvent evaporation, as occurs with many paints; and melted solids which can form a structural material by cooling, for example melted thermoplastic resins. The liquid may be applied by brushing, spraying, pouring or dipping, for example.

An alternative method of forming the stent comprises electrodeposition of the structural material. For example, a metal such as platinum may be deposited by electroplating.

A further method of forming the stent comprises applying at least one sheet of mouldable material, using the said outer surface as a mould, and allowing or causing the mouldable material to set.

Additional structural parts of the bioprosthesis (a surgical sewing ring, for example) can generally be conveniently incorporated during the application of the structural material, by incorporating into the structural material as it is being deposited at least one member to which the additional part is attached, or which forms a portion of that additional part.

Reinforcing material may be incorporated into the stent before and/or during the deposition of the structural material (or the material which produces such a material).

The reinforcing material may be in fabric form, e.g. linen net, glass fibres in fabric form, or a fabric made of a suitable metal.

However, this need not be so, and one may employ glass; fibres or metal strands, for examples in a non-fabric form.

We have found it advantageous in some embodiments to apply to the outer surface of the natural valve a fabric cover, prior to commencement of depositing the structural material (or the material which produces such a material).

In a preferred procedure in accordance with the invention the natural valve employed initially includes tissue additional to that which will be required to produce, in the valve to be produced by the method of the invention, a body of shape suitable for the finally intended use. For example, where the valve is an aortic valve, the aortic root is initially present; and where the valve is a pulmonary valve, the portion of the pulmonary artery which contains the actual valve is initially present. In an example of this preferred procedure, the valve is dissected, at an intermediate stage when only a part of the thickness of the structural material of the stent has been applied, so as to produce a body of shape suitable for cardiac implantation; and the free margins of the valve are attached to the overlying structural material, by sewing, for example, the rest of the thickness of the structural material of the stent being applied subsequently.

All surfaces of the finished bio-prosthesis should be biologically inert. Generally, a biologically inert fabric covers and is attached to the outer surface of the valve, to allow tissue to grow into the bio-prosthesis when installed, and thus increase the security with which the bio-prosthesis is held in place.

The surface underlying such a fabric should be biologically inert also. Where the fabric is applied immediately over the said structural material, this means that at least the outermost portion of the structural material should be biologically inert.

In order that the invention may be more fully understood, some embodiments in accordance therewith will now be described, by way of example, with reference to the accompanying, schematic drawings, which are not to scale, and in which: Fig. 1 is a section through a peripheral portion of a bio-prosthetic cardiac valve which has been made by a method in accordance with a first embodiment of the invention; and Fig. 2 is a section through a peripheral portion of a bio-prosthetic cardiac valve which has been made by a method in accordance with a second embodiment of the invention.

In order to practise the method of the invention, it is necessary to start with a natural valve, e.g. an aortic or pulmonary valve, which may be of human or animal origin. The following description relates to the use of an aortic or a pulmonary valve, but it will be appreciated that the basic principle of the invention could be applied to other natural valves. In the two preferred embodiments to which the present part of the description relates, the valve initially employed is complete with its aortic root, or, as the case may be, with the portion of the pulmonary artery containing the valve. We prefer that the valve to be employed in the method of the invention should be non-viable.

Preferably, during the chemical treatment used to render the valve non-viable, continuous or intermittent pressure is applied so as to ensure that the normal anatomical situation is preserved. One manner in which the required pressure may be applied is to block off one end of the aorta or pulmonary artery and to connect the other end to a supply of the treatment chemicals under hydrostatic pressure. Preferably, before forming a stent in accordance with the method of the invention, the valve, after being rendered nonviable as described above, is treated to dry the external surface thereof (the internal surfaces of the valve being maintained in a moist condition throughout the procedure).

Referring now to Fig. 1, in the first embodiment, a primary layer of a structural coating material, a part of which primary layer is shown at 1, is applied to the dry outer surface of the aortic or pulmonary valve (i.e. onto the outer, peripheral surface of the aortic root or the portion of the pulmonary artery containing the valve, as the caise may be), a portion of the tissue of which is shown at 2. We prefer to apply this primary layer 1 (which is a part of the final thickness of structural material which is to be applied) as a single coating, or a relatively small number of coatings, of a solution of protein in a volatile solvent. During the application of the primary layer (and also during the application of the secondary layer, to be described) the valve cusps and the intimal surface should be protected, for example by the use of cotton plugs inserted into each of the two open ends of the aortic root or pulmonary artery portion. The primary layer 1 follows the shape of the aorta or pulmonary artery, which thus acts as a form or mould.

The resulting structure can now be dissected into its final shape, by cutting the aortic root or the pulmonary artery portion, together in either case with the overlying primary layer 1, so as to produce a body of shape suitable for cardiac implantation.

Following this dissection, the free margins of the valve are atached, by sewing at the position indicated at 4 (i.e. at the top of the valve, as shown in Fig. 1), to the overlying primary layer 1.

Next, a secondary layer, indicated generally at 5, of structural coating material is applied on top of the primary layer 1 so as to complete the application of the structural material, to produce a structure which is of sufficient strength to perform the valve supporting function of a valve stent. This is preferably done by applying a succession of coatings so as gradually to build up the appropriate thickness of the resulting stent at all points. The material which we prefer for this purpose is the same as that used for the primary layer 1, namely protein (again applied in solution), but any other suitable structural material may be employed.

Where the inner coatings are of a material which is not biologically inert, it is necessary to use a biologically inert material for at least the final coating of the secondary layer 5, so that the outer surface of the secondary layer 5 (and thus of the structural material as a whole) is of a material which is biologically inert. Thus, in the first embodiment, the secondary layer 5 consists of several coats of protein indicated at 6, and a final coat 7, also of protein, as this material is biologically inert.

The application of the constituent coats of the primary layer 1 and the secondary layer 5 can be by dipping, painting, spraying, pouring, or any other suitable method.

During the formation of the secondary layer 5, an additional part, a surgical sewing ring 8, is added to the valve by positioning the base 9 of the sewing ring 8 around the periphery of the valve, and applying the remaining coats of the secondary layer 5, the functional portion of the sewing ring 8 being suitably protected during the application of the latter coats.

Finally, a biologically inert fabric 10 is arranged to cover the outer surface of the valve, and is attached thereto by sewing, as at 11.

Referring now to Fig. 2, in the second embodiment, a thin fabric cover, a part of which is shown at 21, is first applied to the dry outer surface of the aortic or pulmonary valve (i.e. onto the outer, peripheral surface of the aortic root or the portion of the pulmonary artery containing the valve, as the case may be), a portion of the tissue of which is shown at 22. The fabric of the cover 21 is preferably a cloth fabric such as linen net, but it is possible to use a fabric made of a suitable metal instead.

Next a primary layer, a part of which is shown at 23, of a structural coating material is applied on top of the fabric 21. We prefer to apply this as a single coating of a solution of polymethyl methacrylate in a volatile solvent. During the application of the primary layer (and also during the application of the secondary layer) the valve cusps and the intimal surface should be protected, as in the first embodiment. The primary layer 23 (together with the underlying fabric cover 21) follows the shape of the aorta or pulmonary artery and is loosely adherent thereto. The resulting structure can now be dissected into its final shape, by cutting the aortic root or the pulmonary artery portion, together in either case with the overlying fabric cover 21 and primary layer 23, so as to produce a body of shape suitable for cardiac implantation.

The subsequent procedure in the . second embodiment is analogous to that employed in the first embodiment. Thus, following this dissection, the free margins of the valve are attached, by sewing at the position indicated at 24 (i.e. at the top of the valve, as shown in Fig. 2), to the overlying fabric cover 21 and primary layer 23.

Next, a secondary layer, indicated generally at 25, of structural coating material is applied on top of the primary layer 23 so as to produce a structure which is of sufficient strength to perform the valve supporting function of a valve stent. Again, this is preferably done by applying a succession of coatings so as gradually to build up the appropriate thickness of the resulting stent at all points.

The material which we prefer for this purpose is the same as that used for the primary layer 23, namely polymethyl methacrylate, but any other suitable structural material may be employed. Where the inner coatings are of a material which is not biologically inert, as is the case with polymethyl methacrylate, it is necessary to use a biologically inert material, such as a biologically inert polyurethane, for at least the final coating, so that the outer surface of the secondary layer 25 is of a material which is biologically inert. Thus, in the second embodiment, the secondary layer 25 consists of several coats of polymethyl methacrylate, indicated at 26, and a final coat 27 of biologically inert polyurethane.

The application of the constituent coats of the primary layer 23 and the secondary layer 25 can be by dipping, painting, pouring or any other suitable method.

As in the first embodiment, during the formation of the secondary layer 25, an additional part, a surgical sewing ring 28, is added to the valve by positioning the base 29 of the sewing ring 28 around the periphery of the valve, and applying the remaining coats of the secondary layer 25, the functional portion of the sewing ring 28 being suitably protected during the application of the latter coats.

Finally, the biologically inert fabric 30 is arranged to cover the outer surface of the valve, and is attached thereto by sewing, as at 31.

WHAT WE CLAIM IS: 1. A method of making a bio-prosthetic valve, the method comprising forming a stent around the outer surface of a natural valve by a process comprising depositing onto the said surface a structural material or a material which is capable of producing such a material, using the said outer surface as a form.

2. A method according to claim 1, wherein said stent is formed by a process comprising applying at least one coating of a liquid which is capable of setting to form a coating of structural material.

3. A method according to claim 1 or claim 2, wherein said stent is formed by a process comprising electroplating at least one layer of metal.

4. A method according to any one of claims 1 to 3, wherein said stent is formed by applying at least one sheet of mouldable material, using said outer surface as a mould, and allowing or causing said mouldable material to set.

5. A method according to any one of claims 1 to 4, wherein at least one additional part is added to the valve, by incorporating into the structural material as it is being deposited at least one member to which the additional part is attached or which forms a portion of that additional part.

6. A method according to claim 5, wherein a surgical sewing ring is added to the valve in the aforesaid manner.

7. A method according to any one of claims 1 to 6, wherein reinforcing material is incorp orated into said stent.

8. A method according to any one of claims 1 to 7, wherein, prior to commencemerit of of depositing said strucural material, a fabric cover is applied to said outer surface of the natural valve.

9. A method according to any one of claims 1 to 8, wherein the natural valve onto which said structural material or structural materialproducing material is deposited initially includes tissue additional to that which is to be present in the finished product of the method; the valve is dissected to remove said additional tissue at a stage when only a part of the thickness of said structural material has been applied; and the free margins of the valve are attached to the overlying structural material, the rest of the thickness of said structural material being applied subsequently.

10. A method according to any one of claims 1 to 9, wherein biologically inert fabric covers, and is attached to, the outer surface of the valve.

11. A method according to any one of claims 1 to 10, wherein the natural valve employed has been treated to render it nonviable.

12. A method of making a bio-prosthetic valve, the method being substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

13. A method of making a bio-prosthetic valve, the method being substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawings.

14. A bio-prosthetic valve, whenever made by a method in accordance with any one of

Claims

claims 1 to 13.