GB2255394A

GB2255394A - Heart valve

Info

Publication number: GB2255394A
Application number: GB9209205A
Authority: GB
Inventors: Dan Rottenburg; Beno Perach; Shmuel Rahat; Ora Gara; Gideon Uretzky; Joseph B Borman
Original assignee: GALRAM Tech IND Ltd
Current assignee: GALRAM Tech IND Ltd
Priority date: 1991-05-03
Filing date: 1992-04-29
Publication date: 1992-11-04
Anticipated expiration: 2012-04-29
Also published as: IL98058A0; FR2675992B1; GB9209205D0; FR2675992A1; IL98058A; GB2255394B; DE4214098A1

Description

Heart Valve 2 3 53 _4

FIELD OFTHE INVENTION ',

There is provided a novel integrM tri-lea,flet,va,lye-sleeve structtAre for use in heart-lung devices, in heart assist devices, and the like. There is further provided a method for the production of such in- tegral tri-leaflet-sleeve one-way heart valves. The leaflets, which are highly flexible, are advantageously produced from hemocompatible polymer reinforced and coated fabric membrane which forms an integral structure with a supporting cylindrical sleeve which is used for the attachment to the heart-assist device. The polymer-imbued flexible thin fabric, provided with a polymer layer of adequate thickness, i manufactured to form an integral structure with a flexible polymer sleeve by casting or by an injection process. The novel valve has improved mechanical properties, durability and ease of connection than conventional three- leaf valves. The material of choice is polyurethane which is used to form tho coating of the polymer fabric and also of the sleeve, although other polymers having hemocompatibility and other required characteristics can also be used.

BACKGROUND OF THE INVENTION There have been many attemptS to produce three-leaves one-way valves which resemble in their geometry the threeleaves heart valve. Various materials of construction have been used, trying to obtain hemocompatible structures of adequate resilience and flexibility to allow for repeated opening-closure cycles of the valve without any damage or deterioration of function. One of the best materials used hitherto has been polyurethane of specific grades. There have also been mentioned silicones, teflon (T. M.), etc.

In conventional structures where reinforced fabric was used,the valve structure proper, i.e. the coated fabric defining the three leaflets and their rim, were generally attached to the support cylinder by means of a glue, sewing or by similar means. This results-in a structure, which during prolonged use, is apt to fail due to detachment of one or more of the three leafTets. The present invention overcomes to a large extent the drawbacks of the prior art, including the-use of valves made of uncoated flexible fabric made of a wide variety of organic and inorganic materials.

SUMMARY OF THE INVENTION: An integral triple-leaf valve for use in artificial heart'machines. The integral structure comprises a cylindrical sleeve from which there extend inwardly three integral light-weight flexible leaflets, the arrangement being such that the sleeve can securely attach to any external structure, and as the leaflets form an integral structure., the danger of detachment is practically eliminated. The materials used for both cylindrical sleeve and leaflets must be hemopompatible, and that used for the three leaflets must have a high degree of flexibility with a minimum of flow resistance. Such thin elastomeric membrane will generally be of the order of from 0.05 mm to about 0.2 mm thickness, and there is preferably provided a polymer fabric such as polyurethane, polyester or similar fabric, which is optionally provided with a thin polymer coating A suitable polymer for use in devices of the invention is Tecoflex SG 80 A or Tecoflex 2-80 A (Thermedics, USA). The manufacture can be carried out in two.variations, lead to the desired product:

both of which a First the leaflets are formed and these are integrated into a final structure by injection molding or casting, forming a sleeveleaflet structure; b. Uncoated fabric is placed in the mold and a polymeric material is cast to coat the leaflets and to form the sleeve integral structure. The leaflets ought to be as strong as possible, yet they also have to be of light weight and as flexible as possible. This enables the valve to pass easily from the fully open state to the fully closed state when the differential pressure changes its direction. The leaflets must be such as to maintain their initial geometry, structural integrity, mechanical strength and flexibility through a very large number of stress- flex cycles. Furthermore, in order to provide a commercially feasible product at a reasonable price, rather simple yet reliable, manufacturing processes are used. According to a preferred embodiment there is provided an integral structure comprising an elastomeric frame: generally iu cylindrical form from which there extend three flexible fabric-reinforced leaflets, meeting at the center of the cylinder,Which three leaflets have the required shape and dimensions. A preferred elastomer used for the manufacture of the sleeve is a polyether polyurethane polymer, but any other suitable polymer or copolymers may be used. Polymers suitable for themanufacture of the sleeve are, for example, Tecoflex 2-80A (Thermedics) or Pelethane 2363 80A (Upjohn Co.). The fabric used for the leaflets can be a fabric made of a suitable polyester such as polyethylene terephthalate, or of a polyamide, such as Nylon. The fabric is imbued with a polymeric composition, such as for example polyether polyurethane Such a leaflet structure is integrally combined with the polymeric sleeve during the process of' manufacture. The sleeve is advantageously produced with two sealing rings at its ends, facilitating attachment of the valve. Such valves can be used in a variety of pumps. It is of special value in heart assist devices and the like. The valve has a low flow resistance, providing substantially unobstructed flow in the one direction, while proViding an efficient closure towards a stream of liquid directed in the opposite direction. The structure imitates that of a heart valve and results in a minimum of turbulence; it has.good hemocompatibility and can be used for a prolonged period of time in an uninterrupted manner. The cylindrical sleeve is advantageously cast while at the same time the polymer-coated fabric is integrated at its rim with the sleeve structure, and where the center part of the fabric is deformed to the required tri-dimensional shape of the valve. The invention is illustrated by way of example only with reference to the enclosed schematical drawings, which are not according to scale and in.which: Figure 1 is a top view of a cut cloth from which the three-leaf valve component is produced. Figure 2 is a sectional side- view of the mold for producing valves according to the invention; Figure 3 is a perspective side-view of a valve of the invention.

As shown in Fig. 1, there is cut a triangle shape with rourded corners of a cloth of polymer fibers, 0.05 mm to about 0.2 mm thick, 11, il.

C ' 1 such as Dacron VPI 200 K Code 931515 produced by Vescotex, USA. The fabric is washed with a solvent which does not attack the polymer so as to remove any contaminauts.- The precut (as illustrated) fabric is provided with an impregnation and surface layer of a hemocompatible, polymer, such as a thermoplastic polyether polyurethane such as Tecoflex 80 A SG. This application is either by dipping the fabrjc into a solution of about 3 to 7 per cent by weight of the polymer in a suitable solvent, such as dimethyl formamide, tetrahydro furane, dioxane, methyl ethyl ketone, chlorobenzene, cyclohexane or the like, withdrawn, dried to a stage where the polymer does not flow and where an applied further layer does not interact with the previous one, and this is repeated until the desired thickness is attained. A multistep dipping process is preferrdd. It is also possible to apply the polymer solution by brushing, by spraying or any other technique. After reaching the required thickness of the impregnated polymer sheet, this is dried at a temperature in the 700C range for several hours, or at a somewhat higher temperature for a shorter period of time. The.coated fabric is then placed in a preheated mold shown in Fig. 2 for the injection of the frame. Techniques such as casting of two - components reactive systems or injection molding of a melt processible grade may be used. The mold comprises a housing 21, male 22 and female 23 members, inlet and/or outlets 24 into which the material is injected to form sleeve 30 within space 25. The cylindrical frame is made from a hemocompatible polymer, one of choice being a segmented polyether-polyurethane such as Tecoflex 2-80 A produced by Thermedics. The final polymerization is at about 110 0 C. The heat applied in the mold results in an integral structure, and there is also attained a deformation of the initially planar three segments of the three-leaflet component, to a required curved form which permits a one-way flow of a liquid, and which, when flow direction is reversed, acts as an efficient barrier preventing such liquid flow.

6 - The produce has the form shown in Figure 3, where 30 is the polymer sleeve, advantageously provided with a rim 31 and 32, respectively, at both its ends and where 33 illustrates the three-leaf component. The coated fabric can be placed in the mold so that the rim of the cutout piece of fabric is inserted into the sleeve, and coated by the polymer of the sleeve, and the sleeve is cast. After demold-Ing the cuts of the membrane can be made, if this is not done before. An ultrasonic knife was found to be suitable for this task. After this, the heart valve is washed and sterilized. As the three-leaf structure and the sleeve form a unitary integral structure, there exists no danger of one or more of the leaflets becoming detached during use, as is the case with such valves where the leaves are attached to the frame by an adhesive or by sewing. The thus produced valve component possesses extraordinary mechanical reliability during prolonged use. As the leaflets are thin, a very small pressure differential is required in order to bend the valve in the direction while a small pressure applied in the opposite direction results in a tight closure of the valve. EXAMPLE.2: As shown in Figure 1, there is cut an essentially triangular shape with rounded corners of a cloth made of polymer fibers of 0.05 mm to about 0.2 mm thickness, such as Dacron VPI 200 K Code 931515 produced by Vescotex, USA. The fabric is washed with a solvent which does not attack the polymer so as to remov any contamination. The precut (as illustrated) fabric is introduced into the mold shown in Figure 2 which is preheated. The uncoated fabric can be placed in the mold so that the rim of the cutout piece of fabric is inserted into the sleeve. Casting of a two component reactive polymer system is conducted to coat the fabric and formi.the sleeve, which polymer forms an integral structure with the rim of the triple-leaf component. During casting the polymer also penetrates the interstices of the fibers. Casting is conducted using a hemocompatible polymer, one of choice being a segmented polyether polyurethane such as Tecoflex 2-80A produced by Thermedics (USA). After polymerization in the mold there is attained a deformation of the initially uncoated planar three segments of the tripleleaflets component fabric to the required curved form of the coated fabric. The product has the form shown in Fig. 3. After demolding the cuts of the membrane can be made. After this the heart-valve is washed and sterilized. The integral three-leaf valve/sleeve structure is characterized by a number of advantages, amongst which there may be mentioned the provision of smooth surfaces compatible with blood flow which to a large extent, prevent deposits of calcium, etc, the stability against hydrolytical influences and against enzymatic activity, and which do not deteriorate when in contact with blood over prolonged periods of time. The material of the valve is chemically stable and does not absorb body fluids or their constituents. The valve can be easily sterilized by. conventional methods and stored. The product is fiber-reinforced and has very good mechanical properties. The novel integral valve is easily manufactured, at greatly reduced cost compared with hand-sewn products or with products where the leaflets are attached to the frame by an adhesive, which tend to become loose after certain periods of use. The new product can be molded with a high degree of accuracy and reproducibility.

The above description is by way of illustration only and various changes and modifications in the shape and configuration as well as in the nature of the materials of construction, can be resorted to without departing from the present invention.

1

Claims

CLAIMS:

1 An integral polymeric unit for use in heart assist devices which comprises an integrated structure of a fabric-r6inforced threeleaflet heart-valve and a sleeve of tubular shape, the center of the threeleaflet valve being coaxial with the axis of the sleeve.

2. An integral unit as claimed in claim 1, where the heart-valve leaflets are made from hemocompatible polymer-fiber fabric which is integral with a heme-compatibde polymer layer which penetrates the interstices of the fabric.

3. A unit according to claim 2, where the fabric has a thickness of from about 0.05 nini to about 0.2 mm, and which can be built up by the polymeric impregnation to a thickness not exceeding about 0.4 mm, and which has high mechanical strength, good flexibility and which provides a minimum of impedance to blood flow in one direction only.

4. A unit according to any of claims 1 to 3, where the polymer used is a polyether-polyurethane or other hemocompatible polymer of adequate strength and flexibility.

5. A process for producing a triple-leaflet valve integral with a surrounding cylindr4cal sleeve, which comprises preparing a suitably sized planar membrane of coated or uncoated fabric of hemocompatible polymer fibers, which coated fabric is constructed by applying to same a plurality of coatings of a hemocompatible thermoplastic polymer in solution form, drying each coating before the subsequent one is applied and drying the membrane thus obtained; introducing the membrane into a mold so that the dimensions of the fabric exceed the cross-sectional area - of the mold and casting a hemocompatible thermosetting polymer forming a sleeve while forming an integral structure with the membrane. If an uncoated fabric is used, coating of the fabric during casting should be allowed; deforming the leaflets by the application of heat in the mold and cutting the membrane to its three leaflet form during casting after de-molding.

6. A process according to claim 5, where an uncoated fabric is used, which fabric is coated with a polymeric coating during the coating step, deforming the leaflets by the application of heat and pressure in the mold, and cutting off any excess to obtain the triple-leaflet form during the casting step after demolding.

7. A process for the produclion of valves according to any of claims 1 to 4, which comprises introducing a planar membrane into a mold, and casting the sleeve, Ibus simultaneously forming a tripleleaflet integral structure between the sleeve and triple-leaflet membrane.

8. A unit substantially as hereinbefore described with 1 reference to the accompanying drawings.

9. A process substantially as hereinbefore described with reference to the accompanying drawings.

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