GB2141629A - Supported tissue - Google Patents

Abstract

The tissue support device shown in Fig. 1 is generally circular and includes an inner ring (2) of plastics material. An outer ring (4) also of plastics material is opened out to surround the inner ring (2). A bovine tissue is placed over the inner ring (2). The two free end portions of the ring (4) carry a clamping arrangement (6) to draw the two free end portions together and so cause the outer ring 4 to be clamped on to the inner ring (2) trapping the edge portion of the tissue between the two rings. <IMAGE>

Description

SPECIFICATION Supported tissue The present invention relates to a bioprosthetic device comprising supported tissue.

Bovine pericardial patches have been used for human implantation, in particular in cardiac surgery, and may be used as a closure material, for atrial patches, inter-atrial baffles and unstented aortic valve replacements.

However, the handling of such patches is inconvenient and cumbersome, and it is an object of the present invention to provide a support device for each tissue which will aid handling both before and during surgery.

Thus, the present invention provides a supported tissue comprising a support device having an inner member providing an open ing, and tissue extending over the opening, the support device including an outer member and a clamping arrangement acting to cause the outer member to clamp the tissue onto the inner member.

Advantageously, the inner and outer members are concentric annular rings.

Preferably, the supported tissue is packed in a hermetically sealed storage container and subjected to a formaldehyde atmosphere within the container.

The tissue is preferably derived from the pericardium of mammals, such as cattle, especially calves, pigs, sheep or horses.

In one form of the support device the inner ring has a circumferentially extending rib on its outer surface and the outer ring has a circumferentially extending rib on its inner surface, the two ribs being offset from one another when the rings are clamped together to effect a secure clamping of the tissue.

The outer ring preferably has two free end portions which carry the clamping arrangement.

The clamping arrangement is advantageously in the form of a screw-threaded rod rigid with one end portion and engaging a Ushaped slot defined in a block rigid with the other end portion, a knurled knob screwthreadedly engages the rod and bears against the block to enable the two end portions to be drawn together or to move apart when the knob is rotated.

A supported tissue will now be described by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a plan view of a tissue support device in an open state; Figure 2 is a side elevation of the device of Fig. 1; and Figure 3 is a section taken on line I-I of Fig.

1.

The tissue support device shown in Fig. 1 is generally circular. The device includes an inner ring 2 of plastics material approximately 100 mm in diameter and 10 mm deep. An outer ring 4 also of plastics material is opened out to surround the inner ring 2.

The two free end portions of the ring 4 carry a clamping arrangement 6 to draw the two free end portions together and so cause the outer ring 4 to be clamped onto the inner ring 2. The clamping arrangement 6 Includes a screw-threaded rod portion 8 rigid with one free end of the ring 4 and a block portion 10 rigid with the other free end of the ring 4.

Both portions 8 and 10 can be integrally formed with the ring 4.

The block portion 10 has a U-shaped slot 14 which is engaged by the rod portion 8.

The clamping arrangement also includes a knob 12 having a shank and a knurled head.

The knob 12 has an internally screw-threaded throughhole which is screw-threadedly engaged by the rod portion 8.

The shank of the knob is of greater diameter than the width of the U-shaped slot 14 so that when the knob 12 is rotated to draw the knob away from the free end of the rod portion 8, the end face of the shank will abut the end face of the block on opposite sides of the U-shaped slot and thereafter draw the two free ends of the outer ring together, clamping the outer ring around the inner ring.

The block 10 carries a pair of projections 16, 16 located on that end face of the block 10 against which the shank of the knob is arranged to bear. The projections 16, 16 lie on the opposite sides of the U-shaped slot 14, adjacent the open top of the slot 14 and act to prevent the shank from riding up the end face of the block. Accidental release of the rod portion from the slot 14 is thus prevented.

The outer face of the inner ring 2 may be provided with a circumferentially extending rib 20. Likewise, the inner face of the outer ring 4 may be provided with a circumferentially extending rib 22. The two ribs 20 and 22 are offset from one another when the two rings 2 and 4 are concentrically arranged. (See Fig.

3).

In this way when the outer ring is clamped onto the inner ring any material located between the two rings will be positively trapped.

The material to be mounted on the inner ring 2 and trapped between the inner and outer rings 2 and 4 is a sheet of tissue such as calf pericardium.

The tissue when mounted on the support device is held in a positive manner and without sagging. Thereafter, the tissue is chemically fixed by a controlled glutaraldehyde procedure.

It has been found that by holding the pericardium positively, without sagging, the material appears more like fresh pericardium than that which had been freely allowed to shrink during fixation.

The preparation of the tissue and its packaging after mounting on the support device will now be described in more detail.

Fresh pericardium from 16-20 week old calves is harvested in the abattoir as entire as possible. The tissue is stripped of fat in the abattoir within hours of slaughter and the cleaned tissue transported to the laboratory in physiological saline at 4"C. The saline wash is changed after two hours and the tissue is left overnight at 4 C.

Each pericardium is carefully examined and a suitable intact area is placed over a 100 mm diameter support ring with the rough, serosal surface uppermost.

The upper surface is carefully examined and any residual fat or other unwanted tissue removed with forceps. An outer clamping ring is now applied so that the pericardium is held in place with an even tension but not taut.

The thickness of the pericardium is measured at four different circumferential positions and one central position. Any pericardium thinner than 0.25 mm or thicker than 0.45 mm is discarded.

Each pericardium is also examined against a light source to ensure that it has an even consistency.

Each selected pericardium mounted with an even tension on a numbered ring is then transferred to an isotonic phosphate buffer solution at pH 7.4.

This solution is then charged with glutaraldehyde to a final concentration of 0.2% and the tissue fixed for a minimum of 7 days at ambient temperature.

Completion of the fixation process of the flat tissue is achieved by treating with 1% glutaraldehyde for 48 hours. Fixed tissue is then sterilised in 4% buffered formaldehyde for 24 hours, The sterile supported tissue is packed in a flat, lidded storage dish in an atmosphere of formaldehyde using a silicone rubber gasket as an hermetic seal.

It will be appreciated that the use of a circular supporting ring to apply an even tension to the pericardium whilst the tissue is fixed by glutaraldehyde, is done in such a way that the tissue does not become taut or stretched during fixation. This is important because tissue fixed under tension does not behave in the same way as loosely fixed tissue, which is more natural. The depth of the supporting ring protects the smooth parietal surface of the pericardium during handling.

Thus, the ring presents pericardium to the surgeon so that he always works onto the smooth surface. Accordingly, there can be no orientation ambiguity.

The ring also supports the pericardium during any tailoring to shape or cutting against templates, and facilitates the positioning of attaching sutures.

Claims (16)

1. A supported tissue comprising a support device having an inner member providing an opening, and tissue extending over the opening, the support device including an outer member and a clamping arrangement acting to cause the outer member to clamp the tissue onto the inner member.

2. A supported tissue according to claim 1 wherein the inner and outer members are concentric annular rings.

3. A supported tissue according to Claim 1 or to Claim 2 is packaged in a hermetically sealed storage container and subjected to a formaldehyde atmosphere within the container.

4. A supported tissue according to any preceding claim wherein the tissue is derived from the pericardium of a mammal.

5. A supported tissue according to Claim 4 wherein the mammal is selected from the group of cattle, pigs, sheep and horses.

6. A tissue in combination with a support device the support deivice comprising an inner ring having a circumferentially extending rib on its outer surface and an outer ring having a circumferentially extending rib on its inner surface, the two ribs being offset from one another when the rings are clamped together to effect a secure clamping of the edge portion of the tissue between the rings when the tissue is laid over the opening defined by the inner ring.

7. A combination according to Claim 6 wherein the outer ring preferably has two free end portions which carry the clamping arrangement.

8. A combination according to Claim 6 or to Claim 7 wherein the clamping arrangement comprises a screw-threaded rod rigid with one end portion and engaging a U-shaped slot defined in a block rigid with the other end portion, and a knurled knob screw-threadedly engaging the rod and arranged to bear against the block to enable to two end portions to be drawn together or to move apart when the knob is rotated.

9. A combination according to any one of Claims 6 to 8 wherein each said ring is of plastics material.

10. A combination according to any one of Claims 6 to 9 packaged in a hermetically sealed storage container and subjected to a formaldehyde atmosphere within the container.

11. A method of preparing a pericardial patch comprising the steps of supporting a pericardial tissue under substantially even tension in a support according to any preceding claim, fixing the tissue, sterilising the tissue and packaging the tissue in a sterile pack.

12. A method according to Claim 11 wherein the step of fixing the tissue comprises the steps of immersing the tissue in glutaraldehyde.

13. A method according to Claim 11 or 12 wherein the step of sterilising the tissue comprises immersion of the tissue in a buffered formaldehyde solution.

14. A method according to any one of Claims 11 to 13 including the step of ta#iloring the tissue to a predetermined shape.

15. A pericardial patch prepared by the method of any one of Claims 11 to 14.

16. A supported tissue substantially as hereinbefore described with reference to the accompanying drawings.