Vascular Prosthetic

Abstract

A vascular prosthetic comprising a multilayered tubular fabric contains an anticoagulant on an inner layer to reduce the likelihood of clot formation. An outer layer does not contain an anticoagulant and may contain an anticoagulant inhibitor or antagonist to permit clot formation adjacent the outer layer to thus prevent exsanguination.

Description

The present invention relates to prosthetic devices, vascular implants and the like for surgical use in the repair and replacement of vessels and tracts in human and animal bodies.

In the practice of vascular surgery, such defects in he vascular system as aneurysms or occlusions are corrected by the technique of suture anastomosis, by which the area or segment of pathology is excised or resected, and replaced by a prosthetic device, or graft, which is implanted, or sutured in. The vascular prosthetic grafts are employed in various sizes and in all parts of the vascular system, and comprise straight or variously branched tubes of flexible, porous construction or fabrication from fibers or strands run together or interlaced in an interstitial or mesh structure.

The vascular prosthetic grafts here concerned desirably are non-toxic and non-allergenic; non-deteriorating upon implantation for prolonged periods; and capable of deforming without collapsing and twisting without kinking. Desirably also the porosity of the grafts on implantation is low enough to permit the implantation without pre-cloting.

The body heals by fibrosis; that is, the organism's reaction to the implantation of the foreign body is to attempt to completely encapsulate the graft with fibrous or scar tissue, forming both an outer layer or capsule of fibrous tissue and an inner capsule of fibrous tissue within the lumen of the graft. The healing process is initiated withing hours of implantation by the deposit of a thin fibrous layer or mat on the inside of the graft in contact with the blood stream. The fibrous mat then organized more slowly, within a period of days to weeks, into a layer of mature scar tissue. The origin of the fibroblasts forming the inner layer or capsule is considered to be migration or growth from the outer capsule through the mesh or interstices of the graft. The fibrous inner layer, then, is dependent for its blood supply and integrity on interstitial tissue ingrowth, and a principal factor limiting the biological fate of the graft is the case with which the fibrous tissue may grow through the implant wall.

It has been proposed to heparinize the prosthetic to reduce the likelihood of clot formation within the lumen of the graft. The use of an anticoagulant, however, inhibits the formation of clots not only in the graft lumen but throughout the implant itself as well which may result in exsanguination. This adverse result may be minimized by reducing porosity, but this has the adverse effect of interfering with the normal healing process as described above. Alternatively, a reduced amount of heparin may be utilized but this results in increased likelihood of clot formation in the graft lumen. Furthermore, in both of these cases, the anticoagulant affects clotting to substantially the same extend throughout the implant.

It is an object of the present invention to provide a vascular prosthetic which includes an anticoagulant but which is free from the disadvantages mentioned above.

BRIEF SUMMARY OF THE PRESENT INVENTION of the Present Invention

The foregoing and other objects are achieved according to the present invention by providing a vascular prosthetic comprising a porous, multilayered tubular fabric comprising a first tubular fabric layer containing an anticoagulant and a second tubular fabric layer surrounding said first fabric layer, said second layer being free of anticoagulant.

DESCRIPTION OF PREFERRED EMBODIMENTS

There follows a detailed description of a preferred embodiment of the invention, together with accompanying drawings. However, it is to be understood that the detailed description and accompanying drawings are provided solely for the purpose of illustrating a preferred embodiment and that the invention is capable of numerous modifications and variations apparent to those skilled in the art without departing from the spirit and scope of the invention.

The drawing is a perspective view, partially cut away, of a vascular prosthetic according to the present invention.

With reference to the drawings, a vascular prosthetic according to the present invention comprises a porous, multilayered tubular fabric 1 comprising a first tubular fabric layer 2 and a second tubular fabric layer surrounding the first tubular fabric layer. A portion of second layer 3 is cut away in the drawing to reveal first layer 2. The multilayered prosthetic is conveniently made by inserting one vascular prosthetic within another and stitching the two together. One or both of the prosthetics may be crimped and each is of conventional construction such as woven or knitted. The composite prosthetic may be in the form shown in U.S. Pat. No. 3,105,492, herein incorporated by reference. The graft may be fabricated from fibers of synthetic resins useful in prosthetics such as polyesters such as polyethylene terephthalate, polyamides such as nylon 66, acrylics and modacrylics such as Orlon, and polyhalogenated hydrocarbons such as Teflon, or from mixtures of these fibers with one another or with animal derivative fibers such as disclosed in U.S. Pat. No. 3,316,557, herein incorporated by reference. Thus, each layer of the prosthetic, as well as the composite prosthetic, is conventional in configuration, the porosity, size and other structural features being selected as desired for a given use according to known considerations.

In accordance with the present invention, a first fabric layer of the implant is provided with an anticoagulant and a second fabric layer of the implant surrounds the first. The anticoagulant is preferably heparin and is provided in the first layer by impregnation of the fibers making up the layer or by impregnation of the layer prior to assembling the composite prosthetic. In a preferred embodiment, a tubular fabric prosthetic of crimped woven Dacron is immersed into a 5 percent aqueous solution of sodium heparin for a few minutes and the thus-impregnated implant is dried providing about 0.5 percent by weight of heparin in the prosthetic.

The impregnated prosthetic is then inserted inside a second tubular prosthetic fabric having an inside diameter slightly larger than the outside diameter of the impregnated prosthetic. The second prosthetic is preferably woven more loosely than the first.

An implant constructed in the foregoing manner is utilized in surgery in the usual manner. The presence of heparin anticoagulant in the inner layer minimizes the risk of clotting within the implant. The outer layer, however, is free of anticoagulant and permits the formation of clots outside the inner layer thus minimizing the likelihood of exsanguination due to the presence of heparin in the prosthetic.

The inhibiting effect of the outer layer on the anticoagulant can be enhanced according to the invention in several ways. First, the second layer may be relatively large in thickness relative to the first layer thus providing greater capacity to absorb the anticoagulant. Alternatively, the second layer may comprise a material which inhibits the effect of the anticoagulant. The inhibitor may be the fabric material itself or a material added thereto such as an anticoagulant antagonist or inhibitor.

Heparin anticoagulant is an organic acid which will react with a base. The fabric may comprise a basic material, such as silk or other protenaceous fiber, which will chemically combine with heparin thus effectively inhibiting the effect of heparin on clotting in the second fabric layer.

Where a material is added to the second fabric layer as an inhibiting agent, that material may simply react chemically with the anticoagulant to form a reaction product having no effect on clotting. For example, the second fabric may be coated or impregnated with a basic salt, such as a quaternary ammonium germicide, for example benzethonium chloride, which will react chemically with heparin to form a highly insoluble material having very little anticoagulating effect. Alternatively, the second fabric may be coated or impregnated with a heparin antagonist such as a protamine or protamine zinc or with an antifibrinolytic agent such as epsilon amino caproic acid. Other heparin inhibitors which may be provided in the second fabric include Acridine Blue, Polybrene, and Toluidine Blue.

The amount of anticoagulant is, in general, less than that which would give the normal dosage of anticoagulant if released. Preferably, the amount of anticoagulant is not more than one-tenth that amount. Thus, the conventional dosage of heparin anticoagulant is about 50 mg i.v. Therefore, the maximum amount of heparin anticoagulant in a prosthetic would generally be about 50 mgm., preferably about 5 mgm. Where a heparin antagonist or inhibitor is utilized in the second fabric layer, the amount thereof will, in general, be at least an amount sufficient to inhibit a substantial amount of the anticoagulant in the first layer. For example, where anticoagulant inhibition is achieved by chemical reaction, the amount of inhibitor is at least sufficient to react with a substantial amount, preferably a major proportion of the anticoagulant present in the prosthetic. The maximum amount of the inhibitor is preferably about five times the amount theoretically needed to inhibit all of the anticoagulant, and more preferably, about twice that amount.

While the preferred prosthetic has two layers as shown, additional fabric layers may be added. However, at least the inner layer will be heparinized in accordance with the invention and at least one outer layer, preferably the outermost layer, will be free of heparin according to the present invention.

Claims

What is claimed is:

1. A vascular prosthetic comprising a porous, multilayered tubular fabric comprising a first tubular fabric layer containing an anticoagulant and a second tubular fabric layer surrounding said first fabric layer, said second layer being free of anticoagulant and containing an inhibitor for said anticoagulant.

2. A vascular prosthetic according to claim 1 wherein said anticoagulant comprises heparin.

3. A vascular prosthetic according to claim 2 wherein said inhibitor comprises a heparin inhibitor.

4. A vascular prosthetic according to claim 3 wherein said heparin inhibitor is selected from the group consisting of epsilon amino caprioc acid, protamine, protamine zinc, acridine blue, polybrene and toludine blue.

5. A vascular prosthetic according to claim 3 wherein said heparin inhibitor comprises a basic salt capable of reacting with heparin to form an insoluble salt with heparin.

6. A vascular prosthetic according to claim 5 wherein said basic salt comprises a quaternary ammonium salt germicide.