Heart valve prosthesis

Claim 1

**WARNING** start of CLMS field may overlap end of DESC **. Adhesive 61 is then applied through the fabric and to the surfaces of both the main frame 22 and the second frame 42, in a continuous line extending between the points b of the respective legs and connecting these three points, As in the previous step, the adhesive material preferably does not penetrate any portion of the leaflet material lying within the main frame 22, and remains out of contact with blood passing through the valve. The foregoing steps essentially complete the fabrication of the leaflet portions of the valve. The remaining steps of fabrication are for the purposes of facilitating the suturing of the prosthesis within the blood vessel. The excess fabric available on the outside of the frame can be rolled and consolidated along the junction line between the main and second frames to provide attachment points for stitches during surgical insertion. The frame material is preferably polypropylene, although other materials have also been employed with success. Polypropylene has excellent flex endurance and chemical stability, but is difficult to attach by adhesive to other materials. To facilitate adhesion, the main and second frames 22 and 42 may be encapsulated with polyurethane by multiple dip coating. The resulting encapsulated frame components have proved to demonstrate the desired characteristics of polypropylene without structural failures or breakdowns at the adhesive junctures. Valves employing the fabric described above have been tested in an accelerated fatigue tester to assess their long term endurance characteristics. Fatigue failures so induced have generally occurred in the region of greatest fabric flexure, that is, along a line in each leaflet that is perpendicular to its free edge and substantially equidistant between the contiguous legs. The failures have generally occurred by breakdown of the filaments in the yarns running parallel to the free edge of the leaflets. As a means of providing greater fabric strength along the last mentioned lines, woven fabrics may be provided with a greater number of load-bearing yarns in this direction. However, there is a limit to the increase that is possible using the plain woven pattern of Figure 10 without seriously disturbing the geometry of the fabric interstices. An alternative fabric construction pattern having improved strength against such fatigue failure is illustrated in Figure 9. The fabric shown is a flat braided ribbon 62 comprising 3 sets of yarns, namely, a first diagonal set 64, a second diagonal set 66 and a longitudinal inlaid set 68. The yarns in each of the three sets are preferably multifilament untwisted yarns similar to those shown in Figure 10. The ribbon 62 is braided on a conventional flat braiding machine. It will be noted that each selvage has uncut yarns and one of those becomes the free edge of each leaflet. Thus fraying of the free edges of the leaflets is avoided as in the example described above. In this embodiment both of the sets 64 and 66 perform -the load-bearing function of a single set of yarns in the earlierdescribed fabric. The result is that a greater number of yarns have a significant component of load bearing capacity oriented parallel to the free edge. The fabric 62 of Figure 9 is preferably formed by braiding the yarn sets 64 and 66 with inlaid longitudinal yarns 68 in a wellknown manner, thus producing a type of triaxial fabric. Such flat braided fabrics have an additional advantage over conventionally woven fabrics, in that they are inherently highly extensible in the cross machine direction, that is, in the direction perpendicular to the yarns 68. Such fabrics make it possible to produce a two-way stretch characteristic with any desired combination of stretch capabilities by compacting in the direction of the yarns 68 only. The frame system for a cardiovascular prosthesis described herein is described and claimed in our co-pending Application No. 22665/80 (Serial No 1598112). WHAT WE CLAIM IS: 1. A fabric for a cardiovascular prosthesis comprising woven multi-filament polymeric yarns extending in first and second directions forming an angle therebetween and having a substantial number of open interstitial spaces having dimensions in the range 20--40 microns evenly distributed throughout the fabric, the stretch characteristic of the fabric having a region of easy elongation up to at least 10% in at least one of said directions.