CELL‐LINED, NONWOVEN MICROFIBER SCAFFOLDS AS A BLOOD INTERFACE*

Abstract

In order to provide blood-compatible interfaces for artificial vascular prostheses, technology has proceeded along several lines, including the use of (1) synthetic materials such as neutral, ionic and polarized polymers and pyrolytic carbons; ( 2 ) additive containing materials such as heparin; ( 3 ) hydrogels; (4) woven and nonwoven fiber scaffolds lined with cells or fibrin; and ( 5 ) composites of the above.', Although fiber scaffolds (in the form of porous woven or knitted fabrics) have been in use for many years, healing is somewhat capricious and is always preceded by the formation of a fibrin coagulum that subsequently undergoes organization and may or may not give rise to a healed endothelium. The use of porous prostheses permits flexion of the vessel as well as adherence of the fibrin coagulum and the potential for transinterstices growth of tissue, which, it is hoped, will lead to a healed pseudointima. Since adherence of the pseudointima (whether cellular or fibrin) and healing depends to a great extent on the surface characteristics and porosity of the p r o s t h e s i ~ , ~ ~ ~ many types of surfaces have been developed (woven, knitted, velours, flocks, lattices, etc.) to promote better healing. Emphasis recently has been on the production of prostheses with smaller fibers and pores such as Weavnit, 0 Microknit, lo and Warpknit for clinical application. On the experimental side, in recent years nonwoven microfiber scaffolds have been produced as an alternative to woven and knitted prostheses. Heart-assist devices must of necessity be nonporous, given the nature of the pneumatic pumps. Since blood pumps have large surfaces exposed to the blood, the potential for thrombus, degradation of blood proteins, and hemolysis is great. To circumvent these problems, fabric-lined pumps have been developed.15-?'I However, such nonporous prostheses or pumps permit no growth of cells except from the natural vessel at the anastomotic line. Since this neointima comes only from the intima or media of the vessels at the suture line in both heart assists or in arterial grafts,'l production of cellular pseudointimas before implantation of the devices would be beneficial. Various methods of pseudointima production have been attempted, including: (1) the use of tissue fragments,16* *O ( 2 ) trypsinization of organs, viscera, and so on, followed by immediate seeding of prostheses with dispersed cells,'o (3) derivation of cells from tissues followed by cultivation in vitro and seeding of subcultured 22-35 Numerous cell sources for culture-derived pseudointimas have been tried, including skin,li, ** arteries, veins,19, 20, 2 2 subcutaneous tissue,l9, 20 lung,162 n pleura,'? fascia,'? granulation tissue,lg~ 2'1 28 bone marrow,lQ macrophages,'3 pericardiurn,'O. 22 fibro-