A scanning and transmission electron microscope study of the luminal coating on Dacron prostheses in the canine thoracic aorta.

The sequence of events occurring in a woven Dacron bypass in the canine thoracic aorta was followed from the first exposure to flowing blood for a period of 27 months. After 10 and 40 minutes exposure to flowing blood the surface was covered with masses of leukocytes, platelets, red cells, and some fibrin. By 24 and 48 hours most of the leukocytes had disappeared leaving the two end areas of the bypass covered with a thick film composed of red cells entrapped in a fibrin net. In the central portion of the bypass the Dacron fibers were covered by a rough film of particulate material and widely spaced clumps of platelets and occasional leukocytes connected by a few fibrin strands. AT 6 AND 7 DAYS THE SURFACE COVERING CONSISTED PRIMARILY OF RED CELLS AND FIBRIN. Between 2 and 8 weeks this was replaced by a matrix that was composed mostly of cells resembling fibroblasts or transition forms between these and smooth muscle cells. Some typical smooth muscle cells were observed in grafts 4 months or older. A sheet of flat cells had grown a few millimeters below the anastomoses at 7, 12, and 14 months. By 27 months the entire length of the graft had a patchy covering of endothelium. Only occasional isolated platelets were stuck to the exposed collagen. Thickening of the intraprosthetic lining was associated with infiltration of the cell-fiber matrix by masses of red cells. Thus it appears that under proper conditions of flow, thrombogenic surfaces such as Dacron and collagen are "conditioned" to become nonthrombogenic by the limited deposition of blood elements.