Pseudointima formation in woven and knitted dacron grafts. A comparative ultrastructural analysis.

Twelve specially designed crimped aortobifurcated grafts (aorta, woven 200 porosity; right limb, woven 500 porosity; left limb, knitted 1200 porosity) were implanted into mongrel dogs that were sacrificed at two, six, eight and twelve-month intervals. Pseudointima from the mid portion of each type of graft was studied with light (LM) and transmission electron microscopy (TEM). An ocular micrometer was used to determine the thickness of the pseudointima. A trilaminar cytoarchitecture resembling the wall of a medium-sized artery existed in the pseudointima. This was characterized by an inner cellular layer, outer fibrocollagenous layer, and multi-interlamination of cells and glycosaminoglycan in the middle layer. The cellular inner layer was thickest in the knitted and thinnest in the woven 200 porosity. A zone of acellularity separated the luminal cells from the underlying myoblasts and myofibroblasts. Specificity of varying types of cell distribution occurred in the pseudointima. Myoblasts and myofibroblasts were located near the lumen while fibroblasts and mesenchymoid cells were situated near the graft. The luminal cells had the combined features of endothelial cells and myofibroblasts. Collagen and glycosaminoglycans were the dominant extracellular matrix. Despite the difference of fluid permeability in high porosity woven and knitted dacron grafts, the pseudointima was well formed and revealed no striking general cytoarchitectural difference between these two types of grafts.