Enhanced neointima formation and attachment on the high-porosity inner surface of modified PTFE vascular grafts

Highly porous PTFE arterial prostheses form endothelium more extensively than the low-porosity grafts in clinical use, but are subject to seroma formation. PTFE vascular grafts were modified to produce a highly porous inner layer (inner layer 60 or 90 microns, outer layer 20 microns). The effect of this modified, composite design on the histology of graft healing was investigated. Twenty-five modified and 25 control grafts, each 4 mm in diameter by 5 cm in length, were implanted into carotid and femoral arteries of dogs. No late seroma formation was observed. After 12 and 18 weeks, the neointima of the grafts was examined by light microscopy and scanning electron microscopy. At 2- and 4-mm distances from the proximal and distal anastomoses, intimal thickness of the control grafts was 238.7 and 96.1 microns, respectively; for the modified grafts it was 236.2 and 202.8 microns at 18 weeks. Thus, the neotinima of modified grafts was thicker than that of control grafts when measured at 4 mm from the anastomoses. Neointimal coverage was less extensive in the control grafts than in modified grafts (26.8 +/- 6.1% vs. 58.8 +/- 13.2%; p < .05). Smooth muscle cells were seen on light-microscopy to penetrate the highly porous inner layer; on scanning electron microscopy, the PTFE fibrils appeared to anchor the neointima of the modified graft. The results suggest that modified PTFE grafts with an inner surface of 60 or 90 microns internodal distance have enhanced formation and anchoring of neointima while remaining impervious to blood.