VUV MODIFICATION PROMOTES ENDOTHELIAL-CELL PROLIFERATION ON PTFE VASCULAR GRAFTS

Small diameter (less than or equal to 6 mm ID) synthetic vascular graf ts, used as lower-limb vessel replacements in patients without suitabl e autologous saphenous veins, have a failure rate of 53% after 4 yr. G raft failure is due to thrombosis and intimal hyperplasia, an increase in smooth muscle cells in the lumen of the vessel which leads to prog ressive dosing and ultimate occlusion of the vessel. In an effort to i ncrease patency rates of synthetic grafts, investigators have seeded v ascular grafts with endothelial cells prior to implantation in an atte mpt to control both thrombosis and smooth muscle proliferation, This t echnique has been successful for the development of an endothelial mon olayer in animal trials, but has met with limited success in humans. T he hydrophobicity, low surface energy, and weak electrical charge of e xpanded polytetrafluoroethylene (ePTFE) provides conditions which are not optimal for endothelial cell attachment. The purpose of this study is to evaluate the effect of vacuum ultraviolet (VUV) modification of ePTFE on endothelial cell adhesion and proliferation. Pieces of ePTFE graft material were exposed to 10, 20 or 40 W VUV radiation for 10, 2 0 or 40 min using a UV excimer lamp. Prior to cell adhesion and prolif eration experiments, the grafts pieces were autoclaved and cut into pl edgets. Half of the pledgets were precoated with fibronectin (20 mu g/ ml). Cell adhesion was measured by seeding H-3-thymidine labeled human umbilical vein endothelial cells (HUVEC) onto the pledgets for 60 min . The pledgets were then washed and the remaining radioactivity assaye d using scintillation counting. For the cell proliferation experiments , pledgets were seeded with unlabeled HUVEC which were allowed to adhe re to the graft material for 18 h. The cells were then exposed to H-3- thymidine (1 mu Ci/ml) for approximately 48 h and then washed to remov e any unincorporated H-3-thymidine. Incorporation of H-3-thymidine was measured using scintillation counting. Four replicate samples each, w ith and without fibronectin, were evaluated for each power and exposur e time for both the adhesion and proliferation experiments. VUV modifi cation had no effect on cell adhesion for all power levels studied. In addition, it appears that cell adhesion is independent of the presenc e of fibronectin. Cell proliferation, on the other hand, is augmented by modification, especially in the presence of fibronectin. These resu lts suggest that VUV modification may provide a better surface for end othelial cell colonization of synthetic vascular grafts. (C) 1998 Publ ished by Elsevier Science B.V. All rights reserved.