LIPID UPTAKE IN EXPANDED POLYTETRAFLUOROETHYLENE VASCULAR GRAFTS

Purpose: The mechanisms of vascular prosthesis failure are reported to be associated, in part, with an atherosclerotic degenerative process that is related to an abnormal lipid infiltration. The lipid uptake in expanded polytetrafluoroethylene (ePTFE) vascular grafts was reproduc ed in vitro, and the effect of time on the permeability of these prost heses was studied. Methods: Water permeability tests were carried out under dynamic flow conditions at various hydrostatic pressures. Lipid uptake was simulated by circulating a phosphatidylcholine suspension i nside an expanded Tenon prosthesis under pulsatile or continuous trans mural pressure ranging between 80 mm Hg and 180 mm Hg, at a flow rate of 500 mL/min and 2000 mL/min, for a duration ranging from 2 hours to 1 month. Results: Water permeability tests indicated that under hydros tatic pressures of 180 mm Hg and 300 mm Hg, water percolated through t he prosthesis wall after an exposure of 720 minutes and 75 minutes, re spectively. After exposing the prostheses to the lipid dispersion unde r the various flow conditions, the fluid convection through the wall o ccurred. Preferential convection pathways with a constant periodicity were observed across the length of each prosthesis and were, therefore , associated with regularly spaced perforations depicted in the struct ure of the devices. Phospholipids gradually agglomerated within the pr osthesis wall, allowing a restrictive molecular mobility. Infrared spe ctroscopy results indicated that the Lipid uptake depended on the tran smural pressure and time of exposure. Conclusion: The occurrence of th e membrane permeability may be associated with the dilatation and plas tic deformation of the prosthesis. Lipid uptake occurs in ePTFE grafts after an aggressive kinetic process.