Modeling lipid uptake in expanded polytetrafluoroethylene vascular prostheses and its effects on mechanical properties

The radial transport across the wall of expanded polytetrafluoroethylene (e PTFE) arterial prostheses has a significant effect on lipid uptake observed in prostheses implanted in humans, which has been postulated to be one of the causes associated with implant failure. The goal of this study was to s timulate radial transport on a lipidic dispersion across the wall of an ePT FE prosthesis and investigate its effects on the circumferential mechanical properties of the prosthesis. An in vitro model was developed to simulate the lipidic radial transport across the wall. Lipids contained in a phospha tidylcholine dispersion were used as the transported molecules. Lipid conce ntration profiles were obtained after exposing commercial ePTFE prostheses to various transmural pressure and/or lipidic concentration gradients. Phos pholipids gradually accumulated up to the external reinforcing wrap of the prosthesis, which clearly acted as a rigid barrier against lipid infiltrati on. Tensile tests performed on the virgin samples showed that the wrap was much more rigid than the microporous part of the prosthesis. After the lipi d simulation, the rigidity of the wrap decreased with respect to what was o bserved for the virgin prosthesis. Finally, some clinical implications of t his phenomena are discussed.