Polyurethane vascular grafts with thorough porosity: does an internal or an external membrane wrapping improve their...

Using a freeze-drying multiple-step technique, porous polyurethane vascular grafts 1.5 mm in diameter with different internal and external surface characteristics were fabricated: Type A: with thorough porosity, Type B: with internal membrane wrapping and Type C: with external membrane wrapping. One centimeter long tubes of each three types of grafts were implanted into the infra-renal abdominal aorta of rats for periods of 2, 4, 8 weeks. All the grafts were patent at harvesting. At the end of 2 weeks postimplantation, the endothelial cells layer developed inside the grafts about 1.2 mm apart from either the distal anastomosis side or both the distal and proximal anastomoses. They spreaded to the middle part of the one cm-long graft at 4 weeks. The luminal surfaces were entirely covered by a layer of endothelial cells at 8 weeks. Smooth muscle cells also migrated underneath the endothelial cell layer through the inner surface from the anastomosis and grew into the porous wall to generate a biocomposite blood conduit. Type B grafts with an internal membrane wrapping, developed a thicker, easy to lift intima after all the durations of implantation because the internal capsule was poorly anchored to the device. It is therefore of paramount importance that a porous structure is exposed to the blood flow to permit an adequate healing together with a good anchorage of the internal capsule.