Microporous hydrophilic polyurethane vascular grafts as substitutes in the abdominal aorta of dogs

Polyurethanes are emerging as promising biomaterials. A microporous vascular graft fabricated from Mitrathane, a new polyetherurethane urea, appeared to be particularly interesting according to in vitro evaluation and was tested in vivo as an infrarenal aortic substitute (i.d. 5 mm) in 24 dogs. After implantation for scheduled periods ranging from 4 h to 6 mnth, morphology evaluation and healing analysis of the grafts were performed. At harvesting, 18 grafts were patent and 6 were thrombosed. The thrombosed grafts had been implanted for 4 h (1 graft), 1 mnth (2 grafts) and 6 mnth (3 grafts). No macroscopic deposits other than red mural thrombi were observed. At 1 mnth complete external encapsulation was observed in 2 grafts. The capsule then contracted and became thinner; over the long term it shrank, became translucent and incomplete at 6 mnth. Yellow and brown stains appeared on many of the grafts. Characterization of the brown stains showed them to be iron (Fe3+) and the yellow stains were associated with the deposition of a bile pigment (bilirubin).