In vivo biostability of a poly(carbonate-urea)urethane graft

In peripheral and coronary bypass surgery, the patency of prosthetic grafts is inferior to autologous vein, mainly due to intimal hyperplasia caused in part by compliance mismatch between rigid graft and elastic host artery. We have developed a compliant poly(carbonate-urea)urethane vascular graft "MyoLink™" which was biostable in vitro degradation studies. To further investigate the biostability of this material, we report a long-term in vivo study on 8 beagle dogs (15±3 kg) implanted with this graft (ID 5 mm) in the aorta–iliac position; three grafts were harvested at 18 months to assess short-term biodegradation, with one animal having died from an unrelated infection. The 4 remaining grafts were harvested at 36 months for analysis by: (1) histology, (2) compliance measurements and (3) environmental scanning electron microscopy (ESEM); gel permeation chromatography (GPC); attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and radial tensile strength analysis. There was no infection or inflammation of the grafts or surrounding tissues. Histological analysis showed a well-developed neointima but only at the distal anastomosis. There were no significant differences in compliance pre- and post-implantation and no evidence of material curvature, radial expansion or chemical breakdown, ESEM and GPC showed no signs of degradation. Peak height analysis with ATR-FTIR of the 1740 cm−1 (CO of carbonate) and 1253 cm−1 bands (C–O–C of CO–O–C) showed a loss of carbonate carbonyl but was not statistically significant. Radial tensile strength remained within batch release specifications. This polyurethane graft retains its compliance post-implantation, whilst exhibiting only a minor hydrolysis of the amorphous segment, confirming its biostability in vivo up to 3 years.