Anisotropic tensile viscoelastic properties of vascular graft materials tested at low strain rates.

Mechanical matching of vascular grafts and host vessels has been suggested to be important in determining graft patency rates. In this context, we have examined the anisotropic viscoelastic properties of natural vessels and some synthetic replacements using low strain rate tensile testing of circumferential and longitudinal strips. The canine iliac artery and iliac vein were compared with 6 mm diameter woven and knitted Dacron grafts, expanded polytetrafluoroethylene (PTFE) grafts, and helically constructed prototype polyurethane grafts at wrap angles of 45, 60 and 75 degrees. A thick-walled pressure vessel analysis was used to approximate physiological stress levels, and SEM was used to correlate anisotropic properties with graft wall structure.