Negative Poisson ratios and strain-dependent mechanical properties in arterial prostheses.

The elastic properties of two artificial arterial prostheses have been measured. One is a fibrillar polyurethane (PU) material, the other is an expanded polytetrafluoroethylene (ex-PTFE). It is shown that the conventional assumption of incompressibility is invalid for both materials and that changes in the thickness of the prosthetic artery wall must be measured directly. The ex-PTFE shows highly strain-dependent properties, the most significant being that of large negative through-thickness Poisson ratios, up to -11. These results have important consequences for matching the properties of prostheses to natural materials.