Rate-Dependent Mechanical Behavior of Human Femoropopliteal Arteries in Biaxial Testing

This study investigates how loading rate influences the biaxial mechanical behaviour of human femoropopliteal arteries. Arterial specimens from 14 donors were tested under planar biaxial loading at rates from 10 to 50 mN/s using equi-biaxial and unequal loading protocols. Across protocols, the arteries showed clear rate-dependent viscoelastic behaviour, with faster loading producing lower stretch at a given stress and therefore a stiffer apparent response. This effect was most pronounced in the circumferential direction, while the longitudinal direction showed relatively limited sensitivity to loading rate. Mixed-design ANOVA showed no significant interaction between sex and loading rate, although male arteries were modestly more compliant on average. Pairwise comparisons indicated that the largest differences generally occurred between the slowest loading rate and higher loading rates, especially in the circumferential direction. Overall, the study demonstrates that human femoropopliteal artery mechanics are anisotropic and rate dependent, reinforcing the need to account for viscoelastic loading-rate effects when interpreting arterial biaxial test data or fitting constitutive models for vascular biomechanics.