Nonlinear anisotropic constitutive description of the human basilic vein and comparison with the vein of the lower limb.

The number of patients undergoing hemodialysis has been steadily increasing in recent decades. Arteriovenous fistula (AVF) is the gold standard for ensuring vascular access in these patients. Despite the prominent role of AVFs in hemodialysis treatment, their maturation and long-term functionality continue to pose challenges as less than a third of fistulas remain patent without further interventions in a 3-year follow-up. Computational biomechanics has become an essential tool for clarifying mechanical conditions accompanying the pathogenesis of various vascular complications, including suboptimal maturation and AVF stenosis. Constitutive description plays a crucial role in the design of computational models and without it simulations remain only at the rigid tube level. However, literature on the mechanical properties and constitutive modeling of upper extremity veins is lacking. This study aims to fill this gap by characterizing the mechanical properties of the human basilic vein (BV) and comparing it to the great saphenous vein (GSV). Uniaxial tensile tests in two perpendicular directions were used to obtain the mechanical response of the tissue. The results suggest that BVs do not significantly differ from GSVs in their elastic properties expressed by means of the tangent modulus. Overall anisotropy, understood as the difference in elastic moduli obtained in different directions, seems to be reduced in BVs. The 4-fiber family exponential model of the strain energy density function was adopted to fit the experimental data. The model fitted the data well, as suggested by the coefficients of determination R2, which ranged from 0.97 to 0.99 for the majority of the average curves. The resulting parameter values can be used within the modeling of the mechanical behavior of veins in computational simulations of vascular access performance.