Mechanical characterization of the human femoral vein wall and its valves

For the development of stent-based intraluminal prostheses to treat chronic venous insufficiency, comprehensive knowledge of morphometric and mechanical parameters of the femoral veins (FV) is crucial for an optimized implant design. These data is essential as input for material models for numerical simulations of venous valves prostheses. However, data on mechanical properties of native/unfixed FV tissue are scarce. Unfixed native tissue, though, has limited availableness and durability due to progressing decay. To address these challenges, this study aimed to determine stress-strain behavior and compliance from native specimens of the human FV and its valves from body donations and compared the data to chemically fixed material. A large data set has been generated in tensile tests with a total of 313 venous wall and 78 valve leaflet specimens in different fixation groups from a total of 41 body donations. Tensile testing was conducted at cut rectangular specimens in longitudinal as well as circumferential direction of the vein walls and in one specific direction for the valve leaflets. Young's moduli E₁ and E₂ in two differently defined strain regions, tensile strength R_m and elongation at break A were determined. Additionally, compliance measurements were performed at whole, unfixed vein segments using optical coherence tomography to determine the vessel diameter at increasing intravascular pressure from 20 to 240 mmHg. Significant differences were found in the tensile parameters between unfixed tissue and the different fixations (exemplary Young's modulus E₁ in longitudinal direction: E_{1, unfixed} = 5.7 ± 5.1 N/mm², E_{1, FA} = 13.1 ± 11.9 N/mm², E_{1, PFA} = 2.3 ± 1.0 N/mm). A distinct anisotropy of the mechanical properties could only be detected for PFA fixed material when comparing longitudinal and circumferential tensile direction. Resultant mean compliance values over all segments and measuring positions of the vein segments for the analyzed pressure stages were in the range from 18.16 to 3.78 %/100 mmHg and showed a distinct decrease with increasing pressure. Fixation (FA, PFA) alters the elastomechanical behavior, but the parameters were still in a similar order of magnitude considering the naturally occurring variability. Thus, testing of fixed tissue appears to be as appropriate as the use of this material for ex vivo testing. The provided material data of femoral veins (longitudinal and circumferential) as well as venous valve leaflets may serve as basis for numerical models, e.g. for the development of artificial venous valves.