Experimental study of ePTFE graft: biaxial testing, loading protocol, microscopy

Modeling the mechanical behavior of ePTFE-grafts is essential for improving surgical planning and enhancing treatment efficacy in cardiac and cardiovascular surgery. Despite their wide clinical application due to biocompatibility and durability, the understanding of this material’s mechanical properties remains incomplete. Researchers often rely on limited uniaxial or biaxial experiments, which do not fully capture the anisotropic and nonlinear aspects of deformation. In our study, we applied and analyzed a biaxial testing protocol with a broad range of deformations originally developed for soft tissues. Multiple loading modes, supplemented by microstructural data obtained via scanning electron microscopy, provide a more comprehensive experimental characterization of the material. The results of biaxial loading under a complex testing protocol demonstrate pronounced nonlinearity and a direction-dependent stress-strain response of ePTFE-grafts, tied to their microstructure. The collected data include seven different loading cases, combined into 127 unique sets for further identification of parameters in four hyperelastic constitutive models, including structurally motivated ones. It is shown that the choice of testing protocol affects the accuracy of the graft’s deformation behavior approximation, and that accounting for the material’s structural features enables a more adequate mechanical description. The experimental dataset, which encompasses stress-strain curves both with and without hysteresis, as well as microstructural visualization, is available in open access. The results support the recommendation to use comprehensive biaxial testing protocols for further research on ePTFE-grafts and for developing more relevant constitutive equations that consider both hyperelastic and viscoelastic properties of the graft.