Effect of interspecies differences on the mechanical behavior of liver and a strain-rate dependent visco-hyperelastic constitutive model

The limited availability of human liver tissue necessitates the use of animal surrogates in biomechanical studies, yet interspecies differences in mechanical behavior remain poorly quantified, especially under high-strain-rate conditions relevant to impact scenarios. This study investigated the mechanical behaviors of porcine, bovine, and monkey livers under uniaxial compression, spanning quasi-static (0.001, 0.01, 0.1 s⁻¹) to high strain rates (2000, 3000, 4000 s⁻¹). Mechanical testing was complemented by microstructural analysis using Masson's trichrome staining to quantify collagen content and organization. Results demonstrated that all livers exhibited significant strain-rate sensitivity, with bovine liver showing the strongest strain-rate sensitivity and porcine liver the weakest. Microstructural analysis indicated that collagen fiber content and alignment are primary contributors to the observed macroscopic mechanical differences. Furthermore, a novel visco-hyperelastic constitutive model was developed to characterize the nonlinear response under high-strain-rate loading, with a mean relative fitting error below 11.32 %. This study provides a theoretical foundation for high-precision numerical simulations of liver injury and offers experimental support for selecting appropriate surrogate animal models.