Exploring the passive anisotropic and viscoelastic behaviour of the fresh-frozen human large bowel.

The mechanical behaviour of the human large bowel is governed by its complex multilayered architecture and by distinctive anatomical structures such as the taeniae coli, whose mechanical role remains poorly assessed and quantified. Moreover, experimental data describing both tensile and compressive mechanical responses of human colonic tissue are currently lacking, despite the relevance of both loading conditions in physiological functionality and tissue-device interactions. This study aimed to experimentally characterize the anisotropic and viscoelastic behaviour of fresh-frozen human large bowel tissue, investigating the effects of loading direction, strain rate, and the presence of the taeniae coli under tensile and compressive loading conditions. Fresh-frozen human colonic samples obtained from surgical donors were tested as an integrated structure without layer separation. Uniaxial tensile tests to failure, unconfined compression tests, and stress-relaxation protocols were performed along longitudinal, circumferential, and radial directions, with and without taeniae coli. Histomorphometric analyses were conducted to relate tissue microstructure to mechanical response. The results revealed an anisotropic, nonlinear, and time-dependent mechanical behaviour. The presence of taeniae coli significantly increased tensile stiffness and toughness, particularly at higher strain rates. Tensile tests confirmed non linearity of stress-strain behaviour and strong anisotropy. Compressive tests highlighted pronounced viscoelasticity, with strain-rate-dependent stiffness and equilibrium stresses influenced by loading configuration. This work provides a comprehensive experimental dataset that contributes to a more physiologically realistic description of colonic biomechanics, supports the development of advanced constitutive models for biomechanical simulations and design of prosthetic and surgical devices. STATEMENT OF SIGNIFICANCE: This study provides a comprehensive experimental characterization of the mechanical behaviour of fresh human large bowel tissue, addressing critical gaps in current literature. Unlike existing studies, it integrates tensile and compressive responses, accounts for anisotropy and viscoelasticity, and evaluates the role of anatomical features such as the taeniae coli. Importantly, it reports the first experimental evidence of compressive mechanics in human colon tissue. The results highlight strong dependencies on loading direction and strain rate, and demonstrate the reinforcing contribution of taeniae coli under tensile loading. These findings deliver a physiologically relevant dataset that enables the development of advanced constitutive models and supports the design and optimization of biomaterials and medical devices interacting with the intestinal wall.