A comprehensive biomechanical material characterization of the human breast fibro-structural support system

Breast surgery for aesthetic purposes, such as breast augmentation or breast reduction, and breast reconstruction after cancer treatment require an accurate structural (anatomical) and mechanical (functional) understanding of the breast components, including the fascial-ligamentous support system of the breast, to achieve optimal results. This paper aims to provide a comprehensive description of the mechanical behavior of the ligamentous and fascial connective tissues of the human female breast. Fasciae and ligaments obtained from 17 patients between 35 and 85 years of age who were undergoing mastectomy and three female cadavers were tested. Uniaxial tensile tests were conducted, and three constitutive models -- the phenomenological Fung exponential model, the invariant-based anisotropic Gasser-Ogden-Holzapfel model, and the meso-scale structural constitutive model -- were employed to fit the experimental stretch-stress curves. Our results show that the stiffness becomes consistent once collagen fibers are fully stretched, regardless of tissue type or patient factors. This paper presents a comprehensive mechanical characterization of all the connective tissues contributing to the fascial support structures of the breast, collectively termed here as the breast fibro-structural support (BFSS) system. A generalized stress-stretch curve with initial stretch as the only variable effectively captures patient-specific variability.