Modeling thoracolumbar fascia mechanical tensile behavior with microstructure-level descriptors

Modeling of fasciae remains limited, despite their recognized role in chronic pain. Developing a comprehensive mechanical model of fasciae could significantly enhance our understanding of their pain-related mechanisms and improve their prevention. This paper presents a computational approach capable of simulating the mechanical behavior of fibrous tissues based on their mesostructure. The thoracolumbar fascia was selected as a case study due to the availability of its experimentally derived mechanical properties in the literature. A discrete element model was developed, representing collagen fibers as bilinear springs and the proteoglycan matrix as elastic beams. The model was subjected to uniaxial tensile tests across various parameter sets defining fiber threshold distributions. Four test configurations were implemented to evaluate key aspects of the model: the influence of fiber properties, validation against experimental data, anisotropic response, and the role of inter-fiber contact. The simulations revealed a broad range of hyperelastic behaviors resulting from subtle variations in fiber properties, suggesting potential adaptability across different fascia types. The numerical outcomes closely matched experimental results, despite the absence of a precise microstructural description of the tested samples. The model demonstrated anisotropic behavior aligned with the preferential fiber orientations, as expected in fibrous tissues. Additionally, contact interactions produced internal force reactions and localized stress within the sample. Overall, the proposed model successfully reproduced experimental tensile behavior while offering valuable insights into local mechanical responses and anisotropy, contributing to a better understanding of fascia mechanics and their potential role in chronic pain. Significance statement Growing evidence links chronic low back pain to altered mechanical properties of the thoracolumbar fascia. As fascia mechanics emerges from its fibrous mesostructure, elucidating this relationship is crucial. Yet, no existing numerical models directly derive macroscopic mechanical behavior from mesoscale structural organization. We developed a discrete element model that predicts the thoracolumbar fascia's mechanical response from its mesostructural architecture. Validated against previous experimental tensile data, the model accurately reproduced the fascia's elastic behavior. By quantitatively bridging mesostructure and mechanical response within the elastic range, this work provides a numerical framework to explore how fascial architecture governs the tissue mechanical properties which contribute to pain mechanisms.