Towards a microstructurally-motivated constitutive model for reproductive soft tissues using an implicit elasticity framework
Pelvic organ prolapse (POP) is a prominent reproductive condition characterized by the descent of the pelvic organs. Although the etiology of POP is not well defined, the loss of mechanical integrity of the surrounding structures may be a contributing factor. To design effective clinical interventions for POP, the mechanical response of the native tissue to applied loads must be characterized. Understanding of the critical mechanisms in both the homeostasis of reproductive tissues and pathological processes can be enhanced by constitutive models. Prior models used to describe the mechanical behavior of reproductive tissues have been limited by mathematical complexity and a lack of physical interpretation of their parameters. Physically relevant parameters are needed to elucidate the contribution of microstructural components with the progression of various pathologies. Therefore, it is desirable to have a framework which is mathematically simple and contains parameters with microstructural significance. These characteristics are found in the conjugate pair fiber approach introduced by Freed, Erel, and Moreno, which represents the compliance of tissue as the sum of a linear implicit elastic solid intertwined with a linear Hookean solid. The framework is derived from thermodynamic principles, making it widely applicable, and includes parameters with microstructural significance. Herein, the model is derived from principles of continuum mechanics with relevant boundary conditions applied, and the descriptive capability of the planar biaxial tensile response of the uterosacral ligament is assessed. Results show promise of the model fit to experimental data and the capability of the model to describe relevant differences in mechanical behavior associated with microstructural changes.