Biphasic Modeling of Fluid-Microstructure Interactions in Fiber-Reinforced Biological Polymer Networks

Soft biological tissues can be viewed as natural polymeric composites - hydrated, porous, and reinforced by networks of collagen and elastic fibers embedded in a proteoglycan-rich matrix. Their mechanical response under rapid or cyclic loading arises from complex interactions between fluid transport, fiber recruitment, and matrix deformation, reminiscent of the coupled behavior observed in cross-linked polymer gels. In this work, we develop a biphasic finite element model to capture the time-dependent mechanics of fiber-reinforced biological polymer networks [1-2]. The model integrates a porous, fluid-saturated matrix with nonlinear anisotropic fiber families, accounting for regional variations in orientation and stiffness. Built upon biphasic-swelling theory, the formulation explicitly couples fluid flow and solid deformation, enabling the prediction of strain-rate sensitivity, relaxation behavior, and energy dissipation under cyclic loading. The model reproduces key experimental phenomena such as auxetic-to-non-auxetic transitions and hysteresis loops linked to fluid redistribution within the microstructure. This analogy between polymer physics and biological tissue biomechanics provides a unified framework for interpreting viscoelasticity, anisotropy, and permeability-driven effects in hierarchical soft materials. By extending theoretical concepts from polymer network mechanics to living biological systems, this study contributes to the multiscale understanding of fluid-structure interactions in complex, multiphase materials.

References:

1. Cachot, U., Kandil, K., Zaïri, F., Zaïri, F, 2025. Role of mechanical representativity in multiaxial and transverse mechanics of human annulus fibrosus: A microstructure-based biphasic finite element study. Acta Biomaterialia 197, 266-282.
2. Cachot, U., Kandil, K., Zaïri, F., Zaïri, F, 2025. Modeling fluid-microstructure interactions in annulus fibrosus transverse mechanics. International Journal of Mechanical Sciences 299, 110384.