Computational modeling of articular cartilage: Mechanical experiments, sensitivity analyses, parameter...

Articular cartilage is a complex, multiphase material whose mechanical behavior is crucial for understanding joint function and diseases such as osteoarthritis. In this study we address the critical need to improve the fidelity of finite element simulations for cartilage by integrating mechanical experiments, sensitivity analyses, parameter identification, and validation to refine a well-established biphasic constitutive model for articular cartilage. Our sensitivity analyses using the Morris method identified fiber stiffness as dominant in uniaxial extension, while permeability and matrix stiffness played significant roles in confined compression. Parameter fitting for uniaxial extension achieved an excellent match with experimental force-displacement curves (R²≥0.989), and fitting permeability parameters for confined compression achieved a similarly excellent match to stress-strain responses (R²>0.998). Independent validation against biaxial extension experiments demonstrated that simulated stress-strain curves fell within the experimental range. Displacement and strain fields from uniaxial extension simulations also showed good agreement with data from digital image correlation, with minor discrepancies attributed to experimental variability and boundary conditions. Our results underscore the importance of fiber reinforcement in tension and interstitial fluid pressurization in compression. We publicly release our work via the data repository of the University of Stuttgart (DaRUS, https://doi.org/10.18419/DARUS-4729). Our validated biphasic model provides a robust tool for investigating cartilage mechanics and could aid in developing improved treatments for cartilage degeneration. Statement of Significance Articular cartilage is an anisotropic, heterogeneous soft tissue facilitating frictionless function of joints. Its complex microstructure determines the load-bearing functionality, and varies among patients and in disease. We advance understanding of cartilage mechanics by employing a specialized, biphasic constitutive model implemented within FEBio (University of Utah) to analyze cartilage under diverse loading conditions. We conduct sensitivity analyses leveraging new experiment data from uniaxial tension and confined compression testing to establish key material parameters and assess the model's sensitivity. Experimental data from uniaxial tension, confined compression, and biaxial tension provide additional insights into the heterogeneous mechanical behavior of this remarkable soft tissue. By combining new experiments, sensitivity analyses, and careful parameter fittings, we validated our fitted model and improved prediction fidelity.