Interstitial Fluid Load Support in Human Articular Cartilage: Effects of Degeneration, Loading, and Material Properties via Combined Experimental Testing and Computational Modeling.

Interstitial fluid pressurization plays a key role in cartilage mechanics, as it enables load support, reduces solid matrix stress, and limits solid-solid contact, thereby minimizing wear and friction. Because direct measurement of interstitial fluid load support is challenging, our modeling approach provides a practical means to estimate it based on experimental data. While its role has been studied experimentally and computationally, the combined effects of osteoarthritis, tissue composition/material parameters, anatomical location, and loading protocols on fluid pressurization remain poorly understood, especially in human cartilage. Here, we investigate these factors and further examine the relationship between fluid load support and friction. Human cartilage plugs (n = 40), obtained from the tibia and femur, representing varying osteoarthritic levels, underwent experimental friction testing. The axial deformation of each sample observed during testing was replicated using a sample-specific finite element model to determine constituent-specific material parameters and track interstitial fluid pressure over time. The results demonstrate that interstitial fluid load support is highly dependent on the loading protocol and particularly sensitive to variations in material parameters related to the extracellular matrix, fibrillar network, and fluid flow. These findings improve our understanding of cartilage function and inform the development of cartilage-mimicking biomaterials and future studies of tissue health and degeneration.