Interstitial Fluid Pressurization
Over the last two decades, considerable progress has been reported in the field of cartilage mechanics that impacts our understanding of the role of interstitial fluid pressurization on cartilage lubrication. In our laboratory, theoretical and experimental studies have demonstrated that the interstitial fluid of cartilage pressurizes considerably under loading, potentially supporting most of the applied load under various transient or steady-state conditions. The fraction of the total load supported by fluid pressurization has been called the interstitial fluid load support, and our experiments have shown that this load support can be predicted from mixture models of cartilage very accurately. A significant component of the doctoral dissertations of Drs. Michael A. Soltz and Seonghun Park have focused on this topic.
Correlation with Frictional Response
Our experimental studies have demonstrated for the first time that the friction coefficient of cartilage correlates negatively with this variable, achieving remarkably low values when the fluid load support is greatest. A theoretical framework that embodies this relationship has been validated against experiments, predicting and explaining various outcomes, and demonstrating that a low friction coefficient can be maintained for prolonged loading durations under normal physiological function. These studies were performed as part of Dr. Ramaswamy Krishnan's dissertation, and continued by Mr. Matteo Caligaris.
Boundary Lubrication by Chondroitin Sulfate
Furthermore, we have shown that interstitial fluid load support and the frictional response of cartilage may be compromised significantly by degradative changes that accompany osteoarthritis. We discovered that chondroitin sulfate, a natural constituent of cartilage, also contributes to reducing friction in cartilage via a boundary lubrication mechanism. The role of this molecule was deduced from a two-pronged approach: Enzymatic degradation of the chondroitin sulfate of cartilage was shown to increase the equilibrium friction coefficient, and supplementation of the tissue bath with chondroitin sulfate was shown to decrease it. These studies were the main topic of Dr. Ines M. Basalo's dissertation.