Directed Ion Transport as Virtual Cause of Some Facilitated Friction–Lubrication Mechanism Prevailing in Articular Cartilage: A Hypothesis

Based on certain characteristics of the acid–base quasi-equilibria and on structural properties of the synovial inhomogeneous fluid in a model articular cartilage (mAC), we try to hypothesize on its facilitated friction–lubrication mechanism. We opt for a scenario that under departure from the acid–base, pH-dependent equilibrium, directed transport of protons (H⁺) is plausible, leading to a certain synergistic kinetic–thermodynamic pathway of the system as a whole. It can be viewed in such a way that protons, and virtually, other ions such as OH⁻; Ca²⁺, may pass through the (intra)micellar, possibly elongated spaces, playing their roles as if they were transported along temporarily formed ion (mainly, H⁺) transmembrane channels. Such a hypothetical scenario would thoroughly contribute to some electrostatics-aided, interstitial (synovial) biofluid pressurization, often reported by experimentalists as the appropriate mechanism of facilitating the lubrication in a real articular cartilage (rAC) in microrheological conditions, encountered in articulating joints of mammals.