ABSTRACT
Articular cartilages swell and shrink depending on the ionic strength of the electrolyte they are bathed in. This electro-chemomechanical coupling is driven by the fixed electrical charge borne by proteoglycans. The electrolyte contains mainly sodium cations and chloride anions but also, under nonphysiological conditions, hydrogen and hydroxyl ions. Therefore, variation of the pH of the electrolyte has strong implications on the electrical charge of cartilages and, by the same token, on their transport and mechanical properties. In fact, as the pH of the tissue decreases, the overall fixed charge becomes less negative. It vanishes at the so-called isoelectric point and becomes positive as pH decreases further. The presence of the hydrogen ions and hydroxyl ions, in addition to metallic ions, affects strongly the transport properties as well.
