Contributions of Proteoglycans to the Biotransport and Electrical Properties of Articular Cartilage: An Experimental Study

Proteoglycans (PGs) are one of the major components in the extracellular matrix (ECM) of cartilage, and are negatively charged due to the charged groups attached to their backbone (i.e., fixed charge groups). PGs play substantial roles in the mechanical, biotransport and electrical events within the tissue.^3,7 More specifically, swelling pressure generated by the interaction between fixed charge groups and ionic interstitial fluid enhances cartilage’s capacity of load-bearing. In addition, biotransport properties (e.g., hydraulic permeability) and electrical properties (e.g., electrical conductivity) have been shown to be affected by water content (i.e., porosity) and fixed charge density (FCD).^2–4 The alteration of proteoglycan content will affect the tissue FCD and water content, which could cause the changes in biomechanical, biotransport and electrical properties of the cartilage. The relationship between the PG content and biomechanical properties has been widely studied,^6,8 but the knowledge on the effects of PG content on biotransport and electrical properties is limited.¹ It is not clear whether the dependences of biotransport and electrical properties on PG content are mainly due to electric effects through the FCD associated with PGs or due to hindrance effects related to the effective pore size (i.e., water content) of the tissue. Therefore, the objectives of this study were (1) to investigate the effects of PG content on cartilage biotransport and electrical properties, (2) to analyze whether these effects are caused by changes of water content or FCD.