The function of aggrecan in articular cartilage. Proteoglycan aggregates are depicted as being entrapped by collagen fibrils. In the relaxed state the aggregates swell as the anionic chondroitin sulfate and keratan sulfate chains draw water into the tissue until an equilibrium is attained in which swelling is balance by tensile forces in the collagen fibrils. Under compression, water is displaced and the chondroitin sulfate and keratan sulfate chains are brought into closer proximity, so increasing their swelling potential and balancing the applied load. The increased swelling potential is dissipated upon removal of the load as the original equilibrium is restored.