Swelling pressures of proteoglycans at the concentrations found in cartilaginous tissues

The osmotic pressure of proteoglycans extracted from human hip, knee and intervertebral disc cartilage and from bovine nasal cartilage, and of chondroitin sulphate was measured by equilibrium dialysis against solutions of polyethylene glycol in 0.15M NaCl and 1.5M NaCl. The osmotic pressure of the proteoglycans at concentrations found in these cartilaginous tissues, viz. 0.08–0.35 meq/gH₂O, was found to lie in the range 0.3–3.5 atm. Molecular size and degree of aggregation were found to have no measurable influence on the value of osmotic pressure. The “Donnan” osmotic pressure was by far the major component; under physiological conditions, not more than 15 per cent of the total osmotic pressure resulted from excluded volume effects.