Quantitative analysis of the effects of hyaluronan and aggrecan concentration and hyaluronan size on the elasticity of hyaluronan–aggrecan solutions

Abstract

We determined elasticity (G′) and viscosity (G″) of various aggrecan–hyaluronan solutions using a controlled‐stress rheometer with high (10 Hz) to low (0.1 Hz) frequencies. Aggrecan solution (50 mg/ml) alone showed little elasticity at any frequency, but the addition of 3300 kDa hyaluronan at 0.001–0.1 mg/ml markedly increased the elasticity, but not the viscosity, at all frequencies. Increasing hyaluronan concentration at >0.1 mg/ml did not further increase the elasticity of the aggrecan solution, and the elasticity of the aggrecan–hyaluronan complex solution reached a plateau at a 500 :1 (w/w) ratio. In studies with increasing concentrations of aggrecan and a constant concentration (0.5 mg/ml) of 3300 kDa hyaluronan, aggrecan induced elasticity only at >20 mg/ml, indicating the presence of a critical concentration for elasticity. In the presence of 50 mg/ml aggrecan, 1000 kDa hyaluronan had far less effect on the elasticity of the aggrecan solution than did 3300 kDa hyaluronan. These findings suggest that only ∼50% reduction in aggrecan concentration (<20 mg/ml), or reduced hyaluronan size (<1000 kDa) – compared with their physiological levels in young cartilage – can abolish the elastic network of the aggrecan–hyaluronan complex.