DETERMINATION OF KINETIC CHANGES OF AGGRECAN-HYALURONAN INTERACTIONS IN SOLUTION FROM ITS RHEOLOGICAL PROPERTIES

The kinetics of interactions between aggregating cartilage proteoglyca n (aggrecan) and hyaluronan was examined through their theological Bow behavior using a cone on plate viscometer. The mixing of the two type s of molecules was carried out directly on the plate of the viscometer , and aggregation process was monitored through the changes of the sam ple's steady-shear viscosity and/or dynamic shear modulus as a functio n of time. The effect of flow conditions on the aggrecan-hyaluronan in teraction rates was examined by subjecting samples to steady-shearing motions at specified shear rates, and to oscillatory shear motions of specified frequencies and amplitudes. The characteristics of the kinet ics of interaction between aggrecan and hyaluronan molecules depended not only on the flow conditions under which proteoglycan aggregation t ook place, but also on the concentration of the components in the solu tion. At high shear rates (> 10 s(-1)), viscosity of the mixture solut ion increased monotonically, starting near the viscosity of the aggrec an solution, and reaching the viscosity of the aggregate solution in a pproximately 35 min. Surprisingly, under slow shearing motions (<10 s( -1)), the viscosities of the mixture solutions exceeded those of contr ol aggregate solutions at identical hyaluronan:aggrecan ratios and con centrations. In addition, the aggregation under oscillatory motions to ok place near physiologic frequency (10 rad s(-1)) although the rate o f aggregation process was much slower than under steady-shearing motio n (> 100 min). However, the high-frequency oscillatory shearing (62.8 rads(-1)) tended to impede aggregation resulting in a reduction of dyn amic modulus over time. The influence of loading conditions on the rat e of aggregation and aggregate size observed in this study seems to su ggest a close relationship between proteoglycan structure and content, and degree of physiological stress throughout the joint and frequency of the joint motion.