ABSTRACT
Ultrasound velocity was measured in hyaluronan solutions of various compositions at different temperatures. The velocity dependence on hyaluronan concentration at constant temperature (25 °C) was linear both in water and in 0.15 M NaCl regardless of hyaluronan molecular weight, confirming diluted-solution behavior. During cyclic heating and cooling, hysteresis on the temperature dependence of ultrasound velocity was observed in the range 30-55 °C in aqueous solutions for all molecular weights. In NaCl solutions, the hysteresis was suppressed and, in contrast to solutions in water where the velocity demonstrated a local maximum with temperature, the velocity decreased with increasing temperature. These findings were attributed to slow and hydration-linked hyaluronan conformation transitions during cooling in water, which were suppressed by the presence of salt, which makes hyaluronan's coiled conformation more compact.
