HYDRATION CHARACTERISTICS OF THE CROSS-LINKED HYALURONAN DERIVATIVE HYLAN

The ability of hylan, the formaldehyde cross-linked derivative of hyal uronan, to interact with water has been studied using differential sca nning calorimetry (DSC). Three types of water can be distinguished: no n-freezing, freezing-bound and free. When the water content of the sys tem is increased, even by up to 10%, almost all the water remains in t he freezing-bound state, with a DELTAH value less than free water. Sev eral metastable states of water can be detected within the structured hylan-water matrix, indicative of defects in the frozen-bound ice stru cture. The maximum amount of non-freezing water, intimately associated with the hydrophilic groups of hylan, corresponds to 13 mol water per disaccharide unit of the hyaluronan chain. The large capacity shown b y hyaluronan entangled networks to build water into their structure co uld also be responsible for their unusually high viscosity and elastic ity after the onset of entanglement. Such viscoelastic properties are the basis for their use in viscosupplementation of arthritic diseased joints.