Effect of preparation method on the hydration characteristics of hylan and comparison with another highly cross-linked polysaccharide, gum arabic

Abstract

The water binding characteristics of hylan are compared with another cross-linked polysaccharide Acacia Senegal gum exudate ( A. Senegal) using differential scanning calorimetry. Both polysaccharide systems bind water effectively, and the transitions characteristic of two types of freezing-bound water can be distinguished from the melting or freezing of free water. There is evidence for the existance of metastable states of freezing-bound water within the two systems. Gum arabic binds considerably less freezing-bound water than hylan systems. A. Senegal does not have the same ability as hyaluronic acid to form structured entangled networks which can incorporate water within the matrix. The hylan samples are of two types: hylan fluid where the hyaluronan chains are crosslinked with formaldehyde, and hylan gel where the cross-linking agent is vinyl sulphone. The hylan gel retains the freezing-bound state of water as a stable thermodynamic state ca 20–50% more effectively than hylan prepared from the freeze-dried solid prepared from either concentrated or dilute hylan fluid. The traps formed from freeze-dried hylan gel are also more stable. Hylan gel prepared by precipitation with isopropanol and freeze-dried is the most effective hylan sample for stabilising the freezing bound state. For this material even in ~6% solution the vast majority of the water is retained in the freezing-bound form.