Glass Transition of Hyaluronic Acid Hydrogel

Abstract

The glass transition of hyaluronic acid hydrogel samples with various water contents ranging from 0 to 0.5 (grams of water per gram of dry hyaluronic acid) was investigated by differential scanning calorimetry (DSC). Water in hydrogel was classified into three types: non-freezing, freezing bound, and free water. For Wc values less than 2.0, hydrogel formed the glassy state by cooling from room temperature to 150 K at 10 K/min. The difference in the heat capacity (ΔCp,) between the glassy state and the liquid state at Tg was measured. The Tg of the system with Wc values higher than 0.5 agreed well with the calculated Tg, assuming the following equation: [formula omitted], where [formula omitted], which are experimentally obtained from the water-hyaluronic acid system with [formula omitted] which are obtained from amorphous ice. The weight fraction (ø2) of the glassy water was estimated from the heat of cold crystallization according to the following equation [formula omitted], where ø1 w1 and w2 are weight fraction of hyaluronic acid, amount of hyaluronic acid and of glassy water, respectively. The ΔCp, of glass water (ΔCp2) was estimated by asumming [formula omitted] where ΔCp is the observed value. The obtained ΔCp value extrapolated to the high Wc range corresponded well with the value of amorphous ice. This result suggests that the state of the glassy water in the system is similar to that of the amorphous ice. © 1989, The Society of Polymer Science, Japan. All rights reserved.