Characterizing Viscoelastic Modulations in Biopolymer Hydrogels by Coherence-Gated Light Scattering

pH-responsive hydrogels are of great interest for the controlled release of drugs. However, the changes in the structural and mechanical properties of hydrogels during the pH-responsive swelling/contraction process remains largely unknown. In this article, we demonstrate that coherence-gated dynamic light scattering can be used to in situ characterize the structural dynamics of chitosan (CS) hydrogels at different pH values and show that the CS hydrogels undergo viscoelastic modulations during the swelling/contraction/recovery process induced by pH changes. The conditions for the CS hydrogels to undergo these modulations are found by continuously monitoring the nonequilibrium, long-term dynamical process. Our findings are in a close correspondence to the macroscopic observations made at time points where the CS hydrogels are at equilibrium.