Characterization of the polysaccharide schizophyllan and schizophyllan-chitosan hydrogel formation by diffusing-wave...

Schizophyllan (SPG) is a semi-flexible, triple-helical polysaccharide with attractive properties as an efficient viscosifying compound and biological response modifier. We report microrheological characterization of schizophyllan as dispersed in solution and the changes associated when crosslinked with chitosan over an extended frequency range using diffusing wave spectroscopy (DWS). A SPG with high molecular weight (M_w = 1.1 × 10⁶ Da) was selectively oxidized in the side chains (20 % or 40 %) to promote Schiff base formation with chitosan (CHI) amine groups, thus inducing crosslinking. The microrheological characterization of the dispersed SPG revealed characteristic features of the semiflexible structure, where also coupling between flexure and longitudinal modes was indicated based on scaling coefficient close to 7/8 of the loss modulus G"(ω) vs ω for ω in the range 3 × 10³-10⁵ rad/s. The in-situ characterization of the gelation process by DWS revealed changes in the scattered intensity-correlation function caused by the embedded colloidal probe-particles, from which the mean-square displacement of the probes and the shear moduli of the SPG-chitosan hydrogel samples were determined for various SPG concentrations and degrees of oxidation. It is found that SPG - chitosan hydrogels can be prepared with a polymer content in the range of 0.5-2.0 mg/mL and that tuning the molecular parameters allowed control of mechanical moduli in soft hydrogels in the range of 0.3 Pa up to 1000 Pa.