Linear and nonlinear rheological properties of gelatin-chitosan hydrogels: Evaluation of crosslinker concentration and temperature effects

This study provided insights into how varying temperature (4 degrees C and 37 degrees C) and genipin (GP) concentration affect the viscoelastic properties of gelatin:chitosan (Gel:Chi) hydrogels, as examined through small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) measurements. Frequency sweeps were conducted to capture changes in the microstructures of the gels before and after the application of large deformations. At 37 degrees C control hydrogels exhibited more liquid-like behavior (tan delta >1) up to gamma(0):10% while at 4 degrees C, they displayed solid-like gel behavior (tan delta <1) across all strain values. G ' remained higher than G '' across all strain levels for all hydrogels prepared with GP, with no crossover observed. As the material transitioned into the LAOS region, there were notable changes in the direction and shape of the elastic Lissajous-Bowditch curves. Beyond gamma(0):102%, the curve deviated from the elliptical shape and narrowed upward, suggesting intra-cycle strain-stiffening behavior at large strains. All hydrogels showed strain-stiffening (e(3)/e(1) > 0) and shear-thinning (v(3)/v(1) < 0) behavior in the nonlinear viscoelastic region, except for the control_37 degrees C. The effect of LAOS deformation on G ' and G '' was more pronounced than viscosity. These findings suggested that incorporating Chi with Gel can improve the mechanical properties of the gels and the gel structure could be adjusted by varying the GP concentration and temperature to achieve the desired elasticity.