Dynamic mechanical analysis of alginate/gellan hydrogels under controlled conditions relevant to environmentally sensitive applications

Hydrogels are suitable for a wide range of applications including wearable sensors, biomedicine and agriculture. However, due to their nature, their performance is sensitive to temperature, humidity, and mechanical strain. In this work, we investigate the mechanical response of filled and unfilled alginate/gellan hydrogels using combined axial-torsional rheometry. Cylindrical samples with large length/diameter ratios are used in a controlled environment. The approach allows dynamic mechanical analysis of the same sample in both torsion and extension under identical conditions in a single measurement run. This ensures consistent initial and boundary conditions, which are essential for reliable estimation of the dynamic moduli G* and E* and their dependence on frequency and environmental factors. Our results indicate that humidity variations critically affect the mechanical response due to the observed sample volume shrinkage, requiring corrections to the moduli. We also find that temperature plays a role only under significant changes in humidity. Unfilled specimens in breaking tests show only slippage due to twist-induced surface water excess, in contrast to the breakage of specimens filled with mesoporous silica particles, which is likely related to restricted water diffusion.