Mechanical reinforcement via amine-functionalized mesoporous silica fillers in gellan/alginate hydrogels under axial-torsional strains

Hydrogels are suitable for many applications: biomedicine, bio-printing, wearable sensors, etc. However, due to their aqueous nature, they are sensitive to humidity and mechanical strain. Previously [1], we investigated the response of alginate/gellan hydrogels with and without non-functionalized silica fillers using combined axial-torsional rheometry. Dynamic mechanical analysis was performed on the same cylindrical sample in a single measurement in torsion and extension under identical environment, allowing reliable estimations of moduli G* and E*. In the present work, we crosslinked amine-functionalized silica fillers to alginate and gellan polymers using glutaraldehyde (GTA) or genipin (GN) crosslinkers. Frequency sweeps show increase factors of 1.4 for GN, and 1 for GTA in torsion, and 1.3 for GN, and 1.1 for GTA in extension. Torsional breaking rod tests were also performed, where a slight strain increase at break was observed without further stress improvement for the GTA sample. Positively, higher strain and stress at break were observed for the GN sample. In the GTA sample, particle–particle network is rigid but poorly connected to matrix, resulting in a reinforcement under large deformations but no enhancement of small-strain stiffness. GN forms an integrated polymer–particle–polymer network, improving both stiffness and toughness through flexible[1], cohesive bonding. Corroboration is now addressed by Raman spectroscopy and X-Ray analysis.

[1] Segovia-Gutiérrez, J. P.; Rodríguez Agudo, J. A.; Utz, J.; Germann, N. Carbohydr. Polym. 2025, 352, 123180.