Development of κ-carrageenan hydrogels with mechanically stronger structures via a solvent-replacement method

Strong κ-carrageenan (KC) hydrogels were fabricated via solvent replacement with sorbitol, and the effects of KC mass fraction and solvent replacement on the structural characteristics encapsulation capability of the hydrogels were evaluated. Microstructural observation showed that the 3D network structures of hydrogels exhibited a complete and continuous skeleton. FTIR spectra of KC hydrogels revealed the formation of intermolecular hydrogen bonds after sorbitol replacement. The stability against heating and freeze-thawing of hydrogels was enhanced due to the addition of sorbitol and the rise in KC mass fraction. The hydrogel with 1.5 wt% KC after sorbitol replacement presented the best stability. Frequency sweep tests suggested that storage modulus of the samples were influenced by sorbitol replacement and KC concentration. Swelling tests revealed that the hydrogels after replacement with a higher KC content (1.25, 1.50 wt%) presented higher swelling capacity, and they were more stable in alkaline and acidic solutions. When epigallocatechin gallate (EGCG) was incorporated within the hydrogels, the hydrogels after sorbitol replacement offered higher protection capability. The information obtained in this study indicated that sorbitol replacement strengthened KC hydrogels, and they could act more appropriately as accountable carriers for bioactives.