Structurally optimized λ-carrageenan hydrogels via GMA functionalization and sepiolite reinforcement

Lambda-carrageenan (LC), unlike its κ and ι homologues, exhibits low thermal gelation capacity and limited structural strength; however, it has a higher density of sulfate groups, offering multiple interaction sites but a poor ability to form stable gels. In this study, a structural modification strategy is presented through the methacrylation of LC using glycidyl methacrylate (GMA), complemented by structural reinforcement with sepiolite as a filler agent. A D-optimal experimental design was applied to evaluate the effect of the GMA/LC mass ratio (1-3) and solvent volume (3-10 mL) on the performance of the resulting hydrogels. The resulting formulations exhibited complex viscosities ranging from 2.63 to 146.65 Pa·s, storage moduli (G') in the range of 14 to 910 Pa, and swelling percentages from 4% to 31%, depending on the degree of modification. Further studies on sepiolite incorporation significantly improved the mechanical and swelling properties of the hydrogel optimized through the experimental design (using a 1:2 mg/mg modification ratio and 6 mL of solvent), reaching G' values above 3000 Pa and a swelling capacity of 90% with an optimal sepiolite loading of 20% w/w-an approximate 60% increase compared to the hydrogel without filler. These findings demonstrate that the synergistic combination of LC chemical functionalization and sepiolite reinforcement enables the development of structurally optimized and tunable hydrogels with potential for advanced functional applications.