Highly flexible thermoresponsive alginate-containing hydrogels: Curcuminoid encapsulation and its release kinetics and mechanism.

This study developed upper critical solution temperature (UCST)-responsive semi-interpenetrating network (semi-IPN) hydrogels incorporating poly (acrylic acid-co-acrylamide) (P(AA-co-AM)) and alginate via one-pot free radical polymerization for controlled curcuminoid extract release. Alginate was incorporated to improve the hydrogel's mechanical properties while preserving the UCST responsiveness of P(AA-co-AM). It enhanced swelling capacity, elasticity, and network uniformity. Morphological analysis revealed a uniform porous network, and mechanical testing confirmed optimal flexibility at 5 % alginate, with elongation at break exceeding 551 %. The curcuminoid extract exhibited the IC50 values for antioxidant activity of 13.81 μg/mL (DPPH assay) and 12.64 μg/mL (ABTS assay), comparable to those of the positive control. Encapsulation efficiency reached 1.04 mg/g of hydrogel, ensuring high and stable curcuminoid extract retention within the semi-IPN networks. Release studies at 20 °C and 40 °C confirmed temperature-triggered diffusion, with minimal release rate at 20 °C (below the UCST) and enhanced release rate at 40 °C (above the UCST). Kinetic analysis identified Fickian diffusion as the dominant mechanism with minor contributions from hydrogel relaxation, as supported by the Korsmeyer-Peppas and Peppas-Sahlin models (R2 > 0.98). These findings indicate that the semi-IPN hydrogels are promising candidates for temperature-responsive, tunable encapsulation and controlled bioactive release.