Construction of double-network hydrogel based on Artemisia sphaerocephala Krasch polysaccharide complexed with gelatin cross-linked by ferric ions and transglutaminase

The major fraction of 60P in Artemisia sphaerocephala Krasch polysaccharide (ASKP) with high molecular weight was reported to be crosslinked by ferric ions to form single-network hydrogels in our previous studies. Here, 60P and gelatin crosslinked by ferric ions and transglutaminase (TG) were employed to fabricate a double-network hydrogel to improve the mechanical properties of the single-network. It was found that the 60P/Fe³⁺-gelatin/TG double-network hydrogel displayed a denser structure with pore size about 20 μm and a significantly enhanced gel strength at 60P: gelatin ratio of 8: 2, 60 mM Fe³⁺, TG: gelatin ratio of 1: 1, and pH 5.0. The elasticity of the double-network hydrogels greatly increased, as presented in the decrease of the platform height in mean square displacement (MSD) and solid liquid equilibrium (SLB) curves. The water holding capacity and swelling ratio of the double-network hydrogels greatly weakened may be due to the restricted water mobility measured by LF-NMR. The interaction between 60P and gelatin was electrostatic interaction proved by QCM-D. These results may be attributed to the fact that the entanglement between the 60P and gelatin via electrostatic interaction formed a dense network. The specific binding of Fe³⁺ to 60P via monodentate and bridging binding formed the first network and acted as the skeleton. The TG-catalyzed gelatin cross-linking via isopeptide bond was developed as the second network and filled in the first gel network, forming the denser double-network hydrogel with enhanced gel strength. This study proposed a new idea to fabricate double-network hydrogel with enhanced mechanical properties, which displayed great potential to be used as a novel gel system in food fields.