Porphyra yezoensis has attracted much attention due to its gelling properties and bioactivity. In this study, the chemical structure of Porphyra yezoensis polysaccharides (PYPSs) was characterized, and the effects of concentration, temperature, pH, and calcium ion (Ca²⁺) addition on the rheological properties of PYPS were systematically investigated. Chemical composition analysis indicated that PYPS primarily contained galactose (89.76%) and sulfate (15.57%). Rheological tests demonstrated that PYPS exhibited typical pseudoplastic properties, with apparent viscosity increasing with an increasing concentration. Temperature elevation from 30 °C to 90 °C weakened the intermolecular forces and reduced the apparent viscosity, whereas neutral pH (7.0) provided an optimal electrostatic equilibrium to maintain the highest viscosity. Ca²⁺ could modulate the interactions between PYPS molecules and affect the formation of the gel network structure. When the Ca²⁺ concentration reached the optimal value of 6 mM, the calcium bridges formed between Ca²⁺ and PYPS molecules not only enhanced the rheological behavior and textural properties but also formed a smooth and well-ordered network structure, achieving the highest value of fractal dimension (D_f = 2.9600), though excessive Ca²⁺ disrupted this well-ordered structure. Furthermore, PYPS possessed significant scavenging ability against DPPH, ABTS, and HO• radicals, demonstrating its potential application as a natural antioxidant in functional foods.

To advance seaweed polysaccharide applications in hydrogel wound dressings, five antibacterial composite hydrogels (groups A~E) were synthesized using oxidized κ-carrageenan (OKC), acrylamide (AM), and progressively increasing concentrations of silver-based metal–organic frameworks (Ag-MOFs). Systematic characterization revealed concentration-dependent effects: (1) positive correlations were obtained for the moisture content (MC, maximized at 82.70% in E) and antibacterial efficacy (dose-dependent enhancement); (2) negative impacts were obtained for the swelling ratio (SR, E: 479% vs. A: 808%); and (3) high-dose drawbacks but low-dose benefits in terms of water resistance (WR), tensile strength (TS), elongation at break (EB), and microstructure were obtained. Group B demonstrated optimal Ag-MOFs loading, enhancing TS and EB, while excessive Ag-MOFs loading in C~E significantly degraded them (p < 0.05). Microstructural analysis showed severe 3D spatial damage in D~E. Furthermore, cytocompatibility assessments revealed that all groups maintained a cell viability exceeding 90%, demonstrating excellent biocompatibility. Among them, A~C showed a viability statistically equivalent to the control (p > 0.05) and were significantly higher than D~E (p < 0.05). In conclusion, group B emerged as the optimal Ag-MOFs formulation and exhibited superior WR, enhanced mechanical strength (TS and EB), and potent antibacterial activity while maintaining microstructural integrity and excellent biosafety. This Ag-MOFs/OKC/PAM hydrogel provides dual infection prevention and tissue support, maximizing seaweed polysaccharide benefits with excellent biocompatibility.

The aim of this study was to investigate the hypoglycemic activity and mechanism of G. lemaneiformis polysaccharide gels (GLP and GLP-HV) based on IR/IRS-2/PI3k/Akt/Glut4 and glycometabolism signaling pathways in HepG2 cells. After H₂O₂-Vc degradation, the molecular weight of G. lemaneiformis polysaccharide gel declined from 1478 kDa to 16 kDa. Molecular weight chromatogram and distribution indicated that GLP-HV had a high molecular weight homogeneity compared to GLP. G. lemaneiformis polysaccharide gels significantly decreased the TC, TG, LDL-C, MDA, and LDH contents and enhanced the activities of HDL-C, T-AOC, CAT, GSH-PX, SOD, insulin, and glycogen in HepG2 cells. Fluorescent staining results showed that G. lemaneiformis polysaccharide gels reduced ROS and calcium ions levels in HepG2 cells. GLP and GLP-HV displayed excellent hypoglycemic activity, with GLP-HV performing better. Furthermore, qPCR and Western blot analysis revealed that G. lemaneiformis polysaccharide gels remarkably strengthened the levels of IR, IRS-2, PI3K, Akt, Glut4, HK, G6PD, PFK, PEPCK, GK, PK genes, and proteins. Spearman’s correlation analysis revealed that the IR/IRS-2/PI3k/Akt/Glut4 signaling pathway played a dominant role in regulating activity. These results show that G. lemaneiformis polysaccharide gels present a prominent hypoglycemic effect mediated by the IR/IRS-2/PI3k/Akt/Glut4 and glycometabolism signaling pathways, with the former playing a dominant role.