Green Synthesis of Alginate/Hydroxyethyl Cellulose (SA/HEC) Hydrogels Cross-Linked by Ca²⁺/Mg²⁺ Ions and Their Anti-Microbial Efficacies

Eco-friendly antimicrobial hydrogels derived from carbohydrate polymers are receiving significant attention for their sustainable and cost-effective properties. This study focuses on developing antimicrobial hydrogels based on alginate and hydroxyethyl cellulose (SA/HEC) using a green chemistry approach. The impact of bivalent metal ions on cross-linking efficiency and the hydrogels' physicochemical properties were analyzed, with hydrogels produced in various forms, such as beads, sponges, and films, characterized by SEM, XRD, TGA, FTIR, and UV-vis spectroscopy. Calcium (Ca²⁺), magnesium (Mg²⁺), and Ca²⁺/Mg²⁺ combinations were explored, revealing that Ca²⁺ and Ca²⁺/Mg²⁺ combinations demonstrated excellent cross-linking efficiency, while Mg²⁺ alone was insufficient for cross-linking. However, adding small amounts of Ca²⁺ improved Mg²⁺ cross-linking capacity, yielding stable SA/HEC hydrogels. Beads exhibited porous structures (2–20 µm), and films with a thickness of ~150 µm were produced, showcasing strong mechanical and thermal stability. Additionally, in-situ synthesized silver nanoparticles (AgNPs) within SA/HEC hydrogels exhibited antimicrobial activity against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, and fungal strains Candida albicans ATCC 14053 and Candida krusei ATCC 6258. This study successfully demonstrates a green chemistry method to synthesize water-insoluble hydrogels cross-linked with Ca²⁺/Mg²⁺ ions with inherent antimicrobial properties.