Structure-guided regulation of polysaccharide composite hydrogels by metal ions, nanomaterials, and their synergistic interactions for extrusion-based 3D printing applications

Natural polysaccharide-based hydrogels have emerged as important material platforms in food science and biomedical research; however, the roles among polymer structure, metal ions, and nanomaterials in determining network formation and printability remain insufficiently understood in an integrated framework. This review systematically examines six representative polysaccharides (chitosan, alginate, starch, pectin, hyaluronic acid, and chondroitin sulfate), with emphasis on how their different functional groups govern ion-mediated crosslinking, nanomaterial incorporation, and the synergistic regulation of hydrogel properties. The reviewed literature indicates that these interactions directly affect gelation behavior, mechanical integrity, and functional performance. In the specific context of extrusion-based 3D printing, these factors collectively regulate the critical balance among shear thinning, post-extrusion recovery, and shape fidelity. As a result, these hydrogels have been applied in printed food systems, packaging, tissue engineering, wound dressings, drug delivery, and flexible sensors. The accumulated evidence indicates that successful hydrogel design requires the coordinated consideration of polysaccharide structure, metal-ion interactions, and nanophase reinforcement, rather than reliance on any single modification strategy. Further development will require standardized printability metrics, rigorous evaluation of post-printing stability under end-use conditions, consistent reporting of key material and processing parameters, and robust safety evidence to support practical applications.