Exploring metal ion-induced crosslinking in alginate networks for next-generation functional hydrogel development: a review

Alginate (ALG) is a naturally occurring anionic polysaccharide primarily derived from brown seaweed, consisting of linear chains of β-D-mannuronic acid (M) and α-L-guluronic acid (G) residues. Its biocompatibility, biodegradability, and non-toxic characteristics have rendered it a material of significant interest in the pharmaceutical, biomedical, and food sectors. One of the most notable properties of ALG is its capacity to produce hydrogels via a moderate and controlled process known as ion-induced gelation (IG). IG occurs when ALG chains interact with metal ions, resulting in the formation of three-dimensional crosslinked networks. This review presents an overview of the gelation mechanism of ALGs, emphasising the fundamental principles behind IG. Furthermore, it highlights the significance of various metal ions, covering monovalent, divalent, and trivalent cations, that affect the gelation behaviour and mechanical properties of ALG-based systems. This review elucidates the interactions between ALG and metal ions, thereby augmenting essential information for future investigations in biomaterials and hydrogel systems.