Alginate crosslinking beyond calcium: Unlocking the potential of a range of divalent cations for fiber formation

Alginate is a promising biopolymer for functional materials' preparation due to its biocompatibility, biodegradability, and high reactivity with metal cations. This study aims to advance the understanding of the crosslinking dynamics of alginate hydrogels, with the hypothesis of developing a reliable wet spinning method for preparing tunable alginate fibers crosslinked not only with Ca2+, but also with Sr2+, Ba2+, Mn2+, Cu2+, Zn2+. We optimized several parameters to successfully produce fibers with consistent cross-sections and lengths of up to several meters. Our findings show that the type of crosslinker significantly affects the fibers' morphology, water absorption, and mechanical properties. Notably, fibers exhibited high Young's modulus and ultimate tensile strength. Small angle X-ray scattering analysis revealed correlations between the polymer chain organization and the metal ion affinity, impacting swelling capacity and thermal stability. This comprehensive comparison of M2+-crosslinked alginate fibers, ensured by consistent preparation conditions, fills a gap in the literature. Our results highlight the tunability of these fibers' properties, making them suitable for applications such as wound healing, water purification, and flame retardancy.