Design of polygalacturonate hydrogels using iron(II) as cross-linkers: A promising route to protect bioavailable iron against oxidation.

•We prepared highly reproducible iron(II)-polygalacturonate hydrogels by external diffusion of Fe(II).•These hydrogels are heterogeneous at macroscopic scale but have a constant mesh size.•Iron/polymer ratio is constant within the hydrogel, despite the high concentration gradient.•These hydrogels protect iron(II) against oxidation even in oxidative conditions.•We propose a gelation mechanism that explains the relationship between macroscopic heterogeneities and the local structure.