Reversible photo-induced formation of iron alginate hydrogels

Abstract

Sodium alginate is well-known to be crosslinked by various polyvalent metal ions. While calcium ions (Ca²⁺) are being the most used, the crosslinking of alginate with other metal ions such are under much less attention as seen in the literature. For instance, Fe²⁺ and Fe³⁺ ions can also crosslink sodium alginate, though with varying strengths. A change in the charge of the iron ion can significantly affect the hydrogel’s crosslinking density, potentially leading to full dissolution. This study demonstrates a novel approach to reversibly control of alginate hydrogel formation and dissolution using visible light as an external stimulus. Visible light irradiation (450 nm) of alginate solution leads to crosslinking of the alginate chains and forming a hydrogel. Conversely, treatment with 405 nm visible light induces hydrogel’s full de-crosslinking and reversion to a solution. Notably, this process can be performed in a single step via visible light irradiation. The photochemical processes are rapid leading to gelation and re-gelation occurring within minutes. Envisaged applications of reversible photo-induced gelation are under discussion.