Photoresponsive nanometer-scale iron alginate hydrogels: a study of gel-sol transition using quartz crystal microbalance

Alginate/Fe3+ hydrogels were fabricated on hyaluronic acid (HA) and polyallylamine hydrochloride (PAH) multilayers to yield photoresponsive nanometer-scale hydrogels. Light irradiation of the resulting hydrogels induced the photo-reduction of “hard” Fe3+ to “soft” Fe2+ cations, leading to changes in the mechanical properties of the hydrogels related to their crosslinking behavior. The buildup and the photo-triggered response of the supported alginate hydrogels were followed in situ by quartz crystal microbalance (QCM) using an open cell allowing light irradiation from a LED source on top of the hydrogel. The results were correlated to the release profiles of folic acid, employed herein as a drug model, obtained from light irradiated supported iron alginate hydrogels.