A silsesquioxane bearing methacrylate and amine groups was synthesized by reacting half of the NH groups of N-[3-(trimethoxysilyl)-propyl] ethylene diamine with glycidyl methacrylate, followed by the hydrolytic condensation of methoxysilane groups. This led to a water-soluble silsesquioxane functionalized with methacrylate and amine groups (SFMA) that was characterized by UV-MALDI TOF MS. A formulation containing safranine-O as sensitizer and SFMA as co-initiator (electron donor)/crosslinker was used for the visible-light photopolymerization of water solutions of 2-hydroxyethylmethacrylate (HEMA) and acrylamide (AAm). Without SFMA addition no reaction was observed while in the presence of 0.8 wt% SFMA with respect to monomers, crosslinked polymers (hydrogels) were obtained. Swelling of the resulting hydrogels in a broad pH range was investigated. (c) 2008 Elsevier Ltd. All rights reserved.