Glycine‐assisted catalysis of sol‐gel process for the synthesis of biocompatible hydrogels

Sol-gel can be used for hydrogel cross-linking, opening an attractive route to design biocompatible hydrogels in soft conditions. Sol-gel can be catalysed at basic and acidic pH or around neutrality with the addition of a nucleophile. Therefore, working around pH 7, unlocks the possibility of direct cell embedment and the preparation of bioinks. With the aim of proposing a generic method for sol-gel 3D bioprinting, we first screened different nucleophilic catalysts using bis-silylated polyethylene glycol (PEG) as a model hydrogel. A synergistic effect of glycine and NaF, used in low concertation to avoid any toxicity, was pointed out. Biocompatibility of the approach was demonstrated by embedding primary mouse mesenchymal stem cells. The measure of viscosity as a function of time showed the impact of reaction parameters on the kinetics of the sol-gel process, such as temperature, complexity of the medium, pH and cells addition, to predict the gelation time.