Poly(gamma-glutamic acid) based thermosetting hydrogels for injection: Rheology and functional parameters evaluation

Biocompatible thermosetting hydrogels are attractive compounds either for the delivery of drugs or as medical devices for tissue regeneration purposes. In this work Poly(Gamma-Glutamic Acid) (G-PGA) and G-PGA based hydrogels were explored. The hypothesis was to evaluate G-PGA and crosslinking agents combinations in order to obtain thermosetting hydrogels suitable for injection. Attention focused on hydrogels that can form by ionic interaction with compounds bearing amine groups, and/or by interaction with polymers such as chitosan and symmetric triblock copolymer (polyethylene glycol-polypropylene glycol- polyethylene glycol). Polymer solutions and related hydrogels characterization involved: rheologic behavior, osmolarity, syringeability and injectability. Results showed that G-PGA solutions syringeability was always acceptable, while injectability test did not meet aspiration by 22G needle. Osmolarity value suitable for injection could be obtain by adding buffering solutions. Only ternary blends made of chitosan, sodium beta-glyceroposphate and -PGA, or G-PGA, Pluronic F68 and L-lysine, with fixed compositions, resulted in thermosetting gels. The obtained thermosetting gels were not reversible.