A pH/Thermo-responsive Injectable Hydrogel System Based on Poly (N-acryloylglycine) as a Drug Carrier

Anovel physically cross-linked, injectable poly(N-acryloylglycine) (PNAG) hydrogel was synthesized based on glycine. The molecular structures of the corresponding monomer and polymer have been confirmed by FTIR and 1H NMR measurements. The sol-gel transition behaviours of PNAG in its aqueous solution were evaluated using test tube-inversion method, as a function of PNAG concentration, pH and ionic strength. PNAG showed a remarkable injectability originating from the H-bonding interaction among amide and carboxyl groups in PNAG chains and water molecules. The swelling behaviours of hydrogel PNAG were systematically investigated at different temperatures and PNAG concentrations. It was found that the PNAG hydrogel demonstrates distinct temperature responsive nature. Using caffeine as a model drug, in vitro drug release behaviour showed that the release rate of caffeine from PNAG hydrogel apparently dropped as PNAG concentration of the system was increased, while the temperature and pH decreased. The amount of caffeine released from PNAG hydrogel, within 120 min, was 69% at room temperature, whereas 88% caffeine was diffused into the medium at 37°C. In addition, PNAG has shown a certain degree of degradability at pH 2.2 of phosphate buffered saline. In this respect, PNAG hydrogel seems to become a promising injectable material in the biomedical field due to its injectability and degradability potentials.