Fabrication of thermo-sensitive hydrogels based on the Diels-Alder reaction and study on their in vivo biosafety

The goal of this study is to develop a novel injectable hydrogel, referred to as PPMF, and evaluate its biosafety profile. The PPMF polymer, which serves as the gelation precursor, was synthesized through a redox radical polymerization and amidation process. The molecular structures of the synthesized polymers were thoroughly characterized using ¹H nuclear magnetic resonance (¹H NMR) and Fourier transform infrared spectroscopy (FTIR). The PPMF hydrogel was formed via Diels-Alder reactions between the PPMF polymer and four-arm polyethylene glycol maleimide (4-armed-PEG-Mal) cross-linkers. A comprehensive assessment was conducted to evaluate the hydrogel's injectability, swelling ratios, hematotoxicity, biodegradability, and overall biosafety. Both FTIR and ¹H NMR spectra confirmed the successful synthesis of the PPMF polymers. The results revealed that the PPMF hydrogel demonstrated remarkable injectability, favorable swelling ratios, and minimal in vitro cytotoxicity. Upon subcutaneous injection into Kunming mice, the PPMF hydrogel degraded and was absorbed within 25 days. Importantly, the PPMF hydrogel showed no significant physiological or pathological changes in the internal organs of the treated mice. No inflammatory responses were observed at the injection sites, and blood routine and biochemical tests further emphasized the hydrogel's excellent biocompatibility and safety. In conclusion, the PPMF hydrogel's outstanding biosafety and unique properties make it a promising candidate for a wide range of applications in biological fields.