2.3.2. Nuclear magnetic resonance spectroscopy (NMR)The chemical structures of HA-DPPE conjugates were confirmed by 1H NMR spectra, which were obtained on a Bruker AV-500 spectrometer(AVACE, Switzerland) with HA and DPPE as controls. Approximately 4 mg of HA were dissolved in 1 mL of D2O, DPPE and HA-DPPE copolymers were dissolved in CDCl3, and all solutions were analyzed using theNMR spectrometer.