The in vitro release curve of nanoparticles in simulated body fluid (37 °C, pH 7.4, n = 3). A rapid release was observed from time 0 h to 12 h, with a cumulative release percentage of 32.4%; a smooth slow-release occurred between day 1 and day 8, with a cumulative release percentage of 93.50%. During days 8 to 10, the release reached a plateau, with a cumulative release percentage of 95.70% at day 10.