2.3.1. Determination of BSA/PLGA microsphere loading efficiency

After preparing microspheres with 100 mg PLGA according to the above method, these microspheres were freeze-dried and weighed. Precisely, 10 mg BSA/PLGA microspheres were dissolved in a solution of 0.9 mL 1 M NaOH and 0.1 mL PBS, stirred at 21 °C for 2 h, and then 1 mL 0.9 M HCl solution was added for neutralization. Using the BCA protein test kit (Biyuntian, Shanghai, China), a 20 μL sample was assessed for BSA determination. BSA loading efficiency (%) was determined as follows: The quantity of BSA (μg)/10 μg × 100 (%).