Synthesis of PLGA5k-TK-PEG2k-FA

PLGA_5k-TK-PEG_2k-NH2 was further modified with FA. The specific method was to dissolve FA (0.088 g, 2 mM), DMAP (0.012 g, 0.1 mM), and DCC (0.412 g, 2 mM) in 30 mL cold DMF of under the protection of nitrogen. After activation for 30 min, a 5 mL DMF solution containing 1 g PLGA_5k-TK-PEG_2k-NH₂ was added into the mixture drop by drop, and the reaction continued for 24 h at room temperature. After the white precipitate was filtered, the concentrated filtrate reprecipitated in the cold n-hexane. The product PLGA_5k-TK-PEG_2k-FA was vacuum-dried at 25°C for 6 h (yield = 79%) and characterized by 1 H NMR (Figure 1A).