PLGA-PEG-COOH (100 mg; 1.0 × 10−5 mol), EDC·HCl (8 mg; 4.1 × 10−5 mol) and NHS (5 mg; 4.3 × 10−5 mol) were dissolved in 5 mL of DMSO. After the mixture was stirred for 20 min at 25 °C, cRGD (6 mg; 1.0 × 10−5 mol) was added to the solution. Then, the solution was stirred for another 4 h at 25 °C. To remove EDC, NHS and any residual, non-cross-linked polypeptide, the transparent solution was dialyzed in distilled water for 24 h by using a dialysis bag (MWCO = 3500 Da). Finally, PLGA-PEG-cRGD was obtained as a white powder by vacuum filtration and dried under vacuum at room temperature.
The chemical structure of PLGA-PEG-cRGD was confirmed by nuclear magnetic resonance (NMR) spectroscopy. In addition, the 1H NMR spectrum was measured in deuterated chloroform using a Bruker Avance 400 (400 MHz) spectrometer (Beijing, China). FTIR was measured using a Nicolet NEXUS-670 Fourier Transform Infrared Spectrometer (Madison, WI, USA).
The chemical structure of PLGA-PEG-cRGD was confirmed by nuclear magnetic resonance (NMR) spectroscopy. In addition, the 1H NMR spectrum was measured in deuterated chloroform using a Bruker Avance 400 (400 MHz) spectrometer (Beijing, China). FTIR was measured using a Nicolet NEXUS-670 Fourier Transform Infrared Spectrometer (Madison, WI, USA).