Matrigel (50 μL) was pipetted into each well of a 12-well plate and polymerized for 2 hours at 37°C. HUVECs (1 × 104) in 150 μL of conditioned medium from each treatment group were added to each well and incubated at 37°C in 5% CO2 for 24 h. Pictures were taken under a × 100 bright-field microscope. The experiment was repeated three times.