Isolation of exosomes
The human umbilical cord was taken from a full-term infant, cut into small pieces, and cultured. Cells were split when the cells reached 80–90% confluence. In the following procedures, only P5 generation cells were used. After the cells grew to 70% confluence, the culture medium was discarded, the cells were washed thoroughly with PBS, and the medium was replaced with serum-free medium for 48 h. Next, the conditioned medium was collected, centrifuged at 1000 ×g for 20 min to remove cell debris, and centrifuged at 2000 ×g for 20 min, and the supernatant was filtered using a 220-nm filter. Next, the filtered supernatant was centrifuged at 10,000 ×g for 60 min at 4°C, and the supernatant was filtered using a 220-nm filter again. The filtered supernatant was centrifuged at 100,000 ×g for 3 h at 4°C, the supernatant was discarded, the pelleted exosomes were diluted in 1 ml of pulse medium, and the effective diameter of exosomes was assessed by dynamic light scattering (DLS, Brookhaven Instruments).