2.8. Cell proliferation assay

The ESCs at the logarithmic growth phase were trypsinized using 0.25% Trypsin‐EDTA (Gibco) and plated on 48‐well plates at a density of 5000 cells/well and cultured for 1‐5 days. Cell proliferation was examined using the Cell Counting Kit‐8 (CCK‐8) kit (Solarbio), following the manufacturer's instructions. Briefly, 1/10 volume of CCK‐8 reagent was added into the culture medium in each well and incubated for 2 hours. The absorbance of each well at 450 nm was measured using a BioTek spectrophotometer.