Morphology of primary cultured and sub-cultured CPSCs. A–I, representative cellular morphologies of CPSCs from passage 0, 1, 3, 5, 10, 15, 20, and 25, respectively (40×). J, the growth curves of CPSCs from P3, P15, and P25 were all typically sigmoidal; the cell density is reflected by the vertical axis. The growth curves consist of the latent period, logarithmic period, stable period, and decline period. The population doubling times (PDTs) during the logarithmic, stable, and decline periods were about 39.66 ± 9.11 h, 40.38 ± 8.89 h, and 43.06 ± 8.84 h, respectively.