Analysis of growth factor content
1–2 ml of the prepared plasma was separately placed into a tube with ethylenediaminetetraacetic acid and immediately frozen at − 80° Celsius. The mean storage time was about 236. 9 ± 66. 8 days (23–304 days). Samples were thawed at the same time for subsequent ELISA (enzyme linked immunosorbent assay) testing. We examined the concentration of the following GFs using the following ELISA Kits: human HGF #DHG00, human TGF beta 1 #DB100B, human EGF #DEG00, human PDGF #DHD00C (R&D, Minneapolis, USA). All ELISA were performed according to the manufacturer’s instructions. All samples were measured in duplicates and the mean value was calculated.