Fig. 6

Typical histological changes of the non-injection control (a, d, g), saline (b, e, h), and platelet-rich plasma (PRP)-releasate groups (c, f, i) stained with Safranin-O. Moderate-to-severe degeneration was observed in the saline (b, e, h) groups. Regenerative changes were observed in the saline and PRPr groups, including cell cloning and rounded cells with intense pericellular matrix staining (e, f). However, the PRPr group displayed more viable cells and cell cloning than the saline group (e, f). d–f Magnification images of the nucleus pulposus area indicated by squares (a–c). g–i Magnification images of the annulus fibrosus area in a–c, respectively. Scale bars: 1 mm (a–c), 50 μm (d–f), 500 μm (g–i)