Evaluation of the multifunctional MNs on treatment for the KOA rat model. (a) Digital images of knee joints of rats in different treatment groups: the normal group, the d-MN group, the n-MN group, and the control group, respectively. (b) Corresponding Safranin O-fast green staining images. The yellow line indicates the tidemark. (c) Corresponding H&E staining images. The blue arrow indicates the disordered cartilage cells. (d) Corresponding Masson staining images. The black arrow indicates the fibrosis. The scale bars are 4 mm in (a) and 200 μm in (b–d).