Fig. 2

Histology of the uterine transverse sections in the treatment groups. A Hematoxylin and eosin (H&E) staining. The endometrial surface is covered with simple high columnar epithelial cells (white arrowhead); abundant blood vessels (yellow arrowheads); numerous endometrial glands (red arrowheads); and normal uterine cavity are noted in the intact group versus the vehicle group with uterine wall adhesion (black arrowheads), avascularization of stromal tissue, decreased ratio of the endometrium to the myometrium (orange line: endometrium; blue line: myometrium), and abnormal epithelium (green arrowhead). These morphological features were improved in the clonal mesenchymal stem cell (cMSC), heterogenous parental MSC (hMSC), EV20K, and EV110K groups. B MT staining showed mechanical damage increased level of collagen fiber depositions (more areas with dark blue: indicator of collagen fibers intense accumulation) severely in vehicle group comparing intact, but cMSC, hMSC, EV20K, EV110K administration diminished fibrotic area in the endometrium (more areas with light blue: indicator of minor mass of collagen fibers). I: Scale bar 1000 µm, II: Scale bar 200 µm