Classification of human synovial mesenchymal stem cells (SMSCs) and exosomes. (A) SMSCs exhibited a representative spindle-like morphology (scale bar: 50 μm). (B) SMSCs showed multi-potential differentiation capacity for osteogenesis (scale bar: 50 μm), adipogenesis (scale bar: 20 μm) and chondrogenesis (scale bar: 50 μm). (C) Flow cytometric analysis of characteristic cell surface markers of SMSCs. Unfilled curves represent isotype controls and solid grey curves represent measured surface markers (CD34, CD44, CD45, CD73, CD90, CD105, CD133 and CD151). This experiment was repeated independently three times. (D) Particle size distribution of exosomes measured by dynamic light scattering (DLS). This experiment was repeated independently three times and representative results are shown. (E) Morphology of exosomes observed by transmission electron microscopy (TEM). Scale bar: 100 nm. (F) Exosome surface markers (Alix, CD81, CD9, and CD63) and carried proteins (Wnt5a and Wnt5b) measured using western blotting. This experiment was repeated independently three times and representative results are shown. (G) Representative immunofluorescence photomicrograph of DiO (green)-labelled exosomes absorbed by chondrocytes, the nuclei of which were stained by DAPI (blue). Scale bar: 50 μm.