Fig. 3

Cartilage regeneration and stability of the implants. a Representative image of immunohistochemical staining of cartilaginous matrix. The protein expression of COL II was increased in the BMSC-Exos and CC-Exos groups, compared to the PBS group. However, COL X is indicative of hypertrophy and was expressed in the BMSC-Exos group, indicating that several of the chondrocytes were exhibiting a hypertrophic phenotype. The black arrows point to the positively stained regions. Scale bars = 50 μm. b, c Western blot of Col II, SOX-9 (markers of chondrogenesis), and Col X, IHH, and MMP13 (markers of hypertrophy) secreted by the implants exposed to different exosomes and PBS. d Gross appearances and immunostaining of CD31 of in vivo implants at 12 weeks. The gross observation showed that the implants with CC-Exos did not lead to any obvious blood vessel formation. However, the BMSC-Exos induced the formation of blood vessels surrounding the implants. CD31 immunostaining and quantification of the density of CD31+ microvessels (MVD) revealed CC-Exos reduced angiogenesis when compared to the control. On the other hand, angiogenesis was promoted in the BMSC-Exos group. Green rectangles: typical CD31-positive vessels, which are in high magnification. In these images, CD31+ are red, and nuclei are blue (DAPI). “V”: CD31-positive blood vessels. Scale bars = 50 μm. e Western blot of VEGF, and SDF-1 secreted by the implants exposed to different exosomes and PBS