FIG. 4.

Histomorphometric and immunohistochemical analyses of bioengineered synovial joint condyle grafts seeded without delivered human cells, with hMSCs, or with hMSC-derived osteogenic cells. After 6 weeks of in vivo implantation, von Kossa staining revealed mineralized tissue accumulation on the wall of the scaffolds' microchannels seeded with MSC-Ob (C), in comparison with little mineralization of the graft seeded with no delivered human cells (A) or hMSCs (B). Osteopontin, a late-stage osteogenesis marker, was immunolocalized on the surface of the microchannel wall of the representative graft seeded with hMSC-Ob (D), corresponding to von Kossa–positive mineral deposition in C. No positive osteopontin was identified with the cell-free PCL-HA scaffold or the hMSC-seeded PCL-HA scaffold (data not shown). Quantitatively, bone volume per total volume in MSC-Ob–seeded grafts was in the range of 11.5% to 19.6% per image analysis of von Kossa–stained sections (I) (n = 10). Safranin O, a cationic dye staining glycosaminoglycans, was positive in the intercellular matrix of the representative graft seeded with MSC-derived chondrocytes (hMSC-Cy) (G), in comparison with little safranin O–positive staining in representative grafts seeded with no delivered human cells (but nonetheless infiltrated by host cells) (E) or the representative graft seeded with hMSCs (F). Type II collagen was immunolocalized to hMSC-derived chondrocytes encapsulated in hydrogel (H). Quantitatively, significantly more cells were present in the hMSC-seeded hydrogel layer than hMSC-Cy (J), suggesting that MSCs are more proliferative than MSC-derived chondrocytes because the initial cell density was equal in both groups. Scale: 400 μm (A–C, F–G), 200 μm (D, H, I). *, p < 0.01. Color images available online at www.liebertonline.com/ten.