Figure 4. Osteogenesis driven by MSC-derived chondrogenic cells in ex vivo samples. (A) Positive reactions of MSC-derived osteogenic cells to alkaline phosphatase (white arrow) and von Kossa silver stain (green arrow) following four-week incubation in oseteogenic medium. (B) Monolayer culture of MSCs from the same population as in (A), cultured for 4 wks with DMEM/FBS but without osteoinduction factors, showed no positive reaction to either alkaline phosphatase or von Kossa silver stains. (C) Von Kossa silver-stained section of PEG-hydrogel encapsulating MSC-derived osteogenic cells showing mineral nodules. (D) The same population of MSCs encapsulated in the PEG-hydrogel construct without exposure to osteogenic medium showed no evidence of mineralization by von Kossa silver staining.