Chondrogenic priming of MSCs seeded into Collagen GAG scaffolds in-vitro leads to bone formation in-vivo. Figure 1A; Chondrogenic potential was confirmed in all three donors by PCR (donors 1 and 2, expression relative to undifferentiated donor matched controls) and collagen type II immunohistochemistry (Figure 1Aii Donors 1-3). Figure 1Aiii, Toluidine Blue staining of a chondrogenically primed scaffold prior to implantation. Figure 1B Micro computed tomography of retrieved constructs (resolution 8.1 μm per pixel). The pattern of bone formation observed histologically matched closely with these images showing bone tissue at the edges of the constructs. Mineralised matrix that did not form bone was also observed in all constructs as well as empty scaffold controls. Figure 1C; Hameatoxylin and Eosin staining of bone formation in chondrogenically primed constructs (1Ciii) as compared to constructs cultured in osteogenic (Figure 1Cii) medium for 4 weeks. While osteogenically primed samples were more mineralised compared to in-vitro samples, no true bone formation was observed. Switch from chondrogenic to osteogenic medium for 7 days also prevented in-vivo bone formation (Figure 1Civ). Insets represent lower magnification images of the constructs. Arrow indicate blood vessels in each construct.