Figure 1.

Experimental design. Porous cylindrical scaffolds (4 mm in diameter × 2 mm high) were made from a silk fibroin solution using the HFIP-based salt-leaching technique, and seeded with human bone marrow MSCs from a consistent pool. The MSCs were differentiated in parallel into two ossification pathways. Hypertrophic chondrocyte constructs (Hyper) were derived from MSCs by cultivation in a chondrogenic medium for 2 weeks and then matured to hypertrophic chondrocytes over 3 weeks in a hypertrophic medium to mimic endochondral ossification. Osteoblast constructs (Osteo) were cultured for 5 weeks in an osteogenic medium to generate osteoblasts and mimic intramembranous ossification. After in vitro cultivation, scaffolds from each ossification pathway were implanted subcutaneously in nude mice and harvested for analysis at 3 weeks, 6 weeks, and 12 weeks after implantation.