Fig. 1

Characterization of osteochondral extracellular matrix (ECM). Femoral condyles used to isolate the subchondral matrix were stained with safranin O-fast green to verify the removal of the articular cartilage and the presence of calcified cartilage interspersed with the subchondral bone (a–b). The digital micrographs represent the status of the cartilage before (a) and after articular cartilage removal (b). Isolated osteochondral ECM strips were stained for the presence of mineralized ECM using von Kossa staining (c–d). The osteochondral strip in c (center) was un-treated whereas the osteochondral strip in d (center) was decalcified prior to staining. Both strips are displayed next to cortical bone slices (c–d, left) and decalcified cortical bone slices (c–d, right), serving as references of calcified matrix. Scale bars represent 1 mm (a–b) and 6 mm (c–d)