Picro-Sirius Red stained section of the interface regions (circled). (a, b) Enzyme treated group, well integrated. (c, d) Untreated control group, not integrated. In panels a and c show crossed polarizing filters without analyzer filter; fibres run in parallel and perpendicular directions relative to the interface. Note the squares around individual chondrocytes, signifying pericellular collagen shell (arrowheads). In panels b and d the same field of view is shown as in panels a and c, but this time with the analyzer filter in place, revealing only those fibres that run in a perpendicular direction relative to the interface(circled), pointed out by the fact that the pericellular fibres that run in the parallel direction have disappeared (arrowheads), as well as the lightening up of the superficial cartilage layer. Clearly visible are the fibres crossing through the interface area, thus connecting both pieces of cartilage (panel b) and fibres along the wound edge projecting into the interface area (panel d). Original magnification: 25×.