Figure 7: IHC of COL II (a) and COL I (b) in micromass cartilages. COL II expressed at weeks 2–4 (a), and COL I expressed at weeks 1–4 (week 3 not shown, b), in micromass cartilages. Articular cartilage of rat knee and human tracheal cartilage served as positive control for COL II; higher magnification of week 4 micromass cartilage shows that it is present in ECM (a). COL I is absent in native articular cartilage in positive control and is present in bone only, whereas COL I is expressed at low level in the bioengineered micromass cartilage (b). Micromass cartilage and rat tibia showed no staining when primary antibody was missing and only mouse IgG was present, which served as negative control (c). M, meniscus; AC, articular cartilage; B, bone; mm, micromass.