Figure 2. Histologic and immunohistochemical characterization of a human-shaped mandibular condyle engineered from mesenchymal stem cells after in vivo implantation. (A) Representative photomicrograph showing positive safranin O staining of the upper cartilage layer, indicating the presence of abundant glycosaminoglycans. In contrast, the osseous portion shows negative safranin O staining. (B) Positive immunohistochemical localization of type II collagen in the cartilage portion. The osseous portion was negative to type II collagen immunolocalization. (C) Positive immunolocalization of osteopontin within the osseous portion. By contrast, the cartilage portion lacks osteopontin expression. (D) Representative micrograph of hydrogel control cell-free construct showing host fibrous-tissue capsule surrounding the construct, but a lack of host cell invasion. Reproduced with permission from Mary Ann Liebert.