Chondrogenic Differentiation. Results of chondrogenic differentiation of pelletted micromasses after 3 weeks. (A) Representative micrographs of differentiated micromasses from passage 1 cells of 6-day-old donors. Safranin O (left), hematoxylin and eosin (middle), and immunohistochemical staining for collagen II (right) staining were used to show the morphological structure and biochemical components of induced pellets. The inset demonstrates the lacunar morphology typically observed in cartilage. Magnification bars represent 100 μm in all images. (B) Micrograms of sulfated GAG per pellet. The '#' sign indicates a significant difference between passage 1 and passage 6 cultures from similarly aged donors, '‡' indicates a significant difference between the indicated group and any passage 1 groups from younger donors, and '¥' indicates a significant difference between the indicated group and any passage 6 groups from younger donors (p < 0.05). At a constant number of passages, significant differences were found across all age groups. Passage related differences were only significant in BMSCs from 1-year-old donors. Error bars designate means ± standard deviation (n = 3).