Figure 2.

Cartilage integrity and migration of chondrocytes out of the cartilage matrix. (A) Histological analysis of cartilage surfaces of non-stimulated and TGF-β1-stimulated cartilage/BNC constructs after in vitro culture for two, four and eight weeks. The superficial layer of non-stimulated samples shows clear signs of beginning erosion and mobilization of chondrocytes. In contrast, the surface of TGF-β1-stimulated samples appears rather smooth and intact. Magnification: 200 x. (B) Scanning electron microscopy images display the smooth surface of fresh cartilage in contrast to uneven cartilage surface after eight weeks of culture, most probably caused by the removal of the lamina splendens. Magnification 2,000 x. (C) Migration of chondrocytes out of the dense cartilage matrix onto the cartilage surface and the BNC. Magnification left panel: 1,000 x, center panel: 200 x, right panel: 5,000 x. (D) Semiquantitative analysis of cartilage erosion and migration of cells from cartilage on the BNC. Stained histological sections were evaluated and scored with 0 to 3 points. Degree of erosion 0 = smooth cartilage surface, 1 = loss of lamina splendens, 2 = moderate erosion of superficial cartilage, 3 = massive erosion with complete loss of cartilage surface; degree of cell migration onto the BNC: 0 = BNC without cells, 1 = single adherent cells (<5/cartilage section), 2 = several adherent cells (<20/cartilage section), 3 = confluent cell layer on BNC. Values are shown as mean ± SEM for n = 5 technical replicates each. BNC, bacterial nana-cellulose; SEM, standard error of the mean; TGF-β1, transforming growth factor-β1.

Pretzel et al. Arthritis Research & Therapy 2013 15:R59   doi:10.1186/ar4231
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