Fig. 2

Human AF matrix ultra-structural characterization with herniation progression (n = 3). A a–d: × 5000 magnification, scale bar: 2 μm; e–l: × 12,000 magnification, scale bar: 1 μm. White arrows point to well organized collagen fibres, while red arrows point to disorganized fibres. B Picro-Sirius Red staining under polarized light, scale bar: 500 μm. C Quantification of collagen fibres per birefringence colour. Kruskal-Wallis test followed by corrected Dunn’s were performed. *p < 0.05; **p < 0.01