Fig. 5

Ultrastructure and micro-mechanical stiffness of peri-ductal tissue in patients with low and high mammographic density (MD). a, b Atomic force microscopy (AFM) height maps of tissue of low (a) and high (b) MD captured at 150 × 150 μm and a sampling frequency of 4992 × 4992. Arrows indicate collagen fibril bundles (fibres) in high MD breast tissue. aii, bii Magnified regions corresponding to the boxes in ai and bi. Low MD tissue, as depicted (ai and aii) was characterised by the presence of loose fibrillar collagen bundles. However (bi, bii), the central large fibrillar bundle is connected to surrounding tissue by a network of fine fibrils (150–450 nm diameter). c, d H&E-stained breast biopsies from patients with low and high MD. Mechanical data were measured by atomic force microscopy (AFM) indentation (20 × 20 points) in 25-μm² peri-ductal regions, shown in blue (low MD) and red (high MD) boxes. e, f Peri-ductal regions were significantly stiffer in patients with high MD compared with low MD (n = 12 patients, p <0.005)