Circular-dichroism SHG microscopy probes the polarity distribution of out-of-plane collagen fibril assemblies

Second harmonic generation microscopy (SHG) is now the gold standard technique for in situ visualization of unstained fibrillar collagen in intact tissues [1] . Collagen is the most abundant protein in mammals and is found in many tissues, such as arteries, skin, bone and cornea. The size and the three-dimensional distribution of collagen fibrils are key distinctive features of every tissue that are crucial for its functional behaviour, notably its mechanical properties. In situ characterization of collagen 3D distribution is therefore a major biomedical challenge.