Expérimental
Second harmonic generation (SHG) microscopy enables imaging of collagen fibrils (10-300 nm diameter) without any labelling and with unequalled sensitivity in intact tissues. This is directly related to the property of SHG to be nonzero only in dense and non-centrosymmetrical materials. Nevertheless, the build-up of this coherent nonlinear signals in heterogeneous collagen-rich tissues (skin, artery, lung, bone…) is a complex issue and proper analysis of SHG images requires complementary information. We have therefore combined SHG with polarimetry, which enables measurements of collagen orientation in each pixel and thus provides in situ quantitative mapping of collagen 3D organization. This is highly relevant as the size and 3D distribution of collagen fibrils governs the biophysical and biomechanical properties of each tissue, and therefore their biological function: opacity and compliance for skin, transparency and rigidity for cornea, stiffness for artery or cervix, etc… pSHG therefore appears as a unique technique to characterize the structure of complex tissues, understand their pathological dysfunctions and develop new diagnostic tools.