Label-free investigation of human collagen morpho-mechanics by correlative SHG, Brillouin, and Raman microscopy

Tissue morpho-mechanics is gaining an increasing relevance in various fields, including biology, medicine, pathology, tissue engineering, and regenerative medicine, since it targets the relationship between morphological features and mechanical properties in biological tissues, which plays an important role in various biological processes including metastasis, wound healing and tissue regeneration. In particular, in every biological tissue, morphological, biochemical and mechanical properties are tightly connected and they influence each other in a correlative manner. For this reason, a correlative approach employing multiple techniques is ideal for targeting tissue morpho-mechanics with an optical approach. Here we report a correlative study performed by optical microscopies, disclosing the supramolecular collagen morphology correlated with its biomechanical and biochemical analyses. In particular, using human corneal tissue as a benchmark, we correlate Second-Harmonic Generation maps with mechanical and biochemical imaging obtained by Brillouin and Raman micro-spectroscopy, demonstrating that the peculiar mechanical functionality of so-called sutural lamellae originates from their distinctive supramolecular organization. A theoretical model based on the ultrastructural symmetry of corneal lamellar domains provides the interpretation of the experimental data at the molecular scale. The proposed methodology opens the way to the non-invasive assessment of tissue morpho-mechanics and holds the potential to be applicable to a broad range of biological and synthetic materials.