Wavy nature of collagen fibrils deduced from the dispersion of their second-order nonlinear optical anisotropy parameters ρ.

From P-SHG experiments, second-order nonlinear optical anisotropy parameters rho = chi(ZZZ)/chi(ZXX) of collagen tissues are calculated assuming the same model of supercoiled collagen fibril characterized by a variable angle theta. Dispersion of experimental rho values is converted into distribution of theta values based on the wavy nature of collagen fibrils deduced from EM studies. For tendon, the results show that the dispersion of experimental rho values is mainly due to Poisson photonic shot noise assuming a slight fibrillar undulation with theta = 2.2 degrees +/- 1.8 degrees. However for skin and vessels, the dispersion of experimental rho values is mainly due to a stronger fibrillar undulation with theta = 16.2 degrees +/- 1.3 degrees. The results highlight that this undulation is reduced during the development of liver fibrosis therefore, contributing to the rigidity of the tissue. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement