Accordion-like collagen fibrils suggested by P-SHG image modeling: implication in liver fibrosis

Second-order non-linear optical anisotropy parameter{rho} ={chi} 33 /{chi} 31 is calculated for collagen-richt issues considering both a single dominant molecular hyperpolarizability tensor element {beta}333 = {beta} at single helix level and a priori known submicrometric triple helical organization of collagen molecules. Modeling is further improved by taking account of Poisson photonic shot noise of the detection system and simple supra-molecular fibrillar arrangements in order to accurately simulate the dispersion of{rho} values in collagen-rich tissues such as tendon, skin and liver vessels. From combined P-SHG experiments and modeling, we next correlate experimental and theoretical statistical distributions of{rho} . Our results highlight that the dispersion of experimental{rho} values is mainly due to (i) Poisson photonic shot noise in tendon and skin, which proves to have a preponderant effect in P-SHG experiments (ii) variance of supercoil angles of accordion-like fibrils in vessels that is further reduced during the development of liver fibrosis therefore contributing to the rigidity of the tissue. These results open new avenue for future modeling correlating the dispersion of{rho} values in P-SHG experiments and the fibrillar architecture as well as the mechanical stiffness of patho-physiological extracellular matrices in collagen tissues.