Probing the 3D structure of cornea-like collagen liquid crystals with polarization-resolved SHG microscopy

• Published in: Optics express Vol. 24; no. 14; pp. 16084 - 16098
• Main Authors: Teulon, Claire, Tidu, Aurélien, Portier, François, Mosser, Gervaise, Schanne-Klein, Marie-Claire
• Format: Journal Article
• Language: English
• Published: United States 11.07.2016
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.24.016084

This work aims at characterizing the three-dimensional organization of liquid crystals composed of collagen, in order to determine the physico-chemical conditions leading to highly organized structures found in biological tissues such as cornea. To that end, we use second-harmonic generation (SHG) microscopy, since aligned collagen structures have been shown to exhibit intrinsic SHG signals. We combine polarization-resolved SHG experiments (P-SHG) with the theoretical derivation of the SHG signal of collagen molecules tilted with respect to the focal plane. Our P-SHG images exhibit striated patterns with variable contrast, as expected from our analytical and numerical calculations for plywood-like nematic structures similar to the ones found in the cornea. This study demonstrates the benefits of P-SHG microscopy for in situ characterization of highly organized biopolymers at micrometer scale, and the unique sensitivity of this nonlinear optical technique to the orientation of collagen molecules.