Imaging the noncentrosymmetric structural organisation of tissue with Interferometric Second Harmonic Generation microscopy

TL;DR

This paper demonstrates the use of Interferometric Second Harmonic Generation microscopy to image the noncentrosymmetric structural organization of tendon tissue, revealing domain structures and fibril orientation over micrometer scales.

Contribution

It introduces I-SHG microscopy for detailed imaging of collagen organization in tendon, providing insights into its nanostructure and domain composition.

Findings

Noncentrosymmetric organization persists over >150 μm along fibrils.

Transverse organization is confined to 1-15 μm.

Tendon consists of domains with biased fibril orientations.

Abstract

We report the imaging of tendon, a connective tissue rich in collagen type I proteins, with Interferometric Second Harmonic Generation (I-SHG) microscopy. We observed that the noncentrosymmetric structural organization can be maintained along the fibrillar axis over more than 150 {\mu}m, while in the transverse direction it is ~1-15 {\mu}m. Those results are explained by modeling tendon as a heterogeneous distribution of noncentrosymmetric nanocylinders (collagen fibrils) oriented along the fibrillar axis. The preservation of the noncentrosymmetric structural organization over multiple tens of microns reveals that tendon is made of domains in which the fraction occupied by fibrils oriented in one direction is larger than in the other.