Monitoring dynamic collagen reorganization during skin stretching with fast polarization-resolved second harmonic generation imaging

TL;DR

This study introduces a fast polarization-resolved second harmonic generation microscopy technique to monitor real-time collagen fiber reorganization during skin stretching, providing quantitative insights into tissue mechanics.

Contribution

It presents a novel fast imaging system that maps collagen orientation dynamically in thick tissues during mechanical deformation.

Findings

Collagen fibers align along the traction direction during stretching.

The collagen orientation distribution entropy varies linearly with stretch ratio.

The method accurately quantifies collagen reorganization in ex vivo skin samples.

Abstract

The mechanical properties of biological tissues are strongly correlated to the specific distribution of their collagen fibers. Monitoring the dynamic reorganization of the collagen network during mechanical stretching is however a technical challenge because it requires mapping orientation of collagen fibers in a thick and deforming sample. In this work, a fast polarization-resolved SHG microscope is implemented to map collagen orientation during mechanical assays. This system is based on line-to-line switching of polarization using an electro-optical modulator and works in epidetection geometry. After proper calibration, it successfully highlights the collagen dynamic alignment along the traction direction in ex vivo murine skin dermis. This microstructure reorganization is quantified by the entropy of the collagen orientation distribution as a function of the stretch ratio. It exhibits a linear behavior, whose slope is measured with a good accuracy. This approach can be generalized to probe a variety of dynamic processes in thick tissues.