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

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 second harmonic generation 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 epi‐detection 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. An original fast polarization‐resolved second harmonic generation microscope based on line‐to‐line switching of polarization using an electro‐optical modulator is implemented to map the dynamic reorganization of the collagen network during mechanical assays. This system successfully highlights the collagen alignment along the traction direction in ex vivo murine skin dermis and enables quantitation of the linear increase of the collagen orientation distribution entropy as a function of the stretch ratio.