Structure of tendon causes highly optical anisotropic properties and transport.

Significance: Tendons are highly anisotropic tissues that exhibit distinct optical properties depending on the direction of light propagation relative to their fiber orientation. Understanding these variations and how to modify them through optical clearing techniques is beneficial for many light-based applications, including photobiomodulation therapy. Aim: To quantify how tendon optical transport depends on fiber orientation and wavelength, comparing light propagation parallel and perpendicular to the tendon's long axis, the axis along which collagen fibers are primarily aligned, and to evaluate glycerol-based optical clearing for increasing light penetration. Approach: The reduced scattering coefficient ( Results: Longitudinal tendon sections exhibited consistently higher Conclusions: Tendons have strong anisotropic optical properties that favor optical propagation along their fiber axis. Glycerol increases light penetration depths, though further research is needed to confirm safe concentrations for clinical use, as 10% glycerol proved insufficient.