Optical anisotropy of collagen fibers of rat calcaneal tendons: An approach to spatially resolved supramolecular organization

Summary l anisotropic characteristics investigated by polarization microscopy have been valuable for the study of the oriented organization of collagen fibers in tendons. However, topographic differences in supramolecular organization of collagen fibers along extensive areas in tendons have not yet been described. Here, the statistical variability of the oriented organization of collagen fibers along extensive areas (105–106 μm2) of 7-μm thick unstained sections of rat calcaneal tendons were studied by assessing their birefringence with polarization microscopy and image analysis, and the periodic frequency distribution in their birefringent images with the fast Fourier transform (FFT). Various levels of birefringence intensity were determined principally by image analysis procedures, and periodicity in the birefringent images was revealed by FFT line profile and spectrum image patterns. Present results support the idea of a helical distribution for collagen bundles along the tendon long axis, and of a statistical architecture for the rat calcaneal tendons in terms of variability in the oriented distribution of their collagen fibers.