Change with age of anisotropic properties of collagen bundles.

Form birefringence curves and linear dichroic properties of aging rat tendons are different from those of adult controls. The steepness of the form birefringence curves and the increased retardations found in aging tendons are ascribed to an increase in collagen aggregation accompanied by loss of tissue water. Based on increase of retardations due to intrinsic birefringence, a rise in crystallinity levels is suggested for the collagen bundles of aging tendons. The inversion of the dichroism signs and the change in the d11 (collagen fibers oriented parallel) and d1 (collagen fibers oriented perpendicular) spectral absorption profiles, mainly at the adsorption peaks for sections stained with toluidine blue solutions at pH 4.0 and 5.0, indicate modificiations at the acid glycosaminoglycan molecular orientation level with advancing age.