Aggregational state and molecular order of tendons as a function of age

Form or textural birefringence (FB) depends on the geometrical characteristics of rod-like molecules, like collagen. The degree of packing and ordered aggregation are factors that also play important roles in the FB. Since current information reports increases in the diameters of collagen fibrils according to age, a search to determine variations of intrinsic birefringence (IB) and FB of collagen in Achilles and tail tendons of rats as a function of age was carried out. The findings support the conclusion that there are increases on FB and IB as the animals age. These increases are a consequence of higher molecular order and aggregation of collagen in tendons of older animals. Furthermore, an accurate methodology was developed to detect and to control the effect of section thickness variation of the material used in this research.