Light and electron microscopic studies of collagen fibers under strain

Summary The correlation of the mechanical properties and the morphological behaviour of collagenous tissue during strain was investigated. Relaxed and strained tendons were examined by incidental and transmitted polarized light microscopy and electron microscopy. It was concluded that the wavy pattern seen at the seminicroscopic level of the collagen fibers vanished at relatively low loads. The direction of birefringence in transmitted light microscopy varied in the relaxed preparations but became even in the strained. The electron microscopy showed that the fibrils had the same periodicity as calculated from X-ray diffraction patterns of moist collagen, i.e. 680 Å, and that straining increased the period lengths of some fibrils. The correlation of these findings to a mechanical analogy of the tissue was discussed.