Simultaneous mechanical and light microscopic studies of collagen fibers

Summary

An apparatus that enables simultaneous stress-strain recording and morphological observation in incidental light microscopy of a specimen surface during tensile loading is described. Results from experiments on parallel-fibred collagenous specimens (tendons) are reported and variations between behavior during the first tensile loading cycle and those in the steady-state cycles (when the plasticity and irreversible viscosity are exhausted) are described. It is found that the “toe” part of the stress-strain curve is longer from a morphological point of view than can be mechanically measured, which means that the waviness of the collagenous bundles is diminished before any measurable load is applied. The steady state means an even longer such “toe” part and a better parallel arrangement of the fibers but the waviness in the relaxed specimen cannot be disturbed by repeated loadings. The functional range of a tendon is also discussed as are the phenomenon of spraining and the possibility of pre-stress.