The Mechanical Properties of Rat Tail Tendon

The load-strain and stress-relaxation behavior of wet rat tail tendon has been examined with respect to the parameters strain, rate of straining, and temperature. It is found that this mechanical behavior is reproducible after resting tile tendon for a few minutes after each extension so long as the strain does not exceed about 4 per cent. If this strain is exceeded, the tendon becomes progressively easier to extend but its length still returns to the original value after each extension. Extensions of over 35 per cent can be reached in this way. Temperature has no effect upon the mechanical behavior over the range 0-37°C. Just above this temperature, important changes take place in the mechanical properties of the tendon which may have biological significance. The application of the techniques used here to studies of connective tissue disorders is suggested. Some of the mechanical properties of tendon have been interpreted with a simple model. I N T R O D U C T I O N Most studies of collagen have been concerned with its chemica l na tu re and react ivi ty, and wi th e lect ron microscope and xray diffract ion examinat ions with a view to de te rmin ing its mac ro and molecu la r s t ruc ture (1-4). As yet there is no ent i re ly satisfactory molecu la r model , and one major s tumbl ing block appears to be the confusion over whe the r collagen is or is not capab le of large extensions. A n u m b e r of measurements have been repor ted on the mechan ica l p roper ties of such col lagen-conta in ing structures as tendons, l igaments, and fascia. T h e r e is no extensive review of the older work available. However , typical results m a y be found in references (5-7) . S t ruc tures conta in ing a h igh per cent of collagen were found difficult to stretch and usually broke before they e longated apprec iab ly , while s tructures with a lower collagen con ten t and a From the Department of Chemistry and the Department of Experimental Biology, University of Utah, Salt Lake City. This work was supported by the National Institutes of Health, United States Public Health Service (Grant H-3039) and the National Science Foundation. Dr. Rigby's present address is Commonwealth Scientific and Industrial Research Organization Wool Research Laboratories, Division of Textile Physics, Ryde, New South Wales, Australia. Dr. Hirai's present address is the Department of Chemistry, Okayama University, Okayama City, Japan. Received for publication, February 18, 1958.