A new clamping and stretching procedure for determination of collagen fiber stiffness and strength relations upon maturation.

Clamping of tendon fibers is a major concern in connective tissue biomechanics. We present here a new clamping method. Also the stretching procedure is different from the conventional extension until the point of failure. Thus we have used a procedure of interval stretches, where 0.01 extensions during 2.5 s are succeeded by periods of relaxation. This procedure reduces the stress on clamps and transducers which causes serious problems in conventional extensions of some older specimen. The influence of stretching rate and periods of relaxation on the observed values of stiffness has been tested and discussed. The fibers from rat tail tendons only show a minor increase in stiffness between 40 day and 90 day old animals, and do not show significant changes from the age of 90 to 240 days. The values of stiffness expressed as Young's modulus of elasticity, had maximal values of 1.2, 1.8 and 1.9 kNmm-2 at the three ages investigated. The fiber strength, however, increases dramatically, thus the ultimate value was 18 Nmm-2 for 40 day old fibers, while at 90 days and 240 days it had increased to 102 Nmm-2 and to 106 Nmm-2, respectively.