Passive transverse mechanical properties as a function of temperature of rat skeletal muscle in vitro

The objective of the current study was to determine the in vitro passive transverse mechanical properties of skeletal muscle with Dynamic Mechanical Thermal Analysis (DMTA) tests. The starting hypotheses was that the time-temperature-superposition principle could be used to expand the DMTA results to a 1 kHz frequency range. Experiments were performed with rat hind leg skeletal muscle tissue samples on a rotational rheometer using a parallel plate geometry. Because of the small size and low modulus of the samples, the standard test geometry was altered and the samples were shifted from the center to the edge of the plates. From strain sweep tests it became clear that for strains smaller than 0.003 the muscle tissue behaves linearly. In the linear region storage moduli ranged between 24 kPa (omega = 1 rad/s) and 42 kPa (omega = 100 rad/s) at T = 4 degrees C and 22 kPa and 33 kPa at 29 degrees C within the experimental frequency range. The loss modulus decreased with increasing frequency and ranged between 7 and 4 kPa at 4 degrees C and 4.5 and 3.5 kPa at 29 degrees C. Although the properties are clearly temperature dependent, a temperature shift in phase angle delta could not be detected, thus Time Temperature Superposition is not allowed for skeletal muscle in vitro.