The effect of storing fiber, fiber bundle, and whole muscle in glycerinated solution on their passive elastic modulus

Storing skeletal muscle specimens in glycerinated solution is a common preservation method before biomechanical testing. This study examined the impact of glycerinated solution on passive elastic modulus in muscle tissues at three scales: fiber, fiber bundle, and whole muscle. Tensile testing was conducted on Tibialis Anterior muscle specimens obtained from nine male Sprague-Dawley rats. In total, 36 fibers, 48 fiber bundles, and 12 whole muscles were tested. Half of the specimens were tested immediately, while the other half were stored in glycerinated solution at -20 °C for 2 weeks prior to testing. The elastic moduli of all specimens were determined from stress-strain curves at 10%, 20%, and 30% strains. The results showed glycerinated solution led to about 50% decrease in elastic modulus for fibers and bundles (p < 0.001) compared to fresh muscle, while whole muscle storage caused fiber damage in the tissue center. Furthermore, the slack sarcomere length of the stored fibers and fiber bundles decreased while their cross-sectional area increased (p < 0.041). For the whole muscles, storing reduced both mass and physiological cross-sectional area of the samples (p < 0.002). These findings highlight the effect of glycerinated storage solution on muscle specimens of different sizes; and indicate that tensile testing of stored fibers and fiber bundles primarily evaluates their passive properties, while testing fresh fibers and fiber bundles assesses both passive and some active mechanical properties.