RESUMEN
The material properties of muscle play a central role in how muscle resists joint motion, transmits forces internally, and repairs itself. While many studies have evaluated muscle's tensile material properties, few have investigated muscle's shear properties. The objective of this study was to quantify the shear moduli of skeletal muscle both along (along-muscle fiber) and perpendicular (cross-muscle fiber) to the direction of muscle fibers. We collected data from the extensor digitorum longus, tibialis anterior, and soleus muscles harvested from both hindlimbs of 12 rats. These muscles were chosen to further evaluate the consistency of shear moduli across muscles with different architectures. We applied strains and measured stress in three configurations: parallel, perpendicular, and across the muscle fibers to characterize the along- and cross-muscle fiber tensile and shear material parameters. We found no significant difference between the shear modulus measured parallel to the fibers (along-muscle fiber) and the shear modulus in the plane perpendicular to the fibers (cross-muscle fiber). Although the shear moduli were not significantly different, there was a greater difference with increasing strain, suggesting that there is greater anisotropy at larger strains. We also found no significant difference in moduli between the muscles with differing muscle architecture. These results characterize the shear behavior of skeletal muscle and are relevant to understanding the role of shear in force transmission and injury.
RESUMEN
Extracellular matrix (ECM) is widely considered to be integral to the function of skeletal muscle, providing mechanical support, transmitting force, and contributing to passive stiffness. Many functions and dysfunctions attributed to ECM are thought to stem from its mechanical properties, yet there are few data describing the mechanics of intact ECM. Such measurements require isolating intact ECM from the muscle cells it surrounds. The objectives of this study were to quantify the efficiency of three techniques for this purpose: Triton, Triton with sodium dodecyl sulfate, and latrunculin B; and to determine their impact on properties of the remaining ECM. Efficiency was quantified by DNA content and evaluation of western blot intensities for myosin and actin. The properties of ECM were quantified by collagen content and uniaxial tensile testing. We found that latrunculin B was the most efficient method for removing skeletal muscle cells, reducing DNA content to less than 10% of that seen in control muscles, and substantially reducing the myosin and actin to 15% and 23%, respectively; these changes were larger than for the competing methods. Collagen content after decellularization was not significantly different from control muscles for all methods. Only the stiffness of the muscles decellularized with latrunculin B differed significantly from control, having a Young's modulus reduced by 47% compared to the other methods at matched stresses. Our results suggest that latrunculin B is the most efficient method for decellularizing skeletal muscle and that the remaining ECM accounts for approximately half of the stiffness in passive muscle.