Effect of mechanical stretching on the maturation of 3-D fascicle-like muscle tissue

Abstract

Skeletal muscle is well known for a rapid adaptation to mechanical environmental changes. Understanding the effects of the mechanical stimulation such as stretching to muscle tissues is important for understanding the nature of muscle development and muscle diseases. While there are many reports studying the effects of stretching on 2-D cultures in vitro, few research groups have investigated their effects in 3-D muscle strips with high volumetric density. Here, we used the muscle strips that have fascicle-like shape, high volumetric density, and optimal alignment in 3-D. We present that the fascicle-like muscle tissue will have stronger performance and more matured structure in response to particular stimulation. We applied the static and cyclic stretching, electrical stimulation and two different co-stimulation. Both the static and cyclic stretching induced stronger cell-ECM adhesions of 3-D cultured muscle cells. The static tension at day 9 caused striated actin of the muscles, but the cyclic tension at day 1 caused weakening of actin structure with less alignment. Similarly, the stretching could affect other proteins, related to muscle development. Therefore, the effect of the stretching to the muscle tissue is highly time-dependent, and it is important to find optimal timing for efficient training. We also show that muscle performance by the co-stimulation is higher than by the electrical stimulation alone. Although conditions of the each mechanical and electrical stimuli were identical, the performances were changed only by phase shift between the two stimuli. We still do not know the exact mechanism, but our results support the potential use of high-performance engineered muscle tissues for moving bio-robots or drug testing platforms.