A Bioreactor for Controlled Electrical and Mechanical Stimulation of Developing Scaffold-Free Constructs

Engineering interfacial tissues: The myotendinous junction

The myotendinous junction (MTJ) is the interface connecting skeletal muscle and tendon tissues. This specialized region represents the bridge that facilitates the transmission of contractile forces from muscle to tendon, and ultimately the skeletal system for the creation of movement. MTJs are, therefore, subject to high stress concentrations, rendering them susceptible to severe, life-altering injuries. Despite the scarcity of knowledge obtained from MTJ formation during embryogenesis, several attempts have been made to engineer this complex interfacial tissue. These attempts, however, fail to achieve the level of maturity and mechanical complexity required for in vivo transplantation. This review summarizes the strategies taken to engineer the MTJ, with an emphasis on how transitioning from static to mechanically inducive dynamic cultures may assist in achieving myotendinous maturity.

Fixation method of a single muscle fiber by magnetic force for stretching, transportation, and evaluation of mechanical properties

Engineered muscle fibers are attracting interest in bio-actuator research as they can contribute to the fabrication of actuators with a high power/size ratio for micro-robots. These fibers require to be stretched during culture for functional regulation as actuators and require a fixation on a rigid substrate for stretching in culture and evaluation of mechanical properties, such as Young's modulus and contraction force. However, the conventional fixation methods for muscle fibers have many restrictions as they are not repeatable and the connection between fixation part and the muscle fibers detaches during culture; therefore, the fixation becomes weak during culture, and direct measurement of the muscle fibers' mechanical properties by a force sensor is difficult. Therefore, we propose a facile and repeatable fixation method for muscle fibers by mixing magnetite nanoparticles at both ends of the muscle fibers to fabricate magnetic ends. The fiber can be easily attached and detached repeatedly by manipulating a magnet that applies a magnetic force larger than 3 mN to the magnetic ends. Thus, the muscle fiber can be stretched fiber during culture for functional regulation, transported between the culture dish and measurement system, and directly connected to the force sensor for measurement with magnetic ends. The muscle fiber connected with magnetic ends have a long lifetime (∼4 weeks) and the cells inside had the morphology of a skeletal muscle. Moreover, the muscle fiber showed a contraction (specific force of 1.02 mN mm-2) synchronized with electrical stimulation, confirming the muscle fiber fabricated and cultured using our method had similar morphology and function as bio-actuators in previous research. This research demonstrates the advantages of the fixation method using muscle fibers with magnetic ends; the fibers are stretched during culture, and the transportation and force measurement of weak and tiny muscle fibers could be finished in 1 min.

Advances in electrospinning and 3D bioprinting strategies to enhance functional regeneration of skeletal muscle tissue

Skeletal muscles are essential for body movement, and the loss of motor function due to volumetric muscle loss (VML) limits the mobility of patients. Current therapeutic approaches are insufficient to offer complete functional recovery of muscle damages. Tissue engineering provides viable ways to fabricate scaffolds to regenerate damaged tissues. Hence, tissue engineering options are explored to address existing challenges in the treatment options for muscle regeneration. Electrospinning is a widely employed fabrication technique to make muscle mimetic nanofibrous scaffolds for tissue regeneration. 3D bioprinting has also been utilized to fabricate muscle-like tissues in recent times. This review discusses the anatomy of skeletal muscle, defects, the healing process, and various treatment options for VML. Further, the advanced strategies in electrospinning of natural and synthetic polymers are discussed, along with the recent developments in the fabrication of hybrid scaffolds. Current approaches in 3D bioprinting of skeletal muscle tissues are outlined with special emphasis on the combination of electrospinning and 3D bioprinting towards the development of fully functional muscle constructs. Finally, the current challenges and future perspectives of these convergence techniques are discussed.