Human induced pluripotent stem cell-derived cardiac muscle rings for biohybrid self-beating actuator.

Cardiac muscle, a subtype of striated muscle composing our heart, has garnered attention as a source of autonomously driven actuators due to its inherent capability for spontaneous contraction. However, conventional cardiac biohybrid robots have utilized planar (2D) cardiac tissue consisting of a thin monolayer of cardiac myotubes with a thickness of 3-5 μm, which can generate a limited contractile force per unit footprint. In this study, 3D cardiac muscle rings were proposed as robotic actuator units. These units not only exhibit higher contractile force per unit footprint compared to their 2D counterparts due to their increased height, but they can also be integrated into desired 3D configurations. We fabricated cardiac muscle rings from human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), evaluated their driving characteristics, and verified the actuation effects by integrating them with artificial components. After the 10th day from culture, the cardiac muscle rings exhibited rhythmic spontaneous contraction and increased contractile force in response to stretching stimuli. Furthermore, after constructing a centimeter-sized biohybrid self-beating actuator with an antagonistic pair structure of cardiac muscle rings, the periodic antagonistic beating motion at its tail portion was confirmed. We believe that 3D cardiac muscle rings, possessing high contractile force and capable of being positioned within limited 3D space, can be used as potent biohybrid robotic actuators.