Since living animals have unique functions that have not been reproduced in mechanical systems, biohybrid robots, consisting of biological components and synthetic components, have recently attracted attention. Among the biohybrid robots, we are interested in biohybrid robots driven by muscle contractions. To control the designs and dimensions of the robots, cultured skeletal muscle tissue is expected to be used as actuators. By culturing muscle cells in hydrogel structures, it is easy to construct skeletal muscle tissues in vitro. However, the contractions of cultured skeletal muscle tissue are limited to a single direction, so it is difficult to use them as actuators to generate multiple directional motions. In contrast, muscles in animal bodies have achieved multiple directional motions without any skeletons (ex. tongues). By mimicking the structure of living muscles, it is possible to achieve multiple directional motions using only muscles. Since the contractile directions of skeletal muscle tissues correspond with the directions of myotubes in the tissues, skeletal muscle tissue enabling contractions for multiple directions is constructible by combining multiple cultured skeletal muscle tissues with different myotube directions.

In this project, we developed a bonding method for multiple cultured skeletal muscle tissues to make single skeletal muscle tissue with multiple directional contractions. As a result, we found that cell-laden hydrogel is usable as an adhesive for cultured skeletal muscle tissues. Moreover, we evaluated the contractility of the constructed skeletal muscle tissue. When electrical pulses were applied to the tissue, we confirmed that the constructed tissue achieved multiple directional motions. In addition, we found that the major direction of contractions was controllable by the distribution of the electrical field, indicating that the patterns of electrodes can control the major contraction direction. As a demonstration, we also achieved tongue-like motions of the constructed skeletal muscle tissue by controlling the position of electrodes. From these results, we believe that our bonding method for skeletal muscle tissue is useful for making the skeletal muscle tissue with multiple contractile directions.