Biohybrid tensegrity actuator driven by selective contractions of multiple skeletal muscle tissues

Biohybrid robots are robots composed of both biological and artificial materials that can exhibit the unique characteristics commonly found in living organisms. Skeletal muscle tissues can be utilized as their actuators due to their flexibility and ON/OFF controllability, but previous muscle-driven robots have been limited to one-degree of freedom (DOF) or planar motions due to their design. To overcome this limitation, we propose a biohybrid actuator with a tensegrity structure that enables multiple muscle tissues to be arranged in a 3D configuration with balanced tension. By using muscle tissues as tension members of tensegrity structure, the contraction of muscle tissues can cause the movement of the actuator in multiple-DOFs. We demonstrate the fabrication of the biohybrid tensegrity actuator by attaching three cultured skeletal muscle tissue made from C2C12 cells and fibrin-based hydrogel to an actuator skeleton using a snap-fit mechanism. When we applied an electric field of more than 4 V mm^-1to the skeletal muscle tissue, the fabricated actuator had a structure to tilt in multiple directions through the selective displacement of about 0.5 mm in a specific direction caused by the contractions of muscle tissue, resulting in 3D multi-DOF tilting motion. We also show that the actuator possesses superior characteristics of tensegrity structure such as stability and robustness by assessing the response of the actuator to external force. This biohybrid tensegrity actuator provides a useful platform for the development of muscle-driven biohybrid robots with complex and flexible movements.