A muscle-machine hybrid crawler: Omnidirectional maneuverability and high load capacity

Biohybrid robots actuated by living cells are promising candidates to develop a new generation of small-scale robots. However, realizing desirable traits of fast motion, agile actuation, and high load capacity are still challenging for the biohybrid robots because of inherent contraction limitation of living cells from mammalians in a small scale. To overcome it, we developed a centimeter-scale muscle-machine hybrid crawler actuated by gracilis minor tissue from bullfrogs with high levels of actuation performance. The gracilis minor tissues could generate large actuation (contractile force: ∼4.40 N, strain: ∼0.28), fast contraction (∼60 ms), long lifetime (> 118 h), and especially contraction direction controllability by electrical stimulation manipulation over the tissues, leading to flexible control of biohybrid robots independent from mechanical design, which surpassed existing living materials as bioactuators. The tissue based biohybrid crawler achieved large actuation (average speed: ∼4.80 mm/s; a continuous motion of ∼700 mm to exhaustion), agile maneuverability in 360 degrees by the contraction direction modulation of the tissue (7.82 º/s and 9.62 º/s for left and right rotation respectively), long-term actuation (∼168 h), and high load capacity (maximum load/actuator-weight ratio: ∼20; maximum speed: ∼8.90 mm/s). As a demonstration, we showed that our robots allowed free maneuvering under a load state. This study provides a platform to break through limitations in conventional biohybrid robots and paves a way to fulfill lifelike motions.