A fast, muscle-actuated biohybrid swimming robot

Integration of biological actuators and sensors with soft, synthetic scaffolds has allowed for the development of a class of microscale, emergent, and motile biohybrid robots, including small scale swimmers and walkers. Swimmers generated thrust from time irreversible dynamics of their flagella-like thin compliant tails. However, these swimmers were limited in their wider application by slow speed (0.7 micrometers per second, 0.014 body lengths/min, with Re ∼ 10-3). Low Reynolds number ( Re ) hydrodynamic theory, appropriate for locomotion with negligible inertial effects, predicts that swimming speed can be increased by orders of magnitude by increasing angular actuation of the tails of these swimmers. This study investigates a novel design for a fast swimmer achieving speeds up to 86.8 micrometers per second, 0.58 body lengths/minute. Here, living muscle tissue applies force on the swimmer scaffold upon electrical actuation. The compliant mechanism transduces the contraction to twisting of the tails by up to 7º, resulting in high speeds. Muscle maturity was modulated through coculture with motor neurons and mechanical coupling to the compliant swimmer scaffold. Although the design was motivated by low Reynolds number theory, the swimmer achieves high speed benefiting from inertial effects with Re ∼ 10 ⁻¹ . Our study provides a simple design for generating high thrust using bio-actuators at small scale and a design for introducing neurons into biohybrid systems with 3D muscle tissues.