A forward-engineered muscle tissue driven soft robotic swimmer

The integration of biological actuators with soft scaffolds has led to biohybrid robots including microscale flagellate-like swimmers which generate thrust by waving their flagella-like tails. However, they achieve swimming speeds of only 0.014 body lengths per minute, Reynolds number ( Re ) ∼ 10⁻³, which is much slower than natural flagellates ( O (10 ² – 10 ³ ) body lengths per minute). To investigate this, we applied theoretical and experimental methods, including fabrication of a swimmer that converts muscle contractions into large angular tail displacements, reaching swimming speeds of 86.8 μm/s (0.58 body lengths per minute), surpassing low- Re predictions. Swimming dynamics sharply transition from a low-Re (∼ 10⁻³) to an intermediate- Re (∼ 0.1) regime when the actuation angle exceeded 4°. We used the swimmer to study the ability of muscle to adapt to mechanical stiffness and the beneficial effects of neuromuscular coculture on muscle development. These insights into mechanical and chemical cues will help optimize future biobots.