Multipole electrodes for driving biohybrid robots via selective muscle contraction

Biohybrid robots that integrate living muscle tissues with synthetic structures have emerged as platforms for studying animal-like movements and developing soft robotic systems. Skeletal muscle tissues are particularly attractive as actuators due to their high controllability through electrical stimulation. However, in conventional field electrical stimulation, electrical signals tend to disperse through the conductive culture medium, often causing unintentional activation of non-target muscle tissues. To address this limitation, we developed a multipole electrode capable of concentrating the electric field within a localized region around the target muscle. In the multipole electrode, increasing the number of electrode poles improved electric field convergence and reduced unwanted signal spread into surrounding areas. As a demonstration of the practical applicability of the multipole electrode, we constructed an ocular-like biohybrid robot composed of four cultured skeletal muscle tissues and four multipole electrodes. Through sequential and selective stimulation, the robot successfully performed complex and directional motions, including elliptical trajectories. These results confirm that the multipole electrode enables non-contact, spatially precise stimulation of cultured muscle tissues and offers a promising approach for enhancing the functional complexity and degrees of freedom in biohybrid robotic systems.